Federal Court of Australia

International Animal Health Products Pty Ltd v Australian Pesticides & Veterinary Medicines Authority [2026] FCA 959

ORDERS

THE COURT ORDERS THAT:

1.    The decision of the Administrative Review Tribunal dated 17 December 2025 be set aside.

2.    The matter be remitted to the Administrative Review Tribunal for reconsideration according to law.

3.    The respondent pay the appellant’s costs of these proceedings.

Note:    Entry of orders is dealt with in Rule 39.32 of the Federal Court Rules 2011.

REASONS FOR JUDGMENT

JACKMAN J:

Introduction

1    This is an appeal on questions of law pursuant to s 172 of the Administrative Review Tribunal Act 2024 (Cth) by the applicant (IAHP) from a decision by the Administrative Review Tribunal (the Tribunal) dated 17 December 2025. The Tribunal affirmed a decision of the respondent (the APVMA) to refuse to register a veterinary chemical product for the treatment of infections in horses due to organisms susceptible to the combination of sulfadimidine and trimethoprim (known as Trimidine Paste) under s 14(2) of the Schedule to the Agricultural and Veterinary Chemicals Code Act 1994 (Cth) (the Agvet Code): International Animal Health Products Pty Ltd v Australian Pesticides & Veterinary Medicines Authority [2025] ARTA 2721 (TD). The basis for the refusal was relevantly that the Tribunal was not satisfied that Trimidine Paste meets either the “safety criteria” in s 5A or the “efficacy criteria” in s 5B of the Agvet Code.

2    Trimidine Paste contains two active ingredients (namely, sulfadimidine and trimethoprim), and two inactive ingredients (namely, propylene glycol and glycerol). A number of other products containing the active ingredients of sulfadimidine and trimethoprim have been, and are currently, registered. The Tribunal said that it was not controversial that sulfadimidine and trimethoprim were well-established antibiotics with a high therapeutic index (at [171]).

Legislative Provisions

3    The object of the Agvet Code is stated in s 1 as follows:

The object of this Code is to make provision for and in relation to:

(a)     the evaluation, approval, and control of the supply, of active constituents for proposed or existing agricultural chemical products or veterinary chemical products; and

(b)    the evaluation, registration, and control of the manufacture and supply, of agricultural chemical products and veterinary chemical products.

4    Subsection 1A(2) provides relevantly as follows:

This Code is to be implemented in a manner that:

(a)    recognises that the health and safety of human beings, animals and the environment is the first priority of the system for regulating chemical products and their constituents, in part to ensure that the use of chemical products at the present time will not impair the prospects of future generations; and

(b)    reflects established best-practice principles for the assessment and management of risk, based on science; and

(c)    balances regulatory effort and any burden imposed by the system of regulation on:

(i)    holders of approvals, registrations, permits and licences; and

(ii)    the domestic industry for manufacturing and formulating chemical products and their constituents; and

(iii)    the users of chemical products;

with the risk of the use of the products and constituents to the health and safety of human beings, animals and the environment …

5    Section 5 defines the term “veterinary chemical product”, and provides relevantly in subs (2) that a veterinary chemical product is a substance or mixture of substances that is represented as being suitable for, or is manufactured, supplied or used for, administration or application to an animal by any means, or consumption by an animal, as a way of directly or indirectly:

(a)    preventing, diagnosing, curing or alleviating a disease or condition in the animal or an infestation of the animal by a pest.

6    Section 5A(1) of the Agvet Code defines the expression “meets the safety criteria” relevantly as follows:

An active constituent or chemical product meets the safety criteria if use of the constituent or product, in accordance with any instructions approved, or to be approved, by the APVMA for the constituent or product or contained in an established standard:

(a)    is not, or would not be, an undue hazard to the safety of people exposed to it during its handling or people using anything containing its residues; and

(b)    is not, or would not be, likely to have an effect that is harmful to human beings; and

(c)    is not, or would not be, likely to have an unintended effect that is harmful to animals, plants or things or to the environment.

7    Section 5B(1) of the Agvet Code defines the term “meets the efficacy criteria” relevantly as follows:

A chemical product meets the efficacy criteria if use of the product, in accordance with instructions approved, or to be approved, by the APVMA for the product or contained in an established standard, is, or would be, effective according to criteria determined by the APVMA by legislative instrument.

8    Section 10(1)(a) and (b) provide that a person may apply to the APVMA for approval of an active constituent for a proposed or existing chemical product, or for registration of a chemical product. Section 14(1)(c) provides that the APVMA must approve the active constituent or label, or register the chemical product, if it is satisfied, in relation to a chemical product, that the product:

(i)     meets the safety criteria, the trade criteria and the efficacy criteria; or

(ii)     complies with the established standard for the product…

9    The legislative instrument referred to in s 5B(1) by which the efficacy criteria are determined by the APVMA is the Agricultural and Veterinary Chemicals Code (Efficacy Criteria) Determination 2014 (the Efficacy Determination). Section 6 of the Efficacy Determination sets out the criteria based on demonstrated effectiveness as follows:

The use of a veterinary chemical product, in accordance with instructions approved, or to be approved, by the APVMA for the product, is also taken to be effective if:

(a)     it would, to a reasonable degree, achieve one of the effects listed in paragraphs 5(2)(a) to (d) of the Agvet Code; and

(b)     this is evidenced or demonstrated by:

(i)     target animal efficacy studies, including dose determination studies, dose confirmation studies or confirmatory clinical or field studies; or

(ii)    pharmacological studies, such as in vivo or in vitro bioequivalence studies in target animals, pharmacokinetic studies or pharmacodynamic studies; or

(iii)    other relevant studies or data, such as clinical case studies, compatibility studies or palatability studies; or

(iv)    full results from overseas efficacy trials or experiments and the associated assessment reports by an overseas regulator that are relevant to the proposed product and use; or

(v)    valid scientific argument; or

(vi)    a combination of 2 or more of the above.

Note:     The APVMA will consider, on a case by case basis, which of the above matters are necessary to demonstrate effectiveness in a particular case. The APVMA also takes into account other relevant matters: see subsection 5B(2) of the Code. The APVMA’s data guidelines and regulatory guidelines made under section 6A of the Code, published on the APVMA’s website, set out information about the kind of data considered sufficient to demonstrate effectiveness in particular cases.

10    The APVMA published “Data Guidelines: Efficacy and target animal safety general guideline (Part 8)” (the Efficacy Guideline), which deals in section 1.6.3 with scientific references or extrapolated scientific argument. It stated that: “A scientific argument is one that is supported by science/data.” One aspect of the Efficacy Guideline on that topic is as follows:

Literature using the proposed final formulation manufactured by or for the sponsor provides the best, most relevant evaluation and the highest evidentiary weight. Unless appropriate justification is provided, literature that does not use the final formulation of the proposed new animal drug product provides less weight in the evidentiary support scheme.

The Tribunal’s Decision

11    Before the Tribunal, IAHP sought a review of a decision made by the Director, Veterinary Medicines of the APVMA on 18 April 2023 to refuse to register Trimidine Paste under s 14(2) of the Agvet Code: TD at [1]. The Tribunal referred to four expert witnesses having given oral evidence, namely Professor Pouton and Dr Scott (both called by IAHP), and Professor Mills and Dr Margerison (both called by the APVMA): TD at [3]. Professor Mills had provided a letter to the APVMA on 12 May 2022, in which he expressed the opinion that the APVMA could not be satisfied that the use of Trimidine Paste would be effective if used according to label instructions (TD at [6]), but also stated that the use of Trimidine Paste according to the label instructions would be unlikely to have harmful unintended effects upon target animals (TD [8] and [201]). The Tribunal expressed the view that each of the expert witnesses was highly qualified and vastly experienced, and regarded them as extremely impressive witnesses: TD at [30]. The Tribunal engaged in a detailed analysis of the evidence given by the four experts: TD [32]–[198].

12    In relation to whether the safety criteria referred to in s 5A of the Agvet Code had been satisfied, the Tribunal referred to several grounds relied on by IAHP. The first was the letter of Professor Mills of 12 May 2022 referred to above, together with the cross-examination of Professor Mills in which he said that he saw no reason for safety to be affected: TD at [202].

13    Second, IAHP relied on the cross-examination of Dr Margerison concerning the safety criteria in the context of a 1 kg (or 1.2 litre pail) and a 500 mg tub: TD at [203]. The issue concerning the packet size (and specifically the 1.2 litre pail) fell away upon the concession made by the APVMA in its closing written submissions at [50] that the 1 kg pack size could be approved. However, the Tribunal was not persuaded that the passage of cross-examination relied on by IAHP enabled the Tribunal to conclude that Dr Margerison considered the safety criteria had been met: TD at [204]. The Tribunal referred to Dr Margerison’s emphasis on the fact that a product which is not stable may lose its potency, and in such circumstances an animal may not recover from whatever infection it was suffering from, which could lead to a violation of the safety criteria: TD at [204]. Dr Margerison said that, in giving understrength antimicrobials, antibacterials and antibiotics to animals, one could potentially be inducing antibiotic resistance or facilitating the growth of resistant microbes, which can have wider implications, not just for the animal being dosed, but also for other animals, and indeed humans: TD at [204]. The Tribunal said that this evidence was not challenged, and the Tribunal accepted it, referring to s 1A(2)(a) of the Agvet Code which provides for implementation of the Agvet Code in a manner that recognises that the health and safety of human beings, animals and the environment is the first priority of the system: TD at [204]. The Tribunal had earlier referred to Dr Margerison’s “extremely important evidence” that if understrength doses were administered, one could potentially be inducing antibiotic resistance, which could have wider implications for other animals, and indeed humans if the microbes were also pathogenic in humans: TD at [193].

14    The Tribunal also referred to IAHP’s reliance, with respect to both the safety criteria and the efficacy criteria, on products previously registered by the APVMA without evidence that such products were bioequivalent: TD at [205]–[208].

15    The Tribunal ultimately was not persuaded by the evidence of Professor Pouton and Dr Scott on the question whether Trimidine Paste met the safety criteria. The first reason given was the evidence of Dr Margerison as to the potential for wider implications, not just for the animal being dosed, but also for other animals and indeed humans, if the microbes were also pathogenic in humans: TD at [212]. Professor Pouton accepted in cross-examination that if the chemical product as administered to a horse was subtherapeutic it could result in outcomes such as antimicrobial resistance: TD at [214]. However, Professor Pouton did not think that was likely to happen because such antibiotics are given in a relatively high dose to guard against such an outcome: TD at [214]. Professor Mills also spoke of the risk of antimicrobial resistance developing if one is not fully treating the disease: TD at [215]. Dr Scott also conceded there was a possibility of antimicrobial resistance: TD at [216]. The Tribunal referred to some of the expert literature on the question of antimicrobial activity, noting the limitations in the information and the fact that many questions were still to be answered: TD at [217]. The Tribunal said that the potential for antimicrobial resistance to develop highlights the “level of scrutiny” that must be applied to an application such as the present one when determining whether the safety criteria have been satisfied: TD at [217]. The Tribunal considered that the possibility of antimicrobial resistance had not been adequately addressed by IAHP with respect to Trimidine Paste, which may have wider implications, not just for the animal being dosed, but also for other animals and indeed humans, if these microbes are also pathogenic in humans: TD at [218]. The Tribunal regarded that as a significant safety issue as contemplated by s 5A of the Agvet Code: TD at [218].

16    The Tribunal also accepted the evidence of Professor Mills to the extent that there was no information in the literature or other technical or scientific data (such as from clinical trials) to demonstrate if and how the removal of an excipient, bromhexine, would affect efficacy and safety: TD at [219]. The Tribunal also accepted Professor Mills’ evidence that in order to determine efficacy and safety, a range of studies are performed, commencing with dose determination, then dose confirmation: TD at [221]. The Tribunal had earlier referred to Professor Mills’ evidence that IAHP had not sought data, information or evidence but presented scientific opinion that the removal of an active ingredient and two excipients would not affect the efficacy or safety of Trimidine Paste as compared to the reference formulation, Bromotrimidine paste: TD at [153]. The Tribunal also accepted Professor Mills’ evidence that changing a formulation, particularly by adding or removing excipients, can change the bioavailability of an orally administered formulation: TD at [222]. The Tribunal referred to the concession by Professor Pouton and Dr Scott that none of the related products or similar products which were already registered had the exact same formulation as the new formulation of Trimidine Paste: TD at [223] (and see TD at [54] in relation to Professor Pouton, and TD at [127] in relation to Dr Scott). The Tribunal reasoned that, because there was a change of formulation which could affect the bioavailability of an orally administered formulation, in the absence of more valid scientific data or information the Tribunal could not be satisfied that both the safety and efficacy criteria had been met: TD at [223].

17    The Tribunal said that IAHP’s contentions concerning “regulatory precedent” and its “comparative formulation analysis” had some attraction in terms of addressing whether or not the safety criteria had been met, but ultimately found that those contentions did not withstand scrutiny: TD at [226]. None of the comparative reference chemical products had the exact same formula, and thus the Tribunal was not persuaded that the evidence of Professor Pouton and Dr Scott could be relied upon to reach the required state of satisfaction that the safety criteria had been met: TD at [226].

18    In terms of what is required for the Tribunal to be “satisfied” as to whether a chemical product meets the safety criteria, the Tribunal referred to the decision of the Full Court in National Disability Insurance Agency v Lampard [2025] FCAFC 139; (2025) 312 FCR 200 (NDIA v Lampard) at [31], in which Bromwich, Neskovcin and Vandongen JJ said that for a decision-maker to be “satisfied” there must be a state of positive satisfaction or relative certainty in relation to each criterion: TD at [227]–[228]. The Tribunal was not satisfied that Trimidine Paste met the safety criteria in s 5A of the Agvet Code: TD at [229].

19    Turning to the efficacy criteria under s 5B of the Agvet Code and the Efficacy Determination, the Tribunal summarised the effect of the evidence of Professor Pouton and Dr Scott as to their expectation that Trimidine Paste would be bioequivalent to other approved products, Trimidine powder and Ilium Sulprin Oral powder, and that there was no need to consider whether they were bioequivalent in relation to the availability of the antibiotics since there were three approved products that contained the same dose as the two antibiotics in the absence of bromhexine: TD at [231]. However, the Tribunal was concerned by a passage in Professor Pouton’s evidence in cross-examination to the effect that there was a lot of confidence but not a lot of certainty that Trimidine Paste would be efficacious: TD at [232]. The Tribunal had referred to that evidence by Professor Pouton earlier in its reasons (TD at [63]) in the context of Professor Pouton’s proposition that an efficacy study, which requires one to show that the infection has actually been cured, is not typically undertaken. The Tribunal stated that: “Confidence, which may well be legitimately held by a highly qualified and experienced expert witness, does not necessarily equal a valid scientific argument as required by the statutory mechanism.”: TD at [232].

20    The Tribunal then referred to a series of texts and articles on various aspects of the efficacy of the active ingredients contained in Trimidine Paste, but observed that those publications did not contain any specific analysis of the exact same formulation of the chemical product for which registration was being sought: TD [234]–[235]. One of the publications stated that there had been few studies published on the bioavailability of trimethoprim/sulphonamide combinations in horses, and the Tribunal considered that such studies would fall within the definition of “valid scientific argument” within the meaning of s 6(b)(v) of the Efficacy Determination: TD at [237]. The Tribunal stated that this highlighted the need for “a significant level of scrutiny” to be applied by the APVMA to an application such as this: TD at [237].

21    The Tribunal reviewed various aspects of the expert literature and stated that the degree of specialist data provided as a result of many intensive studies, surveys and various clinical trials do give some indication of the type of data and comparatively detailed information needed to underpin a contention that there is “valid scientific argument” that the veterinary chemical product for which registration is sought satisfies the efficacy criteria: TD at [242]. That point was emphasised by Professor Mills, who used such terms as the requirement for “clearly defined scientific evidence”, “rigorous science”, “demonstrative proof”, “definitive science” and “I’m looking for valid scientific argument to show [what] the literature is showing for these particular products and demonstrating that the new formulation Trimidine is the same as the reference product from Trimidine, and that wasn’t there”: TD at [242]. The Tribunal accepted Professor Mills’ approach to the information or data required to satisfy the requirement to furnish valid scientific argument. The Tribunal said that Professor Mills’ evidence on this topic conforms with the matters identified in the Efficacy Guideline concerning scientific arguments supported by science/data, the critical evaluation required of scientific papers and literature using the proposed final formulation manufactured, and several other factors contained in that guideline, setting out by way of footnote the passage extracted above from the Efficacy Guideline as to literature using the proposed final formulation providing the most relevant evaluation and the highest evidentiary weight: TD at [242]. The Tribunal referred also to s 1A(2)(b) of the Agvet Code, providing for implementation in a manner that reflects established best-practice principles for the assessment and management of risk, based on science: TD at [242]. In addition, the Tribunal adopted Professor Mills’ requirement that the relevant data or information be identified by way of studies, clinical trials and other investigations: TD at [242]. The Tribunal accepted the APVMA’s contentions that a “valid scientific argument” is “more than simply one expert’s opinion based on subjective assumptions about the efficacy of a product”: TD at [242]. The Tribunal said that IAHP had not provided scientific data, information or other evidence of the classes, categories or types recorded in the several articles and literature that were in evidence before the Tribunal: TD at [242]. The Tribunal noted that “valid scientific argument” under s 6(b)(v) was the only aspect of s 6(b) of the Efficacy Determination which IAHP was relying on to advance its argument that it met the efficacy criteria: TD at [244].

22    The Tribunal then referred to IAHP’s argument that Trimidine Paste satisfied the efficacy criteria by relying on what was described as “regulatory precedent”, namely five reference products which used identical active ingredients and daily doses, with the only difference between those products and Trimidine Paste relating to physical form and/or excipients: TD at [247]. IAHP contended that only two of the five reference products were registered based on bioequivalence studies comparing their paste formulations to powder formulations, and one of them was registered in spite of differences in the level of trimethoprim: TD at [247]. Two products were registered without requiring bioequivalence studies, relying instead on established active ingredients and other published data: TD at [247]. IAHP submitted that the existence of other approved formulations of potentiated sulphonamides products was relevant to the assessment of Trimidine Paste, because those products are all presumed safe and efficacious: TD at [248].

23    The Tribunal did not accept IAHP’s contentions that “regulatory precedent” was an appropriate evidentiary platform or basis for finding that Trimidine Paste satisfies the efficacy criteria: TD at [250]. The Tribunal said that it “considers that such matters are irrelevant, do not accord with the statutory scheme concerning the efficacy criteria created by the Agvet Code and are contrary to established principles of administrative law”: TD at [250]. The Tribunal said that the fact that there are other approved products does not and cannot establish that the requirements of s 6(b) of the Efficacy Determination have been satisfied, and stated that the mere fact that there are other chemical products with the same antibiotics does not mean that the efficacy of Trimidine Paste is “evidenced or demonstrated by” the classes or categories of data, studies, evidence or information as enumerated in s 6(b) of the Efficacy Determination: TD at [250]. Further, the Tribunal said that identifying earlier applications or processes that may have resulted in another product being registered several years previously cannot, on any view, let alone on the proper construction of para 6(b) of the Efficacy Determination, amount to “valid scientific argument”: TD at [250]. The Tribunal reviewed some of the authorities concerning the principles to be applied by a decision-maker when addressing questions for determination in an application such as the present, and concluded by saying (TD at [252]):

There is no authority to support a contention, as submitted by the applicant, that a notion of “regulatory consistency” or “regulatory precedent” can be determinative, or otherwise relied on to decide whether the efficacy criteria created by the statutory scheme under the Agvet Code has been satisfied with respect to Trimidine Paste.

The Tribunal thus rejected IAHP’s reliance on “regulatory consistency” or “regulatory precedent” as an appropriate evidentiary platform or basis for assessing the efficacy criteria: TD at [253].

24    The Tribunal then referred to IAHP as having relied on two grounds to establish that it satisfied the efficacy criteria: TD at [254]. The first ground was that the evidence of Professor Pouton and Dr Scott established “valid scientific argument” within the meaning of s 6(b)(v) of the Efficacy Determination: TD at [255]. The second ground was that of “regulatory precedent” or “regulatory consistency”, which the Tribunal had already addressed and rejected: TD at [256]. The Tribunal did not accept that the opinions expressed by Professor Pouton and Dr Scott constituted valid scientific argument, as they did not produce science or data of the type contemplated by section 1.6.3 of the Efficacy Guideline, and the Tribunal preferred the evidence of Professor Mills concerning the meaning of valid scientific argument: TD at [258]. The Tribunal then stated (at [TD [258]):

Critically, and ultimately fatal to this application, any literature produced does not fit within the description of “literature using the proposed final formulation manufactured by or for sponsor”.

25    The Tribunal then referred to the acceptance by Professor Pouton and Dr Scott of the proposition that none of the other products, or the product formulations that were the subject of earlier studies, was the same as the formulation for the product in question for which IAHP sought registration: TD at [259]–[260]. The Tribunal had referred earlier in the reasons to the concessions by Professor Pouton (TD at [54]) and Dr Scott (TD at [127] and [133]) to that effect. The Tribunal also referred to Dr Scott’s concession that he did not have any hard data to demonstrate that the oral administration of Trimidine Paste would result in the same therapeutic plasma concentrations as for all of the other products that had been registered, and said that the whole crux of the matter was scientific argument: TD at [261]. The Tribunal said that those concessions by Professor Pouton and Dr Scott (that the Trimidine Paste does not have the exact or same specific product formulations as the related or similar products) were “caught by the language” of section 1.6.3 of the Efficacy Guideline”, meaning that its requirement to establish a “valid scientific argument” has not been satisfied: TD at [262].

26    Further, the Tribunal accepted Professor Mills’ evidence that far better data was required than merely a conclusory opinion from two experts in order to satisfy the efficacy criteria, and Professor Mills was not insisting that a bioequivalence study was the only way of satisfying the efficacy criteria: TD at [263]–[264]. The Tribunal had found earlier in the reasons that Professor Mills said that efficacy and safety can be demonstrated using a bioequivalence study, comparing the investigatory drug to a currently registered formulation, but did not say that such a bioequivalence study was essential: TD at [50]–[51]. However, the Tribunal said that in Professor Mr Mills’ opinion, “bioequivalence is the cornerstone of generic medications” (TD at [149]), a proposition with which Dr Scott agreed, adding that a bioequivalence trial was “the gold standard” for Dr Scott (TD at [56]).

27    The Tribunal then said that, even if the opinions of Professor Pouton and Dr Scott could be characterised as “valid scientific argument”, that would not be sufficient to justify registering a veterinary product because such opinions can be contradicted by equally genuinely held valid expert opinions of others: TD at [265]–[267].

28    Accordingly, the Tribunal was not satisfied that Trimidine Paste met the efficacy criteria in s 5B of the Agvet Code, and affirmed the decision under review.

Ground 1: The meaning of “valid scientific argument”

29    By Ground 1, IAHP contends that the Tribunal misconstrued the expression “valid scientific argument” in s 6(b)(v) of the Efficacy Determination. IAHP submits, and I accept, that the argument which it advanced before the Tribunal as constituting valid scientific argument consisted of the opinions of Professor Pouton and Dr Scott, which relied in substantial part on the similarities between Trimidine Paste and other products which were already approved, but without having undertaken clinical trials or bioequivalence studies. The APVMA also accepted that characterisation of IAHP’s argument before the Tribunal (T63.35–64.14). Although counsel for the APVMA also submitted that IAHP was contending that the regulatory precedents alone constituted a valid scientific argument, the APVMA was unable to identify where such an argument was put by IAHP (T64.18–66.20), and I find that it was not put.

30    The Tribunal’s construction of the term “valid scientific argument” is set out in its reasoning at TD [242]. First, the Tribunal reasoned that scientific literature fell within the term, but only if it used “the proposed final formulation manufactured” by the sponsor, citing the passage in section 1.6.3 of the Efficacy Guideline extracted at [10] above. Second, the Tribunal said that data or information from studies, clinical trials and other investigations was required. Third, the Tribunal said that a valid scientific argument is more than simply one expert’s opinion based on subjective assumptions about the efficacy of a product.

31    In my view, that reasoning proceeds on an erroneous construction of the term “valid scientific argument”. The term is not defined in the Efficacy Determination or elsewhere in the relevant legislation, and does not have a technical meaning. In its ordinary and natural meaning, it refers to an argument based on accepted methods of scientific reasoning. That includes the results of empirical studies, but it also includes deductive reasoning using generally accepted scientific premises. The opinions of Professor Pouton and Dr Scott were based on deduction rather than empirical study, and the Tribunal expressed a very high regard for their scientific knowledge and ability.

32    The three aspects of the Tribunal’s reasoning at TD [242], to which I have referred at [30] above, are all misplaced. As to the first proposition, the Efficacy Guideline does not say that any scientific literature sought to be relied upon must be in relation to the same formulation as the product which is sought to be registered. Rather, it says that that is the most relevant evaluation, deserving of the highest evidentiary weight. Literature which uses a different formulation is properly said to be deserving of less weight. However, that does not mean that literature deserving of less weight can be disregarded on the basis that it does not provide valid scientific argument. As to the second proposition, information and data from studies, trials and experiments are encapsulated in the matters listed in s 6(b)(i) to (iv) of the Efficacy Determination. The concept of “valid scientific argument” in s 6(b)(v) is clearly intended to add something additional to those other matters, and s 6(b)(vi) envisages a possible (but not mandatory) combination of s 6(b)(v) with one or more of s 6(b)(i) to (iv). There is no reason to construe s 6(b)(v) as necessarily requiring such a combination. As to the third proposition, the Tribunal did not identify what it intended to refer to by the phrase “based on subjective assessments”, and it appears to be a misplaced characterisation of the opinions of Professor Pouton and Dr Scott, as counsel for the APVMA seemed to accept (T70.24–25).

33    As indicated at [27] above, the Tribunal also reasoned that even if the opinions of Professor Pouton and Dr Scott could be characterised as “valid scientific argument”, that would not be sufficient to justify registering a veterinary product because such opinions can be contradicted by equally genuinely held valid expert opinions of others: TD at [265]–[267]. However, s 6(b) of the Efficacy Determination contemplates that, if something constitutes a “valid scientific argument”, then it may be capable, without more, of evidencing or demonstrating that the product achieves to a reasonable degree one of the effects listed in s 5(2)(a) to (d) of the Agvet Code. Whether it does so must be determined by reference to the merits of the particular “valid scientific argument” in question. It cannot be determined merely by referring to the theoretical possibility that an expert opinion might be contradicted by another equally valid expert opinion.

34    Ultimately, counsel for the APVMA accepted that regulatory precedent in conjunction with the expert evidence of Professor Pouton and Dr Scott can constitute a valid scientific argument (T63.5–9).

35    In my view, Ground 1 has been established.

Ground 2: Regulatory consistency and precedent

36    Ground 2 challenges the Tribunal’s reasoning at TD [250] and [252] to the effect that previous decisions to register products cannot be considered as relevant or relied on in deciding whether the Efficacy Criteria are established. An aspect of IAHP’s case before the Tribunal was to contend that Trimidine Paste was sufficiently similar to other products that had been registered such that it too should be registered. IAHP’s point was that if the APVMA was satisfied that certain products were efficacious and safe, and if Trimidine Paste was like those other products, then APVMA’s conclusions in respect of those products was a circumstance that could assist it (together with other evidence) to be satisfied of the efficacy and safety of Trimidine Paste. IAHP’s case was not that other products or approvals were in themselves, and without more, determinative, but merely that they were relevant as matters to be taken into account.

37    The Tribunal rejected that line of argument in absolute terms at TD [250], saying that other product approvals or registrations were “irrelevant”, and reliance on them was inconsistent with the statutory scheme. The Tribunal was not deciding the matter merely as one of evidentiary weight or probative value in the particular circumstances of this case, but was construing the legislation in emphatic terms as rendering such matters irrelevant.

38    In my view, the Tribunal’s reasoning exposes an error of law. Comparisons with similar products that have been registered on the basis that they meet the safety and efficacy criteria may well inform a decision about the safety and efficacy a new product, and may well form part of a valid scientific argument. There is nothing in the legislative scheme which indicates that such a comparison is ipso facto irrelevant. Indeed, counsel for the APVMA accepted that the regulatory precedents were relevant as a strand of what IAHP advanced on its efficacy case (T67.8–19), and that an element in the Tribunal’s reasoning was knocking out the regulatory precedents as being relevant in any way to demonstrate how the drug is going to work (T71.15–20).

Ground 3: The level of appropriate scrutiny

39    Ground 3 challenges the references by the Tribunal to the need for “a significant level of scrutiny” (TD at [237]) and the way that the expert evidence highlighted “the level of scrutiny” (TD at [217]) that must be applied to an application such as this. IAHP submits that a significant level of scrutiny adds an impermissible gloss on the legislation, which does not require such a cautious attitude.

40    I reject this ground. In those passages, the Tribunal was doing no more than referring to the importance of the decision at stake and the careful scrutiny required by the statutory scheme in reaching it. Those matters were plainly consistent with the legislation, and were commendably reflected in the Tribunal’s references to a significant level of scrutiny being required.

41    Before leaving this ground, there was some debate between the parties concerning the formulation approved by the Full Court in NDIA v Lampard at [31] that being “satisfied” means reaching a state of positive satisfaction or relative certainty. I accept that being satisfied means reaching a state of positive satisfaction, but I do not understand the reference to “relative certainty”. Presumably, “relative certainty” is a higher state of assurance than
“positive satisfaction”, in which case it is otiose. Further, in the present context of legislation which uses terms such as “management of risk” and “risk” (subs 1A(2) of the Agvet Code), and achieving effects “to a reasonable degree” (s 6(a) of the Efficacy Determination), references to “relative certainty” would be inapposite.

Ground 4: Procedural fairness

42    By Ground 4, IAHP contends that the Tribunal denied it procedural fairness in finding that the possibility of antimicrobial resistance in using Trimidine Paste was a significant safety issue for humans within the meaning of s 5A of the Agvet Code.

43    The background circumstances were as follows. Professor Mills’ letter to the APVMA of 22 May 2022 stated his opinion that the use of Trimidine Paste according to the label instructions would not be likely to have an unintended effect that is harmful to the target animals, but otherwise made no reference to safety concerns, and said nothing about human safety. The statement of reasons for the APVMA’s decision of 18 April 2023 did say, however, that the safety criteria for the proposed product had not been satisfied if packaged in the 1.2 litre pack size (at [28]).

44    APVMA’s Statement of Facts Issues and Contentions (SOFIC) dated 11 December 2024 at [26] stated that there were two limbs to the safety criteria issue: the first was the general safety issue covered by Professor Mills’ expert evidence (which was dealt with in APVMA’s SOFIC at [27]–[34]); and the second was the more specific issue concerning only the safety of IAHP’s proposed 1.2 litre pail package for Trimidine Paste (which was dealt with in APVMA’s SOFIC at [35]–[38]). Nothing was said in APVMA’s SOFIC or in Professor Mills’ expert report concerning antimicrobial resistance or potential harm to human health. IAHP responded by way of an Amended SOFIC on 30 March 2025 (dealing with the safety criteria issues at [11]).

45    On the first day of the hearing before the Tribunal, counsel for the APVMA said that the efficacy criteria were the main issue in the case, and that there was a safety criteria issue about the pail or “bucket” (possibly a mistake for “packet”) sizes (transcript of the Tribunal proceedings at T55.40–42 on 6.8.25). A little later that day, Professor Pouton was asked a question in cross-examination as to whether, if a chemical product is administered to a horse in a way that is subtherapeutic, it can result in outcomes such as antimicrobial resistance, with which Professor Pouton agreed (T72.11–14 on 6.8.25). Professor Pouton was then asked whether that was an undesirable outcome, with which he agreed but said that it was not likely to happen because these antibiotics are given in relatively high doses to ensure that that does not happen (T72.16–19 on 6.8.25). Dr Scott also agreed that if he was wrong about the therapeutic impact of this new formulation, one of the risks of “subclinical medication” such as this is that it could result in antimicrobial resistance, although he added that that depends on one’s understanding of antimicrobial resistance (T86.1–10 on 6.8.25).

46    The following day, Dr Margerison was asked a question in cross-examination concerning the statutory test that the 1 kg pail was being presented as achieving or not achieving. In the course of his lengthy answer, Dr Margerison said that if animals were given understrength antimicrobials, antibacterials or antibiotics, there was a possibility of inducing antibiotic resistance or facilitating the growth of resistant microbes, and that “can have wider implications, not just for the animals being dosed, but also for other animals, and indeed, humans if these microbes are also pathogenic in humans” (T12.41–13.22 on 7.8.25). Dr Margerison described the risk of that happening with a 1 kg tub as “somewhere in between” an outside risk and a likelihood, and a “possibility rather than a likelihood” (T13.35–43 on 7.8.25). Dr Mills also gave evidence in cross-examination that day that if antibiotics do not cure the infection then it has failed as an antibiotic, and if the infection is not fully treated then one is “predisposing to antimicrobial resistance developing” (T41.7–11 on 7.8.25).

47    The APVMA’s closing written submissions dated 19 September 2025 referred to the evidence concerning comparisons with products that were already approved, and then referred to the evidence by Professor Pouton, Professor Mills and Dr Scott to the effect that if the infection was not fully cured, then that could result in antimicrobial resistance (at [45]–[47]). The APVMA then submitted that it was open to the Tribunal to find that it could not be satisfied that the safety criteria were met, where it had only the opinion of IAHP’s experts expressing an assumption, but otherwise conceding that there was no actual data demonstrating that Trimidine Paste would be as safe and effective as existing products (at [48]).

48    In considering the issue of the safety criteria in its reasons, the Tribunal referred to what it described as the “extremely important” evidence given by Dr Margerison in cross-examination to the effect that administering less than a prescribed dose of the product on the label posed a risk to animals due to the development of antimicrobial resistance and thus potentially to humans if those microbes are also pathogenic to humans: TD at [193] and [204]. The Tribunal regarded that potential for wider implications as a “significant safety issue within the meaning of s 5A of the Agvet Code”: TD at [212] (and see [218]).

49    IAHP submits, and I accept, that it was never on the cards that what Dr Margerison said in evidence would be relied on by the Tribunal to consider whether there was a risk to human health arising from antimicrobial resistance, and the Tribunal’s reliance on it involved a denial of procedural fairness, for the following reasons:

(a)    at no time did APVMA put human health in issue, nor did the Tribunal raise it as a potential issue;

(b)    human health was not raised in the decision under review, which heightens the importance of the Tribunal making it clear that it was to be an issue on review: see Minister for Immigration and Citizenship v LLR24 [2026] FCAFC 26; (2026) 315 FCR 297 at [32]–[43] (O’Sullivan, McElwaine and Hill JJ);

(c)    the APVMA did not rely on Dr Margerison’s evidence in its closing written submissions, and none of the witnesses to whom the APVMA did refer identified any risk to human health; and

(d)    Dr Margerison’s evidence upon which the Tribunal relied was given in the context of whether Trimidine Paste could be approved for a 1 kg pack size, which had fallen away as an issue in the APVMA’s closing written submissions, and in any event the evidence was hypothetical (being prefaced by the words “if these microbes are also pathogenic in humans”).

50    As IAHP submits, procedural fairness required the Tribunal to bring to IAHP’s attention the critical issues or factors on which its decision was likely to turn so that IAHP may have an opportunity of dealing with them: Kioa v West [1985] HCA 81; (1985) 159 CLR 550 at 587 (Mason J); Commissioner for Australian Capital Territory Revenue v Alphaone Pty Ltd (1994) 49 FCR 576 (Alphaone) at 591 (Northrop, Miles and French JJ). The APVMA submits, and I accept, that the statutory framework within which a decision-maker exercises statutory power is of critical importance when considering what procedural fairness requires: SZBEL v Minister for Immigration and Multicultural and Indigenous Affairs [2006] HCA 63; (2006) 228 CLR 152 at [26] (Gleeson CJ, Kirby, Hayne, Callinan and Heydon JJ). However, this was not an issue which was apparent from the nature of the decision or the terms of the statutory power (see Minister for Immigration and Citizenship v SZGUR [2011] HCA 1; (2011) 241 CLR 594 at [9] (French CJ and Kiefel J), noting that harm to human beings is only one of a wide range of matters referred to in s 5A(1) of the Agvet Code. Nor was this “an obvious and natural evaluation” of the material before the Tribunal (see Alphaone at 591), in circumstances where the APVMA had never raised it as an issue.

51    Although IAHP did make submissions on the issue of antimicrobial resistance in its closing oral address, that was by way of a fall-back to its primary submission (which I regard as well-founded) that APVMA was not entitled to rely on the issue (see IAHP’s written submissions in reply at [2(b)], and transcript of 14.10.25 at 3.35–4.9), as counsel for the APVMA rightly accepted (T88.24–27).

52    Further, contrary to the APVMA’s submissions (at T91.32–92.1), I do not regard the opportunity for IAHP to have re-examined Professor Pouton and Dr Scott on the issues as sufficient to meet the demands of procedural fairness, particularly when their evidence was taken before Dr Margerison’s evidence. It was Dr Margerison’s evidence which the Tribunal regarded as “extremely important”. In any event, legal representatives should have a reasonable and fair opportunity to discuss the issues which are actually in contest with their clients and witnesses. Again contrary to the APVMA’s submissions (at T92.6–7), the opportunity to seek an adjournment of the hearing or to seek leave to adduce further evidence does not cure the denial of procedural fairness.

53    Accordingly, I find that the Tribunal denied IAHP procedural fairness in relation to this issue.

54    Further, IAHP submits, and I accept, that the denial of procedural fairness was material. That was accepted by the APVMA within the confines of Ground 4 (T23.29–38).The question is whether a different decision could have been made, and there will generally be a realistic possibility that a decision-making process could have resulted in a different outcome if a party was denied an opportunity to present evidence or make submissions on an issue that required consideration: Nathanson v Minister for Home Affairs [2022] HCA 26; (2022) 276 CLR 80 at [32]–[33] (Kiefel CJ, Keane and Gleeson JJ); and see to similar effect [46] (Gageler J).

Ground 5: Finding that the possibility of antimicrobial resistance was a significant safety issue for humans

55    By Ground 5, IAHP contends that the Tribunal’s finding that the possibility of antimicrobial resistance was a significant issue for humans in using Trimidine Paste was (a) unreasonable; or (b) based on a misunderstanding of the evidence such that the Tribunal did not consider the applicant’s claim and/or denied the applicant procedural fairness.

56    In light of my finding that Ground 4 is established, it is not necessary to consider this ground. Nor do I regard it as desirable to do so, as there is a high likelihood that the evidence and arguments in relation to this issue on the remitter will be substantially different from the evidence and arguments leading to the decision under review.

Conclusion

57    I have found that Grounds 1, 2 and 4 are established. Those grounds in combination pertain to both the safety criteria and the efficacy criteria. Accordingly, the Tribunal’s decision made on 17 December 2025 should be set aside and the matter should be remitted to the Tribunal for consideration according to law.

58    It is common ground that the costs of these proceedings should follow the event. APVMA should therefore pay IAHP’s costs of these proceedings.

Associate:

Dated:    22 July 2026