What's Included in ECHA's Latest DART Dose-Setting Update?

Like much of the developmental and reproductive toxicity community, Blue Frog's DART team have been waiting eagerly for ECHA’s updated dose setting advice, which was released on June 24^th. Now that the update has landed, we’ve reviewed the revised document and summarised the key changes, including notable changes, wording updates and where Board of Appeal decisions are now in use to support requirements throughout.

Five Key Changes to DART Dose-Setting Advice

Overall, the 2026 version introduces five key changes compared with the previous 2022 advice:

1. It is much more explicit that high-dose selection must be evidence-driven.
2. It sharpens the language around the objective of the highest dose, particularly obtaining clear evidence on reproductive toxicity to support classification.
3. It places greater emphasis on “severe suffering” when defining dose-limiting effects, alongside the directives and guidance that may support this interpretation.
4. It tightens expectations around dose-range finding and supporting studies.
5. It updates a number of the example case studies and adds two new examples.

How Significant are ECHA's Dose-Setting Changes Really?

On paper, many of these changes appear helpful. However, the Blue Frog team’s initial response raises further questions on the motivation and rationale for some of the changes:

• While the guidance focuses in on the highest possible dose and severe suffering, it doesn’t provide reassurances on application and harmonisation of approach, particularly across labs and regulatory regimes. Nor does it provide justification on why and whether the highest possible dose is the ‘best dose’ to generate informative data.
• There’s a heavy lean on OECD Guidance Document 19 in supporting ‘severe suffering’, which hasn’t been updated for 25 years, whilst the science & practise of good animal husbandry and welfare has progressed considerably. 
• Adjustment of TK to a fully secondary role, and removal of consideration for effects like irritation as dose limiting feels somewhat premature, and potentially limiting to ensuring study design is optimal.
• Human relevance isn’t covered, at all. 

In practice, we have little doubt that dose-setting in reproductive toxicity studies will remain an area of active debate between scientific, regulatory and industry stakeholders.

Summary of Main Changes to DART Dose-Setting Advice

Below, we summarise the main material changes in the updated advice.

Cross-Cutting Changes: The Goal Hasn’t Changed, but the Legal Tone Has

The practical aim of the studies has not changed, but the wording is more explicit: 

• ECHA have reframed explicitly the wording relating to classification and labelling requirements such that studies should allow conclusion on whether “a substance either has or does not have reproductive toxic properties warranting a classification as Repr. 1B (either F (Fertility) or D (Development) or both).”
• ECHA has expanded the wording around a need for the top dose to ‘induce developmental toxicity or systemic toxicity [to give] clear evidence of adverse effects on reproduction or…allow exclusion’.

Specific reference to Endocrine Disruption and identification of substances of very high concern (SVHC) has been removed (but as CLP remains, this requirement isn’t gone!): 

The 2026 advice replaces 2022’s statement that “The dose-level selection should ensure conclusive data generation for classification and labelling, risk assessment, and whether the substance meets the criteria for a substance of very high concern regarding endocrine disruption according to Article 57(f) of REACH.” with a simpler, more generalist statement “The dose-level selection should ensure conclusive data generation for classification and labelling and risk assessment…”

There is however, a subtle change in legal tone: 

The language around progression from self- to harmonised classification is softened from “is normally subject to harmonised classification” to “may be subject” throughout the document. In practise, this shift in legal tone suggests the outcome may be less absolute than previously indicated. 

Practical Information on Setting High Dose 

The new advice focuses in on severe suffering: 

The advice places more prominently the condition that “Death and clinical signs indicating severe suffering (e.g. prostration, severe inappetence (lack of appetite)) should be avoided” and includes clear reference to application of animal welfare rules such as the framework for severity assessment under Directive 2010/63/EU (protection of animals used for scientific purposes), supported by OECD Guidance Document (GD) 19 (use of humane clinical endpoints). It does not include comment on national welfare laws.

Irritation has left the list of dose limiting criteria: 

“Dosing should be performed at appropriately high dose levels” to support hazard identification and risk assessment. The qualifying text is slightly updated to include additional conditions under which dose may be limited. Notably, the condition of irritation (respiratory tract or otherwise) as a dose limiting effect has been removed. 

Mention of dose levels above 1000 mg/kw bw/d have been removed: 

The statement “Expected human response may indicate the need to use a dose level above 1000 mg/kg bw/day.” is not present in the 2026 version. Further, the 2026 version includes specific mention of not dosing >1000 mg/kg bw/d for OECD 443 studies via the oral route.

There’s more emphasis on experimental data to evidence dose level selection: 

• Excess dose level spacing should be avoided. 
• Where a steep dose-response curve is expected, the usual 2-4 fold spacing mentioned in the guidelines may not be appropriate. 
• Addition of further dose levels in range finding studies (without increasing the number of animals) should be considered 
• Where existing information does not allow robust decision making on dose setting, additional range finding work should be undertaken
• The need to justify and document dose level selection to allow independent evaluation remains. 

ECHA’s position on use of toxicokinetic data is clarified: 

Whilst they consider that TK information may support adjustment of e.g. dose route and regime, or lactational transfer potential, “setting the dose level by toxicokinetic considerations only is not allowed under REACH because dose-level selection should be based on toxicity to ensure that the data generated are adequate for hazard identification”. 

The new advice clarifies some of the practical challenges of sexual dimorphism in sensitivity. This includes: 

• Clarification on what ECHA considers to qualify as a sensitivity difference (e.g. clear differences in sensitivity to the same effects, or clear differences in type of effects)
• The need to test the less sensitive sex at a higher dose. 
• Practical considerations for cohabitation phases in feed or drinking water studies, with emphasis on application of expert judgement: “it may be needed to adjust the highest dose in a feeding or drinking water study to that of the more sensitive sex, to avoid severe suffering and death in the more sensitive sex.” 

Reporting requirements are slightly expanded: 

ECHA now specify that alongside reporting within IUCLID all preliminary and dose-range finding studies, the justification for dose level setting should make specific reference to OECD GD19 or the framework for severity assessment under Directive 2010/63/EU be included. 

Test Guideline Specific Changes 

For the test guideline specific advice, there are some small language changes which have potentially significant impacts, and some alterations in example case studies throughout. 

For OECD TG 414, both language and case studies have been adjusted: 

• Re. dose setting in rat studies, the language of the 2026 advice narrows the evidence base to use of pregnant rats / same strain (previously this was ‘preferably same strain’ with no reference to pregnancy). 
• Re. dose setting in rabbit studies, new weight-of-evidence language has been included for interpreting steep dose-responses: “When evaluating the results for prenatal development, all existing information should be taken into account in a weight-of-evidence approach. This means that also information on preliminary studies is considered, e.g. to interpret steep dose response curves.”
• Within the case studies, there’s more emphasis on generating additional data if an initial range finding study does not show maternal or developmental effects, and the threshold for embryo-fetal effects is more concrete, stressing biological relevance in driving dose selection. 

For OECD TGs 421/422 (reproductive toxicity screening studies), small language adjustments and changes in case studies also appear: 

• The language on use of the studies as range finders for the OECD 443 is more generalised, allowing – in principle – greater flexibility on study design 
• The OECD 422 (combined repeated dose and reproductive toxicity screening study) section previously included advice on managing conflict between classification requirements for specific target organ toxicity and adverse effects on sexual function and fertility/developmental toxicity (the first being threshold based, the second being without) in dose setting. This has been removed. Presumably this may be navigated via use of additional dose groups, however, the change introduces a level of ambiguity. 

For OECD TG 443, the language used again differs slightly: 

• Scientific justification language is strengthened and more demanding. It states that dose-level selection should be:
  • “based on actual evidence” – was previously ‘based on existing information’ 
  •  and that “there should be a case-specific and scientific justification…” 
• The basis for dose level setting as clear evidence of an adverse effect on sexual function and fertility is now supported by Board of Appeal decision (Decision of 29.08.2023, Case A-006-2022, Symrise and Others, para. 59-70). 

The OECD 443 case studies include some subtle but important differences: 

• Case1: reference to use of doses >1000 mg/kg bw/d is removed
• Case 2: wording relating to classification as Repr. 2 (H361f) not being a valid basis to adapt the OECD 443 is tightened
• Case 3: new emphasis is placed on changes in sperm count as a concern for reproductive health 
• Cases 4-6 include some small language changes, making them easier to understand 
• There are also 2 completely new example case studies included: 
  • Case 7: this attempts to provide an example of inappropriate characterisation of severe suffering. Therein, ECHA notes that existing evidence of limited body weight effects (up to 10% reduction vs. control) and a reduction in sperm numbers (by up to 33%) do not by themselves amount to severe suffering and thus do not justify reducing the top dose level.
  • Case 8: focuses on severe suffering (but not death) in existing studies. Here, an existing dataset includes evidence of prostration and breathing difficulties (both severe suffering according to OECD GD19). ECHA advises that the dose level causing this effect is not appropriate, but that as the next dose level is 3-fold lower, generation of new information may be required to determine an appropriate highest possible dose for an OECD 443. 

The 2026 version includes a more detailed criterion vs. the previous from 2022: "For the purpose of classification and labelling, it is critical that the tested doses are sufficiently high to be able to conclude if a substance either has or does not have reproductive toxic properties warranting a classification as Repr. 1B (either F (Fertility) or D (Development) or both).” 

It also expands on the previous language around results expected: “Consequently, the dose selection should set the highest dose so that it aims at inducing developmental toxicity or systemic toxicity in line with the Test Guideline so that the study provides results which are either clear evidence of adverse effects on reproduction or which allow exclusion of clear evidence on reproduction for the tested parameters”.

Furthermore, there’s more explicit reference to OECD Guidance Document (GD) 19 and the framework for severity assessment under Directive 2010/63/EU (protection of animals used for scientific purposes) when considering severe suffering. 

There’s more emphasis on experimental data to set dose levels: 

The new advice includes two paragraphs on the need for available information which evidences clearly selection of dose levels to meet the requirements of the test guideline (TG) at hand. 

Key Outcomes of ECHA's 2026 Dose-Setting Advice Update 

• The focus (unsurprisingly) remains on the EU, and so the question remains ‘how to achieve a harmonized approach between countries and labs, particularly in geographic locations where welfare limits may not allow dosing to such levels’. 
• There’s more direct reference to welfare guidance in the form of OECD GD19, but as this guideline desperately needs to be updated, Blue Frog doesn’t feel this solves the problem of defining ‘severe suffering’ and how to avoid it. 

If you'd like to discuss these dose-setting advice changes in more detail or have any queries relating to DART, call or email and speak directly with one of our toxicology & human health assessment experts.