A pharmaceutical company.


Bibra was asked to investigate two N-nitrosamines extracted from stoppers for vials used within the pharmaceutical sector. The N-nitrosamines were extracted under exaggerated conditions, but it was assumed as a worst-case that they could also leach into the product during storage and use and be administered to patients.

A key toxic feature of N-nitrosamines following their metabolic activation is potent non-threshold genotoxic carcinogenicity. As a chemical class, they have been assigned to the so-called “Cohort of Concern” (CoC), a group of chemicals for which controlling exposures to default Thresholds of Toxicological Concern (TTCs) for genotoxins might not provide adequate protection against cancer. The European Medicines Agency/European Medicines Regulatory Network and the US Food and Drug Administration have both released guidance on the evaluation of N-nitrosamines in pharmaceutical products. Each has provided Acceptable Intake (AI) values for some N-nitrosamines, which specify the dose (by any route) associated with an increased lifetime cancer risk of 1 in 100,000; lower intakes of individual unavoidable N-nitrosamines may be considered tolerable. Guidance is also provided on the risk assessment of N-nitrosamine mixtures.

Project goals

Bibra were asked to identify the Accepted Intake (AI) values for the detected N-nitrosamines and hence determine the increased lifetime cancer risk that may be posed to patients administered the drugs. It was assumed as a worst-case that both N-nitrosamines would be genuine leachables at the levels detected in the extractables study.

Approach and outcome

TRACE was used to identify key genotoxicity and carcinogenicity data on the two N-nitrosamines. These data were summarised in the bibra report. As expected, both N-nitrosamines appeared to be genotoxic carcinogens. AI values from EMA were available for each chemical, although these had been derived based on more robust rodent studies on read-across compounds. In this instance, one of the AI values was much lower than the other, indicating a much higher potency. As both N-nitrosamines may be present together in the same products, and in line with EMA guidance, the total exposure to both N-nitrosamines on a treatment day was compared with this lower AI to allow a conclusion on risk.

The resulting margin was discussed in the context of the intermittent treatment regime. Under EMA stipulations, a total exposure exceeding a relevant AI would not be considered tolerable. AIs are derived to protect against lifetime daily exposure, but EMA also encourages their use (unadjusted) for the risk assessment of Less-Than-Lifetime (LTL) exposures to N-nitrosamines, in order to avoid overwhelming a cell’s DNA repair capacity. There has, however, been recent evidence that, similar to non CoC chemicals (under ICH M7), some higher exposures to N-nitrosamines may be tolerable over a shorter period of time.

Bibra project team

James Hopkins1

James Hopkins

Toxicology Director and Chairman

RSB/BTS and European Registered Toxicologist
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Beth O Connell

Beth O’Connell

Principal Toxicologist

RSB/BTS and European Registered Toxicologist
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