The assessment and control of genotoxic impurities (GTI) in pharmaceutical products has received considerable attention in recent years. Molecular functional groups that render starting materials and synthetic intermediates useful as reactive building blocks for small molecules may also be responsible for their genotoxicity. As a potential safety concern, it is important to understand the various issues related to GTIs and how they can be addressed for clinical and commercial phases of development. Justification that these impurities are controlled to safe levels must be obtained during development. This article will briefly discuss the multiple sources of anticipated impurities in a drug substance (also known as active pharmaceutical ingredient or API) synthetic route and how they are identified as GTIs in early chemical process development. A risk-based approach consistent with regulatory expectations is described for establishing control of GTIs. The approach includes process design considerations, impurity rejection information, and appropriate application of specifications. Analytical considerations for determination of GTIs at low levels are also discussed.
Despite the benefits of high atom economy and low cost, aerobic oxidations have found limited use in the synthesis of active pharmaceutical ingredients (APIs) because of safety concerns and poor selectivity. In this report, the design, development, and scale-up of a continuous, high pressure aerobic oxidation to produce the penultimate of an API are described. The identification of robust homogeneous conditions for the oxidative C−N coupling of interest and the use of diluted air allowed for the process to be safely and selectively carried out on manufacturing scale as a continuous process using a vertical pipes-in-series reactor to prepare high-quality material.
Controlling impurities during drug development improves product quality and minimizes safety risks to the patient. Recent regulatory guidance on genotoxic impurities (GTIs) state that identified GTIs are unusually toxic and require lower reporting, identification, and qualification limits than outlined in the International Conference on Harmonization (ICH) guideline “Impurities in New Drug Substances Q3A(R2).” [ICH Harmonized Tripartite Guideline: Impurities in New Drug Substances (Q3A)International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH)2006] Patient safety is always the underlying focus, but the overall impurity control strategy is also driven by appropriate “as low as reasonably practicable” (ALARP) procedures that include assessment of process capability and associated analytical techniques. In combination with ALARP, safe and appropriate GTI levels are currently identified using chronic toxicology-based limits calculated under the standard assumption of 70-years for exposure duration. This paper proposes a risk assessment approach for developing GTI limits based on shorter-term exposure durations by highlighting marketed anticancer compounds with limited dosing schedules (e.g., 2 years). These limits are generally higher than the defaulted threshold of toxicological concern (TTC of 1.5 μg/day) and can result in more easily developed and less complex analytical methods. The described approach does not compromise safety and can potentially speed life-saving medicines to patients.
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