On 24 September 2026, FDA reversed a position it had defended for five years. CDER announced that the less-than-lifetime (LTL) approach described in ICH M7(R2) may now be applied to acceptable intake limits for nitrosamine impurities, an approach the agency had previously refused to accept. For sponsors sitting on a borderline NDSRI result in a short-duration product, the arithmetic of their entire control strategy just changed. team-mastery
Why NDSRIs resist conventional impurity thinking
Normal impurities (like NDMA) come from external pollution, but NDSRIs grow directly inside the medicine. Regular nitrosamine impurities usually get into drugs from the outside through dirty liquids, reused chemicals, or contaminated raw materials. NDSRIs form differently. They develop when tiny traces of chemicals called nitrites react directly with the core ingredients (APIs) of the medicine itself. Because they form from the medicine’s own structure, each NDSRI is unique to that specific drug.
Because these impurities are unique to each specific drug, they cause three major issues: companies cannot buy ready-made chemical samples to test against, there is very little animal safety data to show how dangerous they are, and the chemical that triggers them (nitrite) is found everywhere in basic ingredients, factory water, and recycled liquids. This means the danger never really goes away, and the harmful impurities can keep forming throughout the medicine’s entire shelf life instead of just when the raw ingredients are being mixed.
How the AI limit is actually assigned
FDA’s August 2023 guidance, Recommended Acceptable Intake Limits for Nitrosamine Drug Substance-Related Impurities, supplies a methodology that uses structural features of the NDSRI to generate a predicted carcinogenic potency categorisation and a corresponding recommended AI limit, to be applied where no other FDA-recommended limit exists. The scheme assigns five potency categories, with Category 1 set at 26.5 ng/day, equal to the class-specific limit derived from NDEA, the most potent robustly tested nitrosamine and Category 5 at 1500 ng/day, the TTC per ICH M7(R2). fdapropharmagroup
Two differences matter when a drug is being filed in multiple countries. The EMA’s Category 1 limit is 18 ng/day, compared with the FDA’s 26.5 ng/day. This means companies may need to justify their specifications to meet both agencies’ requirements.
When more than one nitrosamine is present, the FDA recommends that the total amount stay within the acceptable intake limit of the most potent impurity found.
The LTL adjustment: what it does and does not unlock
Products with shorter treatment durations, as defined in approved labelling, may now justify higher AI limits, up to 80× the lifetime limit for treatments of one month or less, scaling down to no adjustment for durations exceeding ten years. The adjustment is not available for interim AI limits, including those in Table 3 of the nitrosamine guidance, and applicants with pending applications are expected to notify CDER if they intend to propose an LTL-adjusted limit and amend accordingly. FDA opens the door to LTL adjustment for nitrosamines +2
Treat LTL as a way to justify your control strategy, not as a reason to relax process controls. The permitted duration can change depending on the product label. If your control strategy only works at 80 times the acceptable intake limit, there is very little room for error.
Building the control strategy from the chemistry backwards
Remove the source of nitrite before trying to control the impurity. Check every stage of the process where nitrite could enter, including raw materials, recovered solvents, process water, and excipients in the finished product. Setting limits for nitrite in incoming materials can be less expensive than controlling it through the final drug product specification.
Review the entire manufacturing process, not just the final step. Check for nitrous acid formed during quenching, leftover nitrite from diazotisation, and intermediates containing amines that may carry through to later steps. Under ICH M7(R2) principles, you need evidence to show how effectively these impurities are removed during the process.
Make sure testing methods are sensitive enough. Testing often requires LC-MS/MS or GC-MS/MS methods that can detect impurities at sub-ppb levels. These methods need to be checked against a synthesised and fully characterised NDSRI reference standard. Getting this standard made can become one of the biggest delays in the programme.
Use the 10% rule deliberately. A specification is not required where nitrosamine levels are consistently not more than 10 percent of the recommended AI limit, provided the root cause is well understood and manufacturing process controls are established and validated. That clause rewards mechanistic understanding and penalises sponsors who only have batch data. fda
Design the formulation to reduce the risk. Antioxidants, pH control, and methods to remove or reduce nitrite can help limit NDSRI formation in the finished product. Regulators will look at stability data to see whether these measures work in practice.
Where this lands
Smart companies stop harmful impurities (NDSRIs) before they even form. Instead of waiting for final lab tests to catch problems, these manufacturers study the production process early on. They figure out exactly how these impurities might develop and design safety controls right from the start.
LAXAI Life Sciences supports that work end to end. Our analytical R&D infrastructure, including UPLC-MS, LC-MS, GC-MS and Bruker 400 MHz NMR, underpins method development, impurity characterisation and reference standard qualification, while our process R&D team applies route scouting, process safety evaluation and QbD-based process development to engineer nitrosamine risk out of the synthesis itself. Across scale-up from 20 L to 250 L reactors and into cGMP API manufacture for US, European and Japanese markets, impurity control is designed into the process rather than tested into the batch.
