Nitrosamine Impurities: Staying Ahead of Evolving Pharmacopoeial Requirements

Published 23 April 2026 · By Dr Priya Raghavan, Principal Scientist, Pharmaceutical Reference Standards

What began in 2018 as a contamination incident affecting a single class of antihypertensives has settled into a permanent feature of pharmaceutical quality control. Nitrosamines are no longer treated as an exceptional finding to be investigated when detected; they are a class of impurity that manufacturers are expected to anticipate, assess and control across the full product lifecycle. For quality control laboratories, that shift changes what sits on the shelf as much as what happens at the instrument.

From recall response to routine control

Regulatory expectation has converged around a three-stage approach: a documented risk assessment of every marketed product and pipeline candidate, confirmatory analytical testing where risk is identified, and ongoing control through specifications, process change and, where necessary, reformulation. The European Medicines Agency, the FDA and the pharmacopoeias have each reinforced this structure, and the general chapters now in force treat nitrosamine testing as a standard analytical discipline rather than an emergency measure.

The consequence for the laboratory is practical. Testing at parts-per-billion levels against acceptable intake limits expressed in nanograms per day is no longer occasional work. It requires validated methods that stay validated, and reference standards whose values you can defend years after the batch was released.

The expanding list of analytes

Early work focused on a small group of simple, volatile nitrosamines. The scope has widened considerably and now routinely includes:

• Small alkyl nitrosamines such as NDMA, NDEA, NMBA, NDIPA, NEIPA and NDBA, typically determined by GC-MS/MS or LC-MS/MS.
• Nitrosamine drug substance related impurities (NDSRIs) — nitrosated derivatives of the active substance itself, which are structurally unique to each product and cannot be sourced as generic materials.
• Nitrosated degradants and process-related species arising from secondary or tertiary amine functionality in intermediates, excipients or packaging interactions.

NDSRIs are the harder problem. Because each one is specific to a single molecule, there is no universal catalogue solution, and the carcinogenic potency categorisation approach used to set acceptable intake limits often places them at the most demanding end of the scale. Laboratories increasingly need custom synthesis and full characterisation rather than an off-the-shelf vial.

What your reference standard has to prove

At these concentrations, the standard is the measurement. A certificate that states purity as a single number without explaining how it was determined is not sufficient for a regulatory filing. Look for:

• A mass balance or quantitative NMR assignment of the assigned value, with the method stated.
• An expanded measurement uncertainty with the coverage factor declared.
• A traceability statement linking the value to national or international standards.
• Identity confirmation data — typically NMR, high resolution mass spectrometry and chromatographic purity.
• Stability and storage guidance, with a retest date rather than an arbitrary shelf life.
• Production under ISO 17034 where the material is supplied as a certified reference material.

Isotopically labelled internal standards deserve the same scrutiny. Deuterated nitrosamine analogues are widely used to correct for matrix suppression, and their isotopic purity directly affects the accuracy of low-level quantitation.

Method design choices that age well

Laboratories that have avoided repeated revalidation tend to share a few habits. They design methods with headroom below the current limit rather than at it, so that a tightened acceptable intake does not force a rebuild. They characterise matrix effects for each formulation rather than assuming transferability between products. They control nitrite in reagents, water and excipients, since artefactual formation during sample preparation remains a genuine source of false positives. And they document the entire standards chain in the method record, because an assessor reviewing data three years later will follow that chain first.

A practical review cycle

1. Re-examine the risk assessment whenever a supplier, route or excipient changes — not only at scheduled review.
2. Check that every analyte on your specification maps to a currently held, in-date reference standard.
3. Verify calibration against an independent lot at defined intervals.
4. Track pharmacopoeial and agency updates to acceptable intake values and confirm your limits remain compliant.
5. Retain certificates against the batch record so that traceability survives staff and system changes.

The wider point

Nitrosamine control is demanding because the stakes are real: these are probable human carcinogens present in medicines taken daily, often for life. The laboratories handling it well have stopped treating it as a compliance burden and started treating it as a measurement problem with a metrological answer. Traceable standards, honest uncertainty statements and methods designed with margin are what turn a difficult analysis into a defensible one.