Nitrosamine Impurities: Nitrosamines are a class of organic compounds characterized by a nitroso group (–N=O) bonded to a secondary or tertiary amine (NR₂).
Common examples include N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA). While nitrosamines have industrial applications, their unintended presence in medicines is problematic because many are classified as probable human carcinogens.
Several nitrosamines have been identified in pharmaceuticals, including:
These have been detected in various drug classes like sartans (antihypertensives), ranitidine (acid reducer), and metformin (antidiabetic agent).
Nitrosamine impurities can enter pharmaceutical products through several pathways:
The complexity of pharmaceutical supply chains and variability in manufacturing practices globally make it challenging to eliminate these impurities entirely.
| Nitroso Impurity | Type | Source or Context |
|---|---|---|
| Nitrosamines | Secondary nitroso compounds | Formed from amines + nitrites |
| Nitrosoaniline | Aromatic nitroso compound | Byproduct in dye intermediates |
| N-Methyl-N-nitrosoaniline | Nitrosamine | Intermediate Degradation product |
| N-Nitrosodimethylamine (NDMA) | Nitrosamine | Found in ranitidine, metformin, sartans |
| N-Nitrosodiethylamine (NDEA) | Nitrosamine | Found in valsartan |
| Nitrosophenols | Phenol derivatives | May occur via oxidative degradation |
| N-Nitrosomorpholine | Cyclic nitrosamine | Found as impurity or degradation product |
| N-Nitrosopyrrolidine | Cyclic nitrosamine | Possible byproduct from pyrrolidine use |
Nitrosating agents are chemical compounds that introduce a nitroso group (–NO) into other molecules, typically amines, to form nitrosamines. These agents are key contributors to the unintentional formation of nitrosamine impurities in pharmaceuticals.
Secondary and tertiary amines are key precursors in the formation of nitrosamine impurities due to their reactivity with nitrosating agents, leading to potentially carcinogenic nitrosamines.
Nitrosamines form via a nitrosation reaction involving:
| Factor | Why It Contributes |
|---|---|
| Nucleophilicity of amines | Amines easily attack the electrophilic nitrosating species (like NO⁺). |
| Stability of nitrosamines | Once formed, nitrosamines are stable and persist in the product. |
| Presence of nitrites/nitrates | Common in reagents, water, or excipients — reacts with amines. |
| Reaction under mild conditions | Reaction can occur at room temperature and low pH (e.g., pH 3–5). |
| Amine (Source) | Type | Drug/Product Context | Nitrosamine Formed |
|---|---|---|---|
| Dimethylamine (DMA) | Secondary amine | Degradation product of DMAc, DMF, or certain APIs | NDMA (N-Nitrosodimethylamine) |
| Diethylamine (DEA) | Secondary amine | Impurity or reagent in API synthesis | NDEA (N-Nitrosodiethylamine) |
| Isopropylamine | Secondary amine | Used in synthesis of some APIs | NDIPA (N-Nitrosodiisopropylamine) |
| Methylphenylamine | Secondary amine | Intermediate or impurity | NMPA (N-Nitrosomethylphenylamine) |
| Morpholine | Secondary amine | Solvent or stabilizer | NMOR (N-Nitrosomorpholine) |
| Pyrrolidine | Secondary amine | Intermediate or degradation product | NPYR (N-Nitrosopyrrolidine) |
| Piperidine | Secondary amine | Common ring in drug scaffolds (e.g., antihistamines) | NPIP (N-Nitrosopiperidine) |
| Triethylamine (TEA) | Tertiary amine | Base or pH adjuster in synthesis | Forms DEA, which can form NDEA |
| Tetramethylammonium hydroxide | Tertiary amine | Used in analytical and synthetic processes | Degrades to DMA → NDMA |
| Tributylamine | Tertiary amine | Catalyst or base in synthesis | Can degrade into secondary butylamines |
| 2° amine-containing APIs | Secondary amine | e.g., Ranitidine, Nizatidine | Degrade into NDMA under heat/acid |
| API intermediates with amino groups | Secondary amine | Varies (e.g., sartans, anti-diabetics) | Form specific nitrosamines based on structure |
| Source Type | Examples | Risk Contribution |
|---|---|---|
| Solvents | DMF (Dimethylformamide), DMAc (Dimethylacetamide), NMP, TEA | May contain or degrade to secondary amines like DMA |
| Reagents / Catalysts | Diethylamine, isopropylamine, morpholine, pyrrolidine | Direct sources of secondary amines |
| API / Intermediates | Drug substances with amine functionalities (e.g., piperidine, morpholine rings) | Can participate in nitrosation reactions or degrade to reactive amines |
| Excipients | Magnesium stearate, talc, microcrystalline cellulose (if contaminated) | May contain nitrites or residual amines as impurities |
| Water | Recycled or industrial-grade water | May contain trace nitrites and other ions that support nitrosation |
| Cleaning Agents | Triethylamine-based cleaning solvents used in GMP facilities | Residual amines left on equipment can react during production |
| Degradation Products | From drug substance or excipients during shelf-life | e.g., Ranitidine decomposes to NDMA |
| Packaging Materials | Blister films, inks, adhesives, nitrocellulose-based coatings | Can release amines or nitrites over time or under heat/humidity |
| Gaskets & Liners | Rubber stoppers, laminated seals, container closures | May contain amine-based antioxidants, accelerators, or residuals |
| Ink and Printing | Nitrocellulose inks on foil or label | Can release NOx compounds and react with amines nearby |
Extractables and leachable (E&L) studies are critical when assessing nitrosamine risk.
| Drug | Nitrosamine Found | Amines Involved |
|---|---|---|
| Valsartan | NDMA, NDEA | DMA (from solvent), DEA (impurity) |
| Ranitidine | NDMA | Secondary amine in API itself |
| Metformin | NDMA | Possibly from nitrite contamination |
| Irbesartan | NDIPA | Isopropylamine used in synthesis |
| Losartan | NMBA | Byproduct of butyric acid derivatives |
| Nitrosamine | AI Limit (ng/day) | Source |
|---|---|---|
| NDMA (N-Nitrosodimethylamine) | 96 ng/day | EMA, FDA |
| NDEA (N-Nitrosodiethylamine) | 26.5 ng/day | EMA, FDA |
| NMBA, NDIPA, NEIPA, etc. | Varies | Case-by-case |
This matches the AI limit for NDMA → Acceptable.
4. Calculate Maximum Allowable Nitrosamine Content per Unit: If you need to find how much nitrosamine is allowed per tablet, use:
Max per unit = AI Limit (ng/day) / Max daily dose units
Example for NDMA:
If more than one nitrosamine is present:
Where:
This is known as the “Sum of Ratios” approach per ICH M7 and EMA guidelines
Where: PDE: Permitted Daily Exposure (PDE)
Limit=(0.096×1000)/320=0.3 ppm
NDMA limit in Valsartan = 0.3 ppm
Limit=(0.096×1000)/2000=0.048 ppm
NDMA limit in Metformin = 0.048 ppm
Limit=(0.096×1000)/100=0.96 ppm
NMBA limit in Losartan = 0.96 ppm
Limit=(0.096×1000)/300=0.32 ppm
NDMA limit in Ranitidine = 0.32 ppm
Limit=(0.0265×1000)/300=0.0883 ppm
NDIPA limit in Irbesartan = ~0.088 ppm
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