Mechanistic Evaluation and Analytical Mitigation of Excipient-Induced in-Situ Nitrosamine Formation in Solid Oral Dosage Forms: An Integrated Formulation and Validated Chromatographic Control Strategy

Background: Recurring international recalls of essential oral solid dosage forms contaminated with Nitrosamine Drug Substance-Related Impurities (NDSRIs) expose a fundamental vulnerability in conventional tablet manufacturing. Trace inorganic nitrites (0.1–10.0 µg/g) present across widely used excipients like crospovidone and microcrystalline cellulose react directly with vulnerable secondary amine drugs during standard processing and routine shelf storage. Objective: Here, we developed an economically practical, scalable formulation strategy to suppress excipient-mediated nitrosamine formation using food-grade antioxidant scavengers, paired with an accessible isocratic reverse-phase high-performance liquid chromatography (RP-HPLC-UV) analytical control method validated strictly against ICH Q2(R2) and ICH Q14 requirements. Methods: Propranolol hydrochloride served as a representative aliphatic secondary amine (pKa = 9.45). Direct-compression binary powder mixtures were spiked with 5.0 µg/g sodium nitrite at microenvironmental pH 3.0, then incubated under accelerated thermal stress (60.0°C ± 1.0°C for 48 hours). We tested the protective capacity of L-ascorbic acid (0.1% and 0.5% w/w) against L-histidine (0.5% w/w). Chromatographic resolution was carried out on an Inertsil ODS-3V C18 column (250 × 4.6 mm, 5 µm) using an isocratic mobile phase of acetonitrile and 25 mM potassium phosphate buffer (pH 3.00 ± 0.05) (55:45, v/v) at 1.0 mL/min with photodiode array detection at 290 nm. Results: Positive control blends generated substantial quantities of N-nitroso-propranolol (NNP; mean peak area 142,580 ± 1,820 mAU·s). Incorporating 0.5% w/w L-ascorbic acid suppressed NNP formation by 98.70% ± 0.06% (p < 0.0001), while 0.5% w/w L-histidine yielded 92.30% ± 0.16% inhibition. Our chromatographic assay satisfied every ICH Q2(R2) requirement: linearity spanned 10.0–150.0 µg/mL (R² = 0.9996), system repeatability remained tight at 0.68% RSD, recovery ranged between 99.12% and 100.82%, with limits of detection and quantification established at 0.42 µg/mL and 1.28 µg/mL, respectively. During 6-month accelerated stability testing (40°C ± 2°C / 75% ± 5% RH), finished tablets retained NNP levels at 0.28 ppm (44.8 ng/day daily intake), leaving a 33.5-fold safety margin below the US FDA limit of 1500 ng/day. Conclusion: Blending 0.5% w/w ascorbic acid offers an accessible, zero-cost-penalty platform that halts mutagenic nitrosation well below global regulatory thresholds, without disturbing tablet hardness, disintegration, or dissolution behavior.