The analysis of N-nitrosodimethylamine in antihistamines and cough/cold preparations.

Three antihistamines (diphenhydramine hydrochloride, methapyrilene hydrochloride, doxylamine succinate) and three commercial cough syrups have been analysed by GLC-TEA for N-nitrosodimethylamine (NDMA). Levels of 0.22-3.6 micrograms/kg N-nitrosodimethylamine and, unexpectedly, 0.35-2.7 micrograms/kg N-nitrosodiethylamine were found in the antihistamine drug samples. Of those amounts, 0.24-0.29 micrograms/kg NDMA and 0.15-0.20 micrograms/kg NDEA was shown to be inherent in the water used for analysis. Only one cough syrup contained detectable NDMA (0.05 micrograms/kg) and the level was of the order of that normally found in deionized water. The factors influencing the formation of volatile nitrosamines from these antihistamines in the human stomach are discussed.