Hydrazine Levels in Formulations of Hydralazine, Isoniazid, and Phenelzine Over a 2-Year Period

□ Hydrazine levels in formulations of hydralazine, isoniazid, and phenelzine have been measured over a 2-year period under ambient conditions and under temperature and humidity stress. Hydralazine tablets are stable under ambient conditions, but the hydrazine level in an injectable formulation increased from 4.5 to 10μg/ml over a 23-month period. Isoniazid tablets are also stable, but hydrazine levels in an elixir and a pyridoxine combination product doubled to 44μg/ml and 19μg/tablet, respectively. Levels in phenelzine tablets appeared to remain constant at ~60 μg/tablet, with considerable tablet-to-tablet variation.