Trace decomposition of selegiline. Use of worst-case kinetics for a stable drug

A solution of selegiline hydrochloride reference standard, which contained no detectable impurities at the time of its preparation, was found by HPLC to contain a trace of a compound at the locus of methamphetamine when analyzed after 1 year. Heating selegiline solutions at pH 7 and 105 degrees C produced methamphetamine as the major product at a rate which closely followed the first-order rate equation. Using only these data and worst-case assumptions, rate constants were estimated at various temperatures; the activation energy was estimated to be about 25 kcal, and the stability-indicating validity of the assay used was reaffirmed. Selegiline undergoes degradation at a negligibly slow rate.