Stability of melphalan solutions during preparation and storage.

A stability-indicating high-performance liquid chromatographic assay has been used to investigate the stability of solutions of melphalan under conditions that pertain to setting up in vitro chemosensitivity assays. Melphalan (1 and 20 micrograms/mL) was found to be 30% more stable in 150 mM NaCl solution (normal saline) than in Dulbecco's phosphate-buffered saline. The drug stored at 20 micrograms/mL in normal saline at room temperature (21.5 degrees C) lost 5% of its activity (t0.95) in 1.5 h; at 5 degrees C the t0.95 was 20 h. From an Arrhenius plot of the results, the activation energy of the hydrolysis reaction in normal saline was 100.2 kJ/mol. Less than 5% of drug activity was lost when solutions of melphalan were (a) stored at -20 degrees C and -35 degrees C for 7 months, (b) frozen and thawed up to four times, or (c) filtered through various membranes. Drug degradation was not affected by storage-container material. The half-life of melphalan in a Roswell Park Memorial Institute medium containing 10% fetal bovine serum at 37 degrees C was 1.13 +/- 0.10 h; the presence of 0.3% agar had no effect. It is suggested that melphalan be handled at temperatures greater than 5 degrees C for a minimum of time, but solutions of the drug can be stored for at least 6 and possibly up to 12 months at -20 degrees C without significant deterioration taking place.