Stability of terbinafine hydrochloride in an extemporaneously prepared oral suspension at 25 and 4 degrees C

The stability of terbinafine 25 mg/mL las the hydrochloride salt) in an ext emporaneously prepared oral suspension at 25 and 4 degrees C was studied. Twenty 250-mg terbinafine tablets were crushed to a fine powder and diluted to a concentration of 25 mg/mL with sweetened vehicle. The suspension was stored in amber polyethylene prescription bottles at 25 or 4 degrees C. Sam ples were taken on days 0, 7, 14, 28, 42, 56, 70, and 91 for duplicate anal ysis of terbinafine content by high-performance liquid chromatography and t o observe any changes in color and odor; pH was measured as well. Through the initial 42 days, the mean concentration of terbinafine in the s amples stored at both temperatures was >93% of the initial concentration; b y day 56, the mean concentration was <88%. No appreciable changes in color or odor were observed during the study period. The apparent pH of the suspe nsion decreased slightly over the 91 days, from an initial 5.6 to 5.5. Terbinafine 25 mg/mL (as the hydrochloride salt) in an extemporaneously pre pared oral suspension was stable for up to 42 days in polyethylene prescrip tion bottles at 25 and 4 degrees C.