Stability of zonisamide in extemporaneously compounded oral suspensions

The stability of extemporaneously prepared oral suspensions of zonisamide at room temperature and under refrigeration is evaluated.

Simple-syrup and methylcellulose (0.5%) suspensions of zonisamide (10 mg/mL) were prepared using commercially available 100-mg capsules of zonisamide. Both suspensions were made from three different batches of zonisamide. Each suspension made with each batch of zonisamide capsules was placed in six identical 1-oz amber plastic prescription bottles and kept at room temperature (n = 3) or under refrigeration (n = 3). Immediately after preparation and at days 7, 14, 21, and 28, a 0.5-mL suspension sample was taken from each of the six bottles and assayed by a high-performance liquid chromatography method. The stability of zonisamide was statistically analyzed using one-way analysis of variance tests.

In all sampled suspensions, at least 90% of the initial concentration of zonisamide remained intact throughout the 28-day study period. On day 28, the mean percentages of the initial zonisamide concentration remaining at room temperature and under refrigeration were 102% and 94.7% for the simple-syrup suspensions and 103% and 104% for the methylcellulose suspensions, respectively.

An extemporaneously prepared simple-syrup suspension of zonisamide was stable for at least 28 days when stored at room temperature or under refrigeration. An extemporaneously prepared methylcellulose suspension of zonisamide was stable for 28 days when stored under refrigeration and for 7 days when stored at room temperature.