Effects of various formulation factors on dissolution stability of aztreonam, hydrochlorothiazide, and sorivudine capsules

Abstract

A split-split-plot 3 2 × 2 2 factorial design was used to study the effects of capsule filling machine and formulation factors such as lactose type, lubricant concentration, and capsule shell size on the dissolution stability of 50 mg potency hydrochlorothiazide (HCTZ), sorivudine (BV-araU), and aztreonam capsules packaged in HDPE bottles and stored under different conditions. It was observed that neither magnesium stearate concentration nor the type of capsule machine used to fill the capsule shells had any effect on dissolution stability of capsules of all three drugs for up to 6 months of storage at 50°C. For aztreonam, neither capsule shell size nor the type of lactose had any effect on dissolution stability. On the other hand, HCTZ size no. 1 capsules demonstrated better dissolution stability than size no. 2 capsules. Moreover, dissolution stability of capsules of sorivudine and HCTZ on storage at 50°C, 40°C/75% RH, and 40°C was dependent on the type of lactose used. HCTZ capsules containing Fast-Flo ® lactose, hydrous lactose, or anhydrous lactose showed up to 45, 25, and 10% decrease in dissolution, respectively, compared to initial values, at the 20 min dissolution time point after 6 months storage at 50°C. The extent of decrease in the dissolution rate was less under the conditions of storage at 40°C/75% RH and 40°C. Similar effects of decrease in the dissolution rate with the different types of lactose were observed with sorivudine, although to a much lesser degree compared to HCTZ capsules. No decrease in dissolution rate was observed for any drug after 20 months storage at 30°C. It was hypothesized that the slight decrease in dissolution rate of sorivudine capsules was due to significant caking of the capsule contents in the presence of the moisture liberated from the excipients and the capsule shells. For aztreonam capsules, the caking of their contents was without any discernable effect on dissolution because of the high aqueous solubility. In contrast, for HCTZ capsules, changes in dissolution rate were far too pronounced to be attributed to caking only.