Preformulation Selection of a Proper Salt for a Weak Acid-Base (Rs-82856) - A New Positive Inotropic Agent

Dissolution testing of acetylsalicylic acid by a channel flow method-correlation to USP basket and intrinsic dissolution methods

A new modification of the channel flow dissolution method is introduced together with the theoretical basis to extract the solubility and mass transfer parameters from the dissolution experiments. Correlation of drug dissolution profiles in the channel flow apparatus was evaluated with respect to USP basket and intrinsic dissolution methods at pH 1.2 or 6.8. Acetylsalicylic acid (ASA) was studied as a pure drug substance and as three simple tablet compositions with microcrystalline cellulose (MCC) and/or lactose as excipients. The channel flow measurements of 100% ASA tablets correlated well with the results of intrinsic dissolution tests. In the channel flow method as well as in the USP basket method the release of ASA was fastest from the tablet compositions containing lactose, while the slowest dissolution rate was observed with the composition containing MCC as the only excipient. As presumed, the dissolution rate of the weak acid was decreased as the pH of the medium was lowered, which was clearly confirmed also by the three dissolution methods. MCC forms matrix tablets and in the USP basket method the dissolution profiles followed square root of time kinetics indicating that diffusion was the rate-controlling step of ASA dissolution. Also the channel flow results indicated that the dissolution of ASA was controlled by mass transfer. The swelling behaviour of the tablets is different in the channel flow method as compared to the basket method: only one tablet surface is exposed to the dissolution medium in the channel flow system. The contact between the tablet surface and the dissolution medium is more similar between the channel flow and intrinsic dissolution methods.

Dissolution studies on ampicillin embonate and amoxycillin embonate

The dissolution behaviour of slightly water-soluble embonic acid salts of ampicillin and amoxycillin was studied quantitatively as a function of solution pH (1.15-8.00) using the rotating disk method combined with reversed-phase high-performance liquid chromatography. The dissolution rate of ampicillin embonate was greater than that of amoxycillin embonate at all pH values investigated. The graphs of pH-intrinsic rate of dissolution of the antibiotics from the salts were U-shaped, the minimum being close to the respective isoelectric points of the parent antibiotics. Embonic acid was not detectable below pH 5; above pH 5 the dissolution rate of embonic acid increased as a function of pH.