[Effects of the pH value and of drug-adjuvant interactions on the dissolution rate and the liberation of drugs].

It is reported of the effects of the pH value and of drug-adjuvant interactions on the dissolution profile of chlorpromazine hydrochloride and theophylline, as well as on their liberation from triturations with sodium carboxy-methylcellulose and microcrystalline celluloses. The binding of chlorpromazine hydrochloride to sodium carboxymethylcellulose and (less markedly) to micro-crystalline celluloses acts on the drug liberation only in those pH ranges where the dissolution rate of the drug remains constant. In a pH range where the dissolution rate decreases, the binding is of negligible significance. A prolongation of the dissolution time is sufficient to dissolve out the sodium carboxymethylcellulose-bound chlorpromazine hydrochloride from the associate and to produce an increase in liberation. The binding of the drug to the adjuvant weakens with increasing ionic strength of the liberation medium, which leads to a considerable rise of the liberation rate. Owing to the slight sorption of the drug on microcrystalline celluloses, the drug liberation equalizes the dissolution rate in pH ranges greater than 4.8. The dissolution rate of theophylline and the rate of its liberation from triturations showed no differences since there were no drug-adjuvant interactions.