Hydrophilic ointment formulations containing salicylic acid were prepared at different pH levels by inclusion of phosphate buffers. Percutaneous salicylic acid absorption was studied by measuring salicylate blood levels in rabbits at 1.5‐hr. intervals from 1.5 to 7.5 hr. after ointment application. The effect of 15% dimethyl sulfoxide in the various formulations was also determined. Formulations without dimethyl sulfoxide produced maximal blood concentrations at the highest pH level (10.78) and higher concentrations at the lowest pH (2.97) than at the intermediate ones (4.48, 6.80, 9.23). Proportionally higher concentration of undissociated species appeared to account for the increased absorption observed at the most acidic pH, while increased dissolution was probably responsible for the greater blood levels recorded at the most alkaline pH. Dimethyl sulfoxide produced a more rapid rate of salicylate absorption as well as greater peak blood levels at each pH. However, its influence on rate of absorption and on peak blood levels was less pronounced at the highest pH levels. This finding seems to indicate that the positive effect of dimethyl sulfoxide on percutaneous salicylate absorption is due in part to its ability to enhance the dissolution of salicylic acid.
All Science Journal Classification (ASJC) codes
- Pharmaceutical Science
- Dimethyl sulfoxide effect—salicylate absorption, hydrophilic ointment
- Percutaneous absorption—salicylate in hydrophilic ointment
- Salicylate absorption—hydrophilic ointment
- pH effect—salicylate absorption from hydrophilic ointments