Comparative drug adsorption by activated charcoal

Comparative in vitro studies were carried out to determine the adsorption characteristics of 12 drugs on activated charcoal. At pH 1.3 and 37 degrees, the adsorption capacity of activated charcoal (milligrams per gram of charcoal) was: aspirin, 262; glutethimide, 252; methaqualone, 179; chlordiazepoxide, 157; propoxyphene napsylate, 137; diazepam, 136; amitriptyline, 133; propoxyphene hydrochloride, 127; secobarbital, 124, pentobarbital, 103; phenobarbital, 70; and amobarbital, 51. The adsorption of the weak acids was most markedly decreased at pH 10.8. In patients, actual drug adsorption probably is lower than these maxima because of the presence of mucus, bile salts, and other drugs. In patients investing large amounts of poorly adsorbed drugs, activated charcoal would not be helpful.