Physicochemical characteristics of drugs and response to repeat-dose activated charcoal.

Although the administration of repeated doses of activated charcoal has been advocated to increase the systemic clearance of many drugs, it is unknown whether a drug's physicochemical properties are associated with enhanced removal by repeat-dose activated charcoal. The English language literature was searched to identify clinical studies evaluating repeat-dose activated charcoal. Percent reduction in plasma elimination half-life during repeat-dose activated charcoal was calculated and correlated with the drugs' characteristics. A step-wise multiple regression analysis with the independent variables of the drugs' molecular weight, pKa, plasma protein-binding, intrinsic plasma elimination half-life, and volume of distribution failed to identify potential predictors (P = .1) of effectiveness of repeat-dose activated charcoal. This analysis suggested that charcoal therapy was more effective for drugs with a longer intrinsic half-life (r2 = .24, P = .04). A uniform framework that evaluates the physicochemical characteristics of drugs and their response to repeat-dose activated charcoal is needed to better define which patients would benefit from repeat-dose activated charcoal therapy.