Prevention of amlodipine absorption by activated charcoal: effect of delay in charcoal administration

The purpose of this study was to investigate the effect of activated charcoal on the absorption of amlodipine, with special reference to delayed charcoal administration.

Thirty-two healthy volunteers, eight subjects in four parallel groups, ingested 10 mg of amlodipine on an empty stomach. Activated charcoal (25 g in 300 ml of water) was ingested either immediately afterwards or 2 h or 6 h after amlodipine, or amlodipine was ingested with 300 ml of water only (control). Plasma concentrations and the cumulative excretion of amlodipine into urine were measured by GC-MS for 96 h and 72 h, respectively. In addition, adsorption of amlodipine to charcoal was studied in vitro.

Activated charcoal administered immediately after amlodipine reduced the amlodipine AUC(0.96 h) and the 72-h urinary excretion by 99% (P < 0.0005). After a delay of 2 h in charcoal administration the AUC(0.96 h) was reduced by 49% (P = 0.001), but after a delay of 6 h the reduction was 15% only (P = NS). At a charcoal:drug ratio of 5:1, about 90% of amlodipine was adsorbed by charcoal in vitro; at ratios of 10:1 and 20:1, adsorption was practically complete.

Activated charcoal almost completely prevented amlodipine absorption when administered immediately after amlodipine ingestion. Charcoal also markedly reduced amlodipine absorption when given 2 h after amlodipine; in amlodipine overdose, administration of charcoal may be beneficial even later. We conclude that administration of activated charcoal is the method of choice to prevent absorption of amlodipine in amlodipine overdose.