Monitoring of verapamil enantiomers concentration in overdose

A 52-year-old woman with a history of depression and personality disorders, hypertension, coronary disease and asthma was admitted to the Department of Clinical Toxicology after taking 60 tablets of Staveran (immediate release verapamil), and 4 tablets of acetaminophen. One and a half hours after ingestion her condition was critical. She required endotracheal intubation and artificial respiration. Her heart rate was 75 beats per minute, (bpm) and her blood pressure dropped from 70/50 to 50/00 mmHg. Additionally, drowsiness and headache were observed. On admission, R-(+)- and S-(-)-verapamil serum concentrations were 2252 ng/ml and 810 ng/ ml, respectively. Monitoring of the verapamil serum concentration was carried out over 74 h. Terminal elimination half-lives were 18.7 (21.3) and 17.0 (18.5) hours, respectively, for R-(+)- and S-(-)-verapamil. Monitoring of verapamil enantiomers concentrations in serum indicated a higher concentration of the less active form and slightly faster elimination of the more active enantiomer. The data-support a stereoselective difference between first pass clearance and later systemic clearance of verapamil, when taken in overdose.