Heme catabolism during short-term treatment with phenobarbital, diazepam and oxazepam

Carbon monoxide production (VCO) total body heme (TBH) and serum bilirubin (SB) have been determined in healthy young men before and after 100 mg phenobarbital (10 subjects), 15 mg diazepam (7 subjects) and 75 mg oxazepam (7 subjects), respectively, daily for seven days. None of the drugs had any significant effect on VCO. SB and TBH were also unaffected. Baseline VCO (mean +/- 1 S.E.M.) was 12.6+/-0.6 mumol/mmol TBH and day. The postdrug VCO was 15.1+/-1.8, 14.1+/-1.4 and 14.7+/-1.5 after phenobarbital, diazepam and oxazepam, respectively. The corresponding values for SB were 5.4+/-0.8, 6.0+/-1.5 and 6.2+/-1.0 mug/ml, compared to a baseline value of 6.6+/-0.8 mug/ml. However, when the pooled postdrug data were compared with the pooled baseline values, mean VCO showed a probably significant increase (from 12.6+/-0.6 to 14.7+/-1.0 mumol/mmol TBH and day (p less than 0.05). It is concluded that although phenobarbital is known to increase the hepatic heme turnover, this effect is not measurable in terms of total heme turnover, no more than 20% of which comes from the liver.