Pharmacokinetics of tilidine and metabolites in man

Tilidine is a prodrug from which the active metabolite nortilidine is formed by demethylation. The pharmacokinetics of tilidine (T), nortilidine (NT) and bisnortilidine (BNT) were studied in nine healthy subjects following single intravenous (10 min infusion) and oral 50 mg T-HCl dose as well as following multiple 50 mg T-HCl oral doses. Systemic availability of the parent substance was 6% and of the active metabolite NT 99%. The terminal half-life of NT was 3.3 h following single oral administration, 4.9 h following intravenous administration and 3.6 h following multiple dosing. Following intravenous infusion, concentrations of unchanged substance were found which were 30 times higher than following oral administration. BNT was eliminated with half-lives of 5 h after oral administration and 6.9 h after intravenous administration. Renal elimination of unchanged substance was 1.6% of the dose following intravenous administration and less than 0.1% of the dose following oral administration. Approximately 3% were recovered in urine as NT and 5% as BNT following both routes of administration.