Plasma tenoxicam concentrations after single and multiple oral doses

The pharmacokinetics of single- and multiple-dose administration of tenoxicam 20 mg were evaluated in 8 healthy males. Maximum plasma concentration (Cmax) after the first dose was 2.76±0.48 μg/ml (mean±s.d.) and the time to reach Cmax (Tmax) was 5.0±3.0 h. The area under the plasma concentration-time curve (AUCo-∼) after a single administration of tenoxicam was 242.5±73.5 μg x h/ml. The elimination half-life (t 1/2 ) was 66.3±15.8 h and the plasma concentration at 24 hours after dosing (Cmin) was 1.84±0.33 μg/ml. Steady-state plasma concentrations of tenoxicam were virtually reached after 10 consecutive daily doses. At steady-state, Cmax averaged 13.63±3.33 μg/ml and Tmax remained 5.0±3.0 hours. AUC within a dosing interval at steady-state was 262.2±67.0 μg x h/ml, Cminss was 9.67±3.25 μg/ml, and t 1/2 averaged 74.2±13.3 h. The average fluctuation during multiple-dose administration was 26.8±8.0% and the accumulation ratio was 5.82±0.60. Steady-state pharmacokinetic parameters predicted from the first-dose data slightly underestimated observed values, but the results supported the assumption of linear pharmacokinetics during multiple-dose tenoxicam administration.