Bioavailability of intramuscularly administered tenoxicam relative to single oral and relative to intravenous doses was determined in two separate randomized crossover studies. Twelve healthy volunteers (12 males, age 20-30 years) received a rapid intravenous injection and a single intramuscular dose and 12 other subjects (1 1 males, 1 female, age 21-25 years) a single oral and a single intramuscular dose of 20 mg of tenoxicam on two different occasions. The wash-out period between the two consecutive treatments was 4 weeks. Plasma concentrations after dosing were determined by a specific HPLC method.
Differences in tenoxicam concentration-time profiles after the different routes of administration were limited to the first 2 h after dosing. Later, plasma concentrations were almost superimposable within and across the two studies. The extent of absorption of intramuscularly administered tenoxicam was complete (mean + CV per cent: Fabs 0.99 +_ 20 per cent) with no difference between the two extravascular administrations (Fre, 0.95 + 10 per cent, intramuscular vs oral). After intramuscular administration tenoxicam was more rapidly absorbed compared to the oral dose (Tmm 0.71 h + 80 per cent vs 1.4 h 2 62 per cent; p > 0.05). Peak concentrations after oral and intramuscular administration (C-2.5 mg l-'? 19 per cent vs 2.7 mg I-'? 14 per cent; p<O.O5) were very similar.