Bioavailability of intramuscularly administered tenoxicam

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 (11 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: F(abs) 0.99 +/- 20 per cent) with no difference between the two extravascular administrations (F(rel) 0.95 +/- 10 per cent, intramuscular vs oral). After intramuscular administration tenoxicam was more rapidly absorbed compared to the oral dose (Tmax 0.71 h +/- 80 per cent vs 1.4 h +/- 62 per cent; p > 0.05). Peak concentrations after oral and intramuscular administration (Cmax 2.5 mg l-1 +/- 19 per cent vs 2.7 mg l-1 +/- 14 per cent; p < 0.05) were very similar.