BIOAVAILABILITY OF INTRAMUSCULARLY ADMINISTERED TENOXICAM

Bioavailability of intramuscularly administered tenoxicam relative to single oral and relative to intravenous doses was determined in two se parate randomized crossover studies. Twelve healthy volunteers (12 mal es, age 20-30 years) received a rapid intravenous injection and a sing le intramuscular dose and 12 other subjects (11 males, 1 female, age 2 1-25 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 do sing were determined by a specific HPLC method. Differences in tenoxic am concentration-time profiles after the different routes of administr ation were limited to the first 2 h after dosing. Later, plasma concen trations were almost superimposable within and across the two studies. The extent of absorption of intramuscularly administered tenoxicam wa s complete (mean+/-CV per cent: F(abs) 0.99+/-20 per cent) with no dif ference between the two extravascular administrations (F(rel) 0.95+/-1 0 per cent, intramuscular vs oral). After intramuscular administration tenoxicam was more rapidly absorbed compared to the oral dose (T(max) 0.71 h+/-80 per cent vs 1.4 h+/-62 per cent; p > 0.05). Peak concentr ations after oral and intramuscular administration (C(max) 2.5 mg l-1/-19 per cent vs 2.7 mg l-1+/-14 percent; p < 0.05) were very similar.