Pharmacokinetics of tenoxicam at different dosage regimes

Tenoxicam, a non-steroid anti-inflammatory of the oxicam type, has a molecular structure similar to that of piroxicam, but is more active and better tolerated. Several studies demonstrated that tenoxicam is a potent analgesic. It is completely absorbed after oral and intramuscular administration and slowly eliminated, the long half-life in tissues consenting once-daily administration. In the present study the pharmacokinetics of tenoxicam have been investigated during repeated parenteral administration, with or without loading dose, in order to establish the dose regime that produces constant tissue concentrations over time. Thirty-six patients of both sexes, suffering from acute pain due to arthritis of the spine, were enrolled in the study and divided into three equal groups. The first group was given 40 mg tenoxicam per day (single i.m. injection) for 2 days followed by 20 mg (single i.m. injection) for 10 days. The second group received 20 mg i.m. once a day for 12 days. The third group received 20 mg i.m. twice a day for two days followed by single 20 mg i.m. injections on the following days. Blood was sampled at 0, 0.5, 1,2,4,6,8,12,16 and 24 hours and at 3,5,7,9 and 12 days. Tenoxicam levels in the samples were assayed by an HPLC method. The results showed that single 40 mg loading doses for 2 days, followed by once-daily 20 mg maintenance administration, established the requisite steady-state tissue concentrations of tenoxicam after the second administration. Tenoxicam was very well tolerated in all three groups.