Pharmacokinetics and metabolic pattern after intravenous infusion and oral administration to healthy subjects.

Meloxicam [4-hydroxy-2-methyl-N-(5-methyl-2-thiazolyl)-2H- 1,2-benzothiazine-3-carboxamide-1,1-dioxide] is a new nonsteroidal antiinflammatory drug belonging to the enolic acid group. In a crossover study, 30 mg 14C-labeled meloxicam was administered to four male healthy volunteers as a short-term infusion and as an oral solution. The objectives of the study were to determine the mode of elimination, the excretion balance, the in vivo binding characteristics to serum proteins, and to investigate the metabolic pattern in plasma, urine, and feces. A comparison of plasma concentration measurements of unchanged drug by a specific HPLC assay and total radioactivity by liquid scintillation counting revealed a very close conformity. Over 90% of the plasma radioactivity was represented by unchanged drug. Its terminal and dominant half-life of elimination from plasma, as determined from plasma and urinary data in this study, ranged from 12 to 17 hr in the volunteers. The serum protein binding of the radioactivity from in vivo samples was very high (99.1-99.7%). The excretion balance was complete after 6 days. Average urinary excretion of 14C-radioactivity accounted for 43% of the dose, with the remainder appearing with the feces. Meloxicam was extensively metabolized, with only traces of the drug appearing unchanged in urine and feces. The main metabolites were formed by hydroxylation and further oxidation of the methyl group of the thiazolyl moiety. In addition, two further metabolites were found, particularly in urine. Altogether, > 95% of the dose excreted could be accounted for by the metabolites identified or the parent compound itself.

Meloxicam: metabolic profile and biotransformation products in the rat.

1. The metabolic fate of 14C-labelled meloxicam was investigated in the urine and bile of rat following oral and intraduodenal administration. Structural elucidation of metabolites was performed by nuclear magnetic resonance, mass spectrometry (electron impact and fast atom bombardment). 2. A mean total of 76.3% 14C-radioactivity was recovered in urine over 96 h, with the remainder in the faeces. The metabolic pattern in the excreta was independent of dose (1 versus 10 mg/kg) and collection period (0-8 versus 24-48 h). In bile one of the main metabolites was absent. 3. Meloxicam underwent extensive metabolism with only small amounts of unchanged drug recovered in the urine (< 0.5%) or bile (4.5%). Principal routes of biotransformation were: oxidation of the 5-methyl group of the N-heteroaryl-carbamoyl side chain to yield the 5'-hydroxymethyl derivative (33% of metabolites in urine, 22% in bile) and the 5'-carboxy derivative (16% in urine, 49% in bile). Oxidative cleavage of the benzothiazine-ring yielded an oxamic acid metabolite in urine (23.5%), which was not present in bile. 4. The introduction of a methyl-group into the N-heteroaryl-carbamoyl side chain increased lipophilicity and facilitated metabolic excretion compared with structurally related compounds.