Bioavailability of two metamizole (dipyrone) solutions as single doses of 2 g versus metamizole capsules

The aim of this study was to investigate the extent and the rate of absorption of metamizole, appearing in blood as methylaminoantipyrine (MAA), from a new oral solution and a parenteral solution administered by the oral route relative to capsules.

An open, randomized, 3 single-dose (2 g metamizole), crossover study with intervals of 7 days between periods was performed in 19 male and female healthy volunteers (age 22 - 45 years, body weight 49 - 88 kg, body height 156 - 189 cm). Metamizole metabolites were measured with an HPLC technique. The test formulations were considered bioequivalent with the reference formulation if the 90% confidence limits of the AUC0-->infinity and Cmax ratios and the tmax differences were within the range of 80 - 125%.

The 90% confidence limits of the comparisons between capsules (reference) and oral solution, capsules (reference) and ampoules, and ampoules (reference) and oral solution were 98.5 - 117.8, 99.5 - 132.6 and 81.3 - 105.8 for AUC0-->infinity 98.7 - 119, 101.7 to 129.2, and 82.1 - 104.8 for Cmax, and 84.4 to 115.6, 100 - 105.6 and 70.3 - 100 for tmax, respectively.

The oral solution was bioequivalent to capsules with regard both to the extent and the rate of MAA absorption. Metamizole as oral solution was bioequivalent to reference ampoules in the extent of MAA absorption, but absorption rate was faster. Ampoules showed a higher MAA bioavailability than capsules.