Bioavailability and pharmacokinetics of furosemide tablets marketed in Thailand

Abstract

Thirteen different brands of 40 mg furosemide tablets available in Thailand were evaluated. In vitro studies revealed that all products met the requirement of United States Pharmacopia XX for disintegration time. However, there were only 4 brands that passed the dissolution test specification. Then the original brand (brand A) and the three local brands (brand B, C and D) with differences in dissolution characteristics were selected for in vivo studies. The relative bioavailability of furosemide tablets were performed on eight healthy Thai males using a crossover design. Plasma furosemide concentrations were determined by high – performance liquid chromatographic method. Clinical response to these tablets were also studied by determination of urine output and electrolyte excretion. Individual plasma data was analyzed according to one – compartment open model using the PCNONLIN computer program. There were no statistically significant differences in parameters studied between the original and the local brands (p>0.05). The relative bioavailability of furosemide with respect to brand A were 70.29, 113.41, and 94.93 % for brand B, C and D, respectively. However, in vitro studies and in vivo studies were independent. The biological half –life of furosemide was 1.27 hr (1.00 – 1.76 hr). Following oral administration of 40 mg furosemide tablet, the mean individual peak plasma levels and the time required to reach the peak ranged from 0.61 – 1.12 ug/ml and 1.63 -2.00 hr, respectively. Clinical response, in terms of diuresis and electrolyte excretion, e.g.,sodium, chloride and potassium, to the four brands of furosemide tablets were also not remarkably different (p>0.05), indicating that the four brands are clinically equivalent.