The pharmaceutical equivalence and stability of multisource metronidazole suspensions

To determine the pharmaceutical equivalence and stability of eighteen randomly selected brands of metronidazole suspensions.

The tests conducted include ease of redispersibility, sedimentation volume, particle size measurements, viscosity and assay of drug content.

The results showed that 16 (88.9%) out of 18 brands including the innovator (SR) were redispersed between 30 seconds to one minute, while 2 (11.1%) took more than two minutes. The sedimentation volume for 15 (83.3%) of the brands was less than 0.50 while the innovator brand had a significantly higher (p < 0.001) value (0.91). The particle size of the brands ranged between 1.942 and 5.92 μm and the sedimentation rate was between 20-50 mL/day. The viscosity of the brands were significantly different (p < 0.05) with SA, SB, SC, SD, SE and SF having 250-400cp, brands SG, SH, SI, SM, SP and SQ had 10-50cp while the remaining six brands had 100-190cp. Four brands including the innovator (SK, SP, SQ and SR) met Pharmacopoeal requirement for metronidazole suspension on drug content. Moreover, colour change, reduced viscosity and significant increase (p < 0.05) in particle sizes were observed for samples stored at 42 degrees C for seven weeks while those stored at 4 degrees C and 25 degrees C maintained stability.

Four out of eighteen brands of metronidazole suspensions evaluated in this study were found to be pharmaceutically equivalent. The stability studies showed that there is the need to adhere strictly to storage of metronidazole suspensions in a cool place.