Comparative in-vitro studies on the efficacy of ivermectin against gastrointestinal sheep nematode

Purpose: This study was designed to evaluate the relative efficacy of various brands of ivermectin injection available for use in clinical veterinary practice in Nigeria.
Method: Ivermectin injections were evaluated by a larval development assay (LDVA), using the larvae of Strongyles (predominantly Haemonchus contortus) of sheep. The effect of standard solutions of the drug from the various brands on the transformation of L₁ to L₃ and survival of L₃ larvae was used to assess bioactivity. The 50% lethal concentration (LC₅₀) was determined from regression line obtained by probit transformation of the biological data. The 50 values for each of the brands were compared with that of the innovator brand (Ivomec Super®) for any significant difference.
Results: The LC₅₀ values obtained for the five brands varied widely. It ranges from 1.1±0.17 ng/ml for the innovator brand to 2.3±0.3, 3.0±0.3, 8.0±0.2 and 17.0±0.3 ng/ml for the other four brands. The biological assays performed on each of the five brands were of comparable precision. LC₅₀ for Ivomec super® was significantly different from those of the other four brands (Student's t test, p < 0.01).
Conclusion: The bioactivities of brands of ivermectin injections available in Nigeria are significantly different. This is a probable reason for the varied treatment response to various brands of ivermectin injection in veterinary practice in Nigeria. This justifies the need for drug regulatory bodies in Nigeria to ensure that ivermectin injections registered for use in Nigeria meets approved standards before the drugs are allowed to be imported into the country.