QUALITY-CONTROL IN GENERIC ANTHELMINTICS - IS IT ADEQUATE

We became increasingly concerned about indications of possible substan dard efficacy of some generic anthelmintics, particularly after P.C. v an Schalkwyk (personal communication, 1990) had found some batches of imported generic products obtained from international brokers to be po orly active, despite apparently normal physical characteristics. There fore, considering the serious consequences this would have for sheep f arming, it was decided to test the efficacy of some of the generic raf oxanide products available on the South African market. One of the thr ee commercial formulations (of highly reputable companies) tested agai nst a known susceptible strain of Haemonchus contortus in sheep was ma rkedly substandard, with an arithmetic mean efficacy of 66.2% (Class B , Reinecke, 1973), compared to Class A efficacy of the other two, whic h also differed significantly from one another (Mann-Whitney; P=0.01). Larger differences were found between the three products against a na tural infection with a partially resistant strain of H. contortus than against the susceptible strain, with corresponding arithmetic mean ef ficacies of 28.7% (Class X, or ineffective), 71.3% (Class B) and 87.7% (also Class B). It is concluded that the most likely reason for the o bserved differences is that international brokers do not disclose the sources of supply of different batches of active ingredient (with the result that the companies buying anthelmintics from them have no way o f telling when a source of supply is changed); that the efficacy of su ch batches differs; and that efficacy testing of individual batches in some cases is inadequate. It is suggested that registering authoritie s should consider simplified efficacy testing of each new batch of act ive ingredient before it may be marketed. (C) 1997 Elsevier Science B. V.