[Counterfeiting of eye drops?: a laboratory study of antibiotic eye drops purchased in two African countries]

Counterfeit drugs are often ineffective and are considered a problem with an immense risk potential especially in the treatment of infectious diseases. Emerging and developing countries are particularly affected. Little is known about the extent of counterfeit antibiotic drugs used in eye care. In the present study we investigated antibiotic eye drops purchased in two African countries with respect to the active substance and its concentration in the sample.A total of 33 antibiotic eye drops purchased in Kenya and the Democratic Republic of Congo were tested. The bottles were labeled to contain one of the following substances: the quinolones ciprofloxacin, levofloxacin and ofloxacin and the aminoglycosides gentamicin and tobramycin. Imported quality products as well as cheaper generic drugs were tested. Fluoroquinolones were determined by high pressure liquid chromatography (HPLC) and quantified by fluorescence measurement and aminoglycosides were tested by using a fluorescence polarization immunoassay.All samples were found to contain the declared drug. Nine samples (27%) showed an under-concentration by 10% or less and ten (30%) showed an increased concentration of 10% or more than indicated on the label. 75% of the original drugs but only 12% of the generic drugs had measured concentrations within the standard advisory ranges of ± 5% from the nominal value.Our results provide no evidence for significant criminal counterfeiting of eye drops in the studied countries. The frequent deviation from the stated concentration in the generic samples is cause for concern and justifies further investigation.