Assessing the quality of antimalarial drugs in Equatorial Guinea: a follow-up study.

INTRODUCTION: Poor-quality antimalarial medications, including falsified and substandard formulations, pose significant public health risks, contributing to ineffective treatment and potential drug resistance. Our research conducted in 2013 on Bioko Island, Equatorial Guinea (EG), found 9.6% (n=61) of the artemisinin-containing antimalarials (ACAs) purchased were of poor quality. This study aimed to update the quality of all sold antimalarials and extend to include regions on the mainland. METHODS: A total of 637 samples, 564 ACAs and 73 non-ACAs, were purchased from 424 outlets on Bioko Island and mainland EG using a mystery client sampling approach. Samples were analysed for content using high-performance liquid chromatography with diode-array detection and classified as acceptable, substandard or falsified based on pharmacopoeia tolerance limits. Additionally, bioavailability was assessed through dissolution testing for a select number of samples. RESULTS: Overall, 40.5% of the samples were of acceptable quality, 31.2% were substandard and 28.3% were falsified. Regional differences showed a higher prevalence of falsified samples in Bata, Mangomo, Evinayong and Ebebiyín cities on the mainland (30.9%) compared with Bioko Island (25.6%). Artemether/lumefantrine, the first-line treatment for malaria in EG, showed 25.7% were of acceptable quality, 48.2% substandard and 26.1% falsified. Artemisinin monotherapy tablets had the highest rate of falsification (56.8%). For non-ACAs, 13.3% of sulfadoxine/pyrimethamine tablets were of acceptable quality, 48.9% substandard and 37.8% falsified. All quinine syrups were falsified, and most quinine tablets (87.5%) and injections (75.0%) were substandard. CONCLUSION: The prevalence of substandard and falsified antimalarials in EG has alarmingly increased from 9% in 2013 to 59.5% in 2018, highlighting the urgent need for enhanced regulatory measures. Immediate actions should include strengthening drug quality surveillance, particularly in private sector pharmacies, and implementing low-cost medicine screening methods for early detection of poor-quality medications. Ensuring the quality of antimalarials is critical to maintaining the efficacy of malaria control programmes and preventing the development of drug resistance.