Original Contribution to Pharmacoepidemiology: Mapping the Drug Use Landscape Across Nigeria’s Six Geopolitical Zones Using National Health Facility Survey Data

Pharmacoepidemiology examines the use and effects of drugs in defined populations and is an essential discipline for guiding pharmaceutical policy, rational use interventions, and regulatory decisions at the national level. A comprehensive pharmacoepidemiological mapping of drug use patterns across all six of Nigeria's geopolitical zones has not previously been undertaken using nationally representative data. This study mapped the drug use landscape across Nigeria's six geopolitical zones using data from the Nigeria Health Facility Survey and supplementary primary data collection at 240 health facilities stratified across all zones. The study employed a cross-sectional ecological design with multilevel analytical methods. Drug use indicators assessed included prescribing density per capita, antibiotic dispensing rates, generic prescribing proportions, injectable drug use rates, and adherence to essential medicines lists. Hierarchical logistic and Poisson regression models identified zone-level, facility-level, and patient-level determinants of rational drug use. Marked zonal variation was documented: antibiotic prescribing rates ranged from 41 percent in South East to 67 percent in North West facilities. Generic prescribing was highest in South West at 62 percent and lowest in North East at 29 percent. Essential medicine availability correlated strongly with facility level and zone. Determinants of irrational drug use included low pharmacist-to-prescriber ratio, absence of formulary committees, and poor continuing medical education access. This study contributes an original, nationally scoped pharmacoepidemiological evidence base and proposes a zonal rational drug use index for ongoing national monitoring. Keywords: pharmacoepidemiology, drug use, geopolitical zones, Nigeria, rational drug use