Background: A drug-drug interaction (DDI) is a pharmacologic or clinical response to the administration of a drug that can result in adverse outcomes. DDIs are considered preventable adverse drug reactions because these interactions can be learned, predicted and recognized. Objective: To determine potential drug-drug interactions (pDDI) among medications prescribed to adult patients consulting at a primary care clinic in a government teaching hospital. Methods: This was a 6-month retrospective cross-sectional study of drug prescriptions based on medical records of adult Filipinos who were seen and managed at a primary care clinic in a government teaching hospital. Medical charts were systematically selected based on a sampling frame with inclusion and exclusion criteria. Results: A total of 1,490 medical records of adult Filipino patients were included in the study. There were a total of 261 unique prescriptions based on generic formulations and an overall total of 5,978 drugs for a 6-month period of clinic consultations. An average of 4 medications (SD±1.63) were prescribed for every consultation recorded in the medical chart. From the charts that were reviewed, 23% of all adults were given a prescription of 4 drugs (N=348/1490), 26% had 3 drug prescriptions (N=386/1490) and 18% had two drugs, respectively, per clinic visit. Overall, 714/9054 (7.88%) medication pairs were seen to have potential drug interactions. The top three most common drug pairs with pDDI were amlodipine-simvastatin, losartan/hydrochlorothiazide-metformin and aspirin-furosemide. Five hundred twenty-five drug pairs had pharmacodynamic interactions (525/714) while 94 drug pairs (15%) had pharmacokinetic interactions. Conclusion Potential drug-drug interactions were observed in 8% of medications prescribed to adult Filipinos seen at Family Medicine Clinic in a government hospital. Seventy-four percent (74%) of the drug pairs with pDDIs were pharmacodynamic and 15% were pharmacokinetic interactions.
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