Prevalence of potential drug-drug interactions with disease-specific treatments in patients with pulmonary arterial hypertension or chronic thromboembolic pulmonary hypertension: A registry study.

Polypharmacy increases the risk of drug-drug interactions that may disturb treatment effects. The aim of this study was to investigate the frequency of codispensing of potentially interacting or contraindicated drugs related to PH-specific treatment in the Swedish pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) population. All prescribed drugs, on an individual level, dispensed 2016-2017 at pharmacies to patients with PAH or CTEPH were obtained from The National Board of Health and Welfare's pharmaceutical registry. Potential drug-drug interactions were investigated using the Drug Interaction tool in the IBM Micromedex® database. There were 4785 different dispensed drugs from 572 patients (mean age 61 ± 16 years, 61% female, mean number of drugs per patient 8.4 ± 4.2) resulting in 1842 different drug combinations involving a PH-specific treatment. Of these drug combinations, 67 (3.5%) had a potential drug-drug interaction considered clinically relevant and it affected 232 patients (41%). The PH-specific drugs with the highest number of potential drug-drug interactions was bosentan ( n  = 23, affected patients = 171) while the most commonly codispensed, potentially interacting drug combination was sildenafil/furosemide (119 patients affected). Other common codispensed and potentially interacting drugs were anticoagulants ( n  = 11, affected patients = 100) and antibiotic treatment ( n  = 12, affected patients = 26). In conclusion, codispensing of PH-specific therapy and potentially interacting drugs was common, but codispensing of potentially contraindicated drugs was rare.