Objectives Direct-acting antivirals are the recommended treatment for hepatitis C-infected patients. Drug–drug interactions with concomitant treatments can cause lack of effectiveness and/or safety. The objective of this study is to characterise drug–drug interactions of direct-acting antivirals and to analyse their influence both on the effectiveness of antiviral treatment and on the overall safety of pharmacological treatment in hepatitis C-infected patients.

Methods Observational and prospective cohort study for 3 years in the pharmaceutical care outpatient consultation of a general hospital, undertaking detection, evaluation and management of drug–drug interactions by clinical pharmacists and physicians. The main outcome measures were sustained virologic response at week 12 for effectiveness and serious drug-related adverse events for safety. Multivariate statistical analysis applied to: (a) patient basal characteristics related to presence of drug–drug interactions; (b) previous antiviral treatments, viral genotype, cirrhosis, decompensations and presence of drug–drug interactions related to the effectiveness of direct-acting antivirals.

Results Of a total of 1092 patients, the majority of them were men, around 60 years old and HCV-genotype 1 mono-infected, with a high basal viral load, naive to antiviral treatment, treated with ledipasvir/sofosbuvir and without cirrhosis. 24.5% had drug–drug interactions. Proton pump inhibitors were the concomitant drugs that caused the most drug–drug interactions. Age ≥65 years and direct-acting antivirals based on protease inhibitors were independently related to the presence of drug-drug interactions (p≤0.012). All (100%) of the therapeutic recommendations based on detected drug–drug interactions were implemented; 97.7% of patients with interactions versus 99.0% without them reached sustained virologic failure (p=0.109). The serious adverse events rates were 1.5% and 1.3% in patients with and without drug-drug interactions, respectively (p=0.841).

Conclusions Drug–drug interactions are frequent among hepatitis C-infected patients receiving treatment with direct-acting antivirals. However, the collaboration between physicians and clinical pharmacists makes it possible to detect, evaluate, avoid or clinically manage these drug–drug interactions, in order to maintain whole treatment therapeutic safety and the effectiveness of direct-acting antivirals.