5PSQ-030 Adverse drug reactions due to interaction with cobicistat or ritonavir in HIV positive patients: a case series

Background and importance The main problem of antiretroviral therapy (ART) that includes pharmacokinetic enhancers (cobicistat or ritonavir) is inhibition of the metabolism of numerous drugs, which can lead to adverse drug reactions (ADR) due to overdosing. Aim and objectives To estimate the probability of occurrence of ADR in HIV positive (HIV+) patients due to interaction of cobicistat or ritonavir with chronic treatment (CT). Material and methods An observational, descriptive, retrospective study was conducted in a tertiary hospital. The treatments of all HIV+ patients with cobicistat or ritonavir who attended the outpatient pharmacy department between January and December 2018 were reviewed. Those patients in whom the pharmacist identified signs or symptoms of a probable ADR related to interaction with ART were selected. Collected data were sex, age, ART, concomitant CT, and ADR detected and its consequence (change, suspension or maintenance of ART or CT). To estimate the probability of occurrence of ADR due to interactions, the Naranjo algorithm was used, and to determine the probability that the interactions existed in each patient, the DIPS scale (drug interaction probability scale) was used. Data concerning ART and clinical evolution were obtained from the electronic medical records, and those related to CT by patient interview and review of the primary care database. The Naranjo and DIPS score were evaluated by agreement between two specialist pharmacists. Results The treatment of 894 patients was reviewed, 82.9% men, median age 50.2 (39.7; 55.7) years. Eleven patients (1.2%) presented with 12 ADR due to interactions with cobicistat (91.7%) or ritonavir (8.3%) with their CT. Seven (58.3%) interactions were considered as ‘probable’ cause of ADR (5–8 points), 4 (33.3%) as ‘possible’ cause (2–4 points) and 1 (8.4%) as ‘doubtful’ cause (0–2 points). The drugs involved were atorvastatin (3), fluticasone (3), deflazacort (1), amlodipine (1), tacrolimus (1), trazodone (1), quetiapine (1) and clonazepam (1). Iatrogenic Cushing’s syndrome and muscle pain were the most frequent ADR. In three cases the doctor had to make a change to the patient’s ART. Conclusion and relevance The majority of the analysed interactions were classified as probable or possible causes of ADR. The drugs most frequently involved in ADR due to interactions with cobicistat or ritonavir were atorvastatin and various corticosteroids. References and/or acknowledgements No conflict of interest.