Clinically significant drug interactions among HIV-infected patients receiving antiretroviral therapy

We conducted a cross sectional study of the outpatient medical records of 1000 HIV-infected patients receiving antiretroviral therapy (ART) in 2011 to determine the incidence of clinically significant drug interactions (CSDI). The severities of the CSDI were graded following the Micromedex" 2.0 database and the Department of Health and Human Services (DHHS) 2012 HIV treatment guidelines. Three hundred thirty-five patients (34%) had 554 episodes of CSDI. Of which 337 episodes (61%), 163 episodes (29%) and 54 episodes (10%) had grades 2, 3 and 4 severity CSDI, respectively. The CSDI were caused by protease inhibitor (PI)-based drug regimens in 79%, by efavirenz-based regimens in 34% and by nevirapine-based regimens in 10% (p<0.001). The three most common grade 4 CSDI were: a PI with simvastatin (n=24), simvastatin with gemfibrozil (n=24) and didanosine with allopurinol (n=2). The three most common grade 3 CSDI were: a PI with a statin drug except simvastatin (n=56), fenofibrate with a statin drug (n=28) and amlodipine with simvastatin (n=14). On multivariate analysis, risk factors associated with CSDI were: receiving a PI-based regimen (OR 14.44; 95% CI: 9.10-22.88), having dyslipidemia (OR 3.94; 95% CI: 1.89-8.21), having >5 items prescribed at a time (OR 1.80; 95% CI: 1.23-2.63), seeing a doctor >4 times a year (OR 1.72; 95% CI: 1.20-2.46), having hypertension (OR 0.60; 95% CI: 0.37-0.98), having a duration of receiving ART of >5 years (OR 0.46; 95% CI: 0.28-0.77) and having a CD4 count of >200 cells/mm3 (OR 0.46; 95%CI: 0.26-0.84). CSDI were common among HIV-infected patients receiving ARV in our outpatient clinic. Patients having a low CD, count, having dyslipidemia, receiving PI-based ART, having a frequent number of visits per year and having a large number of items prescribed at each visit had a greater chance of a CSDI.