Clinically Significant Drug Interactions in Younger and Older Human Immunodeficiency Virus‐Positive Patients Receiving Antiretroviral Therapy

STUDY OBJECTIVE: To characterize clinically significant drug interactions (CSDIs) in younger and older human immunodeficiency virus (HIV)-positive patients who were receiving antiretroviral therapy. DESIGN: Retrospective medical record review. SETTING: HIV specialty clinic at a Veterans Affairs medical center. PATIENTS: A total of 110 younger (age < 50 yrs) and older (age ≥ 50 yrs) HIV-positive patients receiving antiretroviral therapy during 2007. MEASUREMENTS AND MAIN RESULTS: Demographic, clinical, and prescription drug data were collected. Pharmacokinetic and pharmacodynamic drug interactions were identified, assigned a severity grade, and evaluated for management according to two sources. Interactions with a grade of 2 (monitoring or timing of doses recommended), 3 (therapy modification recommended), or 4 (contraindicated) were considered CSDIs. Among 36 younger and 74 older patients, 763 CSDIs were identified. At least one CSDI was present in 83.3% and 89.2% of younger and older patients, respectively (p=0.56), with most having both antiretroviral and nonantiretroviral CSDIs. Younger and older patients, respectively, had a median of 3 and 5.5 total CSDIs/patient (p=0.09), 2 and 3 antiretroviral CSDIs/patient (p=0.65), and 0.5 and 2.5 nonantiretroviral CSDIs/patient (p=0.04). The proportions of grade 2, 3, and 4 CSDIs were 74.1%, 25.0%, and 0.9%, respectively, in younger patients and 73.1%, 26.1%, and 0.7%, respectively, in older patients (p=0.92). Younger patients had more CSDIs involving antihistamine, erectile dysfunction, and hormone or corticosteroid agents (p<0.01), whereas older patients had more CSDIs involving antihypertensive and antidiabetic agents (p<0.001). Management and outcomes of grades 3 and 4 antiretroviral CSDIs did not differ significantly by age. A list of frequently mismanaged interactions is provided. CONCLUSION: Clinically significant drug interactions were prevalent in younger and older HIV-positive patients receiving antiretroviral therapy, among which nonantiretroviral interactions should not be overlooked. Knowledge of the drug classes frequently involved in CSDIs by age group and types of CSDIs that are commonly mismanaged may help clinicians optimize care for HIV-infected patients.