Decreased plasma efavirenz concentrations in a patient receiving rifabutin.
OBJECTIVE
The case of a patient with decreased plasma efavirenz concentrations during concomitant rifabutin therapy is reported.


CONCLUSIONS
A 42-year-old Hispanic man newly diagnosed with acquired immune deficiency syndrome (AIDS) and coinfected with aseptic meningitis and disseminated Mycobacterium avium complex (MAC) received efavirenz-based highly active antiretroviral therapy (HAART). When the patient was admitted to the hospital, his medications included enoxaparin, metformin, ganciclovir, clarithromycin, ethambutol, rifampin, pyrazinamide, isoniazid, pyridoxine, trimethoprim-sulfamethoxazole, dexamethasone, and tenofovir-emtricitabine- efavirenz. Rifampin was changed to rifabutin 450 mg daily due to the potential interaction with rifampin and efavirenz. Clarithromycin was replaced with azithromycin for the treatment of MAC infection, and dexamethasone was gradually decreased over three months. The established therapeutic plasma concentration of efavirenz is 1-4 μg/mL. After receiving the standard efavirenz dosage of 600 mg daily, the patient had subtherapeutic plasma efavirenz concentrations. To correct these low concentrations, the patient's efavirenz dosage was increased to 800 mg daily; however, his efavirenz concentrations continued to remain subtherapeutic (two concentrations of 0.58 μg/mL). The patient's viral load decreased slowly while on HAART; however, it only became undetectable 12 days after rifabutin was discontinued. The Drug Interaction Probability Scale demonstrated a probable relationship between the coadministration of rifabutin and the decreased efavirenz concentrations due to the possible induction of efavirenz metabolism by rifabutin.


CONCLUSIONS
A 42-year-old Hispanic man newly diagnosed with AIDS had subtherapeutic efavirenz levels during concomitant treatment with rifabutin.
Hsu
Oliver
O
Department of Clinical Pharmacy, University of California San Francisco, San Francisco, CA 94143, USA. o_hsu@u.pacific.edu
Hill
Catherine J
CJ
Kim
Mina
M
Tan
Benny
B
O'Brien
John G
JG
D000163:Acquired Immunodeficiency Syndrome / Q000150:complications / Q000188:drug therapy; D000328:Adult; D000480:Alkynes; D019380:Anti-HIV Agents / Q000493:pharmacokinetics* / Q000627:therapeutic use; D000904:Antibiotics, Antitubercular / Q000494:pharmacology* / Q000627:therapeutic use; D023241:Antiretroviral Therapy, Highly Active / Q000379:methods; D048588:Benzoxazines / Q000493:pharmacokinetics* / Q000627:therapeutic use; D003521:Cyclopropanes; D004347:Drug Interactions; D006801:Humans; D008297:Male; D008582:Meningitis, Aseptic / Q000150:complications; D015269:Mycobacterium avium Complex / Q000302:isolation & purification; D015270:Mycobacterium avium-intracellulare Infection / Q000150:complications / Q000188:drug therapy; D017828:Rifabutin / Q000494:pharmacology* / Q000627:therapeutic use; D019562:Viral Load / Q000187:drug effects
D000480:Alkynes; D019380:Anti-HIV Agents; D000904:Antibiotics, Antitubercular; D048588:Benzoxazines; D003521:Cyclopropanes; D017828:Rifabutin; C098320:efavirenz