Tuberculosis (TB) and HIV continue to be two of the major causes of morbidity and mortality in the world, and together are responsible for the death of millions of people every year. There is overwhelming evidence to recommend that patients with TB and HIV
co-infection should receive concomitant
therapy of both conditions regardless of the CD4 cell count level. The principles for treatment of active TB disease in HIV-infected patients are the same as in HIV-uninfected patients. However, concomitant treatment of both conditions is complex, mainly due to significant
drug-drug interactions between TB and HIV drugs.
Rifamycins are potent inducers of the
cytochrome P450 (CYP) pathway, leading to reduced (frequently sub-therapeutic) plasma concentrations of some classes of antiretrovirals.
Rifampicin is also an inducer of the
uridine diphosphate glucuronosyltransferase (UGT) 1A1
enzymes and interferes with drugs, such as
integrase inhibitors, that are metabolized by this metabolic pathway.
Rifampicin is also an inducer of the
adenosine triphosphate (
ATP) binding cassette transporter P-glycoprotein, which may also lead to decreased bioavailability of concomitantly administered antiretrovirals. On the other side,
rifabutin concentrations are affected by the antiretrovirals that induce or inhibit CYP
enzymes. In this review, the pharmacokinetic interactions, and the relevant clinical consequences, of the
rifamycins-
rifampicin,
rifabutin, and
rifapentine-with antiretroviral drugs are reviewed and discussed. A
rifampicin-based antitubercular regimen and an
efavirenz-based antiretroviral regimen is the first choice for treatment of TB/HIV co-infected patients.
Rifabutin is the preferred
rifamycin to use in HIV-infected patients on a
protease inhibitor-based regimen; however, the dose of
rifabutin needs to be reduced to 150 mg daily. More information is required to select optimal treatment regimens for TB/HIV co-infected patients whenever
efavirenz cannot be used and
rifabutin is not available. Despite significant pharmacokinetic interactions between antiretrovirals and
antitubercular drugs, adequate clinical response of both
infections can be achieved with an acceptable safety profile when the pharmacological characteristics of drugs are known, and appropriate combination regimens, dosing, and timing of initiation are used. However, more clinical research is needed for newer drugs, such as
rifapentine and the recently introduced
integrase inhibitor antiretrovirals, and for specific population groups, such as children, pregnant women, and patients affected by multidrug-resistant TB.