Rifampicin (Rifadin / Rimactane) is an approved anti-mycobacterial drug that is a standard component of combination regimens for treating tuberculosis. In the United States, it is called rifampin.

Tuberculosis treatment regimens that contain rifampicin are generally more effective than those that do not contain rifampicin. However, rifampicin induces activity of the CYP3A4 enzyme, so has significant interactions with many of the anti-HIV drugs. These interactions mean that rifampicin cannot be used by most HIV-infected people taking antiretroviral therapy: for these patients, rifabutin (Mycobutin) is preferred for the treatment of tuberculosis.

Despite this, rifampicin may be taken by individuals taking the following anti-HIV combinations:

• Efavirenz (Sustiva) plus two nucleoside reverse transcriptase inhibitors (NRTIs). With this combination, the dose of efavirenz may need to be increased to 800mg a day, although some studies have found that this dose can cause side-effects, and that the standard dose of 600mg is adequate in terms of drug levels and HIV suppression, particularly in patients with low body weight^{[1][2][3][4][5]}.
• Full-dose ritonavir (Norvir) plus NRTIs, although this should be used with caution^[6].

Rifampicin should not be co-administered with any of the other approved non-nucleoside reverse transcriptase inhibitors (NNRTIs) or protease inhibitors, due to alterations in levels of the drugs or side-effects such as liver toxicity^{[7][8][9][10][11][12][13][14]}. Rifampicin does not interact with the NRTIs, so triple NRTI combinations may be used by patients taking rifampicin.

Rifampicin interacts with a range of other drugs commonly used in the treatment of HIV and AIDS. Rifampicin dramatically reduces blood levels of the anti-protozoal drug atovaquone (Wellvone), which may be used to treat Pneumocystis pneumonia (PCP) or other opportunistic infections. It also reduces levels of methadone hydrochloride (Methadose), requiring dose increases of up to 50% to avoid withdrawal symptoms.

Rifampicin also increases levels of the meningitis drug fluconazole (Diflucan), although the clinical implications of this remain to be determined^[15]. In addition, levels of rifampicin may be reduced in people who are taking the anti-fungal drug ketoconazole (Nizoral).

Side-effects of rifampicin can include rash, fever, gastrointestinal disorders and jaundice. Cases of kidney failure and of allergic reaction to rifampicin have also been reported^[16][17]. To minimise the gastrointestinal effects, rifampicin should not be taken at the same time as food. Orange discoloration of body fluids such as spit and urine, and of soft contact lenses, also occurs. Despite concerns that the combination of rifampicin and the tuberculosis drug pyrazinamide can cause severe liver damage, the incidence of this seems to be low in HIV-positive patients^[18].

Recent studies have suggested than rifampicin-resistant tuberculosis is becoming more common. For example, 2% of samples from surveys in Botswana and Burundi were found to be resistant to the drug, while tuberculosis resistant to rifampicin and isoniazid is common in eastern Europe, central Asia, China and South Africa^[19].

There is some evidence that HIV-infected people with tuberculosis or diarrhoea may have low levels of rifampicin in the blood, possibly due to impaired absorption^[20]. Further studies are in progress to investigate this observation.

Rifampicin may cause a false-positive result in urine tests for opiates, such as heroin and morphine^[21].