Two African herbal medicines significantly inhibit metabolism of anti-HIV drugs

Michael Carter
Published: 13 January 2005

Two herbs widely used to treat individuals with HIV in Africa have a significant interaction with anti-HIV medication, potentially leading to the poor metabolisation of antiretrovirals, according to an test-tube study published in the January 3rd edition of AIDS. Extreme caution should be taken if using herbal medicines in the treatment of HIV, stress the investigators, who also state that their study shows the importance of undertaking pharmacokinetic studies to show the potential interactions between herbal medication and antiretrovirals.

The South African government has accredited 27 facilities to provide nutritional and micronutrients supplements and complementary and traditional medicines to HIV-positive patients to slow the progression of HIV disease.

Many anti-HIV drugs, including protease inhibitors and non-nucleoside reverse transcriptase inhibitors (NNRTIs) are metabolised using the CYP3A4 pathway. Herbal medicines have been shown to affect levels of anti-HIV because of their impact on CYP3A4 and, in the case of protease inhibitors, P-glycoprotein as well. Some herbal medications are also known to interact with nuclear receptors such as the pregnane X receptor (PXR), which modulates expression of CYP3A and P-glycoprotein.

In a laboratory study investigators examined the effects of Hypoxis hemerocallidea (African potato) and Sutherlandia, two herbs widely used against HIV in Africa, on the metabolisation of antiretroviral drugs.

Capsules, tablets and teas of both herbs were extracted and tested for their ability to inhibit CYP3A4. The affect of the herbs on PXR and P-glycoprotein were also assessed.

African potato showed a significant inhibition of CYP3A4 activity (34% - 85% inhibition in water extraction and 31% - 79% inhibition in ethanol). Sutherlandia also inhibited CYP3A4 (55% - 69% in water extraction, 68% - 96% in ethanol).

In addition, African potato (p <0.05) and Sutherlandia (p <0.01) resulted in significant activation of PXR.

“Our findings have identified the potentially for clinically significant drug interactions for both Hypoxis hermerocallidea and Sutherlandia showing in-vitro inhibition of CYP3A4 and P-glycoprotein expression”, write the investigators.

The investigators add that their findings “suggest that co-administration of these drugs with antiretroviral agents may result in the early inhibition of drug metabolism and transport followed by the induction of decreased drug exposure with more prolonged therapy.”

“These results”, conclude the investigators, “highlight the extreme caution that should be taken in introducing herbal drugs into routine care of HIV patients in any setting including the developing world, and underscore the need for appropriately designed pharmacokinetic studies to unveil the true interaction potential of herbal drugs with antiretroviral drugs.” Failure to undertake such studies could, caution the investigators result in drug interactions, treatment failure, resistant HIV, and drug toxicities.

Reference

Mills E et al. Impact of African herbal medicines on antiretroviral metabolism. AIDS 19: 95 – 97, 2005.

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