undetectable VL have a similar likelihood for discontinuing NVP therapy because of hypersensitivity reactions (HSRs), compared with treatment-naive patients with low CD4 cell counts. This suggests that NVP-based combination therapy may be safely initiated in such patients. However, in similar patients with a detectable VL, it is prudent to continue to adhere to current CD4 cell count thresholds. The U.S. Public Health Service Task Force advocates caution in the use of nevirapine in pregnancy due to toxicity issues, which may be exacerbated during pregnancy. Cases of immune reconstitution syndrome and fat redistribution have also been observed with this drug. The U.S. Food and Drug Administration recommends stopping nevirapine if a person experiences: sign and symptoms of liver issues such as hepatitis increased transaminases in addition to rash or systemic symptoms formation of rash with systemic symptoms severe skin or hypersensitivity reactions Additionally, the U.S. FDA recommends close monitoring during the first 6 weeks of therapy for the above symptoms as there is high risk during this time. Continued monitoring is recommended for up to the first 18 weeks of treatment. If a patient experiences hepatitis plus rash or other systemic symptoms, or severe hypersensitivity or skin rash, nevirapine should not be restarted. Drug interactions Nevirapine is a substrate for liver CYP3A and CYP2B6 enzymes. Concomitant administration of drugs that are inhibitors of these enzymes may increase serum nevirapine levels significantly. Some examples of these drugs include ritonavir, fosamprenavir, and fluconazole. On the other hand, drugs that are inducers of these enzymes such as rifampicin may lower serum nevirapine levels.[18] In addition, concomitant use of St. John's wort (Hypericum perforatum, which has been shown to induce CYP3A4 and CYP1A2) or St. John's wort containing products may significantly lower nevirapine levels. Nevirapine is an inducer of cytochrome P450 isoenzymes CYP3A4 and CYP2B6. It may reduce levels of several co-administered drugs including the antiretrovirals efavirenz, indinavir, lopinavir, nelfinavir and saquinavir, as well as clarithromycin, ketoconazole, forms of hormonal contraception, and methadone. Mechanism of action Nevirapine falls in the non-nucleoside reverse transcriptase inhibitor (NNRTI) class of antiretrovirals. Both nucleoside and non-nucleoside RTIs inhibit the same target, the reverse transcriptase enzyme, an essential viral enzyme which transcribes viral RNA into DNA. Unlike nucleoside RTIs, which bind at the polymerase active site, NNRTIs bind to a hydrophobic pocket in the subdomain of p66 which is about 10 angstrom away from the active site (known as the