abacavir + didanosine + tenofovir + nevirapine + efavirenz

This is a five-drug combination antiretroviral regimen consisting of abacavir, didanosine, tenofovir, nevirapine, and efavirenz. All five are small molecule agents used in the treatment of HIV-1 infection as part of highly active antiretroviral therapy (HAART). Abacavir, didanosine, and tenofovir are nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs), which inhibit HIV reverse transcriptase by acting as chain terminators during viral DNA synthesis. Nevirapine and efavirenz are non-nucleoside reverse transcriptase inhibitors (NNRTIs), which bind directly to reverse transcriptase at a site distinct from NRTIs and cause conformational changes that inhibit enzyme activity. This combination is not available as a fixed-dose product but may be used in special clinical circumstances where multi-class resistance or intolerance necessitates complex regimens[3][9]. The use of more than one NNRTI simultaneously (nevirapine plus efavirenz) is not standard practice due to overlapping toxicity profiles and lack of additive efficacy.