abacavir + efavirenz + didanosine + hydroxyurea

A combination regimen composed of **abacavir**, **efavirenz**, **didanosine**, and **hydroxyurea** is an investigational multidrug antiretroviral therapy primarily for **HIV infection** in patients who are treatment-experienced or failing initial regimens. Abacavir and didanosine are **nucleoside reverse transcriptase inhibitors (NRTIs)**, efavirenz is a **non-nucleoside reverse transcriptase inhibitor (NNRTI)**, and hydroxyurea is an **immunomodulator and antimetabolite** that inhibits ribonucleotide reductase, thus depleting deoxynucleotide pools and enhancing the antiviral efficacy of NRTIs. Their combination aims to provide potent suppression of HIV-1 replication by targeting reverse transcriptase via both nucleoside and non-nucleoside mechanisms and potentiating these effects with hydroxyurea, which may also have direct activity against proliferating cells and viruses. The combination has been tested in phase IV proof-of-concept studies as a second-line therapy in HIV-infected adults, especially those failing protease inhibitor-containing regimens[1][3][5].