Final answer:
For a client with HIV and oral candidiasis, the first choice of therapy is antifungal therapy, specifically with azole antifungal drugs like fluconazole that target fungal growth.
Step-by-step explanation:
The first choice of therapy for a client who is positive for HIV and has oral candidiasis is antifungal therapy. This is because oral candidiasis is a fungal infection that requires antifungal medications for treatment. While antiretroviral therapy is crucial for tackling HIV infection itself and slowing down disease progression, the immediate concern of oral candidiasis is best addressed by using azole antifungal drugs such as fluconazole.
These antifungal agents help in treating the infection by interrupting ergosterol biosynthesis, which is key to fungal cell membrane integrity. The use of antifungals like fluconazole is effective for treating opportunistic infections in patients with AIDS, including oral candidiasis.