What viral and fungal prophylaxis should be given to an adult with Acquired Immunodeficiency Syndrome and a CD4 T‑lymphocyte count less than 200 cells per microliter?

Viral and Fungal Prophylaxis in AIDS with CD4 <200 cells/µL

All adults with AIDS and CD4 count <200 cells/µL must receive trimethoprim-sulfamethoxazole (TMP-SMX) double-strength (800/160 mg) once daily, which simultaneously prevents Pneumocystis pneumonia (PCP), toxoplasmosis in seropositive patients, and reduces bacterial respiratory infections. 1, 2, 3

Primary Prophylaxis Initiation Thresholds

Pneumocystis Pneumonia (PCP)

• Start TMP-SMX double-strength once daily when CD4 falls below 200 cells/µL – this is the cornerstone prophylaxis regimen. 1, 2
• Initiate prophylaxis immediately regardless of CD4 count if the patient has oropharyngeal candidiasis or unexplained fever >100°F lasting ≥2 weeks. 2, 3
• **Begin prophylaxis if CD4 percentage is <14%** even when absolute CD4 count is >200 cells/µL. 2, 4

Toxoplasmosis

• For Toxoplasma-IgG seropositive patients with CD4 <100 cells/µL, the same daily TMP-SMX double-strength tablet provides adequate prophylaxis – no additional agent is required. 1, 3
• Test Toxoplasma IgG serology immediately if not previously documented; if positive and CD4 <100 cells/µL, continue TMP-SMX alone. 1, 3
• Retest seronegative patients for Toxoplasma IgG when CD4 falls below 100 cells/µL to detect seroconversion. 1

Mycobacterium Avium Complex (MAC)

• Initiate azithromycin 1200 mg once weekly when CD4 falls below 50 cells/µL – this is the preferred MAC prophylaxis due to weekly dosing and fewer drug interactions. 1, 5, 3
• Clarithromycin 500 mg twice daily is equally effective but has more interactions with protease inhibitors. 1, 5
• Rifabutin 300 mg daily is second-line, requires dose adjustments with most antiretrovirals, and mandates exclusion of active tuberculosis before starting. 1, 5

Alternative Regimens for TMP-SMX Intolerance

If TMP-SMX causes non-life-threatening reactions, attempt to continue the drug if clinically feasible, or consider gradual reintroduction (desensitization) after the reaction resolves. 1, 2 Approximately 70% of patients can tolerate reinstitution. 1

PCP-Only Coverage

• Dapsone 100 mg daily – provides no toxoplasmosis protection. 1, 2
• Atovaquone 1500 mg daily – provides no toxoplasmosis protection; as effective as dapsone but substantially more expensive. 1, 5
• Aerosolized pentamidine 300 mg monthly via Respirgard II nebulizer – least preferred; no systemic or toxoplasmosis coverage. 1, 5

Combined PCP and Toxoplasmosis Coverage

• Dapsone 50 mg daily + pyrimethamine 50 mg weekly + leucovorin 25 mg weekly – use this regimen for Toxoplasma-seropositive patients who cannot tolerate TMP-SMX. 1, 5, 2
• Check glucose-6-phosphate dehydrogenase (G6PD) status before starting dapsone to avoid hemolytic anemia. 2

Viral Prophylaxis Considerations

Herpes Simplex Virus (HSV) / Varicella-Zoster Virus (VZV)

• Prescribe acyclovir or valacyclovir prophylaxis for patients with prior HSV or VZV infection, especially when CD4 <200 cells/µL. 5
• Consider prophylaxis even without prior documented infection in the setting of severe immunosuppression. 5

Cytomegalovirus (CMV)

• Do not initiate routine primary CMV prophylaxis, but monitor closely for CMV disease when CD4 <100 cells/µL. 5, 6
• Perform dilated fundoscopic examination to screen for CMV retinitis, as 25% of CMVR cases are asymptomatic and detected only on routine screening. 6
• CMV retinitis risk peaks when CD4 <50 cells/µL, with 81.3% of cases occurring at this threshold. 3, 6

Fungal Prophylaxis Beyond PCP

Candidiasis

• Fluconazole prophylaxis may be considered for CD4 <100 cells/µL in patients with recurrent oropharyngeal or esophageal candidiasis. 5
• Routine primary antifungal prophylaxis is not recommended for most patients. 5

Endemic Mycoses

• In endemic areas, consider histoplasmosis and coccidioidomycosis risk when CD4 <100 cells/µL, but routine primary prophylaxis is not recommended. 3

Discontinuation of Prophylaxis After Immune Reconstitution

Prophylaxis may be safely stopped only after sustained CD4 recovery on antiretroviral therapy (ART) for ≥3 months with virologic suppression. 1, 3

Infection	Discontinuation Threshold	Required ART Duration
PCP	CD4 >200 cells/µL	≥3 months sustained
Toxoplasmosis	CD4 >200 cells/µL	≥3 months sustained
MAC	CD4 >100 cells/µL	≥3 months sustained

1, 5, 3

Restarting Prophylaxis

• Reinitiate PCP and toxoplasmosis prophylaxis if CD4 falls below 200 cells/µL. 1, 3
• Reinitiate MAC prophylaxis if CD4 falls below 50–100 cells/µL. 1, 5, 3
• Never base discontinuation on a single CD4 measurement – sustained elevation for the full 3-month period is mandatory. 3

Antiretroviral Therapy Integration

• Initiate ART immediately upon HIV diagnosis, even before genotype results are available, as immune reconstitution is the definitive treatment. 5, 3
• Preferred first-line ART regimens include bictegravir/tenofovir alafenamide/emtricitabine or dolutegravir + tenofovir + emtricitabine. 5
• TMP-SMX has minimal interactions with integrase inhibitor-based ART, making it compatible with modern first-line regimens. 5

Critical Pitfalls to Avoid

• Never delay PCP prophylaxis while awaiting CD4 confirmation if clinical suspicion is high (presence of thrush, unexplained fever, or known recent CD4 <200). 2, 3
• Never use aerosolized pentamidine as sole prophylaxis when CD4 <100 cells/µL – it provides no protection against toxoplasmosis despite preventing PCP. 1, 3
• Never discontinue prophylaxis prematurely – CD4 must remain above threshold for at least 3 consecutive months on ART. 1, 3
• Never combine clarithromycin with rifabutin for MAC prophylaxis – this increases adverse effects without improving efficacy. 1
• Never prescribe fluoroquinolone monotherapy without excluding tuberculosis first – this can mask TB diagnosis and promote resistance. 3
• Never ignore CD4 percentage when absolute count is borderline – 13% of patients show discordance, and CD4% <14% warrants prophylaxis even if absolute count is >200 cells/µL. 4

Drug Interaction Management

• Azithromycin is preferred over clarithromycin for MAC prophylaxis due to fewer interactions with protease inhibitors. 1, 5
• Rifabutin requires dose adjustments when co-administered with most protease inhibitors and non-nucleoside reverse-transcriptase inhibitors. 1, 5
• Exclude active tuberculosis before starting rifabutin to avoid inducing rifampin resistance. 1, 5

Special Populations

Pregnant Women

• Administer TMP-SMX for PCP and toxoplasmosis prophylaxis using the same indications as non-pregnant adults. 1, 2
• Providers may choose to withhold prophylaxis during the first trimester due to theoretical teratogenicity concerns; in such cases, aerosolized pentamidine may be considered due to lack of systemic absorption. 1

Children

• HIV-infected children born to HIV-positive mothers should receive TMP-SMX beginning at 4–6 weeks of age, continuing through the first year of life. 1
• Determine subsequent prophylaxis need based on age-specific CD4 thresholds. 1