Situation: A 34-year-old man was diagnosed with human immunodeficiency virus (HIV) infection 1 week ago and has enrolled at a Department of Health (DOH)–accredited treatment hub, where he starts the once-daily tenofovir–lamivudine–dolutegravir (TLD) tablet today. His CD4 count is 150 cells/mm³, he has never had an opportunistic illness, and he has no drug allergies. Along with TLD, which prophylactic drug and monitoring plan should the nurse anticipate for him?

Opportunistic infection prophylaxis is chosen by CD4 level; with a CD4 count of 150 cells/mm³ he needs trimethoprim–sulfamethoxazole against Pneumocystis pneumonia. Its key adverse effects are rash, hyperkalemia (trimethoprim acts like a potassium-sparing diuretic), and bone marrow suppression. Fluconazole and acyclovir are not the routine prophylaxis at this CD4 level.

Why TMP–SMX is the anticipated prophylaxis

A CD4 count of 150 cells/mm³ places this patient below the threshold of 200 cells/mm³ at which primary prophylaxis against Pneumocystis jirovecii pneumonia (PCP) is indicated. The first-line prophylactic agent at this CD4 level is trimethoprim–sulfamethoxazole (TMP–SMX), not fluconazole or acyclovir. Fluconazole is reserved for specific fungal prophylaxis such as cryptococcal or candidal disease in selected settings, and acyclovir is used for herpes simplex or varicella suppression, not as routine PCP prophylaxis. The once-daily TLD regimen addresses HIV viral suppression, but it does not replace the need for opportunistic infection prophylaxis while the CD4 count remains low.

Monitoring priorities with TMP–SMX

The nurse should anticipate monitoring for the characteristic adverse effects of TMP–SMX. Rash is one of the most common hypersensitivity reactions and may range from mild maculopapular eruption to severe cutaneous reactions. Hyperkalemia is a distinctive metabolic effect because the trimethoprim component acts on the distal nephron in a manner similar to potassium-sparing diuretics such as amiloride, reducing renal potassium excretion. A rise in serum potassium, rather than a fall, is the expected electrolyte change with TMP–SMX. Bone marrow suppression, particularly leukopenia or thrombocytopenia, is another important adverse effect related to folate antagonism, although it is not the focus of the answer choices here.

Watch out! Do not confuse the potassium effect of TMP–SMX with that of loop or thiazide diuretics, which cause hypokalemia. Trimethoprim causes potassium retention, so the correct monitoring is for hyperkalemia. Key point! The need for PCP prophylaxis is driven by the CD4 count below 200 cells/mm³, and the agent of choice is TMP–SMX unless there is a documented allergy or intolerance.

Clinical reasoning for the correct option

Option 1 is correct because it pairs the appropriate drug, TMP–SMX daily, with the correct monitoring focus: rash and a rise in potassium. Option 2 incorrectly states a fall in potassium. Option 3 selects fluconazole and liver enzyme monitoring, which is not the routine PCP prophylaxis at this CD4 level. Option 4 selects acyclovir with renal monitoring, which is not indicated as primary PCP prophylaxis in this scenario. The case report describing rezafungin use in a patient with TMP–SMX allergy reinforces that TMP–SMX remains the standard first-line agent when no allergy is present ^[1]. The guideline-based emphasis on CD4 count monitoring and preventive therapy further supports using the CD4 threshold to guide prophylaxis decisions .

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