Low-Dose Trimethoprim-Sulfamethoxazole Prophylaxis forPneumonia in a Critically Ill Patient with HIV/TB Coinfection: Pharmacokinetics and Clinical Outcomes.

BACKGROUND: pneumonia (PJP) is a life-threatening opportunistic infection disease in immunocompromised patients, particularly those with advanced HIV and tuberculosis (TB) co-infection. Trimethoprim-sulfamethoxazole (TMP-SMZ) is recommended for PJP prophylaxis, but its pharmacokinetics (PK) and clinical efficacy in critically ill patients receiving multi-drug therapies (anti-TB, antiretroviral, and antifungals) remain poorly characterized.

CASE PRESENTATION: This study reported the PK profile, multi-drug management strategies and clinical outcomes of low-dose TMP-SMZ (a combined dose of 480 mg once daily, 50% of the standard prophylactic dose) for PJP prophylaxis in a critically ill patient with disseminated TB, advanced HIV (CD4count: 21 cells/μL), and concurrent infections. The patient received TMP-SMZ alongside anti-TB therapy (isoniazid, rifabutin, levofloxacin, linezolid), voriconazole, and antiretroviral therapy. Therapeutic drug monitoring (TDM) showed peak concentrations of sulfamethoxazole (SMZ) and trimethoprim (TMP) were 18.58 µg/mL and 0.48 µg/mL, with trough concentrations of 1.75 µg/mL and 0.03 µg/mL, respectively. No drug-drug interactions were observed with concurrent voriconazole. The patient achieved stable recovery and without PJP or TMP-SMZ-related adverse events occurred during treatment and 6-month follow-up.

CONCLUSION: This case reported the feasibility of low-dose TMP-SMZ for PJP prevention in high-risk, critically ill patients with HIV/TB coinfection, and described its PK characteristics. It provides a reference for optimizing prophylaxis in resource-limited settings or patients intolerant to standard regimens.