VHOSPITAL.CLINIC · Parasite Treatment Drug
Pyrimethamine plus sulfadiazine (with leucovorin supplementation) is the established first-line treatment for active toxoplasmosis in immunocompromised patients.
Pyrimethamine is a diaminopyrimidine that inhibits dihydrofolate reductase (DHFR) in Toxoplasma gondii, blocking folate synthesis required for parasite DNA replication. Leucovorin bypasses this block in human cells.
Pyrimethamine: 200 mg loading dose, then 50–75 mg/day. Sulfadiazine: 4–6 g/day in 4 divided doses. Leucovorin (folinic acid): 10–25 mg/day — mandatory to prevent bone marrow suppression. Minimum 6-week course.
This is a general reference. Always follow your physician's prescription and local treatment guidelines.
Pyrimethamine blocks folate metabolism in all cells. Leucovorin (folinic acid) rescues human bone marrow cells without rescuing Toxoplasma (which cannot utilise exogenous folate), preventing neutropaenia and anaemia.
Acute treatment continues for at least 6 weeks. HIV patients require lifelong suppressive therapy (pyrimethamine 25–50 mg/day + sulfadiazine 2 g/day + leucovorin) until immune reconstitution with CD4 >200 for 3+ months.
The alternative regimen is pyrimethamine plus clindamycin (600 mg every 6 hours), with leucovorin. Atovaquone with pyrimethamine or TMP-SMX are further alternatives for refractory cases.
Pyrimethamine treats Toxoplasmosis, which can cause these symptoms:
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