sulfadiazine

CLINICAL USE

Antimicrobial agent:Toxoplasmosis in AIDS patients (unlicensed indication)Prevention of rheumatic fever

DOSE IN NORMAL RENAL FUNCTION

Loading dose: 2–4 gMaintenance dose: 2–6 g daily in divided doses

PHARMACOKINETICS

Molecular weight :250.3; 272.3 (as sodium salt)

%Protein binding :20–55

%Excreted unchanged in urine : 80 –

Volume of distribution (L/kg) :0.29

half-life – normal/ESRD (hrs) :17/Prolonged

DOSE IN RENAL IMPAIRMENT

GFR (mL/MIN)

20 to 50 : Dose as in normal renal function

10 to 20 : Use 50% of dose and monitor levels

<10 : Use 25% of dose and monitor levels

DOSE IN PATIENTS UNDERGOING RENAL REPLACEMENT THERAPIES

CAPD :Unknown dialysability. Dose as in GFR <10 mL/min

HD :Dialysed. Dose as in GFR

<10 : mL/min

HDF/high flux :Dialysed. Dose as in GFR

<10 : mL/min

CAV/VVHD :Dialysed. Dose as in GFR=10–20 mL/min

IMPORTANT DRUG INTERACTIONS

Potentially hazardous interactions with other drugs

Antibacterials: increased risk of crystalluria with methenamine

Anticoagulants: effect of coumarins enhanced

Anti-epileptics: antifolate effect and concentration of phenytoin increased

Antimalarials: increased risk of antifolate effect with pyrimethamine

Antipsychotics: avoid concomitant use with clozapine (increased risk of agranulocytosis)

Ciclosporin: reduced levels of ciclosporin; increased risk of nephrotoxicityCytotoxics: increase risk of methotrexate toxicity

ADMINISTRATION

Reconstition

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Route

Oral

Rate of Administration

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Comments

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OTHER INFORMATION

Penetrates into the CSF within 4 hours of oral administration to produce therapeutic concentrations which may be more than half those in the bloodMetabolised in the liver to the acetylated form, with elimination predominantly via the kidneysUrinary excretion of sulfadiazine and its acetyl derivative is dependent on pH; when the urine is acidic about 30% is excreted unchanged in both fast and slow acetylators, whereas when the urine is alkaline about 75% is excreted unchanged by slow acetylatorsCrystalluria may be avoided by adequate hydration and alkalinising the urine to a pH >7.15Blood concentrations of 100–150 micrograms/mL are desirableFor treatment of toxoplasmosis, use sulfadiazine in conjunction with pyrimethamine 25–100 mg daily.

See how to identify renal failure stages according to GFR calculation

See how to diagnose irreversible renal disease

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