ILOSONE SULFA

Clinical safety rating: caution

Comprehensive clinical and safety monograph for ILOSONE SULFA (ILOSONE SULFA).

How it works

Ilosone (erythromycin) is a macrolide antibiotic that inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit. Sulfa (sulfisoxazole) is a sulfonamide that inhibits dihydropteroate synthase, blocking folate synthesis. The combination provides synergistic bacteriostatic activity.

What the body does with it

Metabolism	Erythromycin is primarily metabolized by CYP3A4; sulfisoxazole is acetylated and glucuronidated in the liver, with metabolites excreted renally.
Excretion	Renal: 70-80% as unchanged drug and active metabolite (sulfisoxazole); Biliary: 10-15% as metabolites; Fecal: <5%
Half-life	Erythromycin: 1.5-2 hours; Sulfisoxazole: 4-7 hours; clinical context: dose adjustment in renal impairment (CrCl <50 mL/min) needed for sulfisoxazole
Protein binding	Erythromycin: 65-90% bound to albumin and alpha-1-acid glycoprotein; Sulfisoxazole: 50-60% bound to albumin
Volume of Distribution	Erythromycin: 0.6-0.9 L/kg; Sulfisoxazole: 0.15-0.3 L/kg; clinical meaning: erythromycin distributes into tissues (e.g., prostate, lung), sulfisoxazole remains largely in extracellular fluid
Bioavailability	Oral: 30-65% (erythromycin base), variability due to gastric acid degradation; enteric-coated formulation 30-40%
Onset of Action	Oral: 1-2 hours (therapeutic concentrations); time to clinical effect: 24-48 hours for symptom improvement
Duration of Action	Dosing interval every 6 hours; clinical notes: sustained concentration for 6 hours with typical dosing, longer in renal impairment

Classification & Brands

Dosing & administration

Each 5 mL suspension contains 250 mg erythromycin base and 600 mg sulfisoxazole; typical adult dose is 10 mL (2 tsp) every 6 hours, not to exceed 40 mL/day.

Dosage form	SUSPENSION
Renal impairment	Contraindicated in severe renal impairment (CrCl <15 mL/min); for CrCl 15-50 mL/min, reduce dose by 50% and give every 12-24 hours; monitor for sulfonamide toxicity.
Liver impairment	Child-Pugh A: No adjustment; Child-Pugh B: Caution, reduce dose by 50%; Child-Pugh C: Avoid use due to risk of erythromycin hepatotoxicity and sulfonamide accumulation.
Pediatric use	For children >2 months: based on sulfisoxazole component (50 mg/kg/day) or erythromycin component (30-50 mg/kg/day) divided every 6 hours, maximum 2 g/day sulfisoxazole. Weight-based: <8 kg: 10 mg/kg erythromycin every 6 hours; 8-16 kg: 1/2 tsp every 6 hours; >16 kg: 1 tsp every 6 hours.
Geriatric use	Lower initial dose due to age-related renal and hepatic decline; start at 5 mL every 6 hours, titrate carefully; monitor renal function and serum levels of sulfisoxazole, as increased risk of adverse effects (renal, hepatic, skin reactions).

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for ILOSONE SULFA (ILOSONE SULFA).

Breastfeeding	Erythromycin excreted in breast milk in low amounts (M/P ratio ~0.4); sulfonamides also excreted. Risk of kernicterus in infants with G6PD deficiency or hyperbilirubinemia. Avoid breastfeeding during therapy if infant has known G6PD deficiency, prematurity, or jaundice.
Teratogenic Risk	Pregnancy Category D (erythromycin estolate) and C (trisulfapyrimidines). First trimester: Sulfonamides cross placenta; risk of neural tube defects, cardiovascular anomalies, oral clefts. Later trimesters: Sulfonamides displace bilirubin, risk of kernicterus in fetus; erythromycin estolate associated with hepatotoxicity in mother. Avoid in pregnancy unless no alternative.

Warnings & precautions

■ FDA Black Box Warning

WARNING: HEPATIC DYSFUNCTION — Erythromycin has been associated with severe hepatic toxicity, including jaundice and hepatitis, especially when used in combination with sulfonamides. Discontinue immediately if signs of hepatic injury occur.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Known hypersensitivity to erythromycin, sulfonamides, or any component","Severe hepatic impairment","Porphyria","Concurrent use with pimozide, terfenadine, astemizole (risk of cardiotoxicity)","Infants <2 months of age (risk of kernicterus from sulfisoxazole)"]

Clinical Precautions

Precautions

["Hepatotoxicity: Monitor liver function tests; avoid in patients with pre-existing liver disease","Sulfonamide hypersensitivity reactions (including Stevens-Johnson syndrome)","QT prolongation and risk of cardiac arrhythmias (erythromycin)","Renal impairment: Dose adjustment may be necessary for sulfisoxazole","Crystalluria: Ensure adequate fluid intake to prevent sulfonamide crystal formation"]

Clinical Tips & Counseling

Drug interactions

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ILOSONE SULFA

Clinical safety rating: caution

Comprehensive clinical and safety monograph for ILOSONE SULFA (ILOSONE SULFA).

How it works

What the body does with it

Metabolism	Erythromycin is primarily metabolized by CYP3A4; sulfisoxazole is acetylated and glucuronidated in the liver, with metabolites excreted renally.
Excretion	Renal: 70-80% as unchanged drug and active metabolite (sulfisoxazole); Biliary: 10-15% as metabolites; Fecal: <5%
Half-life	Erythromycin: 1.5-2 hours; Sulfisoxazole: 4-7 hours; clinical context: dose adjustment in renal impairment (CrCl <50 mL/min) needed for sulfisoxazole
Protein binding	Erythromycin: 65-90% bound to albumin and alpha-1-acid glycoprotein; Sulfisoxazole: 50-60% bound to albumin
Volume of Distribution	Erythromycin: 0.6-0.9 L/kg; Sulfisoxazole: 0.15-0.3 L/kg; clinical meaning: erythromycin distributes into tissues (e.g., prostate, lung), sulfisoxazole remains largely in extracellular fluid
Bioavailability	Oral: 30-65% (erythromycin base), variability due to gastric acid degradation; enteric-coated formulation 30-40%
Onset of Action	Oral: 1-2 hours (therapeutic concentrations); time to clinical effect: 24-48 hours for symptom improvement
Duration of Action	Dosing interval every 6 hours; clinical notes: sustained concentration for 6 hours with typical dosing, longer in renal impairment

Classification & Brands

Dosing & administration

Each 5 mL suspension contains 250 mg erythromycin base and 600 mg sulfisoxazole; typical adult dose is 10 mL (2 tsp) every 6 hours, not to exceed 40 mL/day.

Dosage form	SUSPENSION
Renal impairment	Contraindicated in severe renal impairment (CrCl <15 mL/min); for CrCl 15-50 mL/min, reduce dose by 50% and give every 12-24 hours; monitor for sulfonamide toxicity.
Liver impairment	Child-Pugh A: No adjustment; Child-Pugh B: Caution, reduce dose by 50%; Child-Pugh C: Avoid use due to risk of erythromycin hepatotoxicity and sulfonamide accumulation.
Pediatric use	For children >2 months: based on sulfisoxazole component (50 mg/kg/day) or erythromycin component (30-50 mg/kg/day) divided every 6 hours, maximum 2 g/day sulfisoxazole. Weight-based: <8 kg: 10 mg/kg erythromycin every 6 hours; 8-16 kg: 1/2 tsp every 6 hours; >16 kg: 1 tsp every 6 hours.
Geriatric use	Lower initial dose due to age-related renal and hepatic decline; start at 5 mL every 6 hours, titrate carefully; monitor renal function and serum levels of sulfisoxazole, as increased risk of adverse effects (renal, hepatic, skin reactions).

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for ILOSONE SULFA (ILOSONE SULFA).

Breastfeeding	Erythromycin excreted in breast milk in low amounts (M/P ratio ~0.4); sulfonamides also excreted. Risk of kernicterus in infants with G6PD deficiency or hyperbilirubinemia. Avoid breastfeeding during therapy if infant has known G6PD deficiency, prematurity, or jaundice.
Teratogenic Risk	Pregnancy Category D (erythromycin estolate) and C (trisulfapyrimidines). First trimester: Sulfonamides cross placenta; risk of neural tube defects, cardiovascular anomalies, oral clefts. Later trimesters: Sulfonamides displace bilirubin, risk of kernicterus in fetus; erythromycin estolate associated with hepatotoxicity in mother. Avoid in pregnancy unless no alternative.