INTRON A

Clinical safety rating: caution

Comprehensive clinical and safety monograph for INTRON A (INTRON A).

How it works

Interferon alfa-2b exerts antiviral, antiproliferative, and immunomodulatory effects by binding to type I interferon receptors, activating JAK-STAT signaling, inducing expression of antiviral proteins (e.g., Mx proteins, 2',5'-oligoadenylate synthetase), and enhancing natural killer cell cytotoxicity.

What the body does with it

Metabolism	Primarily metabolized via renal tubular catabolism and degradation, with minimal hepatic metabolism. No specific cytochrome P450 involvement identified.
Excretion	Renal (primarily): ~70% unchanged in urine; biliary/fecal: minor (<10%).
Half-life	2–3 hours (subcutaneous), 3–8 hours (intramuscular); terminal elimination half-life is approximately 2–3 hours. Clinical context: short half-life necessitates frequent dosing (e.g., three times weekly) for sustained antiviral/antiproliferative effect.
Protein binding	Approximately 60–70% (to albumin and alpha-1 acid glycoprotein).
Volume of Distribution	0.4–0.5 L/kg; moderate distribution reflecting limited tissue penetration, consistent with a large protein molecule (MW ~19,000 Da).
Bioavailability	Subcutaneous: 34–54% (mean ~45%), Intramuscular: 45–60% (mean ~50%).
Onset of Action	Subcutaneous: 2–4 hours (peak serum concentration); intramuscular: 3–8 hours (peak). Clinical effect (e.g., antiviral response) typically seen within 24–48 hours after first dose.
Duration of Action	Approximately 24–48 hours; clinical effect may persist for several days after last dose due to intracellular signaling pathways. Clinical notes: dosing every other day or three times weekly maintains therapeutic effect.

Classification & Brands

Dosing & administration

3 million IU subcutaneously 3 times per week for chronic hepatitis C; 5-10 million IU subcutaneously 3 times per week for hairy cell leukemia.

Dosage form	VIAL
Renal impairment	CrCl < 50 mL/min: reduce dose by 50%; CrCl < 10 mL/min: contraindicated.
Liver impairment	Child-Pugh class B: reduce dose by 50%; Child-Pugh class C: contraindicated.
Pediatric use	3 million IU/m² subcutaneously 3 times per week for chronic hepatitis C; maximum dose: 6 million IU/m².
Geriatric use	No specific adjustments; monitor renal function and neuropsychiatric effects closely.

Use during pregnancy

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

Clinical note

Comprehensive clinical and safety monograph for INTRON A (INTRON A).

Breastfeeding	Interferon alfa-2b is excreted into human breast milk in low amounts; M/P ratio not reported. Due to potential for adverse effects in the nursing infant, caution is advised. Consider discontinuation of nursing or drug, depending on importance of drug to mother.
Teratogenic Risk	First trimester: Limited data, but interferon alfa-2b may increase risk of spontaneous abortion. Second and third trimesters: Data suggest no significant increase in major malformations; however, fetal growth restriction and preterm labor have been reported. Use only if potential benefit justifies risk.

Warnings & precautions

■ FDA Black Box Warning

WARNING: May cause or aggravate fatal or life-threatening neuropsychiatric reactions, autoimmune disorders, ischemic disorders, and infectious disorders. Patients should be monitored closely with periodic clinical and laboratory evaluations. Discontinue therapy if these develop or worsen.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Known hypersensitivity to interferon alfa-2b or any component of the formulation","Autoimmune hepatitis","Decompensated liver disease (for hepatitis B/C indications)","Existing severe psychiatric disorders (e.g., severe depression, suicidal ideation)","Thrombocytopenia (<50,000/mm³) or neutropenia (<500/mm³) for certain indications","Pregnancy (risk of fetal harm; effective contraception required)"]

Clinical Precautions

Precautions

["Neuropsychiatric effects (depression, suicidal ideation)","Autoimmune disorders (e.g., hemolytic anemia, thrombocytopenia, thyroiditis)","Cardiovascular events (ischemic, hemorrhagic, arrhythmias)","Hepatic decompensation (especially in cirrhosis)","Hypersensitivity reactions (acute urticaria, angioedema)","Ophthalmic disorders (retinal hemorrhages, visual loss)","Pulmonary effects (dyspnea, pneumonitis)","Renal impairment (monitor renal function)","Dental/periodontal disorders (in patients with history)"]

Clinical Tips & Counseling

Drug interactions

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INTRON A

Clinical safety rating: caution

Comprehensive clinical and safety monograph for INTRON A (INTRON A).

How it works

What the body does with it

Metabolism	Primarily metabolized via renal tubular catabolism and degradation, with minimal hepatic metabolism. No specific cytochrome P450 involvement identified.
Excretion	Renal (primarily): ~70% unchanged in urine; biliary/fecal: minor (<10%).
Half-life	2–3 hours (subcutaneous), 3–8 hours (intramuscular); terminal elimination half-life is approximately 2–3 hours. Clinical context: short half-life necessitates frequent dosing (e.g., three times weekly) for sustained antiviral/antiproliferative effect.
Protein binding	Approximately 60–70% (to albumin and alpha-1 acid glycoprotein).
Volume of Distribution	0.4–0.5 L/kg; moderate distribution reflecting limited tissue penetration, consistent with a large protein molecule (MW ~19,000 Da).
Bioavailability	Subcutaneous: 34–54% (mean ~45%), Intramuscular: 45–60% (mean ~50%).
Onset of Action	Subcutaneous: 2–4 hours (peak serum concentration); intramuscular: 3–8 hours (peak). Clinical effect (e.g., antiviral response) typically seen within 24–48 hours after first dose.
Duration of Action	Approximately 24–48 hours; clinical effect may persist for several days after last dose due to intracellular signaling pathways. Clinical notes: dosing every other day or three times weekly maintains therapeutic effect.

Classification & Brands

Dosing & administration

3 million IU subcutaneously 3 times per week for chronic hepatitis C; 5-10 million IU subcutaneously 3 times per week for hairy cell leukemia.

Dosage form	VIAL
Renal impairment	CrCl < 50 mL/min: reduce dose by 50%; CrCl < 10 mL/min: contraindicated.
Liver impairment	Child-Pugh class B: reduce dose by 50%; Child-Pugh class C: contraindicated.
Pediatric use	3 million IU/m² subcutaneously 3 times per week for chronic hepatitis C; maximum dose: 6 million IU/m².
Geriatric use	No specific adjustments; monitor renal function and neuropsychiatric effects closely.

Use during pregnancy

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

Clinical note

Comprehensive clinical and safety monograph for INTRON A (INTRON A).

Breastfeeding	Interferon alfa-2b is excreted into human breast milk in low amounts; M/P ratio not reported. Due to potential for adverse effects in the nursing infant, caution is advised. Consider discontinuation of nursing or drug, depending on importance of drug to mother.
Teratogenic Risk	First trimester: Limited data, but interferon alfa-2b may increase risk of spontaneous abortion. Second and third trimesters: Data suggest no significant increase in major malformations; however, fetal growth restriction and preterm labor have been reported. Use only if potential benefit justifies risk.