PEGASYS
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PEGASYS (PEGASYS).
Pegylated interferon alfa-2a binds to interferon receptors, activating JAK-STAT signaling, leading to antiviral, antiproliferative, and immunomodulatory effects.
| Metabolism | Metabolized primarily by the liver via proteolytic degradation. CYP450 involvement is minimal. |
| Excretion | Renal and hepatic metabolism; unchanged drug excreted in urine is minimal. Biliary/fecal elimination accounts for approximately 65% of the dose. |
| Half-life | Terminal elimination half-life is approximately 80 hours (range 50-100 hours) in healthy adults; allows once-weekly dosing. |
| Protein binding | >99% bound to albumin and α1-acid glycoprotein. |
| Volume of Distribution | 6-14 L (approx 0.1-0.2 L/kg) indicating limited extravascular distribution. |
| Bioavailability | Subcutaneous: 80-90% |
| Onset of Action | Subcutaneous: Serum RNA reduction within 24 hours; maximal antiviral effect at 24-48 hours. |
| Duration of Action | Subcutaneous: Weekly dosing maintains therapeutic levels; viral suppression persists for the dosing interval. |
| Action Class | Interferons |
| Brand Substitutes | Taspiance 180mcg Injection, Taspiance 135mcg Injection |
180 mcg subcutaneously once weekly.
| Dosage form | SYRINGE |
| Renal impairment | For GFR < 30 mL/min, reduce dose to 135 mcg subcutaneously once weekly. |
| Liver impairment | Contraindicated in Child-Pugh class B and C. For Child-Pugh class A, no adjustment recommended. |
| Pediatric use | For patients 5 years and older: 180 mcg/1.73 m² subcutaneously once weekly. |
| Geriatric use | No specific adjustment; monitor for adverse effects and renal function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PEGASYS (PEGASYS).
| Breastfeeding | It is not known whether peginterferon alfa-2a is excreted in human milk. Because many drugs are excreted in human milk and because of the potential for adverse reactions in nursing infants, a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother. M/P ratio: Not available. |
| Teratogenic Risk | PEGASYS (peginterferon alfa-2a) is associated with increased risk of fetal harm if used during pregnancy. In animal studies, administration of peginterferon alfa-2a to pregnant monkeys resulted in increased rates of abortion and fetal abnormalities. Human data are limited, but interferon alfa-2a has been reported to cause fetal growth restriction and spontaneous abortion. Use during pregnancy is contraindicated. Trimester-specific risks: First trimester: Risk of spontaneous abortion and teratogenic effects (based on animal data); Second and third trimesters: Risk of fetal growth restriction. |
■ FDA Black Box Warning
May cause or aggravate fatal or life-threatening neuropsychiatric, autoimmune, ischemic, and infectious disorders. Patients should be monitored closely for signs and symptoms. Depression and suicidal ideation have been reported.
| Serious Effects |
["Hypersensitivity to peginterferon alfa-2a or any component","Autoimmune hepatitis","Decompensated liver disease (Child-Pugh class B or C) in cirrhotic patients","Neonates and infants (contains benzyl alcohol)"]
| Precautions | ["Neuropsychiatric events: depression, suicidal ideation, psychosis","Bone marrow suppression: neutropenia, thrombocytopenia, anemia","Autoimmune disorders: exacerbation of autoimmune hepatitis, thyroiditis","Cardiovascular effects: hypotension, arrhythmia, cardiomyopathy","Ophthalmologic disorders: retinopathy, retinal hemorrhage","Hepatic decompensation in cirrhotic patients"] |
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| Fetal Monitoring | Monitor maternal complete blood counts (CBC) with differential, serum chemistry including liver function tests (ALT, AST, bilirubin), thyroid function tests, and viral load (HCV RNA) at regular intervals. Monitor fetal growth with serial ultrasound assessments if pregnancy occurs. Assess for signs of maternal infection or hematologic toxicity. |
| Fertility Effects | Animal studies have shown that peginterferon alfa-2a can impair fertility. In female monkeys, treatment resulted in prolonged menstrual cycles and reduced ovulation. In male rats, reduced sperm count and motility were observed. Reversibility of these effects in humans is unknown. |