PHESGO
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PHESGO (PHESGO).
PHESGO is a fixed-dose combination of pertuzumab and trastuzumab, both monoclonal antibodies targeting the human epidermal growth factor receptor 2 (HER2). Pertuzumab binds to the extracellular dimerization domain (subdomain II) of HER2, inhibiting ligand-dependent heterodimerization with other HER family members, primarily HER3. Trastuzumab binds to subdomain IV of the HER2 extracellular domain, inhibiting ligand-independent signaling and inducing antibody-dependent cell-mediated cytotoxicity (ADCC). Together, they provide complementary blockade of HER2 signaling pathways.
| Metabolism | Pertuzumab and trastuzumab are monoclonal antibodies, not metabolized by CYP450 enzymes. They are catabolized via general protein degradation pathways (e.g., proteolysis) into small peptides and amino acids. |
| Excretion | Phesgo (pertuzumab/trastuzumab/hyaluronidase-zzxf) is eliminated via intracellular catabolism; renal and biliary excretion are negligible. No specific percentage data available for intact antibodies. |
| Half-life | Pertuzumab: ~18 days; Trastuzumab: ~28 days; terminal half-lives support every-3-week dosing. The extended half-life is consistent with IgG1 monoclonal antibodies. |
| Protein binding | Pertuzumab and trastuzumab: ~100% bound to target HER2 receptors on cell surface; nonspecific serum protein binding is minimal (<1%). |
| Volume of Distribution | Pertuzumab: ~7.4 L; Trastuzumab: ~3.8 L (approximate Vd for 70 kg patient: 0.05-0.1 L/kg), indicating limited extravascular distribution consistent with large antibody molecules. |
| Bioavailability | Subcutaneous: 77% (relative to intravenous co-administration of pertuzumab and trastuzumab), as per the FeDeriCa trial; the fixed-dose combination with hyaluronidase facilitates absorption. |
| Onset of Action | Subcutaneous injection: Clinical effect (e.g., tumor shrinkage) typically observed after 8-12 weeks, correlating with steady-state concentrations achieved after ~3 cycles (9 weeks). |
| Duration of Action | Continuous suppression of HER2 signaling persists for weeks to months after cessation; drug levels decline slowly, with washout period >6 months for trastuzumab component. |
PHESGO (pertuzumab, trastuzumab, and hyaluronidase-zzxf) is administered subcutaneously. The recommended loading dose is 1200 mg pertuzumab, 600 mg trastuzumab, and 30,000 U hyaluronidase administered subcutaneously over approximately 8 minutes, followed by a maintenance dose of 600 mg pertuzumab, 600 mg trastuzumab, and 20,000 U hyaluronidase subcutaneously every 3 weeks.
| Dosage form | INJECTABLE |
| Renal impairment | No dose adjustment is required for patients with mild to moderate renal impairment (creatinine clearance [CrCl] ≥30 mL/min). The effect of severe renal impairment (CrCl <30 mL/min) on the pharmacokinetics of pertuzumab or trastuzumab is unknown; no specific dose adjustment can be recommended. |
| Liver impairment | No dose adjustment is required for patients with mild hepatic impairment (Child-Pugh class A). The pharmacokinetics of pertuzumab and trastuzumab have not been studied in patients with moderate or severe hepatic impairment (Child-Pugh class B or C); no specific dose adjustment can be recommended. |
| Pediatric use | The safety and efficacy of PHESGO in pediatric patients have not been established. No specific dosing guidelines are available. |
| Geriatric use | No specific dose adjustment is required for geriatric patients. Clinical studies included patients aged 65 years and older, but no overall differences in safety or efficacy were observed compared to younger patients. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PHESGO (PHESGO).
| Breastfeeding | No data on human milk excretion. Pertuzumab and trastuzumab are large IgG1 molecules likely to appear in milk, but systemic absorption by infant is minimal due to gastrointestinal degradation. M/P ratio unknown. Consider risk of infant exposure versus benefits of breastfeeding. Discontinue nursing or drug based on importance to mother. |
| Teratogenic Risk | PHESGO (pertuzumab, trastuzumab, and hyaluronidase-zzxf) is associated with oligohydramnios, fetal renal dysfunction, and fetal death when administered during pregnancy. First trimester: No known teratogenic effects, but risk of oligohydramnios begins. Second and third trimesters: Exposure increases risk of oligohydramnios, pulmonary hypoplasia, skeletal abnormalities, and neonatal death due to HER2 receptor inhibition on fetal tissues. |
■ FDA Black Box Warning
Cardiomyopathy: PHESGO can cause left ventricular dysfunction and heart failure. Assess left ventricular ejection fraction (LVEF) prior to initiation and regularly during therapy. Permanently discontinue if LVEF declines significantly or symptomatic heart failure develops.
| Serious Effects |
["Known hypersensitivity to pertuzumab, trastuzumab, or any excipients"]
| Precautions | ["Cardiomyopathy: Monitor LVEF at baseline and every 3-6 months. Withhold for significant LVEF decline.","Infusion-related reactions: Monitor during infusion; reduce rate or discontinue if severe.","Hypersensitivity reactions: Including anaphylaxis; discontinue permanently if severe.","Pulmonary toxicity: Fatal interstitial lung disease reported; discontinue if confirmed.","Embryo-fetal toxicity: Can cause fetal harm; advise effective contraception during and 7 months after last dose.","May need dose adjustment in elderly; no specific dose adjustment for renal impairment.","Neutropenia and febrile neutropenia: When used with myelosuppressive chemotherapy."] |
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| Fetal Monitoring | Prior to initiation, assess left ventricular ejection fraction (LVEF). During pregnancy, monitor fetal ultrasound for oligohydramnios, renal function, and amniotic fluid index; perform serial fetal assessments. Monitor maternal cardiac function (LVEF) every 12 weeks during therapy and more frequently if clinically indicated. |
| Fertility Effects | Animal studies show impaired fertility in females with trastuzumab and pertuzumab; menstrual cycle disruption and ovarian toxicity may occur. Human data limited; women of childbearing potential should use effective contraception during and for 7 months after last dose. Potential for reduced fertility in females; reversibility unknown. |