VECTIBIX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for VECTIBIX (VECTIBIX).
Epidermal growth factor receptor (EGFR) antagonist; binds to EGFR and competitively inhibits ligand binding, leading to inhibition of downstream signaling pathways including RAS/RAF/MAPK and PI3K/AKT, resulting in cell cycle arrest and apoptosis.
| Metabolism | Primarily eliminated via the reticuloendothelial system; not metabolized by cytochrome P450 enzymes; no significant hepatic metabolism. |
| Excretion | Primarily eliminated via the reticuloendothelial system; <3% excreted unchanged in urine; no significant renal or biliary elimination. |
| Half-life | Terminal half-life approximately 7.5 days (range 3.6–10.9 days); supports every-2-week dosing regimen. |
| Protein binding | Approximately 95% bound, primarily to albumin; minimal binding to other plasma proteins. |
| Volume of Distribution | Volume of distribution approximately 3.0–4.0 L/kg; suggests extensive tissue distribution and binding to EGFR-expressing cells. |
| Bioavailability | Subcutaneous: Absolute bioavailability approximately 93% relative to intravenous administration. |
| Onset of Action | Subcutaneous: Clinical effect (tumor response) typically observed within 4–8 weeks; serum concentration peaks at 3–7 days. |
| Duration of Action | Duration of clinical effect sustained with continued dosing; receptor occupancy remains >90% for at least 14 days after single dose. |
6 mg/kg IV every 14 days.
| Dosage form | INJECTABLE |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment. Insufficient data for severe renal impairment (CrCl <30 mL/min) or ESRD. |
| Liver impairment | No dose adjustment required for mild (Child-Pugh A) or moderate (Child-Pugh B) hepatic impairment. Insufficient data for severe (Child-Pugh C) hepatic impairment. |
| Pediatric use | Safety and efficacy not established in pediatric patients. |
| Geriatric use | No specific dose adjustment recommended; no significant differences in safety or efficacy observed in patients ≥65 years compared to younger adults. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for VECTIBIX (VECTIBIX).
| Breastfeeding | No data on presence in human milk, effects on breastfed infant, or milk production. Human IgG is excreted in breast milk, but panitumumab is a large protein likely degraded in infant GI tract. M/P ratio unknown. Because of potential for serious adverse reactions in nursing infants, advise women to discontinue breastfeeding during treatment and for 2 months after last dose. |
| Teratogenic Risk | Pregnancy Category C. Panitumumab is an IgG2 monoclonal antibody; IgG crosses the placenta, with the highest transfer occurring in the third trimester. Based on its mechanism of EGFR inhibition, there is potential for fetal harm. Animal studies (cynomolgus monkeys) with panitumumab at doses 0.5 to 5 times the clinical exposure (AUC) revealed embryotoxicity and developmental delays (e.g., skeletal malformations, increased abortions). No adequate human studies exist. Use only if potential benefit justifies risk; avoid in pregnancy unless absolutely necessary. |
■ FDA Black Box Warning
None.
| Serious Effects |
None known.
| Precautions | Infusion reactions (including severe and fatal), dermatologic toxicity (including severe acneiform dermatitis and infections), increased toxicity with concurrent chemotherapy (especially diarrhea and dehydration), pulmonary fibrosis, hypomagnesemia, ocular toxicity, and potential for fetal harm. |
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| Fetal Monitoring | During pregnancy: monitor fetal growth and development via serial ultrasound; assess for oligohydramnios if used in third trimester. Maternal monitoring: serum magnesium, calcium, potassium, and creatinine prior to and periodically during therapy due to risk of electrolyte disturbances (severe hypomagnesemia, hypocalcemia, hypokalemia). Also monitor for infusion reactions, dermatologic toxicity, and ocular toxicity. |
| Fertility Effects | No human fertility studies. Animal studies in female cynomolgus monkeys showed panitumumab-related absent or irregular menstrual cycles and reduced ovarian function (decreased follicular development) at exposures 0.5 to 5 times clinical AUC. Males: testicular degeneration was observed in some monkeys. Potential for impaired fertility in both sexes. |