Panitumumab Injection

Panitumumab injection (Vectibix) is a targeted cancer treatment approved for adults with metastatic colorectal cancer (mCRC) — but only when the tumor's genetic profile meets specific criteria confirmed by an FDA-approved test.

• Vectibix + FOLFOX chemotherapy: First-line treatment for adults with wild-type RAS mCRC (tumors with no RAS mutations in KRAS or NRAS)
• Vectibix alone (monotherapy): For wild-type RAS mCRC in adults whose cancer progressed after treatment with fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy
• Vectibix + sotorasib: For adults with KRAS G12C-mutated mCRC who have already received fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy — this use requires confirmation of the KRAS G12C mutation by an FDA-approved test
• Vectibix is not indicated for RAS-mutant mCRC (except in the KRAS G12C + sotorasib combination) and is not indicated when RAS mutation status is unknown

Panitumumab targets a protein called EGFR (epidermal growth factor receptor), which sits on the surface of both normal cells and certain cancer cells. In colorectal cancers, EGFR is often overexpressed — meaning there's too much of it — and when activated, it drives tumor cells to grow and spread. Panitumumab binds tightly to EGFR and blocks the signals that tell cancer cells to grow, which can slow tumor growth and trigger cancer cell death.

This blocking strategy only works when the tumor's downstream signaling — through proteins called RAS — can actually be controlled by shutting off EGFR. In tumors with RAS mutations (other than KRAS G12C), those RAS proteins are permanently switched on regardless of EGFR, so blocking EGFR provides no benefit and may cause harm. In KRAS G12C-mutated tumors, EGFR activation is a known escape route that cancer cells use to resist KRAS G12C inhibitors like sotorasib — so combining Vectibix with sotorasib targets both pathways at once.

Vectibix is given by intravenous (IV) infusion — into a vein — in a clinical setting by a healthcare professional. It is administered once every two weeks (every 14 days). Infusions are given slowly over 60 minutes for standard doses, or over 90 minutes for larger doses; it is never given as a fast IV push. There are no food or drink restrictions tied to Vectibix infusions.

• When used with sotorasib, the first sotorasib dose is taken before the first Vectibix infusion
• If sotorasib is paused or stopped, Vectibix must also be paused or stopped — your care team will manage this
• Dose adjustments or temporary holds may be made based on side effects such as skin reactions or infusion reactions — always follow your prescriber's instructions

Side effects with Vectibix are common — especially skin-related ones — so knowing what to expect can help you manage them and know when to call your care team.

• Skin rash and acne-like breakouts — the most common reaction, affecting nearly all patients
• Paronychia — painful inflammation around nails and fingertips
• Fatigue and weakness
• Diarrhea — can be severe and lead to dehydration
• Nausea
• Dry skin, skin cracking (fissures), and skin peeling
• Low magnesium (hypomagnesemia) and other electrolyte changes, found on blood tests
• Mouth sores (stomatitis) and mucosal inflammation

Serious reactions — including severe skin infections, life-threatening blistering, difficulty breathing during infusion, kidney failure from dehydration, or serious eye problems — require immediate medical attention. Contact your care team right away if any of these occur.

• Severe skin toxicity: Nearly all patients develop skin reactions; about 1 in 7 are severe. Life-threatening skin infections, necrotizing fasciitis (deep tissue infection), sepsis, and fatal blistering skin reactions have been reported. Monitor skin carefully and limit sun exposure — sunscreen and protective clothing are recommended throughout treatment.
• Not effective — and potentially harmful — in RAS-mutant tumors: In patients with RAS-mutant mCRC (other than KRAS G12C), Vectibix monotherapy or with oxaliplatin-based chemotherapy can actually worsen outcomes. Genetic testing is required before starting.
• Electrolyte depletion: Vectibix frequently causes drops in magnesium, calcium, and potassium. These require regular blood monitoring before, during, and for 8 weeks after treatment, with replacement as needed.
• Serious infusion reactions: Fever, chills, breathing difficulty, low blood pressure, and bronchospasm can occur — fatal reactions have been reported after marketing. Medical support must be available at every infusion.
• Lung disease (ILD/pulmonary fibrosis): Fatal and nonfatal cases have occurred. Vectibix must be stopped if ILD is confirmed.
• Eye problems: Keratitis (corneal inflammation), ulcerative keratitis, and corneal perforation have been reported. Report any eye pain or vision changes promptly.
• Embryo-fetal harm: Vectibix can cause pregnancy loss based on animal data. Effective contraception is required during treatment and for 2 months after the last dose.
• Avoid with bevacizumab: Adding Vectibix to bevacizumab-plus-chemotherapy regimens increased deaths and serious toxicity — this combination is not recommended.

Vectibix has important interactions with specific cancer treatment combinations that affect both safety and effectiveness.

• Bevacizumab + chemotherapy: Adding Vectibix to this combination increased overall mortality and serious adverse reactions (including pulmonary embolism) — this combination should not be used
• Sotorasib: When Vectibix is used with sotorasib, the two drugs must be managed together — if sotorasib is paused or discontinued, Vectibix must also be paused or discontinued; refer to sotorasib's prescribing information for its own dose adjustments

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Genetic testing required: RAS mutation status (and KRAS G12C status for the sotorasib combination) must be confirmed by an FDA-approved test before starting Vectibix — it is not appropriate when mutation status is unknown
• Pregnancy: Vectibix can cause fetal harm and pregnancy loss — tell your doctor if you are pregnant or may become pregnant
• Contraception: Women who can become pregnant must use effective birth control during treatment and for at least 2 months after the last dose
• Breastfeeding: Do not breastfeed during treatment or for 2 months after the last dose due to potential serious harm to the infant
• Fertility: Vectibix may reduce fertility in women based on animal studies — the effects were reversible in those studies; discuss family planning with your doctor before starting
• Lung disease history: Patients with a history of interstitial pneumonitis or pulmonary fibrosis require careful risk-benefit assessment before starting Vectibix
• Older adults (65+): Patients 65 and older receiving Vectibix with FOLFOX had higher rates of serious adverse events and serious diarrhea compared to younger patients — closer monitoring may be needed
• Children: Safety and effectiveness have not been established in pediatric patients

In cases where doses approximately twice the recommended amount were given, the main effects seen were severe skin toxicity, diarrhea, dehydration, and fatigue. If an overdose is suspected, contact your healthcare team or seek emergency medical care right away.

Panitumumab binds to EGFR on cancer cell surfaces and blocks the receptor from being activated by its natural triggers. This prevents a chain of internal cell signals that would normally drive tumor cells to grow, multiply, and survive. Blocking EGFR with panitumumab also reduces the production of factors that promote tumor blood vessel growth and inflammation. Because EGFR is also present on normal skin and hair follicle cells, blocking it in those tissues explains the characteristic skin and nail side effects seen with this drug.

After IV infusion, panitumumab reaches steady-state blood levels by the third infusion (around 6 weeks into treatment). It has an elimination half-life of approximately 7.5 days, meaning it takes roughly that long for the body to clear half of the drug. The body's clearance of panitumumab decreases as the dose increases, a pattern called nonlinear pharmacokinetics. Age, sex, race, and mild-to-moderate kidney or liver impairment do not significantly affect how the body handles panitumumab.

Store vials in the original carton under refrigeration at 2° to 8°C (36° to 46°F) until time of use. Protect from direct sunlight. Do not freeze or shake.