Panitumumab

Antineoplastic monoclonal antibodies
Antineoplastic monoclonal antibodies
High alert
An error with this medicine can cause serious harm: double checks and protocols are used.
Pregnancy: avoid
Avoid in pregnancy. Can harm the fetus; effective contraception is used during treatment and for a short time after, and breastfeeding is avoided for the same period.

Fully human anti-EGFR antibody for metastatic colorectal cancer without RAS mutations. Rash is nearly universal; magnesium falls.

Updated Nov 1, 2026

Quick facts

Group: Antineoplastic monoclonal antibodies
Target: Epidermal growth factor receptor (EGFR, HER1), extracellular domain III
Key effects: Acne-like rash · Sensitivity to sunlight · Tiredness
Monitor: Magnesium and calcium before · Skin
ATC: L01FE02

No doses: the clinician sets them by the current guideline.

Mechanism of action

Epidermal growth factor receptor (EGFR, HER1), extracellular domain IIIPanitumumab

The crystal shows the panitumumab Fab bound to domain III of human EGFR, the domain that binds EGF.

Target in 3D: Epidermal growth factor receptor (EGFR, HER1), extracellular domain III. PDB structure 5SX4 (RCSB PDB, public domain). View the structure at RCSB PDB

Panitumumab is a fully human IgG2 antibody that binds domain III of the EGFR outside the cell. It blocks EGF and related growth factors from binding, so the receptor's growth signals stop. When the tumour carries an activating RAS mutation, the signal is switched on further down the pathway and blocking the receptor does not help, which is why it is used only in RAS wild-type colorectal cancer. As an IgG2, it triggers immune killing (ADCC) less than cetuximab.

Panitumumab binds EGFR domain III
EGF cannot bind; the RAS–RAF–MAPK signal stops
Useless if RAS itself is mutated and always on

Indications

Metastatic colorectal cancer without an abnormal RAS gene: first line with FOLFOX chemotherapy, or alone after fluoropyrimidine, oxaliplatin and irinotecan. Colorectal cancer →

Adverse effects

Common

Acne-like rash, dry or cracked skin, itching, nail-fold inflammation
Sensitivity to sunlight
Tiredness, nausea, vomiting, abdominal pain, constipation, diarrhoea
Mouth sores; longer eyelashes

Contraindications

Colorectal cancer with a RAS mutation (no benefit)

Key interactions

Chemotherapy regimens (FOLFOX): Intended combination in RAS wild-type disease; diarrhoea and dehydration add up.

What is monitored

RAS testing of the tumour before starting
Magnesium and calcium before, during and after treatment
Skin, nails and eyes at every visit
Breathing symptoms and hydration

Administration and safety

Slow intravenous infusion by a doctor or nurse; the patient is watched for infusion reactions.
The infusion is slowed or stopped for a reaction.

Pregnancy and breastfeeding

Avoid in pregnancy. Can harm the fetus; effective contraception is used during treatment and for a short time after, and breastfeeding is avoided for the same period.

Nursing care

Teach skin care: moisturiser, sun protection with clothing, hat, sunglasses and sunscreen; report blisters, peeling or nail-fold swelling.
Ask about low magnesium or calcium, lung or kidney problems before starting.
Teach to report muscle cramps or twitching, eye pain or redness, new cough and signs of dehydration.
Confirm that a RAS test was done.

Pharmacokinetics

Absorption: Intravenous infusion every two weeks.
Half-life: About 7.5 days (mean); its kinetics are non-linear.

Test yourself

Think of the answer, then tap the question to see it.

Which tumour test must be normal before panitumumab is used in colorectal cancer?

RAS: it works only in RAS wild-type tumours.

Which electrolyte typically falls with anti-EGFR antibodies?

Magnesium (calcium may fall too).

How does panitumumab differ from cetuximab in antibody type?

Panitumumab is a fully human IgG2, which triggers immune cell killing less than cetuximab.

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Connections

← Back to the class: Antineoplastic monoclonal antibodies

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Panitumumab Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); Panitumumab - NCI (National Cancer Institute (U.S.), 2026); Crystal Structure of panitumumab in complex with epidermal growth factor receptor domain 3. (RCSB Protein Data Bank, 2016).

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Representative model, for educational purposes only.