Carbamazepine — NZ Medication Guide
📋 Reviewed by a Registered Pharmacist NZ — This information is for general educational purposes only and does not replace professional medical advice. Always consult your doctor or pharmacist before starting, stopping, or changing any medication.
What is Carbamazepine?
Carbamazepine is an anticonvulsant and mood stabiliser used for epilepsy, trigeminal neuralgia, and bipolar disorder. This medication is funded by Pharmac for epilepsy and trigeminal neuralgia.
What is Carbamazepine Used For?
Used for focal epilepsy, generalised tonic-clonic seizures, trigeminal neuralgia, and as a mood stabiliser in bipolar disorder.
How Does Carbamazepine Work?
Blocks voltage-gated sodium channels in a use-dependent manner, stabilising hyperexcited neuronal membranes and reducing the aberrant electrical activity driving seizures and trigeminal pain.
How to Take Carbamazepine
Titrate slowly from 100–200 mg/day to maintenance 400–1600 mg/day twice or three times daily. Modified-release (Tegretol CR®) can be taken twice daily. Take with food.
Common Side Effects of Carbamazepine
- Dizziness and ataxia
- Double vision
- Drowsiness
- Nausea
- Headache
- Rash (discontinue if extensive)
Serious Side Effects — Seek Medical Attention
Contact your doctor or call 111 immediately if you experience any of the following:
- Stevens-Johnson syndrome/TEN (highest risk in Han Chinese with HLA-B*15:01 — HLA screening recommended)
- Aplastic anaemia and agranulocytosis (rare)
- SIADH and hyponatraemia
- Hepatotoxicity
Drug Interactions
Carbamazepine may interact with other medicines. Always inform your doctor and pharmacist of all medications you are taking. Key interactions include:
- Strong CYP450 inducer — reduces levels of many medicines including oral contraceptive pill, lamotrigine, warfarin, antipsychotics
- Erythromycin/clarithromycin (increase carbamazepine levels — toxicity risk)
- Grapefruit juice (increases levels)
New Zealand Prescribing Information
Carbamazepine (Tegretol® 100 mg, 200 mg; Tegretol CR® 200 mg, 400 mg) is funded by Pharmac. HLA-B*15:01 screening is recommended before starting in patients of Han Chinese, Thai, or other Asian ancestry. Full medication review is essential due to many drug interactions.
Frequently Asked Questions
Why does carbamazepine interact with so many medicines?
Carbamazepine is a potent inducer of liver enzymes (CYP3A4, CYP2C9 and others), greatly increasing breakdown of many medicines including the contraceptive pill, warfarin, and many antidepressants. Always inform every prescriber you are on carbamazepine.
Does carbamazepine affect the contraceptive pill?
Yes — it significantly reduces OCP efficacy. Women should use a long-acting reversible contraceptive (LARC) such as a hormonal IUD or implant for reliable contraception.
⚠️ Disclaimer: This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or a qualified health provider. In New Zealand, medication availability and funding may vary — check with Pharmac or your pharmacist for current information.
Reviewed by a Registered Pharmacist NZ
References & Further Information
The following New Zealand and international resources were used to inform this page: