Carbamazepine

1. Introduction

Carbamazepine, commonly marketed under brand names such as Tegretol, Carbatrol, and Epitol, is an anticonvulsant and mood-stabilising medication. It is primarily used to manage epilepsy, trigeminal neuralgia, and bipolar disorder. Carbamazepine works by reducing abnormal electrical activity in the brain and stabilising neuronal membranes.

2. Indications

  • Approved Indications:
    • Epilepsy: Partial seizures (simple and complex) and generalised tonic-clonic seizures.
    • Trigeminal neuralgia.
    • Acute manic or mixed episodes in bipolar disorder.
  • Off-Label Uses:
    • Neuropathic pain (e.g., diabetic neuropathy).
    • Restless legs syndrome (RLS).

3. Dosage

  • Epilepsy:
    • Adults: 200 mg twice daily; increase by 200 mg/day weekly. Usual maintenance dose: 800–1200 mg/day in divided doses (maximum: 1600 mg/day).
    • Children (6–12 years): 100 mg twice daily; increase by 100 mg/day weekly. Usual maintenance dose: 400–800 mg/day in divided doses.
  • Trigeminal Neuralgia:
    • Initial dose: 100 mg twice daily; increase by 200 mg/day weekly. Usual maintenance dose: 400–800 mg/day in divided doses.
  • Bipolar Disorder:
    • Initial dose: 200 mg twice daily; titrate based on response. Usual maintenance dose: 400–1600 mg/day.

4. Administration

  • Take with food to minimise gastrointestinal discomfort.
  • Extended-release tablets should be swallowed whole; do not crush or chew.
  • Oral suspension should be shaken well before use.

5. Forms Available

  • Tablets: 100 mg, 200 mg.
  • Extended-release tablets: 200 mg, 400 mg.
  • Oral suspension: 100 mg/5 mL.

6. Side Effects

6.1. Common Side Effects

  • Dizziness.
  • Drowsiness.
  • Nausea and vomiting.
  • Blurred vision or double vision.

6.2. Less Common Side Effects

  • Dry mouth.
  • Skin rash.
  • Weight gain.

6.3. Rare but Serious Side Effects

  • Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN).
  • Aplastic anaemia and agranulocytosis.
  • Hepatotoxicity.
  • Hyponatraemia (SIADH).

7. Warnings

  • Patients of Asian descent should be tested for HLA-B*1502 allele before initiating therapy due to the increased risk of SJS/TEN.
  • Risk of suicidal thoughts and behaviour; monitor closely.
  • Use with caution in patients with a history of bone marrow suppression.

8. Precautions

  • Avoid abrupt discontinuation; taper doses gradually to prevent withdrawal seizures.
  • Use with caution in patients with hepatic or renal impairment.
  • Avoid alcohol, as it may enhance CNS depression.

9. Interactions

  • Drug-Drug Interactions:
    • Strong enzyme inducer; may reduce the efficacy of oral contraceptives, warfarin, and other drugs metabolised by CYP3A4.
    • Increased risk of toxicity with macrolide antibiotics (e.g., erythromycin) and azole antifungals.
    • Risk of sedation when combined with other CNS depressants.
  • Drug-Food Interactions:
    • Avoid grapefruit juice, as it can increase carbamazepine levels and toxicity risk.

10. Monitoring Parameters

  • Baseline and periodic complete blood count (CBC) to monitor for blood dyscrasias.
  • Liver function tests (LFTs) and renal function periodically.
  • Serum carbamazepine levels (therapeutic range: 4–12 mcg/mL).
  • Electrolytes, particularly sodium, to monitor for hyponatraemia.

11. Use in Children

  • Approved for use in children aged 6 years and older for epilepsy.
  • Dosage must be weight-adjusted, and side effects should be closely monitored.

12. Use in Pregnancy

  • Category D: Associated with an increased risk of congenital malformations (e.g., neural tube defects).
  • Use only if the potential benefit outweighs the risk.
  • Women of childbearing potential should use effective contraception.

13. Use in Elderly

  • Use with caution due to an increased risk of dizziness, drowsiness, and hyponatraemia.
  • Monitor renal function and serum sodium levels closely.

14. Use in Kidney Disease

  • Use with caution in patients with renal impairment.
  • Adjust dosage as necessary based on renal function and serum drug levels.

15. Use in Liver Disease

  • Use with caution in patients with hepatic impairment.
  • Regular monitoring of liver enzymes is essential.

16. Patient Counselling Points

  • Take medication exactly as prescribed, with food if needed to avoid stomach upset.
  • Avoid driving or operating machinery until you know how the medication affects you.
  • Do not abruptly stop taking carbamazepine without consulting your doctor.
  • Report any unusual symptoms, such as rash, fever, sore throat, or unusual bleeding, immediately.
  • Women should use effective contraception, as carbamazepine can reduce the efficacy of hormonal contraceptives.

17. Table of Brand Names, Manufacturers, and Prices

Brand NameManufacturerPrice (USD)
TegretolNovartis$30–50 (30 tablets, 200 mg)
CarbatrolShire Pharmaceuticals$50–80 (30 ER capsules, 200 mg)
EpitolVarious$20–40 (30 tablets, 200 mg)
Generic OptionsVarious$10–20 (30 tablets, 200 mg)

18. FAQs (15 Questions)

  1. What is carbamazepine used for?
    It is used to treat epilepsy, trigeminal neuralgia, and bipolar disorder.
  2. How does carbamazepine work?
    It stabilises neuronal membranes by inhibiting voltage-gated sodium channels, reducing abnormal electrical activity.
  3. What are the common side effects of carbamazepine?
    Dizziness, drowsiness, nausea, and blurred vision.
  4. Can carbamazepine cause a skin rash?
    Yes, it can cause mild rashes or serious reactions like Stevens-Johnson syndrome (SJS).
  5. Is carbamazepine safe during pregnancy?
    It carries risks of congenital malformations and should be used only if necessary under medical supervision.
  6. How should carbamazepine be taken?
    Take it with food to reduce stomach upset and swallow extended-release tablets whole.
  7. Can carbamazepine interact with other medications?
    Yes, it interacts with many drugs, including oral contraceptives, warfarin, and macrolide antibiotics.
  8. Can I drink alcohol while on carbamazepine?
    No, alcohol can increase the risk of drowsiness and other side effects.
  9. What should I do if I miss a dose?
    Take it as soon as you remember, but skip it if it’s close to the next dose. Do not double up.
  10. How long does carbamazepine take to work?
    Effects may take days to weeks for seizure control or mood stabilisation.
  11. Does carbamazepine cause weight gain?
    Weight gain is a less common side effect but can occur.
  12. What should I avoid while taking carbamazepine?
    Avoid grapefruit juice and any activities requiring alertness until you know how it affects you.
  13. Can carbamazepine cause low sodium levels?
    Yes, it can cause hyponatraemia, especially in elderly patients.
  14. How is carbamazepine monitored?
    Through blood tests to check drug levels, liver function, and blood cell counts.
  15. Is carbamazepine addictive?
    No, it is not addictive, but it must be taken regularly to maintain therapeutic effects.