Carbamazepine

Anticonvulsant

Carbamazepine（中文：卡馬西平）is an anticonvulsant medication used primarily in the treatment of epilepsy and neuropathic pain. Carbamazepine appears to work as well as phenytoin and valproate for focal and generalized seizures. It is not effective for absence or myoclonic seizures. It is used in schizophrenia and as a second-line agent in the management of bipolar disorder unresponsive to lithium.

Drug Names

Generic Name 藥名	HA Code 藥物代碼	Classification藥物分類
Carbamazepine Suspension 100mg/5ml	CARB49	P1S1S3
Carbamazepine tablet 200mg	CARB02	P1S1S3
Carbamazepine CR tablet 200mg	CARB51	P1S1S3

Mechanism of Action

Anticonvulsant medication. It is a sodium channel blocker. It binds to sodium channels and suppresses repetitive neuronal firing.

Dosage

Epilepsy	Oral: initially 100 – 200 mg 1-2 times daily, increased slowly by increments of up 200 mg daily every week to an usual maintenance dose of 0.8 – 1.2 g daily in divided doses; up to 2 g daily may occasionally be necessary. By rectum: for short-term use (Max. 7 days) when oral therapy temporarily not possible; 125-mg suppository approximately equivalent to 100-mg tablet, but final adjustment should always depend on clinical response. Max. 1 g daily in 4 divided doses. Elderly: reduce initial dose. Child: the usual daily dose may be given according to age as follows: Up to 1 year: 100 to 200 mg 1 to 5 years: 200 to 400 mg 5 to 10 years: 400 to 600 mg 10 to 15 years: 0.6 to 1 g Over 15 years: usual adult doses The maximum recommended daily dose, according to age, is as follows: Up to 6 years: 35 mg/kg 6 to 15 years: 1 g Over 15 years: 1.2 g
Trigeminal neuralgia	Oral: initially 100 mg 1-2 times daily, increased gradually according to response; usual dose 200 mg 3-4 times daily, up to 1.6 g daily in some patients
Bipolar disorder	Oral: initially 400 mg daily in divided doses increasleed until symptoms controlled; usual range 400-600 mg daily; max. 1.6 g daily
Treatment of alcohol withdrawal	Oral: initially 800 mg daily in divided doses, reduced gradually over 5 days to 200 mg daily; usual treatment duration 7-10 days.
Diabetic neuropathy	Oral: initially 100 mg 1-2 times daily, increased gradually according to response; usual dose 200 mg 3-4 times daily, up to 1.6 g daily in some patients

Note Plasma concentration for optimum response 4-12 mg/litre (20-50 micromol/litre)

Side Effects

Common side effects include:

• Drowsiness, dizziness and headaches
• Gastrointestinal disturbances, such as nausea and vomiting
• The loss of full control of bodily movements (motor coordination impairment)
• Increased risks of hyponatremia and SIADH
• Blood disorders (such as decreased white blood cell or platelet counts)

Serious side effects may include:

• Skin rashes, exfoliative dermatitis, epidermal necrolysis, Stevens-Johnson syndrome, and SLE
• Decreased bone marrow function
• Suicidal thoughts
• Abnormal heart rhythms
• Blurry or double vision, nystagmus
• Male infertility
• Osteoporosis
• Gynecomastia
• Galactorrhea

Pharmacokinetics

Oral bioavailability	Carbamazepine is slowly but well absorbed after oral administration. It is about 70 to 80% bound to plasma proteins.
Onset of action	Its plasma half-life is about 30 hours when it is given as single dose, but it is a strong inducer of hepatic enzymes and the mean plasma half-life on repeated dosage is about 12 to 24 hours.
Metabolism	Metabolized in the liver by cytochrome P450 isoenzymes CYP3A4 and CYP2C8.
Elimination half-life	Excreted in the urine almost entirely in the form of its metabolites; some are also excreted in faeces.

Drug Management

Monitoring

• Recognize signs of blood, liver, or skin toxicity. Seek immediate medical attention if symptoms such as fever, sore throat, rash, blistering, mouth ulcers, bruising or bleeding develop.
• Patients with heart failure should be weighed regularly to detect fluid retention.
• Patients with pre-existing cardiac conduction disorders should be carefully monitored.
• Hyponatremia (monitor plasma-sodium concentration in patients at risk).

Drug interaction

A few drugs inhibit its metabolism by the cytochrome P450 isoenzyme CYP3A4, resulting in raised plasma concentrations and associated toxicity. Conversely, drugs that induce CYP3a4 may increase the metabolism of carbamazepine, leading to reduced plasma concentrations and potentially a decrease in therapeutic effect. Carbamazepine is itself a hepatic enzyme inducer and induces its own metabolism.

Drugs given with carbamazepine	Potential Effect
CYP3A4 inhibitors: Cimetidine Clarithromycin erythromycin isoniazid	Resulting in raised plasma-carbamazepine concentration and associated toxicity
CYP3A4 inducers: Rifampicin Phenytoin	May reduce plasma-carbamazepine concentration
Analgesic: Tramadol	Carbamazepine reduces effect of tramadol
Anticoagulants: Apixaban, dabigatran, rivaroxaban, coumarins (warfarin)	Carbamazepine possibly reduces their plasma concentration, Advises avoid concomitant use and monitor signs of thrombosis
Antipsychotics: aripiprazole clozapine Haloperidol Olanzapine Paliperidone Quetiapine risperidone	Carbamazepine accelerates their metabolism and reduced their plasma concentration. Avoid concomitant use or increase the dose
Anxiolytics: Clonazepam midazolam	Carbamazepine reduces their plasma concentration
Diuretics: frusemide	ncreased risk of hyponatraemia when carbamazepine given with diuretics
Oestrogens	Carbamazepine accelerates metabolism oestrogens, and reduced contraceptive effect
Theophylline	Carbamazepine accelerates metabolism of theophylline (reduced effect)
Thyroid hormones	Carbamazepine accelerates metabolism of thyroid hormones (may increase thyroxine dosage in hypothyroidism)

Caution

• avoid in patients with cardiac disease
• Genotype test for HLA-B*1502 allele in Han Chinese of Thai origin (avoid Carbamazepine unless no alternative – risk of Stevens-Johnson syndrome in presence of HLA-B*1502 allele);
• may exacerbate absence and myoclonic seizures
• consider vitamin D supplement for immobilized patients or who have inadequate sun exposure or dietary intake of calcium
• susceptibility to glaucoma
• cross-sensitivity reported with oxcarbazepine and with phenytoin

Contraindications

• AV conduction abnormalities
• History of bone-marrow depression
• Acute porphyria

Hepatic impairment

Metabolism impaired in advanced liver disease.

Renal impairment

Use with caution

Pregnancy

Women of child-bearing potential should discuss with a specialist the impact of both epilepsy, and its treatment, on the outcome of pregnancy. There is an increased risk of teratogenicity associated with the use of antiepileptic drug (especially if used during the first trimester)

Breast-feeding

Use during breast feeding is not recommended.

Warning

This medicine may make you sleepy. If this happens, do not drive or use tools or machines Do not stop taking this medicine unless your doctor tells you to stop

FAQ

How should I take the tablet?

Donepezil tablet and orodispersible tablet should be taken orally at bedtime, or as directed by the doctor. The orodispersible tablet should be placed on the tongue and allowed to disperse before swallowing with or without water. Both formulations can be taken with or without food.  

What should I avoid while taking?

Avoid abruptly discontinue the medication.

What happen if I overdose?

Contact your primary care doctor. If emergency situation, call 999

What happen if I miss a dose?

Take it as soon as you remember. If it is near the time of the next dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.