Carbamazepine

BRAND NAMES

• Tegretol

• Carbatrol

• Equetro

MECHANISM OF ACTION

Carbamazepine works by blocking voltage-gated sodium channels in neurons, which stabilizes overactive nerve membranes and reduces the excessive firing of electrical signals. This action helps control seizures, relieve nerve pain, and stabilize mood in bipolar disorder.

PHARMACOKINETICS

Absorption

Carbamazepine is well absorbed from the gastrointestinal tract, with peak blood levels occurring 4–8 hours after oral administration. Its absorption can be affected by food, but overall it has good oral bioavailability.

Distribution

Carbamazepine is widely distributed in body tissues and has a volume of distribution (Vd) of 0.8–1.4 L/kg. About 70–80% of the drug is bound to plasma proteins, mainly albumin, which affects its free active concentration.

Metabolism

Carbamazepine is primarily metabolized in the liver by the enzyme CYP3A4 to its active metabolite, carbamazepine-10,11-epoxide. It undergoes autoinduction, meaning it can increase its own metabolism over time, which may require dosage adjustments.

Excretion

Carbamazepine is mainly excreted through the urine, primarily as metabolites. Less than 5% of the drug is eliminated unchanged. Its half-life ranges from 25–65 hours initially but shortens with long-term therapy due to autoinduction of metabolism.

PHARMACODYNAMICS

Carbamazepine stabilizes hyperactive neuronal membranes by inhibiting voltage-gated sodium channels, which reduces repetitive firing of action potentials

ADMINISTRATION

Carbamazepine is administered orally, available as tablets, chewable tablets, and extended-release formulations. It is usually taken 1–4 times daily with food to improve absorption and reduce gastrointestinal upset.

DOSAGE AND STRENGTH

Carbamazepine is available in 100–400 mg tablets and extended-release forms. Adults usually start with 200 mg twice daily, gradually increasing to a maintenance dose of 800–1200 mg/day in divided doses.

FOOD INTERACTIONS

Carbamazepine absorption is slightly improved when taken with food, which can help reduce gastrointestinal upset. High-fat meals may delay peak levels but do not significantly affect overall drug exposure.

DRUG INTERACTIONS

Carbamazepine interacts with many medications because it induces liver enzymes(CYP3A4), which can reduce the effectiveness of drugs such as oral contraceptives, warfarin, and certain antiepileptics. It may also have additive effects with other central nervous system depressants, increasing drowsiness or dizziness.

CONTRAINDICATIONS

Carbamazepine is contraindicated in patients with a history of hypersensitivity to carbamazepine or tricyclic compounds, bone marrow suppression, or a history of aplasticanemia or agranulocytosis. It should also be avoided in patients with certain cardiac conduction disorders.

SIDE EFFECTS

1.dizziness

2.drowsiness

3. Nausea

4.vomiting

5. blurred vision

OVERDOSE

1. Ataxia

2. Seizures

3. cardiac arrhythmias

4.  severe cases, coma or death

5. supportive care

 6.monitoring vital signs

TOXICITY

Carbamazepine toxicity occurs when blood levels exceed the therapeutic range (usually >12 µg/mL) and can cause dizziness, ataxia, nystagmus, nausea, vomiting, seizures, cardiac arrhythmias, and in severe cases, coma. Regular monitoring of serum levels, liver function, and blood counts helps prevent toxicity.