Carbamazepine (Tegretol)
carbamazepine
Indications
| Indication | Approved Population | Therapy Type | Status |
|---|---|---|---|
| Partial seizures with complex symptomatology | All ages | Monotherapy or adjunctive | FDA Approved |
| Generalized tonic-clonic seizures | All ages | Monotherapy or adjunctive | FDA Approved |
| Mixed seizure patterns | All ages | Monotherapy or adjunctive | FDA Approved |
| Trigeminal neuralgia | Adults | First-line analgesic | FDA Approved |
| Acute manic and mixed episodes (bipolar I) | Adults (Equetro ER capsules) | Monotherapy | FDA Approved |
Carbamazepine is a first-generation antiepileptic drug with established efficacy for focal and generalised tonic-clonic seizures, and remains the gold-standard pharmacotherapy for trigeminal neuralgia. It is structurally related to tricyclic antidepressants and has a unique pharmacokinetic property — autoinduction of its own metabolism — that requires careful dose adjustment over the first weeks of therapy. Carbamazepine is not effective for absence seizures or myoclonic seizures, and may worsen these seizure types.
Neuropathic pain (other than trigeminal neuralgia) — Used for glossopharyngeal neuralgia, diabetic neuropathy, and post-herpetic neuralgia. Evidence quality: Low–Moderate (limited controlled trials; guideline-supported for selected neuropathic pain subtypes).
Alcohol withdrawal — Used as an alternative to benzodiazepines in select settings. Evidence quality: Moderate (supported by RCTs showing comparable efficacy to benzodiazepines for mild-moderate withdrawal).
Dosing
Adult and Adolescent Dosing (>12 Years)
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Focal or GTC epilepsy — monotherapy | 200 mg BID | 800–1200 mg/day in divided doses | 1200 mg/day (usual); 1600 mg/day (rare); 1000 mg/day (12–15 yr) | Increase by ≤200 mg/day weekly Target level 4–12 mcg/mL; recheck levels after autoinduction (3–5 wk) |
| Trigeminal neuralgia | 100 mg BID or 50 mg QID (suspension) | 400–800 mg/day | 1200 mg/day | Increase by 200 mg/day q12h as needed Attempt dose reduction q3 months or withdrawal to minimum effective dose |
| Acute bipolar mania (Equetro ER) | 200 mg BID | Titrate in 200 mg/day increments to response | 1600 mg/day | Adjust based on tolerability and clinical response Only ER capsule formulation (Equetro/Carbatrol) is FDA-approved for bipolar |
Pediatric Dosing
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Epilepsy — children 6–12 years | 100 mg BID (200 mg/day) | 400–800 mg/day | 1000 mg/day | Increase by ≤200 mg/day weekly TID dosing recommended for suspension |
| Epilepsy — children <6 years | 10–20 mg/kg/day in 2–3 divided doses | Increase weekly to clinical response | 35 mg/kg/day | Use suspension; administer TID or QID Start low and increase slowly to minimise CNS effects |
Carbamazepine induces CYP3A4, including its own metabolism. Over the first 3–5 weeks of a fixed dose, clearance increases and plasma levels decline by 30–50%. This means that levels measured early in therapy will overestimate the steady-state level. Recheck levels after 3–5 weeks on a stable dose and adjust upward as needed. The initial half-life of 25–65 hours decreases to 12–17 hours after autoinduction is complete.
Pharmacology
Mechanism of Action
Carbamazepine acts primarily by blocking voltage-gated sodium channels in a frequency- and voltage-dependent manner, selectively inhibiting high-frequency repetitive neuronal firing while preserving normal synaptic activity. It binds to the inactivated state of the sodium channel, stabilising it and reducing the availability of channels for subsequent activation. The active metabolite carbamazepine-10,11-epoxide has comparable anticonvulsant activity to the parent compound and contributes to both efficacy and toxicity. Additional minor effects include potentiation of GABAergic inhibition through modulation of GABA receptors and possible interactions with peripheral benzodiazepine receptors, though the primary mechanism remains sodium channel blockade.
ADME Profile
| Parameter | Value | Clinical Implication |
|---|---|---|
| Absorption | Bioavailability ~100% (IR tabs); 89% (XR tabs); Tmax: 4–5 h (IR tabs), 1.5 h (suspension), 3–12 h (XR); absorption slow and erratic | Take with food to improve tolerance; suspension absorbed faster than tablets (lower starting doses); XR allows BID dosing |
| Distribution | Vd 0.8–1.4 L/kg; protein binding ~76% (24% unbound); CSF:serum ratio 0.22; crosses placenta; enters breast milk | Moderate tissue distribution; free fraction relatively high compared to VPA; brain penetration correlates with unbound fraction |
| Metabolism | CYP3A4 (major) and CYP2C8 (minor) → carbamazepine-10,11-epoxide (active) → epoxide hydrolase → inactive 10,11-dihydrodiol; autoinduction of CYP3A4 complete in 3–5 weeks | Active metabolite contributes to efficacy and toxicity; VPA inhibits epoxide hydrolase increasing epoxide levels; potent enzyme inducer affecting many co-administered drugs |
| Elimination | Initial t½ 25–65 h; after autoinduction t½ 12–17 h; 72% urine, 28% faeces; only ~3% excreted unchanged | Half-life shortens dramatically with chronic dosing; dose adjustments needed 3–5 weeks after initiation; similar PK in children and adults |
Side Effects
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Dizziness | 44% | Most common adverse effect; dose-related; usually improves with dose adjustment or slow titration |
| Somnolence / drowsiness | 32% | Dose-related; minimise by starting low and titrating slowly; more prominent with suspension (faster absorption) |
| Ataxia | 15% | Dose-related; correlates with CBZ and CBZ-epoxide levels; assess fall risk in elderly |
| Nausea / vomiting | 10–15% | Take with food; often improves with continued therapy; more common during titration |
| Elevated GGT | ~64% | Due to hepatic enzyme induction; not clinically significant and not an indication to stop therapy |
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Diplopia / blurred vision | ~6% | Dose-related; correlates with peak levels; XR formulation may reduce by smoothing peaks |
| Rash (benign) | ~5% | Usually maculopapular; cannot reliably distinguish from SJS/TEN early — discontinue unless clearly not drug-related |
| Hyponatraemia (SIADH) | ~5% | More common in elderly and with concomitant diuretics; check sodium if confusion, lethargy, or seizure worsening |
| Headache | ~5% | May improve with dose optimisation |
| Leucopenia (transient) | ~2–5% | Usually benign and transient; differentiate from serious aplastic anaemia or agranulocytosis |
| Adverse Effect | Estimated Frequency | Typical Onset | Required Action |
|---|---|---|---|
| SJS / TEN (BOXED WARNING) | 1–6 per 10,000 (Caucasian); ~10× higher in Asian populations with HLA-B*1502 | First few months; 90% within first months | Screen HLA-B*1502 in Asian ancestry patients before starting; discontinue immediately at first sign of rash |
| Aplastic anaemia (BOXED WARNING) | 5–8× general population risk (baseline ~2 per million/yr; CBZ-treated ~10–16 per million/yr) | Variable | Baseline and periodic CBCs; discontinue if significant bone marrow depression; routine monitoring may not detect early |
| Agranulocytosis (BOXED WARNING) | 5–8× general population risk (baseline ~6 per million/yr; CBZ-treated ~30–48 per million/yr) | Variable | Monitor for fever, sore throat, infection; obtain urgent CBC; most transient leucopenia does NOT progress |
| DRESS / Multiorgan hypersensitivity | Rare | Days to weeks | Discontinue immediately; presents with fever, rash, lymphadenopathy, organ dysfunction |
| AV block / cardiac conduction abnormalities | Uncommon; more common in TN patients at high doses | Variable | Obtain baseline ECG in patients with cardiac history; discontinue if AV block develops |
| Hepatotoxicity | Rare (ranging from LFT elevations to hepatic failure) | Variable | Monitor LFTs; discontinue if significant hepatic dysfunction; elevated GGT from enzyme induction is NOT an indication to stop |
| Suicidality (AED class effect) | 0.43% (vs 0.24% placebo) | As early as 1 week | Monitor for depression, suicidal thoughts, mood changes |
Benign maculopapular rash occurs in approximately 5% of patients and typically appears within the first 1–2 months. However, serious SJS/TEN also presents as rash in its early stages and cannot be reliably distinguished from benign rash at onset. All patients should be instructed to report any rash immediately. Carbamazepine should be discontinued at the first sign of rash unless the rash is clearly not drug-related. Risk is markedly higher in HLA-B*1502 carriers (primarily Asian ancestry populations).
Drug Interactions
Carbamazepine is one of the most interaction-prone drugs in clinical use. It is a potent inducer of CYP3A4, CYP2C9, CYP1A2, and UGT enzymes, significantly reducing levels of dozens of co-administered drugs. Conversely, its own metabolism via CYP3A4 is accelerated by other inducers and inhibited by CYP3A4 inhibitors, which can cause toxicity. The active metabolite carbamazepine-10,11-epoxide adds another layer of complexity — drugs that inhibit epoxide hydrolase (notably valproate) increase its levels and may cause neurotoxicity even when CBZ levels appear normal.
Monitoring
- HLA-B*1502 TestingBefore initiation
RoutineMandatory before starting carbamazepine in patients with ancestry across broad areas of Asia (Han Chinese, Filipino, Thai, Malaysian, Indian, and others). Positive result: do NOT start carbamazepine unless benefit clearly outweighs risk. Also consider HLA-A*31:01 testing in European and Japanese populations for risk of DRESS and milder hypersensitivity. - CBC with DifferentialBaseline, then periodically
RoutineObtain pretreatment CBC. Monitor closely if WBC or platelets decrease. Discontinue if evidence of significant bone marrow depression. Note: routine monitoring may not detect aplastic anaemia or agranulocytosis before they become clinically apparent (FDA PI boxed warning). - CBZ Trough LevelAt steady state (3–5 weeks), after dose changes
RoutineTarget 4–12 mcg/mL. Crucially, levels must be rechecked after autoinduction is complete (3–5 weeks after each dose change). Measure CBZ-epoxide if neurotoxic symptoms present with “normal” CBZ levels (especially with concomitant VPA). - LFTsBaseline, then periodically
RoutineHepatotoxicity ranges from benign enzyme elevations (GGT elevation in ~64% due to enzyme induction — not clinically significant) to rare hepatic failure. Clinically significant transaminase elevations should prompt discontinuation. - Serum SodiumBaseline, then periodically; more often in elderly
RoutineHyponatraemia (SIADH) occurs in ~5% of patients. Risk increases with age, higher doses, and concomitant diuretics. Check sodium if patient develops confusion, lethargy, or seizure worsening. - Skin / RashFirst 3 months intensively
RoutineInstruct all patients to report any rash immediately. 90% of SJS/TEN cases occur within the first few months of treatment. Discontinue at first sign of rash unless clearly not drug-related.
Contraindications & Cautions
Absolute Contraindications
- Known hypersensitivity to carbamazepine or structurally related drugs (e.g., tricyclic antidepressants such as amitriptyline, imipramine)
- History of bone marrow depression
- Concomitant use with MAOIs (or within 14 days of MAOI discontinuation)
- Concomitant use with nefazodone
- HLA-B*1502 positive patients (unless benefit clearly outweighs the risk of SJS/TEN)
Relative Contraindications (Specialist Input Recommended)
- Pre-existing cardiac conduction abnormalities — CBZ can cause AV block; obtain baseline ECG
- Absence seizures or myoclonic epilepsy — CBZ may worsen these seizure types
- Women of childbearing potential — teratogenic (spina bifida, craniofacial defects); also reduces hormonal contraceptive efficacy
Use with Caution
- Hepatic disease — monitor LFTs closely
- Renal impairment — limited data; use with caution
- Elderly patients — increased risk of hyponatraemia, confusion, cardiac effects
- Patients on multiple enzyme-inducing or enzyme-inhibiting drugs — complex interaction potential
Serious and sometimes fatal dermatologic reactions, including toxic epidermal necrolysis and Stevens-Johnson syndrome, have occurred during treatment with carbamazepine. These reactions are estimated to occur in 1 to 6 per 10,000 new users in countries with mainly Caucasian populations, but the risk in some Asian countries is estimated to be about 10 times higher. Studies in patients of Chinese ancestry have found a strong association between SJS/TEN risk and the presence of HLA-B*1502. Patients with ancestry in genetically at-risk populations should be screened for HLA-B*1502 prior to initiating treatment.
Aplastic anaemia and agranulocytosis have been reported in association with carbamazepine. Population-based data demonstrate the risk of developing these reactions is 5–8 times greater than in the general population (general population baseline rates: agranulocytosis ~6 per million/year; aplastic anaemia ~2 per million/year). Patients with a history of adverse haematologic reaction to any drug may be particularly at risk. Obtain baseline and periodic CBCs. However, routine monitoring is unlikely to detect these abnormalities before they become clinically apparent. The vast majority of transient leucopenia or platelet changes do NOT progress to aplastic anaemia or agranulocytosis.
Patient Counselling
Purpose of Therapy
Carbamazepine helps control seizures, relieve nerve pain (trigeminal neuralgia), or stabilise mood by reducing abnormal electrical activity in the brain. It must be taken consistently and the dose must be adjusted carefully over the first few weeks as the body adapts to the medication.
How to Take
Take carbamazepine with food to reduce stomach upset. Tegretol XR and Carbatrol extended-release tablets must be swallowed whole — do not crush or chew. The suspension should not be taken at the same time as other liquid medications. Do not switch between tablets and suspension without consulting your prescriber, as they are absorbed differently.
Sources
- Novartis Pharmaceuticals. TEGRETOL (carbamazepine) prescribing information. FDA LabelPrimary regulatory source for epilepsy and trigeminal neuralgia indications, dosing, boxed warnings, and pharmacokinetics.
- Shire US Inc. CARBATROL / EQUETRO (carbamazepine extended-release capsules) prescribing information. FDA LabelER capsule PI with FDA-approved bipolar I disorder mania indication and HLA-B*1502 boxed warning.
- Lundbeck. CARNEXIV (carbamazepine) injection prescribing information. 2016. FDA InfoIV formulation approved as short-term replacement (up to 7 days) for oral CBZ in adults.
- Mattson RH, Cramer JA, Collins JF, et al. Comparison of carbamazepine, phenobarbital, phenytoin, and primidone in partial and secondarily generalized tonic-clonic seizures. N Engl J Med. 1985;313(3):145–151. DOILandmark VA Cooperative Study demonstrating carbamazepine superiority for partial seizures due to better tolerability.
- Brodie MJ, Richens A, Yuen AW. Double-blind comparison of lamotrigine and carbamazepine in newly diagnosed epilepsy. Lancet. 1995;345(8948):476–479. DOIHead-to-head trial showing comparable seizure control to lamotrigine but higher dropout rate for carbamazepine.
- Weisler RH, Kalali AH, Ketter TA; SPD417 Study Group. A multicenter, randomized, double-blind, placebo-controlled trial of extended-release carbamazepine capsules as monotherapy for bipolar disorder patients with manic or mixed episodes. J Clin Psychiatry. 2004;65(4):478–484. DOIPivotal RCT establishing efficacy of Equetro ER for acute mania in bipolar I disorder.
- Glauser T, Ben-Menachem E, Bourgeois B, et al. Updated ILAE evidence review of antiepileptic drug efficacy and effectiveness as initial monotherapy for epileptic seizures and syndromes. Epilepsia. 2013;54(3):551–563. DOIILAE guideline supporting carbamazepine as a first-line option for focal seizures in adults.
- Cruccu G, Gronseth G, Alksne J, et al. AAN-EFNS guidelines on trigeminal neuralgia management. Eur J Neurol. 2008;15(10):1013–1028. DOIJoint guideline recommending carbamazepine as first-line pharmacotherapy for trigeminal neuralgia (Level A evidence).
- Chung WH, Hung SI, Hong HS, et al. Medical genetics: a marker for Stevens-Johnson syndrome. Nature. 2004;428(6982):486. DOISeminal study identifying the HLA-B*1502 allele as a marker for carbamazepine-induced SJS in Han Chinese patients.
- Leckband SG, Kelsoe JR, Dunnenberger HM, et al. Clinical Pharmacogenetics Implementation Consortium guidelines for HLA-B genotype and carbamazepine dosing. Clin Pharmacol Ther. 2013;94(3):324–328. DOICPIC guideline providing actionable recommendations for HLA-B*1502 and HLA-A*31:01 testing before carbamazepine initiation.
- Bertilsson L. Clinical pharmacokinetics of carbamazepine. Clin Pharmacokinet. 1978;3(2):128–143. DOIClassic PK review establishing autoinduction kinetics and half-life variability.