Carbatrol

Action

Unclear. Chemically related to tricyclic antidepressants (TCAs). Anticonvulsant action may result from reduction in polysynaptic responses and blocking of post-tetanic potentiation.

Availability

Capsules (extended-release): 100 mg, 200 mg, 300 mg

Oral suspension: 100 mg/5 ml

Tablets: 200 mg

Tablets (chewable): 100 mg

Tablets (extended-release): 100 mg,

200 mg, 400 mg

Indications and dosages

➣ Prophylaxis of generalized tonic-clonic, mixed, and complex-partial seizures

Adults and children ages 12 and older: Initially, 200 mg P.O. b.i.d. (tablets) or 100 mg q.i.d. (oral suspension). Increase by up to 200 mg/day q 7 days until therapeutic blood levels are reached. Usual maintenance dosage is 600 to 1,200 mg/day in divided doses q 6 to 8 hours. In children ages 12 to 15, don't exceed 1 g/day. Give extended-release forms b.i.d.

Children ages 6 to 12: Initially, 100 mg P.O. b.i.d. (tablets) or 50 mg q.i.d. (oral suspension). Increase by up to 100 mg weekly until therapeutic levels are reached. Usual maintenance dosage is 400 to 800 mg/day. Don't exceed 1 g/day. Give extended-release forms b.i.d.

Children younger than age 6: Initially, 10 to 20 mg/kg/day P.O. in two or three divided doses. May increase by up to 100 mg/day at weekly intervals. Usual maintenance dosage is 250 to 350 mg/day. Don't exceed 400 mg/day.

➣ Trigeminal neuralgia

Adults: Initially, 100 mg b.i.d. (tablets) or 50 mg q.i.d. (oral suspension). Increase by up to 200 mg/day until pain relief occurs; then give maintenance dosage of 200 to 1,200 mg/day in divided doses. Usual maintenance range is 400 to 800 mg/day.

Off-label uses

• Alcohol, cocaine, or benzodiazepine withdrawal

• Atypical psychoses

• Central diabetes insipidus

• Mood disorders

• Neurogenic pain

Contraindications

• Hypersensitivity to drug or TCAs

• MAO inhibitor use within past 14 days

• Bone marrow depression

• Pregnancy or breastfeeding

Precautions

Use cautiously in:

• cardiac disease, hepatic disease, increased intraocular pressure, mixed seizure disorders, glaucoma

• elderly males with prostatic hypertrophy

• psychiatric patients.

Administration

• Don't give within 14 days of MAO inhibitor.

• Give tablets with meals; may give extended-release capsules without regard to meals.

• Don't give with grapefruit juice.

• If desired, contents of extended-release capsules may be sprinkled over food; however, capsule and contents shouldn't be crushed or chewed.

Adverse reactions

CNS: ataxia, drowsiness, fatigue, psychosis, syncope, vertigo, headache, worsening of seizures

CV: hypertension, hypotension, arrhythmias, atrioventricular block, aggravation of coronary artery disease, heart failure

EENT: blurred vision, diplopia, nystagmus, corneal opacities, conjunctivitis, pharyngeal dryness

GI: nausea, vomiting, diarrhea, abdominal pain, stomatitis, glossitis, dry mouth, anorexia

GU: urinary hesitancy, retention, or frequency; albuminuria; glycosuria; erectile dysfunction

Hematologic: eosinophilia, lymph-adenopathy, agranulocytosis, aplastic anemia, thrombocytopenia, leukopenia

Hepatic: hepatitis

Metabolic: syndrome of inappropriate antidiuretic hormone secretion

Respiratory: pneumonitis

Skin: photosensitivity, rash, urticaria, diaphoresis, erythema multiforme, Stevens-Johnson syndrome

Other: weight gain, chills, fever

Interactions

Drug-drug. Acetaminophen: increased risk of acetaminophen-induced hepatotoxicity, decreased acetaminophen efficacy

Anticoagulants, bupropion: increased metabolism of these drugs, causing decreased efficacy

Barbiturates: decreased barbiturate blood level, increased carbamazepine blood level

Charcoal: decreased carbamazepine absorption

Cimetidine, danazol, diltiazem: increased carbamazepine blood level

Cyclosporine, felbamate, felodipine, haloperidol: decreased blood levels of these drugs

Doxycycline: shortened doxycycline half-life and reduced antimicrobial effect

Hormonal contraceptives: decreased contraceptive efficacy, possibly leading to pregnancy

Hydantoins: increased or decreased hydantoin blood level, decreased carbamazepine blood level

Isoniazid: increased risk of carbamazepine toxicity and isoniazid hepatotoxicity

Lithium: increased risk of CNS toxicity Macrolide antibiotics (such as clarithromycin and erythromycin), propoxy-phene, selective serotonin reuptake inhibitors (such as fluoxetine and flu-voxamine), verapamil: increased carbamazepine blood level, greater risk of toxicity

MAO inhibitors: high fever, hypertension, seizures, and possibly death

Nondepolarizing neuromuscular blockers: shortened carbamazepine duration of action

TCAs: increased carbamazepine blood level and greater risk of toxicity, decreased TCA blood level

Valproic acid: decreased valproic acid blood level with possible loss of seizure control, variable changes in carbamazepine blood level

Drug-diagnostic tests. Blood urea nitrogen, eosinophils, liver function tests: increased values

Granulocytes, hemoglobin, platelets, thyroid function tests, white blood cells: decreased values

Drug-food. Grapefruit juice: increased drug blood level and effects

Drug-herbs. Plantain (psyllium seed): inhibited GI absorption of drug

Patient monitoring

☞ Monitor patient closely. Institute seizure precautions if drug must be withdrawn suddenly.

• Assess for history of psychosis; drug may activate symptoms.

• Monitor baseline hematologic, kidney, and liver function test results.

• During dosage adjustments, monitor vital signs and fluid intake and output. Stay alert for fluid retention, renal failure, and cardiovascular complications.

• With high doses, monitor CBC weekly for first 3 months and then monthly to detect bone marrow depression.

Patient teaching

• Tell patient that he may sprinkle contents of extended-release capsules over food, but that he shouldn't crush or chew capsule or contents.

• Advise patient that coating on extended-release capsules may be visible in stools because it isn't absorbed.

• Tell patient to take drug with meals to minimize GI upset.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration, alertness, and vision.

• Advise patient to avoid excessive sun exposure and to wear protective clothing and sunscreen.

• Inform female patient that drug may interfere with hormonal contraception. Advise her to use alternative birth-control method.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, foods, herbs, and behaviors mentioned above.