CARBAMAZEPINE

(kar ba maz' e peen)
Apo-Carbamazepine (CAN), Atretol, Carbatrol, Epitol, Novo-Carbamaz (CAN), Tegretol, Tegretol-XR
PREGNANCY CATEGORY D

Drug class
Therapeutic actions
Indications
Contraindications and cautions
Available forms
Dosages
  Adults
  Pediatric patients
  Geriatric patients
Pharmacokinetics
Adverse effects
Interactions
  Drug-drug
Nursing considerations Assessment
Interventions
Teaching points

 

Drug class

Antiepileptic agent

Therapeutic actions

Mechanism of action not understood; antiepileptic activity may be related to its ability to inhibit polysynaptic responses and block post-tetanic potentiation. Drug is chemically related to the tricyclic antidepressants (TCAs).

Indications

• Refractory seizure disorders: partial seizures with complex symptoms (psychomotor, temporal lobe epilepsy), generalized tonic-clonic (grand mal) seizures, mixed seizure patterns or other partial or generalized seizures. Reserve for patients unresponsive to other agents with seizures difficult to control or who are experiencing marked side effects, such as excessive sedation
• Trigeminal neuralgia (tic douloureux): treatment of pain associated with true trigeminal neuralgia; also beneficial in glossopharyngeal neuralgia
• Unlabeled uses: neurogenic diabetes insipidus (200 mg bid–tid); certain psychiatric disorders, including bipolar disorders, schizoaffective illness, resistant schizophrenia, and dyscontrol syndrome associated with limbic system dysfunction; alcohol withdrawal (800–1,000 mg/day); restless leg syndrome (100–300 mg/day hs); non-neuritic pain syndrome (600–1,400 mg/day); hereditary or nonhereditary chorea in children (15–25 mg/kg/day).

Contraindications and cautions

• Contraindicated with hypersensitivity to carbamazepine or TCAs; history of bone marrow depression; concomitant use of MAOIs, lactation, pregnancy.
• Use cautiously with history of adverse hematologic reaction to any drug (increased risk of severe hematologic toxicity); glaucoma or increased intraocular pressure; history of cardiac, hepatic, or renal damage; psychiatric patients (may activate latent psychosis).

Available forms

Tablets—200 mg; chewable tablets—100 mg; ER tablets—100, 200, 400 mg; ER capsules—200, 300 mg; suspension—100 mg/5 mL

Dosages

Individualize dosage; a low initial dosage with gradual increase is advised.

Adults

•  Epilepsy: Initial dose of 200 mg PO bid on the first day; increase gradually by up to 200 mg/day in divided doses q 6–8 hr, until best response is achieved. Suspension—100 mg PO qid. Do not exceed 1,200 mg/day in patients > 15 yr; doses up to 1,600 mg/day have been used in adults (rare). Maintenance: adjust to minimum effective level, usually 800–1,200 mg/day.
•  Trigeminal neuralgia: Initial dose of 100 mg PO bid on the first day; may increase by up to 200 mg/day, using 100-mg increments q 12 hr as needed. Do not exceed 1,200 mg/day. Maintenance: control of pain can usually be maintained with 400–800 mg/day (range 200–1,200 mg/day). Attempt to reduce the dose to the minimum effective level or to discontinue the drug at least once every 3 mo.
•  Combination therapy: When added to existing antiepileptic therapy, do so gradually while other antiepileptics are maintained or discontinued.

Pediatric patients

> 12 yr: Use adult dosage. Do not exceed 1,000 mg/day in patients 12–15 yr; 1,200 mg/day in patients > 15 yr.
6–12 yr: Initial dose is 100 mg PO bid on the first day. Increase gradually by adding 100 mg/day at 6- to 8-hr intervals until best response is achieved. Do not exceed 1,000 mg/day. Dosage also may be calculated on the basis of 20–30 mg/kg/day in divided doses tid–qid.
< 6 yr: Optimal daily dose < 35 mg/kg/day.

Geriatric patients

Use caution; drug may cause confusion, agitation.

Pharmacokinetics


Route Onset Peak
Oral Slow 4–5 hr

Metabolism: Hepatic; T ½: 25–65 hr, then 12–17 hr

Distribution: Crosses placenta; passes into breast milk

Excretion: Urine and feces

Adverse effects

Adverse effects in Italics are most common; those in Bold are life-threatening.

•  CNS: Dizziness, drowsiness, unsteadiness, disturbance of coordination, confusion, headache, fatigue, visual hallucinations, depression with agitation, behavioral changes in children, talkativeness, speech disturbances, abnormal involuntary movements, paralysis and other symptoms of cerebral arterial insufficiency, peripheral neuritis and paresthesias, tinnitus, hyperacusis, blurred vision, transient diplopia and oculomotor disturbances, nystagmus, scattered punctate cortical lens opacities, conjunctivitis, ophthalmoplegia, fever, chills; SIADH
•  CV: CHF, aggravation of hypertension, hypotension, syncope and collapse, edema, primary thrombophlebitis, recurrence of thrombophlebitis, aggravation of CAD, arrhythmias and AV block; CV complications
•  Dermatologic: Pruritic and erythematous rashes, urticaria, Stevens-Johnson syndrome, photosensitivity reactions, alterations in pigmentation, exfoliative dermatitis, alopecia, diaphoresis, erythema multiforme and nodosum, purpura, aggravation of lupus erythematosus
•  GI: Nausea, vomiting, gastric distress, abdominal pain, diarrhea, constipation, anorexia, dryness of mouth or pharynx, glossitis, stomatitis; abnormal liver function tests, cholestatic and hepatocellular jaundice, hepatitis, massive hepatic cellular necrosis with total loss of intact liver tissue
•  GU: Urinary frequency, acute urinary retention, oliguria with hypertension, renal failure, azotemia, impotence, proteinuria, glycosuria, elevated BUN, microscopic deposits in urine
•  Hematologic: Hematologic disorders
•  Respiratory: Pulmonary hypersensitivity characterized by fever, dyspnea, pneumonitis or pneumonia

Interactions

Drug-drug

• Increased serum levels and manifestations of toxicity with erythromycin, troleandomycin, cimetidine, danazol, isoniazid, propoxyphene, verapamil; dosage of carbamazepine may need to be reduced (reductions of about 50% recommended with erythromycin)
• Increased CNS toxicity with lithium
• Increased risk of hepatotoxicity with isoniazid (MAOI); because of the chemical similarity of carbamazepine to the TCAs and because of the serious adverse interaction of TCAs and MAOIs, discontinue MAOIs for minimum of 14 days before carbamazepine administration
• Decreased absorption with charcoal
• Decreased serum levels and decreased effects of carbamazepine with barbiturates
• Increased metabolism but no loss of seizure control with phenytoin, primidone
• Increased metabolism of phenytoin, valproic acid
• Decreased anticoagulant effect of warfarin, oral anticoagulants; dosage of warfarin may need to be increased during concomitant therapy but decreased if carbamazepine is withdrawn
• Decreased effects of nondepolarizing muscle relaxants, haloperidol
• Decreased antimicrobial effects of doxycycline

Nursing considerations Assessment

•  History: Hypersensitivity to carbamazepine or TCAs; history of bone marrow depression; concomitant use of MAOIs; history of adverse hematologic reaction to any drug; glaucoma or increased intraocular pressure; history of cardiac, hepatic, or renal damage; psychiatric history; lactation; pregnancy
•  Physical: Weight; T; skin color, lesions; palpation of lymph glands; orientation, affect, reflexes; ophthalmologic exam (including tonometry, funduscopy, slit lamp exam); P, BP, perfusion; auscultation; peripheral vascular exam; R, adventitious sounds; bowel sounds, normal output; oral mucous membranes; normal urinary output, voiding pattern; CBC including platelet, reticulocyte counts and serum iron; hepatic function tests, urinalysis, BUN, thyroid function tests, EEG

Interventions

• Use only for classifications listed. Do not use as a general analgesic. Use only for epileptic seizures that are refractory to other safer agents.
• Give drug with food to prevent GI upset.
• Do not mix suspension with other medications or elements—precipitation may occur.
• Reduce dosage, discontinue, or substitute other antiepileptic medication gradually. Abrupt discontinuation of all antiepileptic medication may precipitate status epilepticus.
• Suspension will produce higher peak levels than tablets—start with a lower dose given more frequently.
• Ensure that patient swallows ER tablets whole—do not cut, crush, or chew.
• Arrange for frequent liver function tests; discontinue drug immediately if hepatic dysfunction occurs.
• Arrange for patient to have CBC, including platelet, reticulocyte counts, and serum iron determination, before initiating therapy; repeat weekly for the first 3 mo of therapy and monthly thereafter for at least 2–3 yr. Discontinue drug if there is evidence of marrow suppression, as follows:

Erythrocytes < 4 million/mm 3
Hematocrit < 32%
Hemoglobin < 11 gm/dL
Leukocytes < 4,000/mm 3
Platelets < 100,000/mm 3
Reticulocytes < 0.3% (20,000/mm 2)
Serum iron 150 g/100 mL

• Arrange for frequent eye exams, urinalysis, and BUN determinations.
• Arrange for frequent monitoring of serum levels of carbamazepine and other antiepileptic drugs given concomitantly, especially during the first few weeks of therapy. Adjust dosage on basis of data and clinical response.
• Counsel women who wish to become pregnant; advise the use of barrier contraceptives.
• Evaluate for therapeutic serum levels (usually 4–12 mcg/mL).

Teaching points

• Take drug with food as prescribed. Swallow extended-release tablets whole, do not cut, crush, or chew.
• Do not discontinue this drug abruptly or change dosage, except on the advice of your physician.
• Avoid alcohol, sleep-inducing, or OTC drugs; these could cause dangerous effects.
• Arrange for frequent checkups, including blood tests, to monitor your response to this drug. Keep all appointments for checkups.
• Use contraceptives at all times; if you wish to become pregnant, you should consult your physician.
• These side effects may occur: drowsiness, dizziness, blurred vision (avoid driving or performing other tasks requiring alertness or visual acuity); GI upset (take the drug with food or milk, eat frequent small meals).
• Wear a medical alert tag at all times so that any emergency medical personnel will know that you are an epileptic taking antiepileptic medication.
• Report bruising, unusual bleeding, abdominal pain, yellowing of the skin or eyes, pale feces, darkened urine, impotence, CNS disturbances, edema, fever, chills, sore throat, mouth ulcers, rash, pregnancy.


Copyright © 2004 Lippincott Williams & Wilkins
Amy M. Karch
2004 Lippincott's Nursing Drug Guide