Carbamazapine

Carbamazepine

Brand Name: Apo-Carbamazepine (CAN), Atretol, Carbatrol, Epitol, Novo-Carbamaz (CAN), Tegretol, Tegretol-XR

Pregnancy Category D

 

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

 

Contraindications

· Contraindicated with hypersensitivity to carbamazepine or TCAs; history of bone marrow depression; concomitant use of MAOIs, lactation, pregnancy.

 

Adverse effects

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

CHF, aggravation of hypertension, hypotension, syncope and collapse, edema, primary thrombophlebitis, recurrence of thrombophlebitis, aggravation of CAD, arrhythmias and AV block; CV complications

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

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

Urinary frequency, acute urinary retention, oliguria with hypertension, renal failure, azotemia, impotence, proteinuria, glycosuria, elevated BUN, microscopic deposits in urine

Pulmonary hypersensitivity characterized by fever, dyspnea, pneumonitis or pneumonia

 

 

Drug Interactions:

· 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

· 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	<>3
Hematocrit	<>
Hemoglobin	< class="spelle">mL
Leukocytes	<>3
Platelets	<>3
Reticulocytes	<>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).