LAMOTRIGINE

LAMOTRIGINE
(la-mo'tri-geen)
Lamictal
Classifications: anticonvulsant;
Therapeutic: anticonvulsant
Prototype: Phenytoin
Pregnancy Category: C

Availability

25 mg, 100 mg, 150 mg, 200 mg tablets; 2 mg, 5 mg, 25 mg chewable tablets

Action

Exact mechanism of anticonvulsant activity is not known; thought to act by inhibiting the release of glutamate, an excitatory neurotransmitter at voltage-sensitive sodium channels, resulting in decreased seizure activity.

Therapeutic Effect

Anticonvulsant action results because it stabilizes neuronal membranes and inhibits neurotransmitter release (i.e., glutamate) in brain tissue, decreasing seizure activity.

Uses

Adjunctive therapy for partial seizures in adults and children (>2 y). Generalized tonic–clonic, grand mal, or myoclonic seizures in adults, treatment of bipolar disorder.

Unlabeled Uses

Absence seizures.

Contraindications

Hypersensitivity to lamotrigine, suicidal ideation; pregnancy (category C), lactation. Safety and efficacy in children ≤2 y are not established.

Cautious Use

Renal insufficiency, concomitant administration of other anticonvulsants, bipolar disorder, history of suicidal tendencies; elderly; CHF, cardiac or liver function impairment. Note: Fatal rash has been reported in children <16 y.

Route & Dosage

Partial Seizures, Patients Receiving Anticonvulsants Other Than Valproic Acid
Adult: PO Start with 50 mg q.d. for 2 wk, then 50 mg b.i.d. for 2 wk, may titrate up to 300–500 mg/d in 2 divided doses (max: 700 mg/d)
Child (2–16 y): PO 1 mg/kg b.i.d. times 2 wk, then 2.5 mg/kg b.i.d. times 2 wk, then 5 mg/kg b.i.d. (max: 15 mg/kg/d or 400 mg/d)

Partial Seizures, Patients Receiving Valproic Acid
Adult: PO Start with 25 mg q.o.d. for 2 wk, then 25 mg q.d. for 2 wk, may titrate up to 150 mg/d in 2 divided doses (max: 200 mg/d)
Child (2–16 y): PO 0.2 mg/kg/d x 2 wk, then 0.5 mg/kg/d x 2 wk, then 1 mg/kg/d (max: 5 mg/kg/d or 250 mg/d)

Bipolar Disorder, Patients Not Receiving Valproate or Carbamazepine
Adult: PO Start with 25 mg q.d. for 2 wk, then 50 mg q.d. for 2 wk, then 100 mg/d for 1 wk, then 200 mg q.d.

Bipolar Disorder, Patients Receiving Valproic Acid
Adult: PO Start with 25 mg q.o.d. for 2 wk, then 25 mg q.d. for 2 wk, then 50 mg q.d. for 1 wk, then 100 mg q.d.

Bipolar Disorder, Patients Receiving Carbamazepine
Adult: PO Start with 50 mg q.d. for 2 wk, then 50 mg b.i.d. for 2 wk, then 100 b.i.d for 1 wk, then 150 mg b.i.d. for 1 wk, then 200 mg b.i.d.

Hepatic Impairment
Reduce dose by 25% in patients with moderate or severe impairment (without ascites); reduce by 50% in patients with severe impairment and ascites.

Administration

Oral

Note: Reduced dose may be warranted with renal and hepatic impairment.
Ensure that chewable tablets are chewed or crushed before being swallowed with a liquid.
When discontinued, drug should be tapered off gradually over a 2-wk period, unless patient safety is at risk.

Adverse Effects (≥1%)

CNS: Dizziness, ataxia, somnolence, headache, aphasia, vertigo, confusion, slurred speech, irritability, depression, incoordination, hostility. GI: Nausea, vomiting, anorexia, abdominal pain, diarrhea, dyspepsia, constipation. Urogenital: Hematuria, dysmenorrhea, vaginitis. Special Senses: Diplopia, blurred vision. Musculoskeletal: Peripheral neuropathy, chills, tremor, arthralgia. Skin: Rash (including Stevens-Johnson syndrome, toxic epidermal necrolysis), urticaria, pruritus, alopecia, acne. Respiratory: Rhinitis, pharyngitis, cough.

Interactions

Drug: Carbamazepine, phenobarbital, primidone, phenytoin, fosphenytoin, oral contraceptives may decrease lamotrigine levels. Valproic acid may increase lamotrigine levels. Lamotrigine may decrease serum levels of valproic acid. May affect efficacy of oral contraceptives. Chronic acetaminophen use may affect serum concentrations of lamotrigine. Herbal: Ginkgo may decrease anticonvulsant effectiveness. Evening primrose oil may affect seizure threshold.

Pharmacokinetics

Absorption: Readily absorbed from GI tract; 98% reaches systemic circulation. Onset: 12 wk. Peak: 1–4 h. Distribution: 55% protein bound; crosses placenta; distributed into breast milk. Metabolism: In liver to inactive metabolite. Elimination: Can induce own metabolism; excreted in urine. Half-Life: 25–30 h.

Nursing Implications

Assessment & Drug Effects

Withhold drug if rash develops and immediately report to physician.
Monitor the plasma levels of lamotrigine and other anticonvulsants when given concomitantly.
Monitor patients with bipolar disorder for worsening of their symptoms and suicidal ideation. Withhold the drug and immediately report to physician.
Monitor for adverse reactions when lamotrigine is used with other anticonvulsants, especially valproic acid.
Be aware of drug interactions and closely monitor when interacting drugs are added or discontinued.

Patient & Family Education

Do not take drug if a skin rash develops. Contact your physician immediately.
Notify physician for any of the following: Worsening seizure control, skin rash, ataxia, blurred vision or diplopia, fever or flu-like symptoms.
Do not drive or engage in other potentially hazardous activities until response to the drug is known.
Use protection from sunlight or ultraviolet light until tolerance is known; drug increases photosensitivity.
Women using oral contraceptives to avoid pregnancy should add a barrier contraceptive.
Schedule periodic ophthalmologic exams with long-term use.
Do not discontinue lamotrigine abruptly.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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