GABAPENTIN

(gab-a-pen'tin)

Neurontin, Gabarone
Classifications: anticonvulsant; gaba analog;
Therapeutic: anticonvulsant
Pregnancy Category: C

Availability

100 mg, 300 mg, 400 mg capsules; 100 mg, 300 mg, 400 mg, 600 mg, 800 mg tablets; 250 mg/5 mL solution

Action

Gabapentin is a GABA neurotransmitter analog; however, it does not interact with GABA receptors, and it does not inhibit GABA uptake or degradation. Mechanism of action is unknown.

Therapeutic Effect

Used in conjunction with other anticonvulsants to control certain types of seizures in patients with epilepsy. Effective in controlling painful neuropathies.

Uses

Adjunctive therapy for partial seizures with or without secondary generalization in adults, post-herpetic neuralgia.

Unlabeled Uses

Add-on therapy for generalized seizures, peripheral neuropathy, migraine prophylaxis.

Contraindications

Hypersensitivity to gabapentin; pregnancy (category C), lactation. Safety and efficacy in infants and children <3 y are not established.

Cautious Use

Status epilepticus, renal impairment, older adults.

Route & Dosage

Adjunctive Therapy for Seizure Disorder
Adult/Child (>12 y): PO Start 300 mg on day 1, 300 mg b.i.d. on day 2, 300 mg t.i.d. on day 3, and continue to increase over a week to an initial total dose of 400 mg t.i.d. (1200 mg/d); may increase to 1800–2400 mg/d depending on response (most patients receive 900–1800 mg/d in 3 divided doses) 400 mg t.i.d. (1200 mg/d)
Child (3–12 y): PO Start 10–15 mg/kg/d in 3 divided doses, titrate q3d to target dose of 40 mg/kg/d in pts 3–4 y or 25–35 mg/kg/d in pts ≥5 y in 3 divided doses

Post-Herpetic Neuralgia
Adult: PO Start 300 mg day 1, 300 mg b.i.d. day 2, and 300 mg t.i.d. day 3; may increase up to 600 mg t.i.d. if needed

Renal Impairment
Cl_cr >60 mL/min: 400 mg t.i.d.; 30–60 mL/min: 300 mg b.i.d.; 15–30 mL/min: 300 mg q.d.; <15 mL/min: 300 mg q.o.d.
Hemodialysis: 200–300 mg following dialysis

Administration

Oral

Adjust dosage for patients with creatinine clearance of 60 mL/min or less. See manufacturer's recommendations.
Separate doses of gabapentin and antacids by 2 h.
Withdraw drug gradually over 1 wk; abrupt discontinuation may cause status epilepticus.
Store at 15°–30° C (59°–86° F); protect from heat, moisture, and direct light.

Adverse Effects (≥1%)

CNS: Drowsiness, fatigue, dizziness, tremor, slurred speech, impaired concentration, headache, increased frequency of partial seizures. Endocrine: Weight gain. GI: Nausea, gastric upset, vomiting. Special Senses: Blurred vision, nystagmus. Skin: Rash, eczema.

Interactions

Drug: Increase in phenytoin levels at higher doses (300–600 mg/d gabapentin). Does not affect serum levels of other anticonvulsants. antacids reduce absorption of gabapentin. Herbal: Ginkgo may decrease effectiveness.

Pharmacokinetics

Absorption: 50–60% from GI tract. Peak: Peak level 1–3 h; peak effect 2–4 wk. Distribution: Crosses the blood–brain barrier; readily passes into cerebrospinal fluid; not bound to plasma proteins; highest concentrations found in pancreas and kidneys. Metabolism: Does not appear to be metabolized. Elimination: 76–81% unchanged in 96 h; 10–23% recovered in feces. Half-Life: 5–6 h.

Nursing Implications

Assessment & Drug Effects

Monitor for therapeutic effectiveness; may not occur until several weeks following initiation of therapy.
Assess frequency of seizures: In rare cases, the drug has increased the frequency of partial seizures.
Assess safety: Vision, concentration, and coordination may be impaired by gabapentin.

Patient & Family Education

Learn potential adverse effects of drug.
Notify physician immediately if any of the following occur: increased seizure frequency, visual changes, unusual bruising or bleeding.
Do not drive or engage in other potentially hazardous activities until response to drug is known.
Do not abruptly discontinue use of drug; do not take drug within 2 h of an antacid.

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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