Horizant

Generic name:

Gabapentin enacarbil

Drug class:

GABA analogue; anticonvulsant; neuropathic pain agent

Dosage form:

Extended-release tablets: 600 mg

Root of administration:

Oral

Dose:

• Restless legs syndrome (RLS): 600 mg once daily at 5 PM (maximum 1,200 mg/day)
• Postherpetic neuralgia (PHN): 600 mg twice daily (maximum 1,200 mg/day)
• Off-label indications: Varies by indication; consult label.

Mechanism of action:

Gabapentin enacarbil is a prodrug converted by nonspecific esterases to gabapentin, which binds the α₂δ subunit of voltage-gated calcium channels, reducing excitatory neurotransmitter release.

Drug usage cases:

• Approved: Moderate-to-severe primary restless legs syndrome (RLS)
• Approved: Postherpetic neuralgia (PHN)
• Off-label: Diabetic peripheral neuropathy
• Off-label: Fibromyalgia
• Off-label: Migraine prophylaxis
• Off-label: Bipolar disorder (adjunctive)
• Off-label: Anxiety disorders
• Off-label: Other neuropathic pain conditions

Drug contra indications:

• Hypersensitivity to gabapentin enacarbil, gabapentin, or any component of the formulation

Side effects:

• Dizziness
• Somnolence
• Fatigue
• Headache
• Nausea and vomiting
• Dry mouth
• Weight gain
• Peripheral edema
• Ataxia
• Diplopia and other visual disturbances
• Tremor
• Confusion
• Infection
• Mood changes (depression, euphoria, irritability)
• Gastrointestinal symptoms (diarrhea, constipation)
• Respiratory depression (especially with CNS depressants)
• Withdrawal symptoms upon abrupt discontinuation

Warnings:

• Suicidal ideation and behavior: monitor for changes in mood or behavior
• CNS depression: caution with other CNS depressants and alcohol
• Respiratory depression: risk increased with opioids, elderly, or pulmonary disease
• Potential for abuse and misuse
• Renal impairment: adjust dose based on creatinine clearance
• Discontinuation: taper gradually to avoid withdrawal symptoms
• Hypersensitivity reactions: angioedema, rash, anaphylaxis
• Peripheral edema: monitor in patients with heart failure or vascular disease
• Geriatric patients: increased risk of sedation, dizziness, and falls
• Impaired driving or operating machinery: dose-related somnolence and cognitive impairment

Use during pregnancy or breastfeeding:

Pregnancy: Animal studies have shown fetal harm at exposures ≥ human therapeutic levels; no adequate well-controlled human studies. Use only if potential benefit justifies potential risk (Category C).

Breastfeeding: Gabapentin is excreted in human milk; infant exposure is likely. Evaluate benefits versus risks, monitor infant for sedation and feeding difficulties, and consider discontinuing drug or formula feeding if necessary.