Gabapentin

# Gabapentin ## Overview - **Classification**: Anticonvulsant, analgesic. - **Mechanism**: A structural analog of GABA that does not bind to GABA receptors. Modulates voltage-gated calcium channels (α2δ subunit), reducing neurotransmitter release. ## Primary Indications 1. **Postherpetic Neuralgia (PHN)** - Neuropathic pain following shingles. 2. **Partial Seizures** - Adjunctive therapy for adults and children ≥3 years. ## Adult Dosing ### Standard Dosing **Postherpetic Neuralgia (PHN)** - **Dose**: Day 1: **300 mg** once evening. Day 2: **300 mg** twice daily. Day 3: **300 mg** three times daily. - **Frequency**: Titrated over 3 days. - **Route**: Oral. - **Target Dose**: Usually **1800 mg/day** to **3600 mg/day** in 3 divided doses. - **Maximum Dose**: **3600 mg/day**. **Adjunctive Therapy for Partial Seizures** - **Dose**: Day 1: **300 mg** once evening. Day 2: **300 mg** twice daily. Day 3: **300 mg** three times daily. - **Frequency**: Titrated over 3 days. - **Route**: Oral. - **Target Dose**: Usually **900 mg/day** to **1800 mg/day** in 3 divided doses. - **Maximum Dose**: **3600 mg/day**. ### Dose Adjustments - **Renal Impairment**: Adjust based on CrCl: - CrCl ≥60 mL/min: **900-3600 mg/day** in 3 divided doses. - CrCl 30-59 mL/min: **400-1400 mg/day** in 2 divided doses. - CrCl 15-29 mL/min: **200-700 mg/day** once daily. - CrCl <15 mL/min: **100-300 mg/day** once daily. - Hemodialysis: Administer **300-400 mg** loading dose, then **200-300 mg** post-dialysis. - **Hepatic Impairment**: No specific adjustment needed. - **Elderly Patients**: Start low, go slow; dose adjust for age-related renal decline. ## Pediatric Dosing ### Neonates (0-28 days) - **Dose**: Not generally recommended due to lack of safety/efficacy data. - **Frequency**: N/A. - **Maximum**: N/A. - **Special Notes**: Use only if potential benefit outweighs risks with expert consultation. Monitor closely for respiratory depression, sedation. ### Infants (1-12 months) - **Indication**: Adjunctive therapy for partial seizures (off-label). - **Dose**: Initial **10 mg/kg/day** in 3 divided doses. - **Frequency**: Three times daily (TID). - **Maximum**: Titrate up to **40 mg/kg/day**. - **Special Notes**: Limited data, use with extreme caution. Closely monitor for sedation and respiratory depression. ### Children (3-12 years) - **Indication**: Adjunctive therapy for partial seizures. - **Initial Dose**: **10-15 mg/kg/day** in 3 divided doses. - **Frequency**: Three times daily (TID). - **Titration**: Increase over 3 days to target dose. - **Target Dose**: **25-35 mg/kg/day** in 3 divided doses. - **Maximum**: **50 mg/kg/day** (absolute max), or **4800 mg/day** (whichever is lower). - **Formulation**: Oral solution (250 mg/5 mL) or capsules/tablets. ### Adolescents (13-18 years) - **Indication**: Adjunctive therapy for partial seizures, PHN. - **Dose**: Approach adult dosing, starting **300 mg** three times daily. - **Titration**: Increase daily by **300 mg** increments as tolerated. - **Maximum**: **3600 mg/day** in 3 divided doses. - **Special Notes**: Consider renal function and monitor for CNS side effects. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to gabapentin or its components. - **Relative**: Acute pancreatitis (reported, but causal link unclear). - **Relative**: Myasthenia gravis (may exacerbate muscle weakness). ### Common Adverse Effects - **Very Common (>10%)**: Dizziness, somnolence, ataxia, fatigue, peripheral edema. - **Common (1-10%)**: Nausea, tremor, blurred vision, nystagmus, headache. - **Serious but Rare**: Anaphylaxis/angioedema, suicidal thoughts/behavior, DRESS syndrome, respiratory depression. ### Key Drug Interactions - **Opioids**: Increased risk of respiratory depression, profound sedation. - **Clinical Significance**: Life-threatening respiratory depression. - **Monitoring**: Close monitoring; consider lower opioid doses, educate patients. - **Antacids (containing aluminum/magnesium)**: Decreased gabapentin bioavailability. - **Clinical Significance**: Reduced gabapentin efficacy. - **Monitoring**: Administer gabapentin at least **2 hours after** antacids. - **Ethanol/CNS Depressants**: Increased CNS depressive effects (sedation, dizziness). - **Clinical Significance**: Impaired coordination, respiratory depression. - **Monitoring**: Advise against concurrent use; caution with activities requiring mental alertness. ## Monitoring & Follow-up - **Before Treatment**: Assess renal function (CrCl). - **During Treatment**: - Clinical monitoring for seizure control or pain relief. - Watch for CNS depression (sedation, dizziness, respiratory issues). - Monitor for behavioral changes, suicidality (especially early in treatment or with dose changes). - Observe for signs of DRESS syndrome (rash, fever, lymphadenopathy, eosinophilia). - **Clinical Signs**: Changes in mood, unusual thoughts/behavior, worsening depression/anxiety, difficulty breathing, rash, swelling. ## Clinical Pearls - 💡 **Titrate Slowly**: Essential to minimize CNS side effects like dizziness and somnolence. - 💡 **Consistent Timing**: For optimal efficacy, especially in seizures, take doses evenly spaced (e.g., every 8 hours for TID). - 💡 **Don't Stop Abruptly**: Abrupt discontinuation can precipitate seizures; taper over at least 1 week. - 💡 **Abuse Potential**: Gabapentin has recognized abuse potential, especially at high doses or with CNS depressants. Educate patients. - 💡 **Food Effect**: Can be taken with or without food. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.