D 24 WHITE OVAL PILL - IDENTIFICATION, MECHANISM OF ACTION, DOSAGE

The white, oval (elliptical) pill debossed with D and 24 on either side of a score line is an oral prescription medication containing Gabapentin (600 mg). It is a generic bioequivalent formulation to brand-name Neurontin 600 mg.

(Note: Another white oval medication bearing “D 24” in its full imprint is the over-the-counter allergy combination Claritin-D 24 Hour [loratadine 10 mg / pseudoephedrine sulfate 240 mg], which is debossed with the full text CLARITIN D 24 HOUR. The debossed D 24 scored tablet specifically identifies generic Gabapentin 600 mg).

Pill Identification

Attribute – Specification

Active Ingredient – Gabapentin, USP (600 mg)
Imprint – D on one side of the break line, 24 on the other side; plain on reverse
Color & Shape – White, biconvex, elliptical / oval, film-coated tablet
Break Line | Deep break line / score mark on both sides
Primary Manufacturers / Distributors – Aurobindo Pharma Limited / Ascend Laboratories
Drug Class – Gabapentinoid / Anticonvulsant / Neuropathic pain agent
Prescription Status – Rx-only (Monitored in many state prescription drug monitoring programs)

Mechanism of Action

Despite being a structural analog of gamma-aminobutyric acid , gabapentin does not bind directly to receptors, nor does it alter uptake or degradation.

Subunit Binding: Gabapentin selectively binds with high affinity to the auxiliary and subunit proteins of presynaptic voltage-gated calcium channels (VGCCs) in the central nervous system.
Reduction in Calcium Influx: Binding reduces the calcium currents required to trigger vesicle exocytosis at presynaptic nerve terminals.
Suppression of Excitatory Neurotransmitter Release: This decreases the presynaptic release of excitatory neurotransmitters – chiefly glutamate, substance P, calcitonin gene-related peptide (CGRP), and norepinephrine—in hyper-excited neuronal pathways.
Clinical Effects: By dampening neuronal hyper-excitability, gabapentin inhibits abnormal seizure propagation in epilepsy and interrupts pathological central sensitization in neuropathic pain states.

Indications and Clinical Uses

Postherpetic Neuralgia (PHN): Management of neuropathic pain following shingles (Herpes zoster) infection in adults.
Partial Onset Seizures (Epilepsy): Adjunctive therapy in the treatment of partial seizures with and without secondary generalization in adult and pediatric patients.
Off-Label Uses: Widely prescribed for diabetic peripheral neuropathy, fibromyalgia, restless legs syndrome (RLS), sciatica / lumbar radiculopathy, perioperative pain management, and alcohol use disorder / withdrawal.

Dosage and Administration

Gabapentin tablets should be swallowed whole with water and can be taken with or without food. If the tablet is split along the score line to administer a 300 mg half-dose, the remaining half should be used for the next scheduled dose.

Postherpetic Neuralgia (PHN) Adult Titration:
Day 1: 300 mg as a single dose.
Day 2: 600 mg/day (taken as 300 mg twice daily).
Day 3: 900 mg/day (taken as 300 mg three times daily).
Maintenance: May be titrated up to 1,800 mg/day (administered as 600 mg three times daily). Doses up to 3,600 mg/day are occasionally used, though evidence of additional benefit above 1,800 mg/day is limited.

Epilepsy (Adjunctive Adult Dosing):
Starting Range: 300 mg three times daily (900 mg/day).
Maintenance Range: 900 mg to 1,800 mg/day divided into three equal doses. The maximum time between doses should not exceed 12 hours to avoid breakthrough seizure activity.

Non-Linear Bioavailability: Gabapentin is absorbed via the saturable L-amino acid transport system (LAT1) in the proximal small bowel. As the single dose increases, percentage bioavailability decreases (60% at 300 mg down to ~35% at 1,600 mg), requiring divided daily dosing (TID) rather than large single daily boluses.
Renal Impairment Dosing: Gabapentin is eliminated solely by renal excretion. Dosages must be adjusted based on creatinine clearance
400 mg to 1,400 mg/day (divided BID).
200 mg to 700 mg/day (single daily dose or divided BID).
100 mg to 300 mg once daily.
Hemodialysis: Post-dialysis supplemental doses are required.

Side Effects

Common Adverse Reactions:

Central Nervous System: Dizziness (up to 28%), somnolence/drowsiness (up to 21%), ataxia, fatigue, tremor, cognitive slowing, nystagmus
Gastrointestinal: Dry mouth, nausea, constipation, diarrhea
Systemic / Metabolic: Peripheral edema (fluid retention in extremities), weight gain, amblyopia/blurred vision

Serious Adverse Reactions:

Life-Threatening Respiratory Depression: Particularly when combined with opioids, benzodiazepines, or other CNS depressants, or in patients with underlying COPD or sleep apnea.
Suicidal Thoughts and Behaviors: Antiepileptic drugs, including gabapentin, carry an increased risk of suicidal ideation and depression.
Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS / Multiorgan Hypersensitivity): Severe, life-threatening allergic reaction presenting with fever, rash, lymphadenopathy, and organ involvement (hepatitis, nephritis, myocarditis).
Anaphylaxis & Angioedema: Sudden swelling of the lips, tongue, and throat, causing airway compromise.
Status Epilepticus & Rebound Seizures: Triggered by abrupt cessation.

Side Effects

Common Adverse Reactions:

Central Nervous System: Dizziness (up to 28%), somnolence/drowsiness (up to 21%), ataxia, fatigue, tremor, cognitive slowing, nystagmus
Gastrointestinal: Dry mouth, nausea, constipation, diarrhea
Systemic / Metabolic: Peripheral edema (fluid retention in extremities), weight gain, amblyopia/blurred vision

Serious Adverse Reactions:

Life-Threatening Respiratory Depression: Particularly when combined with opioids, benzodiazepines, or other CNS depressants, or in patients with underlying COPD or sleep apnea.
Suicidal Thoughts and Behaviors: Antiepileptic drugs, including gabapentin, carry an increased risk of suicidal ideation and depression.
Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS / Multiorgan Hypersensitivity): Severe, life-threatening allergic reaction presenting with fever, rash, lymphadenopathy, and organ involvement (hepatitis, nephritis, myocarditis).
Anaphylaxis & Angioedema: Sudden swelling of the lips, tongue, and throat, causing airway compromise.
Status Epilepticus & Rebound Seizures: Triggered by abrupt cessation.

Key Drug Interactions

Opioids (e.g., Morphine, Oxycodone, Hydrocodone): Co-administration causes synergistic CNS and respiratory depression, significantly elevating the risk of fatal overdose. Opioids can also increase gabapentin AUC concentrations.
Antacids Containing Aluminum and Magnesium (e.g., Maalox, Mylanta): Reduce gabapentin bioavailability by approximately 20%. Gabapentin should be taken at least 2 hours after taking an antacid.
Alcohol and Sedatives: Additive sedative and psychomotor-impairing effects.
Lack of Hepatic CYP450 Interactions: Gabapentin does not undergo significant hepatic metabolism and does not induce or inhibit cytochrome P450 enzymes, meaning it has a low risk of pharmacokinetic interactions with drugs metabolized by liver enzymes.

Warnings and Precautions

FDA Warning on Serious Breathing Difficulties: The FDA cautions that serious, life-threatening breathing problems can occur when gabapentin is used in patients with respiratory risk factors (such as elderly patients, those with COPD, or those using opioids).
Suicidal Ideation Monitoring: Monitor patients for the emergence or worsening of depression, suicidal thoughts, or unusual changes in mood and behavior.
Tapering and Discontinuation: Gabapentin must never be discontinued abruptly. Abrupt cessation can precipitate withdrawal symptoms (insomnia, nausea, headache, anxiety, diaphoresis) and increase seizure frequency or trigger status epilepticus in patients with seizure disorders. A gradual taper over at least one week is required.
Impaired Coordination and Driving: Patients should not drive, operate heavy machinery, or perform hazardous tasks until they know how gabapentin affects their alertness and motor control.
Misuse and Diversion: While not federally classified as a scheduled controlled substance, gabapentin carries potential for misuse (often used to potentiate the euphoric effects of opioids or self-manage withdrawal).