1. Clinical Overview
A fixed-dose combination (FDC) of Pregabalin, a gabapentinoid anticonvulsant and neuropathic pain agent, and Nortriptyline, a tricyclic antidepressant (TCA). This combination is primarily used for the management of neuropathic pain conditions, particularly diabetic peripheral neuropathy (DPN) and post-herpetic neuralgia (PHN), where monotherapy is insufficient. It offers synergistic action by modulating both calcium channels and monoamine reuptake.
| Onset | Duration | Bioavailability |
|---|---|---|
| Pregabalin: 1-2 hours. Nortriptyline: 2-4 weeks for antidepressant effect; analgesic effect may be seen earlier. | Pregabalin: 5-7 hours. Nortriptyline: 24-48 hours (due to long half-life). | Pregabalin: ≥90% (not dose-dependent). Nortriptyline: ~50% (due to first-pass metabolism). |
2. Mechanism of Action
The combination provides a dual mechanism for neuropathic pain relief. Pregabalin binds to the alpha-2-delta subunit of voltage-gated calcium channels in the central nervous system, reducing the release of excitatory neurotransmitters (glutamate, noradrenaline, substance P). Nortriptyline primarily inhibits the reuptake of norepinephrine and, to a lesser extent, serotonin at presynaptic neurons, increasing their concentration in the synaptic cleft. It also exhibits sodium channel blockade, NMDA receptor antagonism, and anticholinergic activity, contributing to its analgesic and side effect profile.
3. Indications & Uses
- Diabetic Peripheral Neuropathy (DPN)
- Post-herpetic Neuralgia (PHN)
- Fibromyalgia (as per some guidelines)
4. Dosage & Administration
Adult Dosage: Usually 1 capsule (Pregabalin 75mg + Nortriptyline 10mg) once or twice daily, preferably at bedtime to minimize daytime sedation. Initiate with once daily at bedtime. Dose can be titrated based on response and tolerability, typically after 3-7 days. Maximum recommended dose is 2 capsules per day (Pregabalin 150mg + Nortriptyline 20mg).
Administration: Administer orally with or without food. Taking with food may reduce dizziness and drowsiness. Swallow whole with a glass of water. Do not crush or chew. Evening administration is preferred to capitalize on sedative effects for improving sleep. Avoid abrupt discontinuation; taper over at least one week to prevent withdrawal symptoms (especially for pregabalin).
5. Side Effects
Common side effects may include:
- Dizziness
- Somnolence (drowsiness)
- Dry mouth
- Constipation
- Weight gain
- Fatigue
- Blurred vision
- Peripheral edema (swelling)
- Headache
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Monoamine Oxidase Inhibitors (MAOIs) - Phenelzine, Selegiline | Risk of hypertensive crisis, serotonin syndrome, hyperpyrexia, death. | Contraindicated |
| Other CNS Depressants (Alcohol, Benzodiazepines, Opioids) | Additive CNS depression, severe sedation, respiratory depression, impaired motor skills. | Major |
| CYP2D6 Inhibitors (Fluoxetine, Paroxetine, Quinidine) | Increased nortriptyline plasma levels, leading to toxicity. | Major |
| Anticholinergics (Atropine, Oxybutynin, TCAs) | Enhanced anticholinergic effects (dry mouth, constipation, urinary retention, confusion). | Moderate |
| Antihypertensives | Potentiation of hypotensive effect, especially postural hypotension. | Moderate |
| Tramadol | Increased risk of seizures and serotonin syndrome. | Moderate |
| Warfarin | Nortriptyline may alter anticoagulant response; monitor INR. | Moderate |
7. Patient Counselling
- DO take the medicine exactly as prescribed by your doctor.
- DO take it at the same time each day, preferably at bedtime.
- DO inform all your doctors and dentists you are taking this medicine.
- DO NOT stop taking this medicine suddenly; it must be tapered off under medical supervision.
- DO NOT consume alcohol in any form while on this medication.
- DO NOT take any other prescription, over-the-counter, or herbal medicine without consulting your doctor.
- DO NOT drive or operate heavy machinery until you know how this medicine affects you.
- DO get up slowly from a sitting or lying position to avoid dizziness.
8. Toxicology & Storage
Overdose: Pregabalin: Severe drowsiness, agitation, restlessness, confusion, depression, blurred vision, diplopia, speech disorder, peripheral edema, tachycardia, hypotension, seizures, coma. Nortriptyline: Symptoms appear within 4-6 hours. Includes severe anticholinergic effects (dry mouth, blurred vision, urinary retention, hyperthermia), CNS (drowsiness, stupor, coma, seizures), cardiovascular (tachycardia, arrhythmias, hypotension, heart block, QRS/QT prolongation), respiratory depression.
Storage: Store below 30°C in a cool, dry place, protected from light and moisture. Keep the container tightly closed. Keep out of reach of children and pets. Do not use after the expiry date printed on the pack. Do not flush unused medication down the toilet or drain. Dispose of as per local regulations or return to a pharmacy take-back program.