1. Clinical Overview
Imipramine hydrochloride is a prototypical tricyclic antidepressant (TCA) with a dibenzazepine nucleus. It is a tertiary amine TCA, acting as a potent inhibitor of presynaptic norepinephrine and serotonin reuptake, with a higher affinity for norepinephrine transporters. It also exhibits significant anticholinergic, antihistaminic (H1), and alpha-1 adrenergic blocking activity. In the Indian context, it is a well-established, cost-effective treatment for major depressive disorder and nocturnal enuresis, though its use is often reserved for treatment-resistant cases or specific indications due to its side effect profile and toxicity in overdose.
| Onset | Duration | Bioavailability |
|---|---|---|
| Antidepressant effect: 2-3 weeks. Initial sedative effects may be seen within hours to days. | The pharmacological effect extends beyond its plasma half-life due to active metabolites and downstream neuroadaptive changes. Dosing is typically once or twice daily. | Approximately 29-77% due to significant first-pass metabolism. |
2. Mechanism of Action
The primary mechanism is the inhibition of the presynaptic reuptake of the neurotransmitters norepinephrine (noradrenaline) and serotonin (5-hydroxytryptamine) into the presynaptic neuron, thereby increasing their concentration in the synaptic cleft and enhancing neurotransmission. This action is believed to underlie its antidepressant efficacy. Its anti-enuretic effect is attributed to its anticholinergic properties, which reduce bladder contractility, and its ability to increase arousal from sleep.
3. Indications & Uses
- Major Depressive Disorder (MDD)
- Nocturnal Enuresis in children (aged 6 years and above)
4. Dosage & Administration
Adult Dosage: Depression: Initial: 25 mg 2-3 times daily. Usual therapeutic range: 75-150 mg/day in divided doses or as a single bedtime dose. Maximum: 200 mg/day for outpatients; 300 mg/day for inpatients under supervision. Start low, go slow.
Administration: Take with or after food to minimize gastric upset. For single daily dosing, take at bedtime to leverage sedative effects and minimize daytime drowsiness. Do not crush or chew sustained-release formulations (if available). Swallow whole with water. Avoid abrupt discontinuation; taper over several weeks.
5. Side Effects
Common side effects may include:
- Dry mouth
- Constipation
- Blurred vision
- Drowsiness/sedation
- Dizziness
- Weight gain
- Increased sweating
- Postural hypotension
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Monoamine Oxidase Inhibitors (MAOIs) - Phenelzine, Tranylcypromine | Risk of hypertensive crisis, hyperpyrexia, serotonin syndrome. Potentially fatal. | Contraindicated |
| Other Serotonergic Drugs (SSRIs, SNRIs, Tramadol, Linezolid) | Increased risk of serotonin syndrome. | Major |
| Antiarrhythmics (Quinidine, Procainamide), Antipsychotics | Additive QT prolongation, increasing risk of torsades de pointes. | Major |
| Anticholinergics (Atropine, Trihexyphenidyl, Antihistamines) | Potentiated anticholinergic effects (ileus, urinary retention, hyperthermia). | Moderate |
| CYP2D6/CYP2C19 Inhibitors (Fluoxetine, Paroxetine, Fluvoxamine, Cimetidine) | Markedly increased imipramine plasma levels, leading to toxicity. | Major |
| Clonidine | Imipramine antagonizes the antihypertensive effect of clonidine. | Major |
| Sympathomimetics (Adrenaline, Noradrenaline) | Exaggerated pressor response, risk of severe hypertension. | Moderate |
| Alcohol (Ethanol) | Enhanced CNS depression, impaired psychomotor performance. | Major |
7. Patient Counselling
- DO take the medication exactly as prescribed by your doctor.
- DO take it at the same time(s) each day, preferably at bedtime if on once-daily dosing.
- DO inform all your doctors and dentists you are taking imipramine.
- DO report any thoughts of self-harm or worsening depression immediately.
- DON'T stop taking the medicine suddenly without consulting your doctor.
- DON'T consume alcohol while on this medication.
- DON'T drive or operate heavy machinery until you know how it affects you.
- DON'T take any other prescription, OTC, or herbal medicine without checking with your doctor/pharmacist.
8. Toxicology & Storage
Overdose: Symptoms can be severe and life-threatening. Includes: CNS (drowsiness progressing to stupor, coma, seizures, delirium, hyperreflexia), Cardiac (sinus tachycardia, conduction delays - widened QRS (>100 ms), prolonged QT, arrhythmias - ventricular tachycardia, torsades de pointes, heart block, hypotension), Anticholinergic (dry mouth, blurred vision, hyperthermia, ileus, urinary retention), Respiratory depression. Death usually from cardiac arrhythmias, seizures, or circulatory collapse.
Storage: Store below 30°C, in a cool, dry place, protected from light and moisture. Keep the container tightly closed. Keep out of reach and sight of children. Do not use after the expiry date printed on the pack. Do not flush unused medication. Dispose of as per local pharmaceutical waste guidelines.