1. Clinical Overview
Tolterodine is a competitive, specific muscarinic receptor antagonist used primarily for the treatment of overactive bladder (OAB) syndrome. It acts on the detrusor muscle of the urinary bladder, reducing involuntary contractions and increasing bladder capacity. The 4mg strength is typically the extended-release (ER) formulation, designed for once-daily administration, offering smoother plasma concentrations and potentially improved tolerability compared to the immediate-release (IR) form.
| Onset | Duration | Bioavailability |
|---|---|---|
| Peak plasma concentration (Tmax) for the extended-release formulation is reached in approximately 4-6 hours. Clinical symptom relief may be observed within 1-2 weeks of starting therapy. | The extended-release formulation provides a 24-hour duration of action, supporting once-daily dosing. | Approximately 65% for the extended-release formulation. Food does not significantly affect the overall bioavailability but may increase absorption by up to 17%. |
2. Mechanism of Action
Tolterodine is a competitive antagonist of muscarinic (M) acetylcholine receptors. In the treatment of overactive bladder, its primary effect is on the M2 and M3 receptor subtypes in the detrusor muscle of the urinary bladder. By blocking acetylcholine binding, it inhibits involuntary detrusor muscle contractions (detrusor overactivity), increases bladder capacity, and delays the initial desire to void, thereby reducing urinary frequency, urgency, and urge incontinence.
3. Indications & Uses
- Treatment of overactive bladder (OAB) with symptoms of urinary urgency, frequency, and urge incontinence.
4. Dosage & Administration
Adult Dosage: 4mg once daily (Extended-Release formulation). The recommended starting dose for most patients is 4mg ER OD. For patients with significant CYP3A4 inhibitor use or poor tolerability, a dose of 2mg ER OD may be considered.
Administration: Swallow the extended-release capsule or tablet whole with a glass of water. Do not crush, chew, or divide. Can be taken with or without food, preferably at the same time each day. Taking with food may minimize minor gastrointestinal upset.
5. Side Effects
Common side effects may include:
- Dry mouth (reported in ~23% with 4mg ER)
- Headache (~6%)
- Constipation (~6%)
- Dry eyes
- Dyspepsia
- Abdominal pain
- Vision blurred (accommodation abnormality)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Ketoconazole, Itraconazole, Voriconazole, Posaconazole | Potent CYP3A4 inhibitors. Increase tolterodine plasma concentration significantly. Contraindicated in patients with renal/hepatic impairment. In others, max dose 2mg ER. | Major |
| Clarithromycin, Erythromycin, Telithromycin | Moderate CYP3A4 inhibitors. May increase tolterodine levels. Use with caution; consider dose reduction. | Moderate |
| Fluoxetine, Paroxetine, Quinidine | Potent CYP2D6 inhibitors. May increase tolterodine levels and decrease active metabolite levels, altering net effect. Monitor. | Moderate |
| Other anticholinergics (e.g., oxybutynin, tricyclic antidepressants, first-gen antihistamines, phenothiazines) | Additive anticholinergic side effects (dry mouth, constipation, blurred vision, urinary retention, confusion). | Moderate |
| Metoclopramide | Tolterodine may antagonize the prokinetic effect of metoclopramide. | Moderate |
| Drugs that prolong QT interval (e.g., Class Ia/III antiarrhythmics, macrolides, some antipsychotics) | Additive risk of QT prolongation and cardiac arrhythmias. | Major |
7. Patient Counselling
- DO swallow the extended-release capsule/tablet whole. Do NOT crush, chew, or break it.
- DO take the medicine at approximately the same time each day.
- DO inform your doctor if you have liver, kidney, or heart problems.
- DO inform your doctor about all other medicines, including herbal supplements.
- DO maintain adequate fluid intake unless advised otherwise by your doctor.
- DONT take with grapefruit juice in large amounts.
- DONT stop the medication abruptly without consulting your doctor; symptoms may return.
- DONT take a double dose if you miss one. Take the next dose at the regular time.
8. Toxicology & Storage
Overdose: Symptoms are predictable extensions of its anticholinergic activity: severe dry mouth, blurred vision, tachycardia, palpitations, QT prolongation, urinary retention, constipation, nausea, vomiting, CNS disturbances (restlessness, confusion, hallucinations, convulsions), respiratory depression, circulatory failure.
Storage: Store at room temperature (15-30°C), protected from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the pack.