1. Clinical Overview
A fixed-dose combination of a typical antipsychotic (phenothiazine derivative) and an anticholinergic agent. Trifluoperazine is a high-potency antipsychotic used for schizophrenia and other psychotic disorders. Trihexyphenidyl is added to counteract the extrapyramidal symptoms (EPS) induced by trifluoperazine, particularly in the initial phase of treatment. This combination is primarily used for the management of psychotic disorders where EPS is a significant concern.
| Onset | Duration | Bioavailability |
|---|---|---|
| Trifluoperazine: Oral - 1 to 2 hours for initial effects; full antipsychotic effect may take 2 to 4 weeks. Trihexyphenidyl: Oral - 1 hour. | Trifluoperazine: Up to 24 hours, allowing for once or twice-daily dosing. Trihexyphenidyl: 6 to 12 hours. | Trifluoperazine: Approximately 50-60% orally. Trihexyphenidyl: Well absorbed, but specific percentage not well quantified; estimated >80%. |
2. Mechanism of Action
Trifluoperazine exerts its antipsychotic effect primarily by blocking postsynaptic dopamine D2 receptors in the mesolimbic pathway of the brain. It also has moderate antagonistic activity at alpha-1 adrenergic receptors and histamine H1 receptors. Trihexyphenidyl is a competitive antagonist at central muscarinic acetylcholine receptors (M1, M4), reducing the relative cholinergic excess in the striatum caused by dopamine blockade, thereby preventing or treating extrapyramidal symptoms.
3. Indications & Uses
- Management of schizophrenia and other psychotic disorders
- Prophylaxis and treatment of drug-induced extrapyramidal symptoms (EPS) from typical antipsychotics
4. Dosage & Administration
Adult Dosage: Initially, 1 tablet (Trifluoperazine 2.5mg + Trihexyphenidyl 1mg) twice daily. May be increased gradually based on response and tolerance. Usual maintenance: 2-4 tablets per day in divided doses. Maximum trifluoperazine dose typically 30-40mg/day; anticholinergic dose should be the minimum effective.
Administration: Administer orally with or after food to minimize gastric upset. Tablet can be taken with a full glass of water. Do not crush or chew unless advised. Avoid abrupt discontinuation.
5. Side Effects
Common side effects may include:
- Dry mouth
- Blurred vision
- Constipation
- Drowsiness/sedation
- Dizziness
- Postural hypotension
- Urinary hesitancy
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Other CNS Depressants (Alcohol, Opioids, Benzodiazepines) | Additive CNS depression, respiratory depression | Major |
| Anticholinergics (Atropine, Antihistamines, TCAs) | Additive anticholinergic toxicity (delirium, hyperthermia, ileus) | Major |
| Levodopa, Dopamine Agonists | Mutual antagonism; reduced efficacy of both | Major |
| QT-prolonging drugs (Class IA/III antiarrhythmics, Macrolides, Fluoroquinolones) | Increased risk of torsades de pointes | Major |
| Enzyme Inducers (Phenobarbitone, Carbamazepine, Rifampicin) | Reduced plasma levels of trifluoperazine | Moderate |
| Enzyme Inhibitors (Fluoxetine, Paroxetine, CYP2D6 inhibitors) | Increased plasma levels of trifluoperazine, risk of toxicity | Moderate |
| Antihypertensives | Potentiated hypotension | Moderate |
| Metoclopramide | Increased risk of EPS | Moderate |
7. Patient Counselling
- DO take the medication exactly as prescribed by your doctor.
- DO inform all your doctors and dentists you are on this medication.
- DO rise slowly from sitting/lying position to avoid dizziness.
- DO maintain good oral hygiene and use sugar-free gum/candies for dry mouth.
- DO use sunglasses if experiencing light sensitivity.
- DO NOT stop taking the medicine suddenly without consulting your doctor.
- DO NOT consume alcohol while on this medication.
- DO NOT drive or operate heavy machinery until you know how it affects you.
- DO NOT take any other prescription, OTC, or herbal medicine without checking with your doctor.
8. Toxicology & Storage
Overdose: CNS: Deep sedation, coma, seizures, agitation, delirium, EPS. Anticholinergic: Hyperthermia, hot dry skin, flushed face, mydriasis, tachycardia, ileus, urinary retention. Cardiovascular: Hypotension, arrhythmias, QT prolongation. Respiratory: Depression, cyanosis.
Storage: Store below 30°C in a cool, dry place. Protect from light and moisture. Keep the container tightly closed. Keep out of reach and sight of children.