1. Introduction
Promethazine is a first-generation antihistamine with sedative, antiemetic, and anticholinergic properties. It is widely used to manage allergies, motion sickness, nausea and vomiting, and insomnia. Promethazine works by blocking histamine (H1) receptors and has additional effects on muscarinic receptors, making it effective in reducing nausea and providing sedation.
2. Indications
- Allergic conditions (e.g., rhinitis, urticaria, and anaphylaxis adjunct)
- Nausea and vomiting (including motion sickness and post-operative nausea)
- Insomnia (short-term use)
- Pre-operative sedation
- Motion sickness prevention
- Cold and flu symptoms (as a component of combination therapies)
3. Dosage
Adults:
- Allergic conditions: 25 mg at night or 10–20 mg 2–3 times daily.
- Nausea and vomiting: 12.5–25 mg every 4–6 hours as needed (maximum: 100 mg/day).
- Motion sickness: 25 mg 30–60 minutes before travel, then 12.5–25 mg every 6–8 hours as needed.
- Insomnia: 25–50 mg at night.
Children (≥2 years):
- Allergic conditions or nausea/vomiting: 0.1–1 mg/kg every 6–8 hours (maximum: 25 mg/dose).
- Motion sickness: 0.5 mg/kg 30–60 minutes before travel; repeat after 8–12 hours if needed.
Elderly:
- Start with the lowest effective dose due to increased sensitivity to side effects.
4. Administration
- Take orally with water, with or without food.
- If using rectal suppositories, ensure proper hygiene before insertion.
- Liquid formulations should be measured with an appropriate measuring device.
5. Forms Available
- Tablets: 10 mg, 25 mg
- Oral syrup: 6.25 mg/5 mL, 12.5 mg/5 mL
- Injectable solution: 25 mg/mL, 50 mg/mL
- Suppositories: 12.5 mg, 25 mg, 50 mg
6. Side Effects
6.1 Common Side Effects:
- Drowsiness
- Dry mouth
- Dizziness
- Blurred vision
- Constipation
6.2 Less Common Side Effects:
- Restlessness or agitation (paradoxical in children)
- Nausea or vomiting
- Skin reactions (rash, itching)
6.3 Rare but Serious Side Effects:
- Respiratory depression (especially in young children)
- Neuroleptic malignant syndrome (NMS)
- Seizures
- Severe hypotension
- Prolonged QT interval leading to arrhythmias
7. Warnings
- Respiratory Depression in Children: Contraindicated in children under 2 years due to the risk of fatal respiratory depression.
- CNS Depression: Use cautiously with other sedatives or alcohol, as it may enhance CNS depression.
- Extrapyramidal Symptoms: Rarely, promethazine can cause muscle stiffness, tremors, or other movement disorders.
8. Precautions
- Use cautiously in patients with glaucoma, prostatic hypertrophy, or respiratory conditions like asthma or COPD.
- Avoid prolonged use for insomnia due to the risk of tolerance and dependency.
- Monitor in patients with cardiovascular disease, as promethazine may cause hypotension or QT prolongation.
9. Interactions
- CNS depressants (e.g., alcohol, opioids, benzodiazepines): Increased sedation and respiratory depression.
- Anticholinergics (e.g., atropine): Additive anticholinergic effects (e.g., dry mouth, constipation).
- MAO inhibitors: May enhance sedative and anticholinergic effects.
- Levodopa: Reduced efficacy due to dopamine receptor antagonism.
10. Monitoring Parameters
- Monitor for symptom relief (e.g., reduction in nausea, allergic symptoms, or insomnia).
- Assess for signs of excessive sedation or anticholinergic side effects.
- Observe for any cardiovascular abnormalities, particularly QT prolongation in high doses or prolonged use.
11. Use in Children
- Contraindicated in children under 2 years.
- For children aged 2 years and older, use cautiously at the lowest effective dose and monitor for paradoxical effects like agitation.
12. Use in Pregnancy
- Category C: Use only if the potential benefit outweighs the risk. Promethazine is sometimes used for pregnancy-related nausea and vomiting under medical supervision.
13. Use in Elderly
- Use with caution due to increased sensitivity to sedation, dizziness, and anticholinergic effects. Lower doses are recommended.
14. Use in Kidney Disease
- No specific dose adjustments required, but monitor for increased sedation and anticholinergic side effects.
15. Use in Liver Disease
- Use cautiously in severe liver impairment due to reduced metabolism of the drug.
16. Patient Counselling Points
- Take promethazine exactly as prescribed. Avoid alcohol and other sedatives while on this medication.
- Avoid activities requiring mental alertness (e.g., driving) until you know how the medication affects you.
- Inform your doctor if you experience excessive drowsiness, difficulty breathing, or unusual movements.
- Keep this medication out of reach of children, especially those under 2 years, as it can be fatal.
- For motion sickness, take the first dose 30–60 minutes before travel for best results.
17. Table of Brand Names, Manufacturer, and Prices in USD
| Brand Name | Manufacturer | Strength/Dosage Form | Price (USD) |
|---|---|---|---|
| Phenergan | Sanofi | 25 mg Tablet | $15 (30 tablets) |
| Promethegan | Various | 25 mg Suppository | $20 (12 suppositories) |
| Generic Promethazine | Various | 25 mg Tablet | $10 (30 tablets) |
| Phenergan Elixir | Sanofi | 6.25 mg/5 mL Syrup | $15 (100 mL) |
18. 15 FAQs (Frequently Asked Questions)
1. What is Promethazine used for?
Promethazine is used to treat allergies, nausea, vomiting, motion sickness, and insomnia.
2. How does Promethazine work?
It blocks histamine (H1) receptors and muscarinic receptors, reducing nausea, allergies, and providing sedation.
3. Can Promethazine cause drowsiness?
Yes, drowsiness is a common side effect. Avoid driving or operating machinery if affected.
4. Can children take Promethazine?
It is contraindicated in children under 2 years due to the risk of respiratory depression. For older children, use at the lowest effective dose.
5. Can Promethazine be used for nausea during pregnancy?
Yes, it is sometimes prescribed for pregnancy-related nausea and vomiting under medical supervision.
6. How long does Promethazine take to work?
Effects are typically noticeable within 20–30 minutes after oral or rectal administration.
7. Can Promethazine be used long-term?
Long-term use is not recommended due to the risk of side effects like tolerance, dependence, and anticholinergic effects.
8. Is Promethazine addictive?
Promethazine itself is not addictive, but it can cause dependence if used frequently for sedation or sleep.
9. Can Promethazine cause dry mouth?
Yes, dry mouth is a common anticholinergic side effect.
10. Can Promethazine interact with alcohol?
Yes, alcohol can enhance the sedative effects of promethazine and should be avoided.
11. How should I store Promethazine?
Store at room temperature, away from moisture and heat.
12. Can Promethazine cause weight gain?
Weight gain is not common but can occur due to increased appetite or water retention.
13. What should I do if I miss a dose?
Take the missed dose as soon as you remember, but skip it if it’s close to your next scheduled dose.
14. Can Promethazine cause seizures?
In rare cases, promethazine may lower the seizure threshold. Use cautiously in patients with epilepsy.
15. Is Promethazine available over-the-counter?
In some countries, low-dose promethazine is available OTC for motion sickness or allergies. Higher doses typically require a prescription.
