Promethazine Theoclate

First-Generation Antihistamine / Anti-Allergic / Antiemetic

Generic Name

Drug Class

First-generation H1 receptor antagonist, antiemetic, sedative

Indications

Allergic conditions: rhinitis, urticaria, dermatitis
Motion sickness and nausea/vomiting
Preoperative sedation
Mild insomnia (short-term use)

Dosage

Adults: 12.5–25 mg orally every 4–6 hours as needed (maximum 100 mg/day)
Children (2–12 years): 0.25–0.5 mg/kg/dose orally every 6–8 hours (maximum 25 mg/dose)
For motion sickness: Take 30–60 minutes before travel

Note: Dosage should be adjusted for elderly or patients sensitive to sedation.

Route of Administration

Oral, IM, IV (depending on formulation)

Mechanism of Action

Promethazine is a first-generation H1 receptor antagonist that blocks histamine-mediated effects. It also has anticholinergic, sedative, and antiemetic properties via central H1 and muscarinic receptor blockade.

Common Adverse Effects

Drowsiness / sedation
Dry mouth
Dizziness
Blurred vision
Constipation

Serious Adverse Effects

Severe respiratory depression (especially in children <2 years)
Extrapyramidal symptoms (rare)
Severe hypotension or cardiac arrhythmias (rare)
Severe allergic reactions (rare)

Contraindications

Hypersensitivity to promethazine or other phenothiazines
Comatose states or severe CNS depression
Children <2 years (risk of respiratory depression)
Concurrent use with MAO inhibitors (within 14 days)

Precautions

Use with caution in elderly (sedation, hypotension)
Monitor for respiratory depression in pediatric patients
Avoid alcohol and CNS depressants
Use caution in patients with glaucoma, urinary retention, or cardiovascular disease

Drug Interactions

Alcohol, opioids, sedatives – additive CNS depression
Other anticholinergics – additive anticholinergic effects
MAO inhibitors – increased risk of severe hypotension or CNS depression

Pregnancy & Lactation

Use only if clearly needed; may cause sedation in neonates if used near term. Excreted in breast milk – monitor infant.

Patient Counseling

Take as prescribed; do not exceed recommended dose
May cause drowsiness – avoid driving or operating machinery
Report respiratory difficulty, severe dizziness, or allergic reactions
Store in a cool, dry place away from sunlight