What is the recommended IV (intravenous) dose of promethazine for adults?

Recommended IV Dose of Promethazine for Adults

The recommended intravenous (IV) dose of promethazine for adults is 12.5 to 25 mg, administered at a rate not exceeding 25 mg per minute and in a concentration no greater than 25 mg per mL. 1

Administration Guidelines

Proper IV Administration Technique

• Promethazine should NEVER be administered by intra-arterial injection due to risk of severe arteriospasm and potential gangrene 1
• When administered IV, promethazine should be:
  • Given in a concentration no greater than 25 mg/mL
  • Administered at a rate not exceeding 25 mg per minute
  • Preferably injected through the tubing of a functioning IV infusion set 1
• Stop injection immediately if patient complains of pain to evaluate for possible arterial injection or perivascular extravasation 1

Dosing by Indication

• Nausea and vomiting: 12.5 to 25 mg IV, not to be repeated more frequently than every 4 hours 1
• Allergic conditions: 25 mg IV 1
• Sedation in hospitalized patients: 25 to 50 mg IV 1
• Pre/post-operative use: 25 to 50 mg IV 1

Safety Considerations

Severe Risks

• Promethazine can cause severe chemical irritation and tissue damage regardless of administration route 1
• Risks include:
  • Perivascular extravasation
  • Unintentional intra-arterial injection
  • Intraneuronal or perineuronal infiltration 1
  • Burning, pain, thrombophlebitis, tissue necrosis, and gangrene with inadvertent extravasation 2

Adverse Effects

• Common adverse effects include:
  • Sedation
  • Anticholinergic effects (dry mouth, urinary retention, blurred vision)
  • Extrapyramidal symptoms
  • Hypotension
  • CNS depression, especially when combined with other CNS depressants 3

Evidence for Lower Dosing

Recent research suggests that lower doses may be equally effective with fewer side effects:

• Low-dose promethazine (6.25 mg IV) has been shown to be as effective as ondansetron 4 mg IV for treating nausea and vomiting, with similar sedation profiles 4
• A comparison of 6.25 mg vs. 12.5 mg IV promethazine for postoperative nausea and vomiting found that 97% of subjects reported total relief of nausea with either dose, but the lower dose resulted in less sedation 5
• In elderly patients, 6.25 mg IV was found to be as effective as higher doses with significantly fewer adverse drug reactions 6

Special Populations

Elderly Patients

• Starting dose should be reduced to 6.25 mg for elderly patients due to:
  • Increased sensitivity to anticholinergic effects
  • Higher risk of sedation and confusion
  • Altered drug metabolism and elimination 3
  • Longer half-life (9-16 hours) that may be further prolonged in elderly patients 3

Pediatric Patients

• Promethazine is contraindicated for use in pediatric patients less than 2 years of age 1
• For patients 2 years and older, the dosage should not exceed half the suggested adult dose 1

Drug Interactions

• When used with other CNS depressants (opioids, barbiturates), dosage of these medications should be reduced accordingly 1
• Increased risk of adverse effects when combined with other sedative medications 3

Remember that the preferred parenteral route for promethazine is deep intramuscular injection, with IV administration being a secondary option that requires careful administration to prevent tissue damage 1.