What is the use and dosage of promethazine (phenothiazine) rectal suppositories?

Promethazine Rectal Suppositories: Use and Dosage

Promethazine rectal suppositories are indicated for nausea and vomiting when oral medication cannot be tolerated, with a standard adult dose of 25 mg that can be repeated every 4-6 hours as needed. 1

Indications for Promethazine Rectal Suppositories

• Nausea and Vomiting: Primary indication when oral medication cannot be tolerated, particularly useful in postoperative settings 1, 2
• Motion Sickness: Can be used for prevention and treatment, though oral route is typically preferred when possible 1
• Allergic Reactions: May help control minor allergic reactions 1
• Sedation: Provides relief from apprehension and induces quiet sleep from which patients can be easily aroused 1
• Pre- and Post-operative Use: Helps relieve apprehension and produce quiet sleep before surgery 1

Dosage Guidelines

Adults:

• Nausea and Vomiting: 25 mg per dose, repeated every 4-6 hours as necessary 1
• Sedation: 25 mg to 50 mg at bedtime for nighttime sedation 1
• Pre-operative: 50 mg the night before surgery 1

Children:

• CONTRAINDICATED in children under 2 years of age (Black Box Warning) 1
• Nausea and Vomiting: 0.5 mg per pound of body weight, adjusted to age and condition severity 1
• Sedation: 12.5 mg to 25 mg at bedtime 1

Pharmacokinetic Considerations

• Rectal administration of promethazine results in slower absorption compared to oral solutions or intramuscular injections 3
• Bioavailability after rectal administration is less than intramuscular injection but similar to oral solution 3
• There is high intersubject variation in the bioavailability of promethazine rectal suppositories 3
• Rectal administration partially bypasses hepatic first-pass metabolism, though less effectively than some other medications 4

Clinical Efficacy

• In a study of outpatient surgical patients, 89% of patients who used promethazine suppositories for post-discharge nausea and vomiting reported improvement in their symptoms 2
• No significant adverse effects were reported in this population 2

Alternative Antiemetic Options

• For patients seeking non-sedating alternatives, 5-HT3 receptor antagonists like ondansetron are more effective with less sedation 5
• Metoclopramide is a less sedating option than promethazine but requires monitoring for extrapyramidal symptoms 5
• In pregnancy-related nausea and vomiting, promethazine is considered after first-line therapies (vitamin B6, doxylamine) have failed 6

Important Considerations and Precautions

• Sedation: Promethazine causes significant sedation, which may be beneficial or problematic depending on the clinical situation 1
• Extrapyramidal Effects: Monitor for drug-induced extrapyramidal adverse effects, especially with prolonged use 6
• Administration Technique: Proper insertion technique is important for effectiveness and patient comfort 4
• Patient Acceptability: Some patients may find rectal administration uncomfortable or unacceptable 4
• Interruption of Absorption: Defecation shortly after administration may interrupt drug absorption 4

Promethazine rectal suppositories provide an important alternative route of administration when oral medication cannot be tolerated, particularly in settings of nausea, vomiting, or when sedation is desired.