Promethazine (Phenergan)

Anesthesia Implications

Classification: Antihistamine, Phenothiazine, Dopamine antagonist
Therapeutic Effects: PONV prophylaxis, antiemetic, antipsychotic, antihistamine, anticholinergic, sedation
Time to Onset: 15 minutes

Duration: up to 20 hours

Contraindications

Glaucoma
Prostate hypertrophy
The contraindications are due to the anticholinergic effects of promethazine

Use with caution in:
The parturient – Phenergan readily crosses the placenta. Reduces fetal heart rate variability

Primary Considerations

PONV prophylaxis – the primary use for this drug is as an antiemetic and PONV prophylaxis. A dose of 6.25mg in adults was seen to be most effective (versus higher doses). Studies show that promethazine is as effective as ondansetron (Zofran) in PONV prophylaxis.  This has not been confirmed in pediatric patients.

Vesicant – make sure to have this drug diluted before giving IV!

Thrombophlebitis and sedative effects – these are the primary concerns when administering this drug.  However, respiratory drive is generally unaffected.

MAC – No effect on minimum alveolar concentration (MAC)

Side effects – Anticholinergic effects include blurred vision, urinary retention, dry mouth, and potential to exacerbate extrapyramidal symptoms – these are possible side effects but are very infrequent.

central anticholinergic syndrome – Phenergan is associated with central anticholinergic syndrome

IV push dose

0.25 – 0.5 mg/kg
Most common doses: 6.25 – 12.5 mg (Adult).
Textbook dose range: 25-50 mg (adult)

IM dose

0.25 – 0.5 mg/kg

Method of Action

H1 Blocker

Metabolism

Hepatic. Inactive metabolites