What is the appropriate dosage and usage of promethazine (phenothiazine) for adults?

From the Guidelines

Promethazine should be prescribed for adults at a dosage of 12.5 to 25 mg taken orally every 4 to 6 hours as needed, with a maximum daily dose of 100 mg, as this dosage range is supported by the most recent and highest quality study 1. When considering the use of promethazine, it's essential to understand its mechanism of action, which includes blocking histamine H1 receptors and possessing anticholinergic properties, helping to reduce nausea, vomiting, and allergic reactions, as well as having sedative effects 1.

Key Considerations

• The dosage of 12.5 to 25 mg every 4-6 hours is recommended for nausea and vomiting, with the option to adjust based on individual patient needs 1.
• Patients should be cautioned against consuming alcohol and other CNS depressants while taking promethazine, as these can intensify sedation.
• Elderly patients typically require lower doses due to increased sensitivity to side effects.
• Those with certain medical conditions like glaucoma, urinary retention, or severe heart disease should use promethazine with caution or avoid it altogether.

Administration and Monitoring

• Promethazine can be administered orally or per rectally, with the oral route being more common for outpatient use.
• Peripheral IV administration can cause tissue injury, including gangrene or thrombophlebitis, and should be avoided if possible 1.
• Baseline ECG is advised for patients taking promethazine, especially those with a history of heart conditions, due to the potential for prolonged QTc interval.

From the FDA Drug Label

DOSAGE AND ADMINISTRATION Promethazine Hydrochloride Tablets USP ... Allergy The average oral dose is 25 mg taken before retiring; however, 12.5 mg may be taken before meals and on retiring, if necessary. Single 25-mg doses at bedtime or 6.25 to 12. 5 mg taken three times daily will usually suffice. Motion Sickness The average adult dose is 25 mg taken twice daily Nausea and Vomiting ... The average effective dose of promethazine hydrochloride for the active therapy of nausea and vomiting in children or adults is 25 mg Sedation ... Adults usually require 25 to 50 mg for nighttime, presurgical, or obstetrical sedation.

The appropriate dosage and usage of promethazine for adults is:

• Allergy: 25 mg taken before retiring, or 12.5 mg before meals and on retiring
• Motion Sickness: 25 mg taken twice daily
• Nausea and Vomiting: 25 mg, repeated at 4- to 6-hour intervals as necessary
• Sedation: 25 to 50 mg for nighttime, presurgical, or obstetrical sedation 2

From the Research

Dosage and Usage of Promethazine for Adults

The appropriate dosage and usage of promethazine (phenothiazine) for adults can be understood through various studies:

• Promethazine is used as an antiemetic agent for the treatment of nausea and vomiting in adults, with a common dosage of 25 mg administered intravenously 3.
• The drug has a sedating effect, which may be desirable in certain situations, but it also has the potential for vascular damage upon intravenous administration 4.
• Patient-specific factors, institutional policies, medication shortages of alternative agents, and the efficacy and toxicities of injectable promethazine itself should be considered when using injectable promethazine 5.
• The U.S. Food and Drug Administration has added dilution and administration recommendations for intravenous administration and stated a preference for intramuscular administration to minimize the risk of serious patient harm 5.

Safety and Efficacy

Key points regarding the safety and efficacy of promethazine include:

• Promethazine has been associated with rare but serious limb-threatening adverse effects after extravasation or inadvertent intra-arterial injection 5.
• The drug offers a suitable alternative antiemetic for use in the emergency department due to its distinct mechanism of action 5.
• Promethazine and ondansetron have similar efficacy in reducing nausea among emergency department patients, but promethazine is associated with greater sedation 3.
• The use of promethazine has been reported to cause significant sedation, agitation, hallucinations, seizures, dystonic reactions, and possibly apparent life-threatening events or sudden infant death syndrome, particularly in pediatric patients 6.

Misuse and Abuse

It is essential to note that:

• Promethazine has a misuse potential, especially in adolescents, with increasing levels of misuse/abuse/dependence issues reported over time 7.
• A high number of fatalities have been described, mostly recorded as 'drug toxicity/drug abuse' cases, with opiates/opioids being the most commonly reported concomitant drugs used 7.
• Healthcare professionals should be warned about the possible misuse of promethazine and be vigilant, as in some countries medicinal products containing promethazine can be purchased over the counter 7.