From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
The maximum daily dose for promethazine with dextromethorphan is typically 6 teaspoons (30 mL) per day for adults, which provides 60 mg of promethazine and 120 mg of dextromethorphan per day. This is usually divided into doses of 1-2 teaspoons (5-10 mL) taken every 4-6 hours as needed. Children's dosing varies by age and weight, and should be determined by a healthcare provider. It's essential to note that exceeding the recommended maximum daily dose can lead to significant sedation, anticholinergic effects, and potential cardiac issues due to promethazine, while dextromethorphan can cause dissociative effects and other adverse reactions when taken in excessive amounts, as reported in studies such as 1 and 2.
Important Considerations
- The medication combination is typically used for short-term management of cough and cold symptoms and should not be used for extended periods without medical supervision.
- Patients should avoid alcohol and other CNS depressants while taking this medication, as these can dangerously enhance the sedative effects.
- A study from 3 found that a one-time dose of dextromethorphan 120 mg did not demonstrate driving impairment, but doses greater than the currently recommended maximum daily dose are necessary to perturb driving behavior.
Key Points to Remember
- Promethazine and dextromethorphan can have serious side effects when taken in excess, including sedation, anticholinergic effects, and dissociative effects.
- The combination should be used with caution, especially in adolescents and young adults, due to the potential for misuse and abuse, as highlighted in 1.
- Healthcare professionals should be vigilant and monitor patients closely when prescribing this medication combination, as reported in 1.