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Does Promethazine Hydrochloride And Codeine Phosphate Interact with Phenytoin?

Promethazine Hydrochloride And Codeine Phosphate and Phenytoin have a major drug interaction according to U.S. FDA drug labeling data. CYP3A4 inducer reduces codeine levels and morphine formation, decreasing efficacy or causing withdrawal syndrome. Avoid use; if necessary, monitor for reduced efficacy. The mechanism involves induction of cyp3a4 decreases codeine metabolism by cyp2d6, lowering morphine levels. Patients taking both medications should consult their healthcare provider before starting, stopping, or changing the dosage of either drug. This information is based on official FDA drug labeling sourced from OpenFDA and the NIH National Library of Medicine.

Severity
Major
Phenytoin Class
Anti-epileptic Agent
Management
Close medical supervision required
Data Source
U.S. FDA via OpenFDA

How This Interaction Works

The interaction between Promethazine Hydrochloride And Codeine Phosphate and Phenytoin occurs because induction of cyp3a4 decreases codeine metabolism by cyp2d6, lowering morphine levels. Clinically, this means cyp3a4 inducer reduces codeine levels and morphine formation, decreasing efficacy or causing withdrawal syndrome. avoid use; if necessary, monitor for reduced efficacy. This is classified as a major interaction, meaning it could cause serious harm if not properly managed. Your healthcare provider may need to adjust dosages, substitute one medication, or increase monitoring frequency.

What To Tell Your Doctor or Pharmacist

If you are taking Promethazine Hydrochloride And Codeine Phosphate and your doctor is considering prescribing Phenytoin (or vice versa), make sure to:

  • Inform your doctor and pharmacist of all current medications, including over-the-counter drugs and supplements
  • Ask whether the benefits of combining these medications outweigh the risks for your specific situation
  • Ask what symptoms to watch for that would indicate the interaction is causing problems
  • Ask how frequently you should be monitored while these are co-prescribed
  • Ask whether any dosage adjustments are needed
  • Never stop or change either medication without first consulting your healthcare provider
💊 Promethazine Hydrochloride And Codeine Phosphate(Promethazine Hydrochloride And Codeine Phosphate)+💊 Phenytoin(Phenytoin Infatabs)

Severity & Interaction Details

⚠️
major
Use with caution — major interaction
Serious risk of clinically significant harm. Generally avoid; if used, monitor closely.
Severity scale
MinorContra
On record
Yes
Drug A class
—
Drug B class
Anti-epileptic Agent
Source
NLP:promethazine hydrochloride and codeine phosphate

What this means in plain English

CYP3A4 inducer reduces codeine levels and morphine formation, decreasing efficacy or causing withdrawal syndrome. Avoid use; if necessary, monitor for reduced efficacy.

What the FDA label says

"Induction of CYP3A4 decreases codeine metabolism by CYP2D6, lowering morphine levels"

📖 Source: NLP:promethazine hydrochloride and codeine phosphate

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Data sourced from U.S. FDA drug labeling via openFDA and the NIH National Library of Medicine. For informational purposes only. Always consult your pharmacist or physician.