Efavirenz and Promethazine and codeine interaction
Efavirenz and Promethazine and codeine: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Promethazine and codeine (Promethazine Hydrochloride and Codeine Phosphate) label · effective 2025-12-18
Interactions with Drugs Affecting Cytochrome P450 Isoenzymes The effects of concomitant use or discontinuation of cytochrome P450 3A4 inducers, 3A4 inhibitors, or 2D6 inhibitors with codeine are complex, requiring careful consideration of the effects on the parent drug, codeine, and the active metabolite, morphine.
Avoid the use of Promethazine HCl and Codeine Phosphate Oral Solution in patients who are taking a CYP3A4 inhibitor, CYP3A4 inducer, or 2D6 inhibitor [ see Warnings and Precautions (5.9) , Drug Interactions (7.1 , 7.2 , 7.3 ) ].
The effects of concomitant use or discontinuation of cytochrome P450 3A4 inducers, 3A4 inhibitors, or 2D6 inhibitors with codeine are complex, requiring careful consideration of the effects on the parent drug, codeine, and the active metabolite, morphine.
Avoid the use of Promethazine HCl and Codeine Phosphate Oral Solution in patients who are taking a CYP3A4 inhibitor or CYP3A4 inducer.
Avoid the use of Promethazine HCl and Codeine Phosphate Oral Solution while taking a CYP3A4 inhibitor.
From the Efavirenz label · effective 2024-03-31
Prophylaxis with appropriate antihistamines before initiating therapy with efavirenz in pediatric patients should be considered.
QT Prolonging Drugs There is limited information available on the potential for a pharmacodynamic interaction between efavirenz and drugs that prolong the QTc interval.
Narcotic analgesic: Methadone ↓ methadone * Monitor for signs of methadone withdrawal and increase methadone dose if required to alleviate withdrawal symptoms. * The interaction between efavirenz and the drug was evaluated in a clinical study.
Appropriate antihistamines and/or corticosteroids may improve the tolerability and hasten the resolution of rash.
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.