Drug interactions
Phendimetrazine + Promethazine
Severity: Moderate
Phendimetrazine and Promethazine: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phendimetrazine is a sympathomimetic anorectic, while promethazine is a sedating phenothiazine. The stimulant and sedative effects may partly oppose each other, and both can contribute to tachycardia or arrhythmia in susceptible patients.
What this interaction means in plain words
Phendimetrazine and Promethazine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Opposing CNS effects and possible additive cardiac effects; the mechanism is not firmly established.
What to do
Monitor heart rate and rhythm, particularly in patients with cardiac disease or other QT-prolonging drugs. Do not rely on either drug to offset the effect of the other.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Promethazine
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
- Amiodarone + Promethazine Major
- Amisulpride + Promethazine Major
Frequently asked questions
Can I take Phendimetrazine with Promethazine?
MediHelp rates the interaction as moderate. Phendimetrazine and Promethazine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Phendimetrazine is a sympathomimetic anorectic, while promethazine is a sedating phenothiazine. The stimulant and sedative effects may partly oppose each other, and both can contribute to tachycardia or arrhythmia in susceptible patients.
How serious is the interaction between Phendimetrazine and Promethazine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor heart rate and rhythm, particularly in patients with cardiac disease or other QT-prolonging drugs. Do not rely on either drug to offset the effect of the other.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Ibutilide, Pimozide, Thioridazine. The full list is on the Promethazine page.
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