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Phenytoin Sodium and Tagamet

Determining the interaction of Phenytoin Sodium and Tagamet and the possibility of their joint administration.

Check result:

Phenytoin Sodium <> Tagamet

Relevance: 26.07.2022 Reviewer: Shkutko P.M., M.D., in

In the database of official manuals used in the service creation an interaction registered by statistical results of studies was found, which can either lead to negative consequences for the patient health or strengthen a mutual positive effect. A doctor should be consulted to address the issue of joint drug administration.

Consumer:

Ask your doctor before using phenytoin together with cimetidine. Using phenytoin with cimetidine may increase the effects of phenytoin. Contact your doctor if you experience twitching eye movements, slurred speech, loss of balance, tremor, muscle stiffness or weakness, nausea, vomiting, feeling light-headed, fainting, and slow or shallow breathing. If your doctor does prescribe these medications together, you may need a dose adjustment or special test to safely use both medications. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

Professional:

GENERALLY AVOID: Coadministration with cimetidine may significantly increase the plasma concentrations of phenytoin. The proposed mechanism is cimetidine inhibition of CYP450 2C9 and 2C19, the isoenzymes responsible for the metabolic clearance of phenytoin. In pharmacokinetic studies, cimetidine administered at dosages of 1000 to 1200 mg/day has consistently been found to increase phenytoin plasma levels, with wide intersubject variability ranging from a 13% to almost 300% increase and phenytoin toxicity developing in some. There have also been rare reports of severe and life-threatening thrombocytopenia, agranulocytosis, and cutaneous reactions including toxic epidermal necrolysis in patients receiving phenytoin and cimetidine, with or without glucocorticoids. Whether these events are related to a pharmacokinetic or pharmacodynamic interaction is unknown. Cimetidine at a dosage of 400 mg/day for two weeks did not significantly affect phenytoin serum levels or seizure frequency in a study of nine patients on long-term phenytoin therapy.

MANAGEMENT: The use of cimetidine should generally be avoided in patients treated with phenytoin because safer alternatives exist, such as other H2-receptor antagonists or proton pump inhibitors. These agents (except omeprazole) have demonstrated a lack of interaction with phenytoin in pharmacokinetic studies, and only rare cases of suspected interaction have been reported, if any.

References

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Phenytoin Sodium

Generic Name: phenytoin

Brand name: Dilantin, Dilantin Infatabs, Phenytek, Phenytoin Sodium, Prompt

Synonyms: n.a.

What is Phenytoin Sodium?

Tagamet

Generic Name: cimetidine

Brand name: Tagamet HB, Tagamet

Synonyms: n.a.

What is Tagamet?

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In the course of checking the drug compatibility and interactions, data from the following reference sources was used: Drugs.com, Rxlist.com, Webmd.com, Medscape.com.

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