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Drug Interactions between fosphenytoin and guaifenesin / oxtriphylline

This report displays the potential drug interactions for the following 2 drugs:

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Interactions between your drugs

Moderate

oxtriphylline fosphenytoin

Applies to: guaifenesin / oxtriphylline and fosphenytoin

MONITOR: Phenytoin has been reported to increase the clearance of theophylline by 40% to 50%, presumably by enhancing the hepatic CYP450 metabolism of theophylline. Also, coadministration of theophylline has been reported to lower serum phenytoin concentrations. Other hydantoins and hepatically metabolized methylxanthines may also interact.

MANAGEMENT: Management consists of monitoring clinical response and serum concentrations of both drugs and adjusting dosages as necessary. Patients should be advised to report loss of seizure control or worsening of respiratory symptoms to their physician.

References (4)
  1. Upton RA (1991) "Pharmacokinetic interactions between theophylline and other medication (Part I)." Clin Pharmacokinet, 20, p. 66-80
  2. Miller M, Cosgriff J, Kwong T, Morken DA (1984) "Influence of phenytoin on theophylline clearance." Clin Pharmacol Ther, 35, p. 666-9
  3. Crowley JJ, Cusack BJ, Jue SG, et al. (1987) "Cigarette smoking and theophylline metabolism: effects of phenytoin." Clin Pharmacol Ther, 42, p. 334-40
  4. Sklar SJ, Wagner (1985) "Enhanced theophylline clearance secondary to phenytoin therapy." Drug Intell Clin Pharm, 19, p. 34-6

Drug and food interactions

No alcohol/food interactions were found. However, this does not necessarily mean no interactions exist. Always consult your healthcare provider.

Therapeutic duplication warnings

No warnings were found for your selected drugs.

Therapeutic duplication warnings are only returned when drugs within the same group exceed the recommended therapeutic duplication maximum.

See also

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Drug Interaction Classification

These classifications are only a guideline. The relevance of a particular drug interaction to a specific individual is difficult to determine. Always consult your healthcare provider before starting or stopping any medication.
Major Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.
Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.
Minor Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan.
Unknown No interaction information available.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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