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Drug Interactions between phenytoin and roflumilast

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

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Interactions between your drugs

Moderate

phenytoin roflumilast

Applies to: phenytoin and roflumilast

GENERALLY AVOID: Coadministration with potent CYP450 inducers may significantly reduce the systemic exposure to roflumilast and its pharmacologically active N-oxide metabolite, the former of which is metabolized by CYP450 1A2 and 3A4, and the latter of which is metabolized by CYP450 2C19 and 3A4. In 15 healthy volunteers, administration of a single 500 mcg oral dose of roflumilast in combination with the potent CYP450 3A4 inducer rifampin (600 mg once daily for 11 days) resulted in a 68% reduction of roflumilast peak plasma concentration (Cmax) and 80% reduction of systemic exposure (AUC) compared to administration of roflumilast alone. In addition, rifampin increased the Cmax of roflumilast N-oxide by 30% and decreased its AUC and half-life by 56% and 2.5-fold (from 24 to 9.9 hours), respectively. Total phosphodiesterase 4 inhibitory activity (i.e., combined effect of both roflumilast and roflumilast N-oxide) decreased by 58% in association with these changes.

MANAGEMENT: Due to the potential for reduced therapeutic effectiveness of roflumilast, concomitant use with potent CYP450 enzyme inducers such as carbamazepine, phenobarbital, phenytoin, rifampin, and St. John's wort is not recommended.

References (2)
  1. Nassr N, Huennemeyer A, Herzog R, et al. (2009) "Effects of rifampicin on the pharmacokinetics of roflumilast and roflumilast N-oxide in healthy subjects." Br J Clin Pharmacol, 68, p. 580-7
  2. (2011) "Product Information. Daliresp (roflumilast)." Astra-Zeneca Pharmaceuticals

Drug and food interactions

Moderate

phenytoin food

Applies to: phenytoin

ADJUST DOSING INTERVAL: Phenytoin bioavailability may decrease to subtherapeutic levels when the suspension is given concomitantly with enteral feedings. The mechanism may be related to phenytoin binding to substances in the enteral formula (e.g., calcium, protein) and/or binding to the tube lumen. Data have been conflicting and some studies have reported no changes in phenytoin levels, while others have reported significant reductions.

MONITOR: Acute consumption of alcohol may increase plasma phenytoin levels. Chronic consumption of alcohol may decrease plasma phenytoin levels. The mechanism of this interaction is related to induction of phenytoin metabolism by ethanol during chronic administration. Other hydantoin derivatives may be similarly affected by ethanol.

MANAGEMENT: Some experts have recommended interrupting the feeding for 2 hours before and after the phenytoin dose, giving the phenytoin suspension diluted in water, and flushing the tube with water after administration; however, this method may not entirely avoid the interaction and is not always clinically feasible. Patients should be closely monitored for clinical and laboratory evidence of altered phenytoin efficacy and levels upon initiation and discontinuation of enteral feedings. Dosage adjustments or intravenous administration may be required until therapeutic serum levels are obtained. In addition, patients receiving phenytoin therapy should be warned about the interaction between phenytoin and ethanol and they should be advised to notify their physician if they experience worsening of seizure control or symptoms of toxicity, including drowsiness, visual disturbances, change in mental status, nausea, or ataxia.

References (16)
  1. Sandor P, Sellers EM, Dumbrell M, Khouw V (1981) "Effect of short- and long-term alcohol use on phenytoin kinetics in chronic alcoholics." Clin Pharmacol Ther, 30, p. 390-7
  2. Holtz L, Milton J, Sturek JK (1987) "Compatibility of medications with enteral feedings." JPEN J Parenter Enteral Nutr, 11, p. 183-6
  3. Sellers EM, Holloway MR (1978) "Drug kinetics and alcohol ingestion." Clin Pharmacokinet, 3, p. 440-52
  4. (2001) "Product Information. Dilantin (phenytoin)." Parke-Davis
  5. Doak KK, Haas CE, Dunnigan KJ, et al. (1998) "Bioavailability of phenytoin acid and phenytoin sodium with enteral feedings." Pharmacotherapy, 18, p. 637-45
  6. Rodman DP, Stevenson TL, Ray TR (1995) "Phenytoin malabsorption after jejunostomy tube delivery." Pharmacotherapy, 15, p. 801-5
  7. Au Yeung SC, Ensom MH (2000) "Phenytoin and enteral feedings: does evidence support an interaction?" Ann Pharmacother, 34, p. 896-905
  8. Ozuna J, Friel P (1984) "Effect of enteral tube feeding on serum phenytoin levels." J Neurosurg Nurs, 16, p. 289-91
  9. Faraji B, Yu PP (1998) "Serum phenytoin levels of patients on gastrostomy tube feeding." J Neurosci Nurs, 30, p. 55-9
  10. Marvel ME, Bertino JS (1991) "Comparative effects of an elemental and a complex enteral feeding formulation on the absorption of phenytoin suspension." JPEN J Parenter Enteral Nutr, 15, p. 316-8
  11. Fleisher D, Sheth N, Kou JH (1990) "Phenytoin interaction with enteral feedings administered through nasogastric tubes." JPEN J Parenter Enteral Nutr, 14, p. 513-6
  12. Haley CJ, Nelson J (1989) "Phenytoin-enteral feeding interaction." DICP, 23, p. 796-8
  13. Guidry JR, Eastwood TF, Curry SC (1989) "Phenytoin absorption in volunteers receiving selected enteral feedings." West J Med, 150, p. 659-61
  14. Krueger KA, Garnett WR, Comstock TJ, Fitzsimmons WE, Karnes HT, Pellock JM (1987) "Effect of two administration schedules of an enteral nutrient formula on phenytoin bioavailability." Epilepsia, 28, p. 706-12
  15. Cerner Multum, Inc. "UK Summary of Product Characteristics."
  16. Cerner Multum, Inc. "Australian Product Information."
Minor

roflumilast food

Applies to: roflumilast

Food intake does not affect the total exposure to roflumilast and its pharmacologically active N-oxide metabolite, but delays the time to maximum concentration (Tmax) of roflumilast by one hour and reduces its peak plasma concentration (Cmax) by approximately 40%. The Tmax and Cmax of
roflumilast N-oxide are unaffected. Roflumilast may be taken with or without food.

References (3)
  1. Cerner Multum, Inc. "UK Summary of Product Characteristics."
  2. (2011) "Product Information. Daxas (roflumilast)." Nycomed Inc
  3. (2011) "Product Information. Daliresp (roflumilast)." Astra-Zeneca Pharmaceuticals

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.

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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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