Skip to main content

Drug Interactions between Di-Phen and rifampin

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

Edit list (add/remove drugs)

Interactions between your drugs

Major

rifAMPin phenytoin

Applies to: rifampin and Di-Phen (phenytoin)

MONITOR CLOSELY: Coadministration with rifampin may decrease the serum concentrations of phenytoin. The proposed mechanism is rifampin induction of CYP450 2C9 and 2C19, the isoenzymes responsible for the metabolic clearance of phenytoin. In 6 study subjects, intravenous administration of phenytoin following a two-week treatment with rifampin 450 mg daily resulted in a 109% increase in phenytoin clearance and a 53% decrease in phenytoin half-life compared to administration of phenytoin alone. In 14 patients with pulmonary tuberculosis receiving daily treatment with rifampin 450 mg, isoniazid 300 mg, and ethambutol 900 to 1200 mg, clearance of phenytoin increased by 73% and half-life decreased by 47% after two weeks of antituberculosis treatment. Since isoniazid is an inhibitor of both CYP450 2C9 and 2C19, there may have been an attenuation of the inducing effect of rifampin relative to rifampin given alone. Six of the 14 patients were re-examined after 3 months of antituberculosis treatment, and no further changes were observed in the pharmacokinetic parameters of phenytoin.

MONITOR CLOSELY: Coadministration with phenytoin may decrease the plasma concentrations of rifampin. Phenytoin is a potent inducer of CYP450 3A4 and may increase the metabolism of rifampin beyond that due to auto-induction by rifampin. However, no clinical data are available regarding this potential interaction.

MANAGEMENT: Pharmacologic response and serum phenytoin levels should be monitored more closely whenever rifampin is added to or withdrawn from therapy, and the phenytoin dosage adjusted as necessary. Patients should be advised to contact their physician if they experience loss of seizure control during coadministration. The potential for diminished therapeutic effects of rifampin should also be considered when given with phenytoin.

References

  1. Venkatesan K (1992) "Pharmacokinetic drug interactions with rifampicin." Clin Pharmacokinet, 22, p. 47-65
  2. Borcherding SM, Baciewicz AM, Self TH (1992) "Update on rifampin drug interactions." Arch Intern Med, 152, p. 711-6
  3. Abajo FJ (1988) "Phenytoin interaction with rifampicin." Br Med J, 297, p. 1048
  4. Kay L, Kampmann JP, Svedsen L, et al. (1985) "Influence of rifampicin and isoniazid on the kinetics of phenytoin." Br J Clin Pharmacol, 20, p. 323-6
  5. Strayhorn VA, Baciewicz AM, Self TH (1997) "Update on rifampin drug interactions, III." Arch Intern Med, 157, p. 2453-8
  6. Van Berkel MA, Hurdle AC, Twilla JD (2013) "Phenytoin-rifampin drug interaction in a hypoalbuminemic, renal failure patient: a complex clinical case." Pharmacotherapy, 33, e96-100
View all 6 references

Switch to consumer interaction data

Drug and food interactions

Moderate

rifAMPin food

Applies to: rifampin

GENERALLY AVOID: Concurrent use of rifampin in patients who ingest alcohol daily may result in an increased incidence of hepatotoxicity. The increase in hepatotoxicity may be due to an additive risk as both alcohol and rifampin are individually associated with this adverse reaction. However, the exact mechanism has not been established.

ADJUST DOSING INTERVAL: Administration with food may reduce oral rifampin absorption, increasing the risk of therapeutic failure or resistance. In a randomized, four-period crossover phase I study of 14 healthy male and female volunteers, the pharmacokinetics of single dose rifampin 600 mg were evaluated under fasting conditions and with a high-fat meal. Researchers observed that administration of rifampin with a high-fat meal reduced rifampin peak plasma concentration (Cmax) by 36%, nearly doubled the time to reach peak plasma concentration (Tmax) but reduced overall exposure (AUC) by only 6%.

MANAGEMENT: The manufacturer of oral forms of rifampin recommends administration on an empty stomach, 30 minutes before or 2 hours after meals. Patients should be encouraged to avoid alcohol or strictly limit their intake. Patients who use alcohol and rifampin concurrently or have a history of alcohol use disorder may require additional monitoring of their liver function during treatment with rifampin.

References

  1. (2022) "Product Information. Rifampin (rifAMPin)." Akorn Inc
  2. (2022) "Product Information. Rifampicin (rifampicin)." Mylan Pharmaceuticals Inc
  3. (2023) "Product Information. Rifadin (rifampicin)." Sanofi
  4. (2024) "Product Information. Rifadin (rifaMPICin)." Sanofi-Aventis Australia Pty Ltd
  5. Peloquin CA, Namdar R, Singleton MD, Nix DE (2024) Pharmacokinetics of rifampin under fasting conditions, with food, and with antacids https://pubmed.ncbi.nlm.nih.gov/9925057/
  6. (2019) "Product Information. Rofact (rifampin)." Bausch Health, Canada Inc.
View all 6 references

Switch to consumer interaction data

Moderate

phenytoin food

Applies to: Di-Phen (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

  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."
View all 16 references

Switch to consumer interaction data

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

Report options

Loading...
QR code containing a link to this page

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.

Medical Disclaimer