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Drug Interactions between amoxicillin / omeprazole / rifabutin and fosphenytoin

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

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Interactions between your drugs

Moderate

omeprazole fosphenytoin

Applies to: amoxicillin / omeprazole / rifabutin and fosphenytoin

MONITOR: Omeprazole may increase phenytoin serum concentrations and the risk of toxicity. The proposed mechanism is decreased clearance due to omeprazole-mediated inhibition of CYP450 2C19. Omeprazole may interact in a similar manner with other hydantoins. The clinical significance is unknown; however, higher omeprazole doses (more than 40 mg/day) may be more likely to interact.

MANAGEMENT: Clinical and laboratory monitoring may be appropriate whenever omeprazole is added to or withdrawn from therapy with phenytoin. Dosage adjustments may be considered if an interaction is suspected. Patients should be advised to notify their doctor if they experience symptoms of phenytoin toxicity (e.g., drowsiness, visual disturbances, change in mental status, seizures, nausea, or ataxia).

References (6)
  1. Andersson T (1991) "Omeprazole drug interaction studies." Clin Pharmacokinet, 21, p. 195-212
  2. Gugler R, Jensen JC (1985) "Omeprazole inhibits oxidative drug metabolism: studies with diazepam and phenytoin in vivo and 7-ethoxycoumarin in vitro." Gastroenterology, 89, p. 1235-41
  3. Prichard PJ, Walt RP, Kitchingman GK, et al. (1987) "Oral phenytoin pharmacokinetics during omeprazole therapy." Br J Clin Pharmacol, 24, p. 543-5
  4. (2022) "Product Information. PriLOSEC (omeprazole)." Merck & Co., Inc
  5. Cerner Multum, Inc. "UK Summary of Product Characteristics."
  6. Cerner Multum, Inc. "Australian Product Information."
Moderate

rifabutin fosphenytoin

Applies to: amoxicillin / omeprazole / rifabutin and fosphenytoin

MONITOR: Rifampin and rifabutin may decrease plasma concentrations and effectiveness of hydantoins by inducing their CYP450 hepatic metabolism.

MANAGEMENT: Close observation for clinical and laboratory evidence of altered hydantoin effect is recommended. Patients should be advised to notify their physician if they experience loss of seizure control. Dosage should be increased as necessary.

References (3)
  1. Venkatesan K (1992) "Pharmacokinetic drug interactions with rifampicin." Clin Pharmacokinet, 22, p. 47-65
  2. Abajo FJ (1988) "Phenytoin interaction with rifampicin." Br Med J, 297, p. 1048
  3. 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

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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