Phenytoin
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Anticonvulsant
Phenytoin
Dilantin
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Interactions
Pharmacogenomic + mechanism interactions
Pharmacogenomic guideline recommendationsCPIC and Dutch Pharmacogenetics Working Group clinical guidelines
CPIC rec 8094759 [Strong]: If patient is phenytoin-naive, do not use phenytoin/fosphenytoin. Avoid carbamazepine and oxcarbazepine. CPIC pair-level A (CYP2C9, HLA-B and Phenytoin) [PMID 25099164, 32779747] FDA labeling (Warnings and Precautions, Use in Specific Populations, Clinical Pharmacology)
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CPIC rec 8094759 [Strong]: If patient is phenytoin-naive, do not use phenytoin/fosphenytoin. Avoid carbamazepine and oxcarbazepine. CPIC pair-level A (CYP2C9, HLA-B and Phenytoin) [PMID 25099164, 32779747]
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CPIC rec 8094760 [Strong]: If patient is phenytoin-naive, do not use phenytoin/fosphenytoin. Avoid carbamazepine and oxcarbazepine. CPIC pair-level A (CYP2C9, HLA-B and Phenytoin) [PMID 25099164, 32779747] FDA labeling (Warnings and Precautions, Use in Specific Populations, Clinical Pharmacology)
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CPIC rec 8094762 [Strong]: If patient is phenytoin-naive, do not use phenytoin/fosphenytoin. Avoid carbamazepine and oxcarbazepine. CPIC pair-level A (CYP2C9, HLA-B and Phenytoin) [PMID 25099164, 32779747] FDA labeling (Warnings and Precautions, Use in Specific Populations, Clinical Pharmacology)
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CPIC rec 8094756 [Strong]: For first dose, use typical initial or loading dose. For subsequent doses use approximately 50% less than typical maintenance dose. Subsequent doses should be adjusted according to therapeutic drug monitoring, response, and side effects. An HLA-B*15:02 negative test does not eliminate the risk of phenytoin-induced SJS/TEN, and patients should be carefully monitored according to a usual standard. CPIC pair-level A (CYP2C9, HLA-B and Phenytoin) [PMID 25099164, 32779747]
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CPIC rec 8094753 [Strong]: No adjustments needed from typical dosing strategies. Subsequent doses should be adjusted according to therapeutic drug monitoring, response, and side effects. An HLA-B*15:02 negative test does not eliminate the risk of phenytoin-induced SJS/TEN and patients should be carefully monitored according to a usual standard. CPIC pair-level A (CYP2C9, HLA-B and Phenytoin) [PMID 25099164, 32779747]
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CPIC rec 8094755 [Moderate]: For first dose, use typical initial or loading dose. For subsequent doses, use approximately 25% less than typical maintenance dose. Subsequent doses should be adjusted according to therapeutic drug monitoring, response and side effects. An HLA-B*15:02 negative test does not eliminate the risk of phenytoin-induced SJS/TEN, and patients should be carefully monitored according to a usual standard. CPIC pair-level A (CYP2C9, HLA-B and Phenytoin) [PMID 25099164, 32779747]
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CPIC rec 8094754 [Moderate]: No adjustments needed from typical dosing strategies. Subsequent doses should be adjusted according to therapeutic drug monitoring, response and side effects. An HLA-B*15:02 negative test does not eliminate the risk of phenytoin-induced SJS/TEN and patients should be carefully monitored according to a usual standard. CPIC pair-level A (CYP2C9, HLA-B and Phenytoin) [PMID 25099164, 32779747]
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CPIC rec 8094779 [Optional]: If the patient has previously used phenytoin continuously for longer than three months without incidence of cutaneous adverse reactions, cautiously consider use of phenytoin in the future. The latency period for drug-induced SJS/TEN is short with continuous dosing and adherence to therapy (4-28 days), and cases usually occur within three months of dosing. CPIC pair-level A (CYP2C9, HLA-B and Phenytoin) [PMID 25099164, 32779747]
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CPIC rec 8094779 [Optional]: If the patient has previously used phenytoin continuously for longer than three months without incidence of cutaneous adverse reactions, cautiously consider use of phenytoin in the future. The latency period for drug-induced SJS/TEN is short with continuous dosing and adherence to therapy (4-28 days), and cases usually occur within three months of dosing. CPIC pair-level A (CYP2C9, HLA-B and Phenytoin) [PMID 25099164, 32779747]
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Pharmacokinetic mechanismSubstrate / metabolism relationships from primary literature
FDA Drug Interactions Table: strong inducer of CYP3A4.
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Inferred from pharmacokinetic dataMaterialised by the inference engine; provenance shown per row
Phenytoin induces CYP3A4 (inducer_strong, intensity 90); Triazolam is a substrate_major of CYP3A4 (intensity 80). Derived: Triazolam exposure lowered.
Inferred via Enzyme:CYP3A4 (exposure lowered)
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Phenytoin induces CYP3A4 (inducer_strong, intensity 90); Midazolam is a substrate_major of CYP3A4 (intensity 80). Derived: Midazolam exposure lowered.
Inferred via Enzyme:CYP3A4 (exposure lowered)
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Summary
Classes
Anticonvulsant
Common uses
Pharmacy
Pharmacology
Purported mechanism
Sodium channel blocker