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Phenytoin

CHEMBL16 Phase 4 承認済み Small molecule
Half-Life
22 hours
Bioavailability
—
Protein Binding
—
Molecular Weight
252.3 g/mol
LogP
2.5
Phase
4

Controlling seizures through blockade of voltage-gated sodium channels, phenytoin stabilizes those channels in their inactivated form and thereby suppresses the sustained, high-frequency firing that propagates epileptic activity. It is used to prevent and manage several seizure types. What most defines its clinical handling is a narrow therapeutic index: the gap between an effective concentration and a toxic one is small, and its elimination shifts from proportional to saturable as levels rise, so modest dose changes can produce large swings in blood concentration. Regular level monitoring accompanies its use for this reason. A hydantoin small molecule (C15H12N2O2) with a representative half-life near 22 hours, phenytoin is an approved, long-standing antiepileptic that remains important for acute and chronic seizure control.

A medication used to prevent and control seizures in epilepsy by stabilizing the electrical activity in the brain. It requires careful dosing and regular blood level monitoring because the difference between an effective dose and a toxic dose is narrow.

分子量

252.2680 g/mol

LogP

2.50

TPSA

58.20 Ų

リピンスキーの五則

適合

治療領域

Pancreatic Cancer Glaucoma Pain Management Asthma Epilepsy Schizophrenia Generalized Anxiety Disorder Multiple Sclerosis Non-Alcoholic Fatty Liver Disease Stroke Lymphoma Breast Cancer Chronic Pain Prostate Cancer Leukemia

薬物分類

N — N - Nervous System

作用機序

Sodium channel blocker stabilizing inactive state.

Pharmacokinetics (PK)

Half-Life 22 hours

Pharmacodynamics (PD)

機序

Sodium channel blocker stabilizing inactive state.

2D構造

SVG PNG

Cite this structure


                        

                            
                            
                        

                    

                


                
                

                    

                    

                        
Embed this structure

                        

                        

                            
                            
                        

                    

                

                

                
                

                    
SMILES

                    
O=C1NC(=O)C(c2ccccc2)(c2ccccc2)N1

                

                

                
                

                    
InChI

                    
InChI=1S/C15H12N2O2/c18-13-15(17-14(19)16-13,11-7-3-1-4-8-11)12-9-5-2-6-10-12/h1-10H,(H2,16,17,18,19)

                

                

                

                    
                    

                        
Molecular Formula

                        
C15H12N2O2

                    

                    
                    

                        
HBD / HBA

                        
2 / 2

                    

                    
                    

                        
回転可能結合数

                        
2

                    

                    
                    
                    

                        
重原子数

                        
19

                    

                    
                

            


            
            

                
                

                    
                    

                        

                            SCN9A (Sodium Channel Nav1.7)
                            Blocker
                        

                        
                        Primary Target
                        
                    

                    
                    

                        

                            CYP3A4 (Cytochrome P450 3A4)
                            Inducer
                        

                        
                    

                    
                    

                        

                            ABCB1 (P-glycoprotein)
                            Substrate
                        

                        
                    

                    
                

                
            


            
            

                
                

                    
                    
                        

                            

  
  Major


                            
                                Phenytoin + Tacrolimus
                            
                        

                        
                        
Phenytoin is a strong CYP3A4 inducer that can reduce tacrolimus exposure by more than 50%, putting transplant patients at risk for graft rejection.

                        
                    
                    
                    
                        

                            

  
  Major


                            
                                Phenytoin + Quetiapine
                            
                        

                        
                        
Phenytoin drastically reduces quetiapine plasma levels through potent CYP3A4 induction, risking complete loss of antipsychotic effect.

                        
                    
                    
                    
                        

                            

  
  Major


                            
                                Phenytoin + Warfarin
                            
                        

                        
                        
Phenytoin and warfarin have a complex bidirectional interaction: phenytoin initially inhibits warfarin metabolism (raising INR) but then induces it (lowering INR), making anticoagulation management unpredictable.

                        
                    
                    
                    
                        

                            

  
  Minor


                            
                                Phenytoin + Ranitidine
                            
                        

                        
                        
Ranitidine may slightly increase phenytoin bioavailability through modest inhibition of CYP2C9, though the interaction is less significant than with cimetidine.

                        
                    
                    
                    
                        

                            

  
  Moderate


                            
                                Phenytoin + Topiramate
                            
                        

                        
                        
Phenytoin reduces topiramate plasma levels via enzyme induction, potentially compromising seizure control when topiramate is added to phenytoin therapy.

                        
                    
                    
                    
                        

                            

  
  Moderate


                            
                                Phenytoin + Valproic Acid
                            
                        

                        
                        
Valproic acid displaces phenytoin from protein binding and inhibits its metabolism, leading to increased free phenytoin levels despite total levels that may appear unchanged or decreased.

                        
                    
                    
                    
                        

                            

  
  Moderate


                            
                                Phenytoin + Sertraline
                            
                        

                        
                        
Phenytoin significantly reduces sertraline plasma concentrations via CYP enzyme induction, potentially causing antidepressant treatment failure.

                        
                    
                    
                    
                        

                            

  
  Minor


                            
                                Phenytoin + Montelukast
                            
                        

                        
                        
Phenytoin, a potent CYP inducer, can increase the metabolism of montelukast, potentially reducing its plasma levels and therapeutic efficacy.

                        
                    
                    
                    
                        

                            

  
  Moderate


                            
                                Phenytoin + Carbamazepine
                            
                        

                        
                        
Carbamazepine and phenytoin have complex bidirectional interactions that can alter plasma levels of either drug in unpredictable ways.

                        
                    
                    
                    
                        

                            

  
  Moderate


                            
                                Phenytoin + Acyclovir
                            
                        

                        
                        
Acyclovir has been associated with reduced phenytoin plasma concentrations in some patients, potentially compromising seizure control during antiviral therapy.

                        
                    
                    
                    
                        

                            

  
  Moderate


                            
                                Phenytoin + Dexamethasone
                            
                        

                        
                        
Phenytoin induces CYP3A4-mediated metabolism of dexamethasone, significantly reducing dexamethasone plasma concentrations and risking loss of efficacy (e.g., in cerebral edema or cancer treatment).

                        
                    
                    
                    
                        

                            

  
  Moderate


                            
                                Phenytoin + Acetaminophen
                            
                        

                        
                        
Phenytoin induces hepatic CYP enzymes that increase the formation of acetaminophen's toxic metabolite NAPQI, raising hepatotoxicity risk; conversely, large doses of acetaminophen may transiently reduce phenytoin levels.

                        
                    
                    
                

                
            


            
            

                
                


    
    
        
    
    
    
No side effects recorded

    
    
Side effect data is not yet available for this drug.

    



                
            


            
            
            

                
よくある質問

                

                    
                    

                        
                        

                            
A medication used to prevent and control seizures in epilepsy by stabilizing the electrical activity in the brain. It requires careful dosing and regular blood level monitoring because the difference between an effective dose and a toxic dose is narrow.

                        

                    

                    

                    

                    
                    

                        
                        

                            
Sodium channel blocker stabilizing inactive state.

                        

                    

                    

                    
                    

                        
                        

                            
Key pharmacokinetic parameters for Phenytoin: Half-life: 22 hours.

                        

                    

                    

                    

                        
                        

                            
Yes, Phenytoin is an approved drug. It has reached clinical phase 4. It is classified as a Small molecule.

                        

                    

                

            

            

            
            

            
            
            

                
Related Drugs


                
                

                    
Same Drug Class

                    

                        
                        
                            Acetaminophen
                            Small molecule
                        
                        
                        
                            Aspirin
                            Small molecule
                        
                        
                        
                            Sertraline
                            Small molecule
                        
                        
                        
                            Escitalopram
                            Small molecule
                        
                        
                    

                

                

                
                
                
            

            

            
            
{# References & Data Sources section for drug detail pages.
   Renders standard pharmacological database links plus the drug's data_sources field. #}


    
References & Data Sources

    
    
        
        
  • 
            
            
                ChEMBL — European Bioinformatics Institute (EBI).
                CHEMBL16.
                Open-access bioactivity database.
            
        
    • 
        
        
        
  • 
            
            
                PubChem — National Center for Biotechnology Information (NCBI).
                CID 1775.
                Chemical information database.
            
        
    • 
        
        
        
        
    

    
Data aggregated from publicly available pharmacological databases. Last updated 2026-03-28.




        


        
        
    


    



    
医学的免責事項

    

        This content is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making medication decisions.
    

    

        Data sources:
        ChEMBL,
        PubChem,
        DailyMed.