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Study Information
Study Attribute Value
CEBS Accession Number: 002-01525-0001-0000-6
Chemical Name: 5,5-Diphenylhydantoin (phenytoin)
CASRN: 57-41-0
NTP Study Type: Genetic Toxicology - Mammalian Cell Cytogenetics
NTP Study ID: 335957_SCE
Study Result: Positive

Study Result: Positive
Activation Trial Trial Call
No Activation  1  Negative 
Induced Rat Liver S9  1_S9  Positive 

Trial #: 1    Activation: No Activation    Date: 08/13/1981    Trial Call: Negative   
  Dose
µg/mL		 Number
Cells
Examined		 Number
Chromosomes
Examined		 Total
Number
SCEs		 SCE /
Chromosome		 SCE /
Cell		 Hours in
BRDU		 % Increase
Over Solvent
Control
Vehicle Control Dimethyl Sulfoxide 
0         
 50 1046 502 0.480 10.04 26.0 0.000
Test Chemical 5,5-Diphenylhydantoin (phenytoin) 
16         
 50 1044 525 0.503 10.50 26.0 4.782 
50         
 50 1047 503 0.480 10.06 26.0 0.104 
160         
 50 1043 486 0.466 9.72 26.0 -2.909
Positive Control Triethylenemelamine 
 0.015     
 50 1048 1611 1.537 32.22 26.0 220.304
Trend: -0.669        
Probability: 0.748        

Trial #: 1_S9    Activation: Induced Rat Liver S9    Date: 08/13/1981    Trial Call: Positive   
  Dose
µg/mL		 Number
Cells
Examined		 Number
Chromosomes
Examined		 Total
Number
SCEs		 SCE /
Chromosome		 SCE /
Cell		 Hours in
BRDU		 % Increase
Over Solvent
Control
Vehicle Control Dimethyl Sulfoxide 
0         
 50 1045 395 0.378 7.90 26.0 0.000
Test Chemical 5,5-Diphenylhydantoin (phenytoin) 
16         
 50 1048 448 0.427 8.96 26.0 13.093 
50         
 50 1049 473 0.451 9.46 26.0 19.290 
160         
 50 1048 475 0.453 9.50 26.0 19.909 
1600         
 50 1037 488 0.471 9.76 28.0 24.497 
5000         
 50 1046 485 0.464 9.70 28.0 22.667
Positive Control Cyclophosphamide 
1         
 50 1050 1291 1.230 25.82 26.0 225.279
Trend: 3.188        
Probability: 0.001