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Study Information
Study Attribute Value
CEBS Accession Number: 002-02759-0001-0000-6
Chemical Name: Pyrimethamine
CASRN: 58-14-0
NTP Study Type: Genetic Toxicology - Mammalian Cell Cytogenetics
NTP Study ID: 074874_SCE
Study Result: Weakly Positive

Study Result: Weakly Positive
Activation Trial Trial Call
No Activation  1  Weakly Positive 
No Activation  2  Positive 
Induced Rat Liver S9  1_S9  Negative 

Trial #: 1    Activation: No Activation    Date: 02/24/1983    Trial Call: Weakly 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 1049 428 0.408 8.56 26.0 0.000
Test Chemical Pyrimethamine 
 0.35      
 50 1046 444 0.424 8.88 26.0 4.036 
 0.45      
 50 1045 439 0.420 8.78 26.0 2.963 
 0.55      
 50 1034 472 0.456 9.44 26.0 11.880 
 0.65      
 50 1047 518 0.495 10.36 26.0 21.259 
 0.75      
 50 1042 507 0.487 10.14 26.0 19.254
Positive Control Mitomycin-C 
 0.005     
 25 525 619 1.179 24.76 26.0 188.977
Trend: 3.660        
Probability: 0.000        

Trial #: 2    Activation: No Activation    Date: 05/05/1983    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 1049 399 0.380 7.98 26.0 0.000
Test Chemical Pyrimethamine 
 0.5       
 50 1044 541 0.518 10.82 26.0 36.238 
 0.6       
 50 1048 544 0.519 10.88 26.0 36.471 
 0.7       
 40 821 434 0.529 10.85 26.0 38.979
Positive Control Mitomycin-C 
 0.005     
 25 524 735 1.403 29.40 26.0 268.773
Trend: 4.594        
Probability: 0.000        

Trial #: 1_S9    Activation: Induced Rat Liver S9    Date: 01/26/1983    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 451 0.431 9.02 26.0 0.000
Test Chemical Pyrimethamine 
2         
 50 1043 437 0.419 8.74 26.0 -2.826 
6.4       
 50 1049 446 0.425 8.92 26.0 -1.391 
20         
 50 1046 425 0.406 8.50 26.0 -5.765 
64         
 50 1044 372 0.356 7.44 26.0 -17.359
Positive Control Cyclophosphamide 
1         
 50 1046 800 0.765 16.00 26.0 77.384
Trend: -2.598        
Probability: 0.995