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Study Information
Study Attribute Value
CEBS Accession Number: 002-02966-0003-0000-8
Chemical Name: Trimethoprim
CASRN: 738-70-5
NTP Study Type: Genetic Toxicology - Mammalian Cell Cytogenetics
NTP Study ID: 811628_SCE
Study Result: Positive

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

Trial #: 1    Activation: No Activation    Date: 03/21/1981    Trial Call:   
  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 Negative (Not Specified) 
0         
 50 1025 410 0.400 8.20 26.5 -25.989
Dimethyl Sulfoxide 
0         
 50 1038 561 0.540 11.22 26.5 0.000
Test Chemical Trimethoprim 
16.67      
 50 1026 480 0.468 9.60 26.5 -13.438 
55         
 50 1037 566 0.546 11.32 26.5 0.989 
166.7       
 50 1016 517 0.509 10.34 26.5 -5.848 
550         
 0 0 0 0.000 0.00 31.0 N/A
Positive Control Triethylenemelamine 
 0.015     
 50 1039 1946 1.873 38.92 26.5 246.547
Trend: -0.154        
Probability: 0.561        

Trial #: 2    Activation: No Activation    Date: 04/19/1981    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         
 14 265 136 0.513 9.71 26.0 0.000
Negative (Not Specified) 
0         
 50 1002 474 0.473 9.48 26.0 -7.824
Test Chemical Trimethoprim 
200         
 50 1040 658 0.633 13.16 32.0 23.282 
300         
 46 940 608 0.647 13.22 32.0 26.033 
350         
 50 1028 628 0.611 12.56 32.0 19.035 
400         
 0 0 0 0.000 0.00 32.0 N/A 
450         
 0 0 0 0.000 0.00 32.0 N/A 
600         
 0 0 0 0.000 0.00 32.0 N/A
Positive Control Triethylenemelamine 
 0.015     
 50 1040 2625 2.524 52.50 26.0 391.816
Trend: 0.896        
Probability: 0.185        

Trial #: 1_S9    Activation: Induced Rat Liver S9    Date: 03/25/1981    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 1029 460 0.447 9.20 26.0 0.000
Negative (Not Specified) 
0         
 50 1022 446 0.436 8.92 26.0 -2.379
Test Chemical Trimethoprim 
55         
 50 1036 448 0.432 8.96 26.0 -3.267 
166.7       
 50 1028 414 0.403 8.28 26.0 -9.912 
550         
 50 1035 435 0.420 8.70 26.0 -5.983
Positive Control Cyclophosphamide 
1.5       
 50 1046 1246 1.191 24.92 26.0 166.467
Trend: -1.194        
Probability: 0.884        

Trial #: 2_S9    Activation: Induced Rat Liver S9    Date: 04/19/1981    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 Negative (Not Specified) 
0         
 50 1024 456 0.445 9.12 26.3 -15.298
Dimethyl Sulfoxide 
0         
 13 641 337 0.526 25.92 26.3 0.000
Test Chemical Trimethoprim 
300         
 50 1037 545 0.526 10.90 26.3 -0.035 
400         
 50 1034 560 0.542 11.20 26.3 3.014 
500         
 50 1028 600 0.584 12.00 26.3 11.016 
600         
 0 0 0 0.000 0.00 0.0 N/A
Positive Control Cyclophosphamide 
2         
 50 1031 1410 1.368 28.20 26.3 160.129
Trend: 1.754        
Probability: 0.040