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Study Information
Study Attribute Value
CEBS Accession Number: 002-02966-0001-0000-6
Chemical Name: Trimethoprim
CASRN: 738-70-5
NTP Study Type: Genetic Toxicology - Mammalian Cell Cytogenetics
NTP Study ID: 522207_SCE
Study Result: Weakly Positive

Study Result: Weakly Positive
Activation Trial Trial Call
No Activation  1  Negative 
Induced Rat Liver S9  1_S9  Weakly 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 Trimethoprim 
8         
 50 1048 519 0.495 10.38 26.0 3.189 
26         
 50 1049 501 0.478 10.02 26.0 -0.485 
80         
 50 1050 454 0.432 9.08 26.0 -9.906
Positive Control Triethylenemelamine 
 0.015     
 50 1048 1611 1.537 32.22 26.0 220.304
Trend: -1.684        
Probability: 0.954        

Trial #: 1_S9    Activation: Induced Rat Liver S9    Date: 08/13/1981    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 1045 395 0.378 7.90 26.0 0.000
Test Chemical Trimethoprim 
80         
 50 1050 469 0.447 9.38 26.0 18.169 
260         
 50 1045 458 0.438 9.16 26.0 15.949 
800         
 50 1042 514 0.493 10.28 26.0 30.501
Positive Control Cyclophosphamide 
1         
 50 1050 1291 1.230 25.82 26.0 225.279
Trend: 3.669        
Probability: 0.000