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Study Information
Study Attribute Value
CEBS Accession Number: 002-01525-0012-0000-8
Chemical Name: 5,5-Diphenylhydantoin (phenytoin)
CASRN: 57-41-0
NTP Study Type: Genetic Toxicology - Mammalian Cell Mutagenicity
NTP Study ID: 404495
Study Result: Negative


Table Instructions and Notes:
Studies are indicated to be "Nontoxic" when the observed reductions in relative total growth did not indicate that the maximum tolerated dose was achieved.

Nonactivation Trial: 1 Experiment Call: Negative
  Conc.
ug/mL 		Cloning
Efficiency 		Relative Total
Growth 		Mutant Colonies Mutant Frequency Avg Mutant Frequency
Vehicle Control Dimethyl Sulfoxide 
 0         
 70 104 65 31 26
    83 112 44 18
    73 94 63 29
    84 90 69 27
Test Chemical 5,5-Diphenylhydantoin (phenytoin) 
31.25      
 59 84 46 26 28
    70 96 61 29
  
62.5       
 75 84 84 37 34
    69 84 62 30
  
125         
 57 52 51 30 33
    54 46 58 36
  
250         
 50 32 74 50 36
    47 32 30 21
  
500         
 56 31 58 35 30
    46 13 35 25
Positive Control Methyl Methane Sulfonate 
15         
 46 39 106 77 88*
    35 35 103 99
Methyl Methane Sulfonate 
250         
 34 47 271 266 270*
    37 42 304 274

Nonactivation Trial: 2 Experiment Call: Positive
  Conc.
ug/mL 		Cloning
Efficiency 		Relative Total
Growth 		Mutant Colonies Mutant Frequency Avg Mutant Frequency
Vehicle Control Dimethyl Sulfoxide 
 0         
 74 89 84 38 38
    85 106 121 48
    85 98 90 35
    99 106 92 31
Test Chemical 5,5-Diphenylhydantoin (phenytoin) 
15         
 76 95 101 44 43
    76 100 96 42
  
30         
 78 88 99 42 38
    78 79 80 34
  
60         
 70 74 112 54 53
    65 60 103 53
  
120         
 52 35 91 58 53
    58 21 83 48
  
240         
 58 22 169 96 90*
    65 29 162 84
Positive Control Methyl Methane Sulfonate 
15         
 29 17 169 195 205*
    31 19 199 214
Methyl Methane Sulfonate 
250         
 57 52 540 316 312*
    68 62 631 308

Nonactivation Trial: 3 Experiment Call: Negative
  Conc.
ug/mL 		Cloning
Efficiency 		Relative Total
Growth 		Mutant Colonies Mutant Frequency Avg Mutant Frequency
Vehicle Control Dimethyl Sulfoxide 
 0         
 52 85 65 41 40
    50 74 80 53
    81 124 75 31
    78 118 77 33
Test Chemical 5,5-Diphenylhydantoin (phenytoin) 
17.5       
 41 58 62 51 53
    50 77 82 55
  
35         
 46 73 46 33 40
    49 72 70 47
  
70         
 64 68 62 33 37
    72 54 91 42
  
140         
 67 36 56 28 34
    66 31 79 40
  
280         
 73 32 76 35 39
    58 28 74 43
Positive Control Methyl Methane Sulfonate 
20         
 7r 4 139 647
    6r 4 113 611
Methyl Methane Sulfonate 
250         
 56 58 648 387 387*
    48 53 555 388

Nonactivation Trial: 4 Experiment Call: Negative
  Conc.
ug/mL 		Cloning
Efficiency 		Relative Total
Growth 		Mutant Colonies Mutant Frequency Avg Mutant Frequency
Vehicle Control Dimethyl Sulfoxide 
 0         
 86 90 58 22 24
    116 88 105 30
    95 114 64 22
    106 107 61 19
Test Chemical 5,5-Diphenylhydantoin (phenytoin) 
17.5       
 102 105 75 25 28
    93 77 89 32
  
35         
 107 85 98 31 27
    101 79 73 24
  
70         
 101 78 70 23 30
    114 85 125 37
  
140         
 90 27 86 32 32
    77 22 74 32
  
280         
 88 12 69 26 26
    85 11 67 26
Positive Control Methyl Methane Sulfonate 
15         
 29 17 219 249 241*
    37 18 256 234

Induced S9 Trial: 1 Experiment Call: Negative
  Conc.
ug/mL 		Cloning
Efficiency 		Relative Total
Growth 		Mutant Colonies Mutant Frequency Avg Mutant Frequency
Vehicle Control Dimethyl Sulfoxide 
 0         
 84 103 88 35 32
    83 104 68 27
    86 94 84 32
    70 99 72 35
Test Chemical 5,5-Diphenylhydantoin (phenytoin) 
18.75      
 83 85 80 32 32
    84 94 80 32
  
37.5       
 72 112 64 30 29
    76 106 66 29
  
75         
 86 80 88 34 35
    72 58 79 37
  
150         
 73 48 76 35 29
    89 43 60 23
  
300         
 78 15 74 32 28
    63 14 47 25
Positive Control 3-Methylcholanthrene 
2.5       
 50 32 477 319 360*
    41 28 490 400

Induced S9 Trial: 2 Experiment Call: Negative
  Conc.
ug/mL 		Cloning
Efficiency 		Relative Total
Growth 		Mutant Colonies Mutant Frequency Avg Mutant Frequency
Vehicle Control Dimethyl Sulfoxide 
 0         
 76 91 50 22 25
    90 103 118 44
    81 98 47 19
    75 108 31 14
Test Chemical 5,5-Diphenylhydantoin (phenytoin) 
50         
 102 123 64 21 24
    82 107 66 27
  
100         
 74 49 56 25 26
    85 31 70 28
  
150         
 99 34 55 19 19
    64 21 36 19
  
200         
 81 66 47 19 24
    96 51 85 30
  
250         
 93 41 58 21 28
    90# 66 96 35
  
300         
 59 22 68 38 33
    69 32 56 27
  
350         
 79# 21 108 46 36
    88 26 70 26
Positive Control 3-Methylcholanthrene 
2.5       
 66 43 479 241 223*
    56 36 344 205

Footnotes:
Asterisks(*) indicate significant responses.
r = rejected value due to quality control criteria
# = reduced sample size because of the loss of one culture dish due to contamination