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https://ntp.niehs.nih.gov/go/10203

Primidone (primaclone): Target Organs and Levels of Evidence for TR-476

Toxicology and Carcinogenesis Studies of Primidone (CASRN 125-33-7) in F344/N Rats and B6C3F1 Mice (Feed Studies)

Chemical (Study Title)
CASRN		Peer Review DateRoute/Exposure LevelsStudy Laboratory
Primidone (primaclone)
125-33-7		12/12/1996Dosed-Feed
M: 0, 0.03, 0.06, OR 0.13% R: 0, 0.06, 0.13, OR 0.25% (50/SEX/SPECIES)		Battelle Columbus Laboratory

Levels of Evidence

Male Rats: Equivocal Evidence
TypeOrgan/Tissue (Lesion)
Neoplastic Lesions
  • Thyroid Gland Follicular Cell: ADENOMA 1/50 1/50 6/49 3/49 OR CARCINOMA 1/50 3/50 1/49 1/49 COMBINED 2/50 4/50 7/49 4/49
  • Kidney Tubular Cell: (SINGLE SECTIONS) ADENOMA 2/50 1/50 1/50 1/50 OR CARCINOMA 0/50 0/50 0/50 1/50 COMBINED 2/50 1/50 1/50 2/50; (SINGLE AND STEP SECTIONS) ADENOMA 4/50 2/50 4/50 6/50 OR CARCINOMA 0/50 0/50 0/50 1/50 COMBINED 4/50 2/50 4/50 7/50
Non-Neoplastic Lesions
  • LIVER: CYTOPLASMIC VACUOLIZATION; CENTRILOBULAR HYPERTROPHY
  • KIDNEY: INCREASED SEVERITY OF NEPHROPATHY; RENAL TUBULE HYPERPLASIA
Female Rats: No Evidence
TypeOrgan/Tissue (Lesion)
Non-Neoplastic Lesions
  • LIVER: CYTOPLASMIC VACUOLIZATION; CENTRILOBULAR HYPERTROPHY; EOSINOPHILIC FOCUS
Male Mice: Clear Evidence
TypeOrgan/Tissue (Lesion)
Neoplastic Lesions
  • Liver: ADENOMA 22/50 41/50 39/50 32/50, CARCINOMA 12/50 31/50 35/50 38/50 OR HEPATOBLASTOMA 0/50 17/50 26/50 7/50 COMBINED 31/50 49/50 49/50 46/50
  • Thyroid Gland Follicular Cell: ADENOMA 0/49 3/48 3/50 6/50
Non-Neoplastic Lesions
  • LIVER: CENTRILOBULAR HYPERTROPHY
  • THYROID GLAND: FOLLICULAR CELL HYPERPLASIA
Female Mice: Clear Evidence
TypeOrgan/Tissue (Lesion)
Neoplastic Lesions
  • Liver: ADENOMA 15/50 42/50 45/49 47/50, CARCINOMA 3/50 11/50 19/49 38/50 OR HEPATOBLASTOMA 1/50 4/50 4/49 4/50 COMBINED 16/50 42/50 46/49 50/50
Non-Neoplastic Lesions
  • LIVER: CENTRILOBULAR HYPERTROPHY; CYTOPLASMIC VACUOLIZATION; EOSINOPHILIC FOCUS
  • THYROID GLAND: FOLLICULAR CELL HYPERPLASIA