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After oral application of aminophenazone to animals (170 and 340 mg/kg daily, over up to 17 weeks), the authors investigated the effect of this drug on some liver functions and performed also a morphological study. They found that aminophenazone produces an increase of the smooth ER, peripheral fatty degradation and reactive-inflammatory responses of the liver, the intensity of these phenomena being dependent upon the dose and time of application. The increase of the smooth ER is the expression of the inductive effect which persists throughout the whole experimental period and manifests itself by accelerated degradation of hexobarbital, increased N-demethylation, increased ascorbic acid synthesis and increased liver weight. The increase in body weight is reduced in the animals treated. The enzyme activities in the plasma lie within the range observed with control animals; they are no indicator of the slight live changes stated. Reactive metabolites and/or the impairment of other metabolic reactions may be considered to be the cause of the hepatotoxic effect of aminophenazone.

Morphological studies by means of light microscopy are important for toxicological drug testing. More complete information on potential damage can be obtained only by combination of pharmacological, biochemical, hepatofunctional, and morphological tests and studies. No systematic tests had been applied to rats, in the past. Therefore, aminophenazone, phenazone, and propyphenazone were tested for periods up to 16 weeks. Long-term application of the three pyrazolone derivatives resulted in the following dose-dependent and time-dependent alterations: hepatocyte enlargement, fatty degeneration and reactive-inflammatory changes along with single-cell necrosis, round cellular infiltration of periportal fields, and Kupffer cell activation. The alterations differed in intensity by the following order: aminophenazone greater than phenazone greater than propyphenazone.