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PubMed1976

The role of biotransformation in chemical-induced liver injury.

The role of drug metabolism in chemical-induced liver injury is reviewed. Parameters for studying the formation of chemically reactive metabolites are discussed and the factors that alter the formation and covalent binding of reactive metabolites are selectively emphasized. Some of the experimental work that led to these concepts is discussed, especially the chemical toxicology of the hepatic injury produced by acetaminophen, bromobenzene, furosemide, isoniazid and iproniazid.

Acetaminophen↗
PubMed1984

Combined and individual effects of isoniazid and thiacetazone on human lymphocyte chromosomes in vitro and in vivo.

Genetic effects of the drugs, isoniazid and thiacetazone used for antituberculosis chemotherapy were investigated on human lymphocyte chromosomes in vitro and in vivo. Therapeutic concentrations of these drugs did not induce chromosome aberrations in vitro both in combination and individually during any of the treatment period in 72 h lymphocyte cultures. At higher concentrations both the drugs were found to be cytotoxic. The frequency of chromosome damage was increased significantly in first-division metaphases of the patients, i.e. in vivo during treatment with isoniazid (300 mg) + thiacetazone (150 mg); this could be due to the synergistic action between the metabolites of the two drugs in the body or due to the metabolites of thiacetazone since isoniazid was found to be nonclastogenic in vivo. The frequency of sister chromatid exchanges was not increased in any of the patients except in one, who probably had a higher baseline level. These results suggest that chromosome aberrations and sister chromatid exchanges represent two different lesions. Chromosome damage induced by drugs could lead to congenital malformations, cancer, ageing and therefore contributes to the overall toxicology of the drugs and hazard to human genetic health. Hence drugs like isoniazid and thiacetazone which induce chromosome damage, should be used with caution.

Cell Division↗
PubMed1983

Physiological factors affecting drug toxicity.

Physiological factors that affect the fate of drugs in the body and thereby have effects on their pharmacology and toxicology involve the systems that control absorption, distribution, metabolism, and excretion. The main factors are disease, genetics, and age. Nutritional status, sex, hormonal status (e.g., the effects of pregnancy), and circadian rhythm have important influences. Maternal toxicity will affect the fetus. The absorption and excretion of drugs are frequently reduced by diseases. Excretion is reduced by impaired renal function, often found in the elderly, which may increase the toxic response. Distribution is affected by body weight and build, for example, the proportion of fat. The disposition of many drugs has been shown to be significantly influenced by circadian rhythms such that therapeutic doses may exhibit toxicity if administered at an inappropriate time of day. Metabolism is modified by environmental influences including previous food and drug experience, and various factors such as age, sex, and disease. Intersubject variations in drug disposition can be very great with possibly severe consequences for the individual; in this regard, knowledge of genetic polymorphism in drug metabolizing enzymes is rapidly increasing. The toxicology of a drug may be profoundly affected by a particular disease state, for example, the administration of a drug that might be a tumor promoter when a cancerous or precancerous condition exists. These effects are illustrated with examples from the literature and recent studies undertaken in the Bureau of Drug Research.

Acetylation↗
PubMed1995

Stable expression of human cytochrome P450 2E1 in V79 Chinese hamster cells.

A V79 Chinese hamster cell line was constructed for stable expression of human cytochrome P450 2E1 (CYP2E1) by integration of a SV40 Early promoter recombinant CYP2E1 cDNA into the chromosomal DNA. The cDNA encoded CYP2E1 was effectively expressed and enzymatically active, as shown by hydroxylation of chlorzoxazone and of p-nitrophenol, at rates of about 70 pmol x mg-1 total protein x min-1. CYP2E1 content and activity was increased upon cultivation in the presence of ethanol indicating a substrate mediated stabilization effect. A similar stabilizing effect was also observed for inhibitors of CYP2E1, e.g. imidazole, 4-methylpyrazole, and isoniazid. The feasibility of the newly established cell line V79MZh2E1 for toxicological studies was shown by CYP2E1-mediated activation of N-nitrosodimethylamine and p-nitrophenol and a dose-dependent cytotoxic and mutagenic effect.

Animals↗
PubMed2003

[Acute pharmacologic poisoning (II). Analgesics and anticonvulsants].

In this second chapter on Acute Drugs Poisoning we deal with two groups of substances of great transcendence from the point of view of their use and morbidity/mortality. Within the group of analgesic-anti-inflammatory drugs we consider paracetamol and the salicylates, which are easily available to the population. With respect to the anticonvulsants, although they are barely involved in the ensemble of acute drug poisonings, their effects can be serious. We concentrate on four drugs: valproic acid, phenobarbitol, carbamacepine, and phenytoin. Finally, a section is dedicated to isoniazid, a drug that, with the renewed incidence of tuberculosis, is of toxicological interest.

Acute Disease↗