The effect of therapeutic doses of paracetamol on sulphur metabolism in man

Metabolic profiling and population screening of analgesic usage in nuclear magnetic resonance spectroscopy-based large-scale epidemiologic studies

The application of a (1)H nuclear magnetic resonance (NMR) spectroscopy-based screening method for determining the use of two widely available analgesics (acetaminophen and ibuprofen) in epidemiologic studies has been investigated. We used samples and data from the cross-sectional INTERMAP Study involving participants from Japan (n = 1145), China (n = 839), U.K. (n = 501), and the U.S. (n = 2195). An orthogonal projection to latent structures discriminant analysis (OPLS-DA) algorithm with an incorporated Monte Carlo resampling function was applied to the NMR data set to determine which spectra contained analgesic metabolites. OPLS-DA preprocessing parameters (normalization, bin width, scaling, and input parameters) were assessed systematically to identify an optimal acetaminophen prediction model. Subsets of INTERMAP spectra were examined to verify and validate the presence/absence of acetaminophen/ibuprofen based on known chemical shift and coupling patterns. The optimized and validated acetaminophen model correctly predicted 98.2%, and the ibuprofen model correctly predicted 99.0% of the urine specimens containing these drug metabolites. The acetaminophen and ibuprofen models were subsequently used to predict the presence/absence of these drug metabolites for the remaining INTERMAP specimens. The acetaminophen model identified 415 out of 8436 spectra as containing acetaminophen metabolite signals while the ibuprofen model identified 245 out of 8604 spectra as containing ibuprofen metabolite signals from the global data set after excluding samples used to construct the prediction models. The NMR-based metabolic screening strategy provides a new objective approach for evaluation of self-reported medication data and is extendable to other aspects of population xenometabolome profiling.

Acetaminophen misconceptions

Examination of the pharmacokinetics of acetaminophen can decrease misconceptions involved in clinical evaluation. Enzyme patterns and acetaminophen levels must be related to time and known metabolic phenomena. A careful look at ethanol and nutrition, especially fasting demonstrates that therapeutic doses of acetaminophen do not place patients at a greater risk in either of these instances. An overdose of acetaminophen in a chronic alcohol abuser may result in more severe hepatotoxicity than in the nonalcoholic. CYP2E1 and glutathione must be evaluated simultaneously rather than in isolation. Glucuronidation capacity in humans is not a factor except in massively overdosed patients.

Inhibition of DNA synthesis by paracetamol in different tissues of the rat in vivo

DNA synthesis in the spleen, testis, thymus, stomach, small intestine and bone marrow was inhibited by 70-90% at 1 h following an oral dose of paracetamol (1 g/kg). This inhibitory effect was still apparent using a lower dose of 125 mg/kg paracetamol, but not when the dose was reduced to 60 mg/kg. In contrast, the liver was resistant to the inhibitory action of paracetamol on DNA synthesis, there being no significant inhibition of DNA synthesis at 500 mg/kg or 1 g/kg paracetamol. These doses and the associated plasma levels are in the range found in human overdose. Tissue levels of paracetamol in the liver, spleen, thymus, kidney and testis were essentially the same as the plasma level. However the apparent paracetamol tissue levels in the stomach wall and duodenum were orders of a magnitude higher than the plasma level. The tissue levels of paracetamol did not explain the differences between tissues in the degree of inhibition of DNA synthesis, in particular the high levels of paracetamol in the tissue of the stomach and duodenum did not result in higher levels of inhibition in these tissues. This study also shows that the inhibitory effect of paracetamol on DNA synthesis is transient. All the tissues, except the spleen, no longer showed inhibition of DNA synthesis by 4 h post paracetamol dosing.

Cell injury and protection in long-term incubation of liver slices after in vivo initiation with paracetamol: cell injury after in vivo initiation with paracetamol

Short-term in vitro methods (2-6 h) for study of cell injury by paracetamol are often used but, in vivo, injury is not apparent until 12 h or later. Many agents which protect in the short-term in vitro systems, such as fructose and glycerol which are effective, even in the late phase, after paracetamol has initiated injury, do not provide any protection in vivo. We have extended the in vitro liver slice system to a more realistic 18 h. Secondly, we have initiated injury with paracetamol in vivo, then followed the progression of injury in an in vitro system. Control liver slices incubated in a HEPES Ringer solution with antibiotics over 18 h show little sign of injury as demonstrated by leakage of lactate dehydrogenase (LDH) into the medium or loss of potassium. Liver slices exposed to 10 mM paracetamol for 2 h in vitro show extensive LDH leak at 6 h which is even more severe at 18 h. Liver slices from animals treated with paracetamol (1 g/kg i.p.) in vivo for 3 h show little LDH leakage at 6 h in vitro but by 18 h injury is very apparent. Fructose and glycerol which protect against paracetamol injury in the short-term (6-h) in vitro system, do not do so when observations are extended to 18 h. They also fail to provide any protection to the slice from animals pre-treated in vivo with paracetamol. Other agents show similar affects. There is no convincing evidence that these short-term protective agents afford any protection in vivo and we show that ibuprofen and dexamethasone do not protect in vivo. It is clear that short-term assays for cell protection have only a limited explanatory value.