Analgesics and glutathione

Drug Interactions with Paracetamol

Paracetamol (acetaminophen) is one of the most commonly used analgesic antipyretic drugs worldwide, and it is widely available by prescription and over the counter (OTC). Fortunately, few clinically significant drug interactions have been documented. There is probable potentiation of hepatotoxicity following an overdose from the paracetamol metabolite NAPQI by enzyme-inducing drugs. There is considerable controversy regarding the possible interaction with warfarin in its potential to increase its anticoagulant effects because of discrepancies between observational studies and those in healthy volunteers. Otherwise, no serious adverse drug interactions with therapeutic doses of paracetamol have been confirmed in humans. Because the absorption of paracetamol is so dependent on gastric emptying, other drugs that alter gastric emptying can change its pharmacokinetics; but this would not cause serious adverse effects. Although animal experiments have demonstrated that many compounds can modify paracetamol hepatotoxicity, these are unlikely to be important at therapeutic doses.

Tolerability of Paracetamol

The excellent tolerability of therapeutic doses of paracetamol (acetaminophen) is a major factor in the very wide use of the drug. The major problem in the use of paracetamol is its hepatotoxicity after an overdose. Hepatotoxicity has also been reported after therapeutic doses, but critical analysis indicates that most patients with alleged toxicity from therapeutic doses have taken overdoses. Importantly, prospective studies indicate that therapeutic doses of paracetamol are an unlikely cause of hepatotoxicity in patients who ingest moderate to large amounts of alcohol. Controlled clinical trials have found that paracetamol is very well tolerated by the gastrointestinal tract. While variable results have been found in case control studies, most studies have shown no change or a small increase in the relative risk of perforations, ulcer or bleeding in the upper gastrointestinal tract. However, associations between the use of paracetamol and gastrointestinal toxicity, as well as with chronic renal disease and asthma, are very likely to reflect biases in some case control studies. In particular, such biases may be caused by the perceived high tolerability of paracetamol in these diseases. The consequent use of paracetamol in these diseases states then leads to an apparent association between paracetamol and the disease. Despite metabolism of paracetamol to reactive compounds, hypersensitivity reactions are rare, although urticaria occurs in occasional patients. Paracetamol appears to be well tolerated during pregnancy although prospective studies are required.

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.

Liver necrosis and fulminant hepatic failure in rats: protection by oxyanionic form of tungsten

The hepatic lesion produced as a result of oxidative stress is of wide occurrence. In the present study, the effect of tungsten on liver necrosis and fulminant hepatic failure (FHF) has been studied in rats treated with various compounds known to produce oxidative stress. Supplementation of animals with sodium tungstate for 7 weeks before the induction of liver injury by chemicals including thioacetamide (TAA), carbon tetrachloride (CCl(4)), or chloroform (CHCl(3)) could protect progression of hepatic injury. Various biochemical changes associated with liver damage and oxidative stress were measured. Hepatic malondialdehyde content, endogenous tripeptide, and reduced glutathione were measured as oxidative stress markers. The activity of xanthine oxidase, which generates reactive oxygen species (ROS) as a by-product, was also determined and found to be perturbed. Tungsten supplementation to rats caused a significant decrease in lipid peroxidation and lowered the levels of the biochemical markers of hepatic lesions produced by TAA, CCl(4) (CCl(4)), or CHCl(3). Tungsten could also cause an increase in the survival rate in rats receiving lethal doses of TAA, CCl(4), or CHCl(3). The protective effect of tungsten, however, is suggested to be limited to the conditions where the hepatic lesion is reported to be due to the generation of ROS. The progression of liver injury produced by the compounds causing oxidative stress without initiating the generation of free radicals such as bromobenzene (BB), or acetaminophen (AAP), could not be inhibited by tungsten. The possible mechanism explaining the role of oxyanionic form of tungsten in free radical-induced hepatic lesions is discussed.

Paracetamol in the Treatment of Osteoarthritis Pain

Osteoarthritis (OA) is the most common joint disease and OA of the knee, in particular, is the major cause of chronic disability among people > 65 years. Because nonsteroidal anti-inflammatory drugs (NSAIDs) improve symptoms in many patients with OA, it is widely considered that OA pain is due to synovial inflammation. However, OA pain may arise also from subchondral bone, the joint capsule ligaments, tendons, entheses and periarticular muscle spasm. In many patients, the relief of OA pain and overall satisfaction with therapy may be as great with paracetamol (acetaminophen [APAP]) as with an NSAID. Cyclo-oxygenase (COX)-1-sparing NSAIDs (coxibs) are no more effective in the treatment of OA pain than non-selective NSAIDs and, although they may significantly decrease the risk of serious adverse effects related to gastrointestinal ulcers (GI) and ulcer complications, their gastroprotective effect may be reduced by concomitant administration of low-dose aspirin. Also, they may increase the risk of myocardial infarction in predisposed individuals. Because coxibs do not inhibit platelet aggregation, if prophylaxis against thromboembolic disease is required in patients being treated with a selective COX-2 inhibitor, low-dose aspirin should be used in conjunction with the coxib. Furthermore, nonselective NSAIDs and coxibs may have adverse effects on the kidney, fracture healing and salt and water homeostasis. This paper discusses the relative positioning of APAP, NSAIDs and coxibs in the management of OA, on the basis of considerations of tolerability, efficacy and costs.