Long-Term Ingestion of Paracetamol and Liver Disease1

Long-term adverse effects of paracetamol - a review

Paracetamol (acetaminophen) is the most commonly used drug in the world, with a long record of use in acute and chronic pain. In recent years, the benefits of paracetamol use in chronic conditions has been questioned, notably in the areas of osteoarthritis and lower back pain. Over the same period, concerns over the long-term adverse effects of paracetamol use have increased, initially in the field of hypertension, but more recently in other areas as well. The evidence base for the adverse effects of chronic paracetamol use consists of many cohort and observational studies, with few randomized controlled trials, many of which contradict each other, so these studies must be interpreted with caution. Nevertheless, there are some areas where the evidence for harm is more robust, and if a clinician is starting paracetamol with the expectation of chronic use it might be advisable to discuss these side effects with patients beforehand. In particular, an increased risk of gastrointestinal bleeding and a small (~4 mmHg) increase in systolic blood pressure are adverse effects for which the evidence is particularly strong, and which show a degree of dose dependence. As our estimation of the benefits decreases, an accurate assessment of the harms is ever more important. The present review summarizes the current evidence on the harms associated with chronic paracetamol use, focusing on cardiovascular disease, asthma and renal injury, and the effects of in utero exposure.

Can paracetamol (acetaminophen) be administered to patients with liver impairment?

Although 60 years have passed since it became widely available on the therapeutic market, paracetamol dosage in patients with liver disease remains a controversial subject. Fulminant hepatic failure has been a well documented consequence of paracetamol overdose since its introduction, while short and long term use have both been associated with elevation of liver transaminases, a surrogate marker for acute liver injury. From these reports it has been assumed that paracetamol use should be restricted or the dosage reduced in patients with chronic liver disease. We review the factors that have been purported to increase risk of hepatocellular injury from paracetamol and the pharmacokinetic alterations in different pathologies of chronic liver disease which may affect this risk. We postulate that inadvertent under-dosing may result in concentrations too low to enable efficacy. Specific research to improve the evidence base for prescribing paracetamol in patients with different aetiologies of chronic liver disease is needed.

Mannan binding lectin and viral hepatitis

Mannan binding lectin (MBL) is a pattern recognition molecule of the innate immune system that binds to sugars on the surface of invading micro-organisms. Target binding, complement activation and other functions of MBL are dependent on the presence of multiple carbohydrate recognition domains. Several polymorphisms in the promoter and structural regions of MBL2 adversely affect the plasma concentration and oligomeric state of MBL. The possession of mutant alleles has been linked to disease outcome for a variety of bacterial and viral infections. Viral hepatitis is caused by unrelated viruses referred to as hepatitis virus A-E. The disease usually has both acute and chronic phases, the latter leading to cirrhosis and hepatocellular carcinoma. Hepatitis viruses B and C (HBV and HCV, respectively) are a significant cause of morbidity worldwide. HBV encodes envelope glycoproteins termed large, middle, and small that may exist in glycosylated or unglycosylated forms on the virion. An interaction between HBV glycoproteins and MBL has been demonstrated in vitro. Significant associations between MBL levels, determined by MBL2 haplotypes, and HBV persistence and disease progression have been described. HCV encodes two highly glycosylated envelope proteins, E1 and E2, which are potential targets for interaction with MBL. Mutant MBL2 haplotypes have been linked to disease progression and response to therapy in HCV infection. Here we summarise the effect of MBL2 polymorphisms on MBL function and how this may relate to disease outcome in HBV and HCV infection.

Analgesics abuse: theoretical and practical considerations

Three important issues must be addressed in any attempt to determine whether combination painkillers play a role in analgesic nephropathy. The first issue, namely that of a causal link between the combination itself and nephrotoxicity, has never been adequately documented. On the contrary, there is much evidence that the combination as such has no influence whatsoever. The cause of the nephrotoxicity is most likely the painkilling mechanism, i.e. the antagonism to prostaglandins; the most potent prostaglandin-antagonists, the non-steroidal anti-inflammatory drugs, whether used in combination or singly, also most frequently cause renal pathology. The second issue, i.e. the safety of combination painkilling drugs in comparison with that of single substances, is intimately bound up with the advantages of the former with respect to both activity and the activity-side-effects ratio. The third issue, abuse, should be recast in a broader context. The central element here is not the painkilling drug but rather the labile personality of the user in conjunction with a more or less stressful environment in which a wide variety of drugs and stimulants are available and taken for better 'coping'. To a great extent analgesics abuse can be prevented by information (i.e. social medicine). In a broader perspective, man experiences considerable difficulty adapting to the sweeping social, technological and ideological changes of recent decades, and this transition contributes in no small measure to the analgesics problem. It should be a priority of government to find remedies for this state of affairs.

Effects of sulfur-amino acid-deficient diets on acetaminophen metabolism and hepatotoxicity in rats

Cysteine is required for the synthesis of cosubstrates for two pathways of acetaminophen metabolism: 3'-phosphoadenosine-5'-phosphosulfate (PAPS) for sulfation and glutathione (GSH) for detoxification of the reactive metabolite (N-acetyl-p-benzoquinoneimine, NAPQI). Dietary deficiency of cysteine may reduce hepatic production of PAPS and GSH and thereby reduce metabolism of the drug (by sulfation and detoxification of NAPQI) and hence lead to potentiation of acetaminophen liver injury. Conversely, limitation of sulfur-containing amino acids could result in depression of protein synthesis and hepatic cytochrome P450 levels, and hence in decreased reactive metabolite formation and decreased liver injury. To determine whether the potentiating effects exceed the protective effects, rats were fed isocaloric AIN-76 liquid diets containing various levels of methionine as the sole source of sulfur in the diet for 3 weeks prior to administration of acetaminophen. Sulfur deficiency was assessed by measuring urinary inorganic sulfate levels. Sulfur-deficient diets retarded growth but did not affect nitrogen balance. Sulfur-deficient animals had lower basal levels of hepatic GSH. Pharmacokinetic studies revealed that at low doses of acetaminophen (20 mg/kg), animals fed sulfur-deficient diets metabolized the drug more slowly due to a markedly reduced sulfation capacity, whereas at the high dose of acetaminophen (400 mg/kg), rats that were fed sulfur-deficient diets had a higher clearance of the drug than rats that were fed the complete diet. The increase in clearance was due largely to an enhanced glucuronidation capacity and an enhanced P450-dependent oxidation as indicated by mercapturate formation. Histologic studies revealed that rats fed sulfur-deficient diets showed increases in both incidence and severity of acetaminophen hepatic necrosis. Thus, the potentiating effects exceeded the protective effects. These observations raise the possibility that nutritional inadequacy of sulfur-containing amino acids which could occur during protein malnutrition may similarly enhance susceptibility to acetaminophen liver injury in humans.

Liver function in patients on long-term paracetamol (co-proxamol) analgesia

Eleven patients on long term co-proxamol therapy for pain, in general practice, showed no abnormalities of liver or renal function, as assessed by serum prealbumin concentrations and blood enzyme and electrolyte activities. This indicates that although the preparation is hepatotoxic when taken acutely in overdose, in chronic therapeutic dosage it appears to be free from this hazard.

Effects of non-narcotic analgesics on the liver

Serious hepatotoxicity is uncommon with the proper therapeutic use of non-narcotic analgesics but experience with new non-steroidal anti-inflammatory drugs (NSAIDs) is limited. Drugs such as ibufenac, fenclofenac and benoxaprofen were withdrawn from the market because of hepatotoxicity, and liver damage has been reported on occasion with virtually all non-narcotic analgesics. However, a clear pattern of toxicity with characteristic clinical, biochemical and histopathological abnormalities has emerged with relatively few. With the exception of acute hepatic necrosis following overdosage of paracetamol, little is known of the mechanisms of liver injury induced by non-narcotic analgesics. Involvement of the liver in a generalised drug reaction does not imply specific hepatotoxicity. About 50% of patients given aspirin regularly in anti-inflammatory doses develop mild, dose-dependent reversible liver damage as shown by elevation of the plasma aminotransferase activity. Liver damage is more severe in a small minority and it may rarely be complicated by disseminated intravascular coagulation and encephalopathy with a fatal outcome. There have also been isolated reports of chronic active hepatitis associated with the use of salicylates. Salicylate hepatitis has been reported most often in young females with connective tissue diseases. Many patients with Reye's syndrome have been given aspirin during the prodromal phase, and this serious condition closely resembles subacute salicylate intoxication in children. Salicylate probably has a causal or contributory role in Reye's syndrome, but many refuse to accept this and the issue is the subject of heated debate. Paracetamol in overdosage causes acute hepatic necrosis, and liver damage has been attributed to its therapeutic use. However, most reports have involved chronic alcoholics who took excessive doses and in these patients the clinical, biochemical and pathological findings were typical of paracetamol overdosage. Many authors have failed to make the distinction between therapeutic use and a therapeutic dose. In other cases liver damage could have been caused by exposure to other agents, viral infection or naturally occurring liver disease. If these cases are excluded, there are very few reports of liver damage associated with the proper therapeutic use of paracetamol. In some cases, the picture resembled chronic active hepatitis but no causal relationship has been established between this condition and paracetamol use. Paracetamol does not cause deterioration in liver function in patients with chronic liver disease.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetaminophen: a practical pharmacologic overview

Acetaminophen is an effective analgesic and antipyretic agent with few adverse effects when used in recommended dosages. The drug is metabolized mainly in the liver, and the several end products have no harmful effects. An intermediate compound in a minor metabolic pathway, however, is toxic; it is normally inactivated by glutathione. In the case of an acetaminophen overdose the hepatic stores of glutathione seem to become depleted, leaving the toxic intermediate free to damage liver tissue. Such damage is unlikely to occur unless the plasma concentration of acetaminophen peaks above 150 micrograms/mL--a level far in excess of the 5 to 20 micrograms/mL achieved with therapeutic doses of the drug. Long-term therapeutic use of acetaminophen does not appear to be associated with liver damage, although some case reports suggest the possibility. Acetaminophen poisoning follows an acute overdose and, if untreated, is manifested clinically by an initial phase of nonspecific signs and symptoms, a latent period in which the liver transaminase levels rise and then, 3 to 5 days after the ingestion, signs of more serious hepatic dysfunction. Most patients do not progress beyond the first or second phase. They and those who survive the third phase recover with no residual injury to the liver. Appropriate antidotal therapy markedly reduces the severity of the initial damage.

Hepatotoxicity following the therapeutic use of antipyretic analgesics

The potential for hepatic injury associated with the therapeutic use of salicylates and acetaminophen has recently attracted considerable attention. About 300 cases have been reported in which elevated transaminase levels or other evidence of hepatic injury developed following treatment with salicylates. Review of the spectrum of abnormalities reveals a group of patients (4 percent) with symptomatic liver damage in whom progressive or chronic liver disease is a possibility with continued use of the drug. In a few patients in this group, jaundice developed; several had abnormal prothrombin times; 11 (70 percent) had transaminase values in excess of 500 units; and five patients (30 percent) had encephalopathy and/or Reye's syndrome. In several reports liver damage has also been associated with the use of acetaminophen in therapeutic or near-therapeutic dosages. Of 18 patients, nine appeared to have ingested acetaminophen in amounts approaching overdose. Of the remaining nine patients, six were alcoholics. In the entire group, only five patients did not have a history of alcohol abuse; in three, glutathione depletion was suggested as a possible explanation for hepatotoxicity. The association with alcoholism or glutathione depletion suggests that host susceptibility may play a critical role. In two patients, long-term use of acetaminophen resulted in liver injury suggestive of chronic active hepatitis, possibly on the basis of an idiosyncratic reaction. In a study of chronic liver disease, acetaminophen half-life was prolonged (168 percent) without accumulation at 4 g a day over five days. In a double-blind, two-week, cross-over study, no clinical or laboratory evidence of adverse effects was found. There is, therefore, no evidence that chronic liver disease increases the risk of hepatotoxicity following the administration of acetaminophen in therapeutic doses. Thus, acetaminophen is the preferred antipyretic analgesic in patients with liver disease. Salicylates should be avoided since many of the adverse effects associated with these drugs are similar to the complications of chronic liver disease.

The use of non-prescription analgesics in an older population

Older patients are frequent users of aspirin and acetaminophen, either recommended by physicians or self-prescribed, for the aches and pains that accompany aging. These mild analgesics provide effective pain relief when used appropriately. Aspirin and acetaminophen are equianalgesic on a milligram-for-milligram basis for most indications. Both are safe for most patients. Aspirin use may be associated with salicylate intoxication or salicylate interactions with other agents. There have been reports of an association of hepatotoxicity with acute massive overdosages of acetaminophen.

Complications of alcohol use combined with drug therapy in the elderly

Chronic ingestion of ethanol in alcoholic beverages can impair drug therapy, lead to sometimes hazardous interactions, or compromise adherence to a well-planned drug treatment program. Various drugs consistently interact with alcohol: CNS depressants, such as benzodiazepines, barbiturates, muscle relaxants, antihistamines, and psychotropic agents; analgesics, including aspirin and narcotics; anticoagulants and other cardiovascular drugs, namely digitalis glycosides, diuretics, antihypertensives, and antiarrhythmics; and antidiabetic agents. Abstinence from alcohol by elderly patients receiving these drugs is recommended.