Potential use of cimetidine for treatment of acetaminophen overdose

Metabolic and mitochondrial treatments for severe paracetamol poisoning: a systematic review

BACKGROUND

Paracetamol (acetaminophen) remains a leading cause of poisoning in Europe, North America, and Australia. For over four decades, acetylcysteine has been the antidote of choice. However, despite the use of acetylcysteine, some patients who ingest very large doses of paracetamol or who reach hospital late in the course of their poisoning, develop acute liver failure. Some will develop metabolic acidosis indicating mitochondrial toxicity.

OBJECTIVE

We review the experimental and clinical data reported with the use of cimetidine, fomepizole, and calmangafodipir in the treatment of paracetamol toxicity to determine if these treatments alone or in combination with acetylcysteine might be of benefit.

METHODS

We searched Ovid Medline 1946-2020, Embase 1947-2020, Scopus 2004-2020, Cochrane Databases of Systematic Reviews (CDSR), Cochrane Central Register of Controlled Trials (CENTRAL), and clinicaltrials.gov 1997-2020 for records including the concepts of paracetamol poisoning and cimetidine, fomepizole, calmangafodipir, and acetylcysteine. We included basic science studies in animals and all available study types in humans. We reviewed the reference lists of included articles to search for references missed in the original search. We registered the protocol in PROSPERO.

RESULTS

We completed all search strategies on 20 August 2019, 27 January 2020, and 15 June 2020. These produced 6,826 citations. We identified and deleted 2,843 duplicate resulting in a total of 3,856 unique citations. After applying inclusion and exclusion criteria, 89 studies remained. The largest numbers of studies described the past use of cimetidine, and the more recent use of fomepizole.Cimetidine: There is good animal evidence that cimetidine blocks CYP 2E1 with the potential to inhibit the toxic metabolism of paracetamol. Early case reports were inconclusive regarding the benefit to humans in paracetamol poisoning. Two comparative trials found no benefit of cimetidine in paracetamol poisoning, but few patients had severe poisoning.Fomepizole: There is good animal evidence that fomepizole blocks CYP 2E1 with the potential to inhibit the toxic metabolism of paracetamol. There are no comparative trials of fomepizole for acute paracetamol poisoning. Case reports are inconclusive due to multiple other interventions including the use of acetylcysteine in all cases. The benefit of fomepizole as adjunct treatment has not been demonstrated.Calmangafodipir: Calmangafodipir, a drug mimicking superoxide dismutase, has emerged as a potential treatment for severe paracetamol toxicity because the formation of superoxide free radicals appears to explain part of the mitochondrial toxicity of extremely large paracetamol overdoses. Calmangafodipir has reached Phase I/II trial of safety in humans with acute paracetamol overdose. Planning for a Phase III study of efficacy is currently underway.

CONCLUSIONS

The vast majority of patients with acute paracetamol overdose enjoy excellent outcomes with acetylcysteine alone. Although cimetidine and fomepizole inhibit CYP 2E1 in animals, there is insufficient evidence to recommend their use either as a primary treatment or adjunct therapy in paracetamol poisoning. Calmangafodipir remains investigational.

Comparison of the therapeutic efficacy of 4-methylpyrazole and N-acetylcysteine on acetaminophen (paracetamol) hepatotoxicity in rats

Obtaining effective analgesia with a minimal erosive effect on gastric mucosal tissue has increased the consumption of acetaminophen (paracetamol), especially among the elderly. However, the hepatotoxic effects of acetaminophen have also increased. We aimed to compare the effects of 4-methylpyrazole (4-MP), N-acetylcysteine (NAC) and their combined use on the hepatotoxicity of acetaminophen in a rat model. Male Wistar Albino rats were divided into six groups. Groups 1-5 received 2,000 mg/kg acetaminophen by gavage while the control group was group 6. Group 2 animals were given NAC (loading dose 140 mg/kg followed by seven doses at 4 h intervals); group 3 received 50 mg/kg 4-MP; group 4 received 200mg/kg 4-MP; and group 5 received NAC as in group 2 plus 200 mg/kg 4-MP. Blood samples were taken for measurements of serum AST and ALT levels. The livers of the rats were removed for microscopic examination and grading of hepatic necrosis. AST and ALT levels in groups 2-5 were lower than that of group 1 (p < 0.001), although no significant difference was noted between groups 2-5 (p > 0.05). Higher levels of ALT were found in group 5 than in group 2 (p < 0.05), and higher levels of AST were found in group 5 than in group 3 (p < 0.01). Median necrosis scores were 3.36 for rats receiving acetaminophen alone (p < 0.001, compared with groups 2-6), 1.45-1.81 for groups 2-5 (p > 0.05, compared with each other), and 0.18 for control rats (p < 0.001, compared with groups 1-5). In conclusion, the administration of 4-MP and/or NAC after 4 h of administering toxic dose of acetaminophen, inhibits hepatotoxicity in rats. There was no difference between the 4-MP and NAC-treated groups as reflected by comparable levels of serum transaminases and the degree of hepatic necrosis. Combining of 4-MP and NAC offers no benefit.

Management of drug-induced liver disease

The treatment and prevention of drug-induced liver injury starts with the recognition of hepatotoxicity at the earliest possible time so that the suspected drug can be discontinued expeditiously. Both liver enzyme monitoring and vigilance for signs of hypersensitivity involving the liver are useful strategies for many agents known to cause hepatocellular necrosis leading to liver failure. Specific antidotes to prevent or limit hepatic damage exist for only a few drugs, the most important being N-acetylcysteine for the treatment of acetaminophen hepatotoxicity. Corticosteroids are of unproven benefit in the setting of fulminant failure. Ursodiol may be helpful in instances of cholestatic injury. For other agents, supportive measures and the increasing use of liver-assist devices as well as emergency liver transplantation are available when drug injury evolves into irreversible liver failure. It is hoped that a better understanding of hepatotoxicity mechanisms will lead to the development of more specific and effective forms of therapy in the near future.

Update: the clinical importance of acetaminophen hepatotoxicity in non-alcoholic and alcoholic subjects

Acetaminophen (paracetamol) is one of the most commonly used over-the-counter medications. Taken in doses greater than 150 mg/kg/day (>10 g), it usually causes acute liver failure. The authors review mainly the management of acetaminophen toxicity in both users and nonusers of alcohol. Chronic alcoholics are a special subgroup, who risk serious toxicity when taking acetaminophen, even in therapeutic doses. The acetaminophen-alcohol interaction is complex, because acute and chronic ethanol have opposite effects. This review also considers physiological and clinical changes, as well as the diagnosis and treatment of acetaminophen poisoning.

Inhibition of acetaminophen oxidation by cimetidine and the effects on glutathione and activated sulphate synthesis rates

The aim of the present study was to examine the effects of the hepatotoxic drug, acetaminophen, on the synthesis rates of glutathione, activated sulphate (PAPS, adenosine 3'-phosphate 5'-phosphosulphate) and the acetaminophen metabolites, acetaminophen-glutathione and acetaminophen-sulphate after inhibition of cytochrome P-450 drug oxidation by cimetidine in isolated rat hepatocytes. The synthesis rates of glutathione and PAPS were determined simultaneously by an established method based on trapping of radioactivity (35S) in the prelabelled glutathione and PAPS pools. Preincubation of the hepatocytes with 60 micrograms/ml cimetidine for 30 min. did not affect PAPS (1.71 versus 1.78 nmol/10(6) cells) nor glutathione concentration (16.0 versus 16.4 nmol/10(6) cells). The subsequent incubation with 5 mM acetaminophen resulted in decreased PAPS synthesis in the cimetidine treated cells [0.79 x 10(3) versus 0.92 x 10(3) nmol/(10(6) cells.hr)] (P < 0.05). There was no difference in PAPS concentration or acetaminophen-sulphate synthesis [1.73 versus 1.79 nmol/10(6) cells and 13.0 versus 12.9 nmol/(10(6) cells.hr), respectively]. Decreased PAPS synthesis may be related to decreased ATP supply or may be the result of a feed-back regulation due to diversion of sulphur from glutathione synthesis to sulfoxidation. The glutathione synthesis was not significantly affected by cimetidine treatment [57 x 10(3) versus 27 x 10(3) nmol/(10(6) cells.hr)]. As expected acetaminophen-glutathione synthesis decreased by 38% [1.66 versus 2.68 nmol/(10(6) cells.hr)] (P < 0.01). Also the glutathione concentration was lower in cimetidine treated cells [15.2 versus 15.9 nmol/10(6) cells] (P < 0.05). We have previously shown that glutathione synthesis was reduced if substrate availability decreased (acetaminophen concentration lowered).(ABSTRACT TRUNCATED AT 250 WORDS)