Acetaminophen overdose. 662 cases with evaluation of oral acetylcysteine treatment

A pharmacokinetic comparison of acetaminophen products (Tylenol Extended Relief vs regular Tylenol)

OBJECTIVE

To compare the pharmacokinetics of Tylenol Extended Relief (ER APAP) with those of immediate-release acetaminophen (IR APAP) at supratherapeutic doses.

METHODS

A prospective, double-blind, randomized, crossover comparison trial involving 14 adult volunteers. Each subject ingested 75 mg/kg of either ER APAP or IR APAP and 1 week later received the other APAP preparation. On both occasions plasma APAP concentration ([APAP]) was determined 0.5, 1, 2, 3, 4, 6, 8, 12, and 16 hours after ingestion. The times to maximum [APAP] (Tmax); the maximum [APAP] values (Cmax); the elimination half-lives 4-16 hours postingestion (t1/2), and the areas under the [APAP] vs time curve (AUC) for ER APAP and IR APAP were compared using the paired t-test.

RESULTS

All the subjects completed both study phases. The mean APAP dose ingested was 5.6 g (range 4.2-7.8 g). Both the AUC and the Cmax were less after ER APAP than after IR APAP; otherwise, there was no evident difference in any measure. Graphically, ER APAP yielded a flatter, plateau-shaped curve initially, but after 4 hours the curve was nearly identical to that for IR APAP. Results are summarized in the table: [table: see text]

CONCLUSION

In this model involving a single supratherapeutic dose, ER APAP evidenced no pharmacokinetic features that would suggest the need for an alternate poisoning screening strategy. When compared with IR APAP, ER APAP had a lower AUC, all peak [APAP] occurred in < 4 hours, and terminal eliminations were identical. The data suggest that, in most cases, the diagnostic approach to an overdose of ER APAP need not deviate from that used for an IR APAP overdose.

A redox-based mechanism for cardioprotection induced by ischemic preconditioning in perfused rat heart

Recent studies have suggested that mild redox alterations can regulate cell function. Therefore, we tested the hypothesis that alteration in the thiol redox state might be responsible for the cardioprotective effects conferred by ischemic preconditioning in the perfused rat heart. We find that preconditioning with four 5-minute periods of ischemia, each separated by 5 minutes of reflow, is associated with a significant loss of glutathione (3.98 +/- 0.32 mumol/g dry wt, n = 8) compared with no preconditioning (6.38 +/- 0.24 mumol/g dry wt, n = 14). We further find that the addition of N-acetylcysteine (NAC, a glutathione precursor and antioxidant) during the preconditioning protocol not only blocks the loss of glutathione (5.60 +/- 0.31 mumol/g dry wt, n = 9) but also blocks the protective effects of preconditioning. It is observed that after 20 minutes of ischemia followed by 20 minutes of reflow, untreated hearts recover 38 +/- 7% (n = 5) of their initial preischemic contractile function, whereas preconditioned hearts recover 91 +/- 11% (n = 7). Hearts preconditioned in the presence of NAC recover 24 +/- 3% (n = 7) of their preischemic function. Similarly, the addition of NAC reverses the protective effect of preconditioning on creatine kinase release. On reflow after 60 minutes of ischemia, creatine kinase release from control hearts was 271 +/- 20 IU.20 min-1.g dry wt-1 (n = 5), whereas preconditioned hearts release only 170 +/- 26 IU.20 min-1.g dry wt-1 (n = 6), and hearts preconditioned in the presence of NAC release 361 +/- 30 IU.20 min-1.g dry wt-1 (n = 5). We also find that hearts preconditioned in the presence of NAC have less attenuation of the decline in pHi than hearts preconditioned in the absence of drug. Thus, a redox-sensitive mechanism may be involved in the protection afforded by ischemic preconditioning.

Beneficial effects of N-acetylcysteine and cysteine in stunned myocardium in perfused rat heart

1. The objective of this study was to evaluate the effects of three sulphydryl (SH) compounds, N-acetylcysteine (NAC), cysteine (Cys) and cystamine, on functional recovery and ventricular arrhythmias (VF) in stunned myocardium in the isolated perfused heart of the rat. 2. Hearts (n = 7-8 per group) were perfused by the Langendorff procedure for 20 min to stabilize and then assigned to one of five groups: saline, sham, NAC, Cys and cystamine. After the stabilizing period, the drugs (at 3.6 microM min-1) or their vehicle (saline) were infused into coronary vessels throughout the experimental period. Ten min after administration of drugs, the left anterior descending coronary artery (LAD) was ligatured for 20 min and then untied to reperfuse for 30 min. In the sham group, a ligature was placed around the LAD but not tied. 3. NAC and Cys had a significant effect in attenuating myocardial stunning: the percentage recovery of rate-pressure product measured 30 min after reperfusion as an index of heart function, was improved with the NAC (98.3 +/- 4.5) and Cys groups (104.0 +/- 6.5) compared with the saline (only 73.6 +/- 3.8, P < 0.01) group. Cystamine did not show these beneficial effects. This may be due to the difference in chemical structure between NAC, Cys and cystamine since the latter does not have a free SH group with a disulphide bond formed. This phenomenon suggests that a free SH group is essential for the protective effects of compounds like NAC and Cys in myocardial injury. 4. NAC and Cys prevented the fall in coronary flow during the LAD occlusion and enhanced coronary flow during reperfusion but cystamine did not have such a beneficial effect. 5. The incidence of VF in the saline, cystamine, Cys and NAC groups was 6/8 (75.0%), 4/7 (57.1%), 3/8 (37.5%) and 2/7 (28.6%), respectively, and no significant differences (P > 0.05) were noted between the saline- and drug-treated groups. 6. An in vitro study with electron spin resonance indicated that Cys effectively scavenged the hydroxyl radical (-OH) generated by Fenton's reaction but did not scavenge superoxide generated in an irradiated riboflavin system. NAC and cystamine showed a scavenging effect on -OH to a certain extent but this effect did not reach statistical significance (P > 0.05 vs saline). 7. Our results demonstrate that NAC and Cys treatment before ischaemia and reperfusion can reduce myocardial stunning. This beneficial effect may be mainly due to their ability to preserve and enhance coronary flow during coronary occlusion and reperfusion and in part due to scavenging -OH and/or replenishing intracellular glutathione. The results also indicate that the condition of coronary perfusion can produce a great impact on postischaemic ventricular performance.

Protection against acetaminophen-induced liver injury in vivo by an iron chelator, deferoxamine

BACKGROUND

Recent data indicate that iron ions play a major role in lipid peroxidation, a hepatotoxic effect of acetaminophen (APAP).

METHODS

We investigated whether an iron chelator, deferoxamine (DFO), can protect against APAP-induced liver injury in vivo in rats.

RESULTS

DFO diminished the increase in serum alanine aminotransferase (ALAT) in a dose-dependent manner after APAP administration and also reduced mortality. Administration of 750 mg/kg APAP resulted in an increased ALAT (11,666 +/- 4633) after 8 h, and the mortality at 24 h was 88%. Pretreatment with 200 mg/kg DFO for 1 h significantly reduced ALAT (to 3406 +/- 894) and mortality (38%). DFO also attenuated histopathologic changes. Treatment with DFO depressed malondialdehyde formation by APAP without inhibiting glutathione depletion in the liver or reducing covalent binding of [3H]APAP to liver proteins.

CONCLUSIONS

These results indicate that the protective effect of DFO against APAP-induced liver injury may be attributable not to changes in APAP metabolism but to the chelation of iron, which can catalyze the generation of active oxygen species, in hepatocytes.

The role of N-acetylcystein administration on the oxidative response of neutrophils during cardiopulmonary bypass

The role of N-acetylcystein (NAC) administration on the oxidative response of neutrophils during cardiopulmonary bypass (CPB) was evaluated in a double-blind study. Twenty-four adult patients undergoing coronary artery bypass were included in the study. Twelve patients received NAC as a bolus of 100 mg/kg followed by a continuous infusion of 20 mg/kg/h in the bypass circuit from the beginning to the end of bypass. A further 12 patients received placebo. Citrated blood samples for measurement of oxidative burst response of neutrophils were obtained at different time points during bypass. The oxidative burst response of neutrophils in the patients receiving NAC was significantly low at all times during bypass. Based on these findings NAC appears to act as an oxygen free radical scavenger during open-heart surgery.

4-Methylpyrazole blocks acetaminophen hepatotoxicity in the rat

STUDY OBJECTIVE

To determine whether 4-methylpyrazole inhibits the hepatotoxic effects of acetaminophen in a rat model. DESIGN AND TYPE OF PARTICIPANTS: A nonblinded experiment using male Sprague-Dawley rats.

INTERVENTIONS

Animals were divided into four groups. Groups 1 through 3 received 2,000 mg/kg acetaminophen by gavage; group 4 acted as a control. At four or eight hours, group 2 received 400 mg/kg 4-methylpyrazole; group 3 received 50 mg/kg 4-methylpyrazole. Blood samples were taken for measurements of serum AST and ALT levels. Livers were removed for microscopic examination and grading of necrosis.

RESULTS

Lower AST and ALT levels were obtained for both the 400-mg/kg (P < .01) and 50-mg/kg (P < .05) doses of 4-methylpyrazole administered four hours after acetaminophen. Although mean AST and ALT levels also were lower when 400 and 50 mg/kg 4-methylpyrazole were administered eight hours after acetaminophen, these results were not statistically significant. Median necrosis scores were 3 for rats receiving acetaminophen alone, 0.5 for those receiving acetaminophen and 400 mg/kg 4-methylpyrazole (P < .05), 1 for those receiving acetaminophen and 50 mg/kg 4-methylpyrazole (P < .05), and 0 for control rats (P < .05).

CONCLUSION

When administered four hours after a toxic dose of acetaminophen, 4-methylpyrazole significantly inhibits hepatotoxicity in the rat, as reflected by lower levels of serum transaminases and lesser degrees of hepatic necrosis.

A prospective evaluation of the effect of activated charcoal before oral N-acetylcysteine in acetaminophen overdose

STUDY OBJECTIVE

To evaluate whether activated charcoal (AC) reduces the efficacy of subsequent oral N-acetylcysteine therapy during acute acetaminophen overdose.

DESIGN

Prospective observational case series of all acute acetaminophen overdoses reported to three certified regional poison centers. TYPES OF PATIENTS: All patients with acute acetaminophen overdose in whom N-acetylcysteine therapy was initiated within 16 hours after ingestion.

INTERVENTIONS

All patients were treated with oral N-acetylcysteine therapy for 72 hours. The decision to use AC was left to the treating physician without input from the investigator.

MEASUREMENTS AND RESULTS

One hundred twenty-two patients were evaluated. Maximum recorded SGOT levels of more than 125 U/mL were defined as evidence of hepatotoxicity. AC was used in addition to N-acetylcysteine in 82 of 122 patients. Hepatotoxicity developed in four of 82 patients who received AC versus ten of 40 patients who did not receive AC (P < .005). An increasing dose of N-acetylcysteine provided no additional benefit (P > .05). Spacing the administration of AC and oral N-acetylcysteine less than or more than two hours apart did not affect outcome (P > .05).

CONCLUSION

Administration of AC before the administration of oral N-acetylcysteine in acetaminophen overdose does not reduce the efficacy of N-acetylcysteine therapy and may provide some additional hepatoprotective benefit. The practice of increasing the dose of oral N-acetylcysteine therapy after the administration of AC appears unwarranted.

Prediction of acetaminophen concentrations in overdose patients using a Bayesian pharmacokinetic model

A pharmacokinetic program using population-based parameter estimates and a Bayesian forecasting model was retrospectively evaluated for predicting acetaminophen serum concentrations in overdose patients. Dynamic disposition factors known to affect acetaminophen disposition (emesis, activated charcoal, N-acetylcysteine, etc.) were included in the program. Twenty six patients who reported an acetaminophen ingestion of at least 70 mg/kg within 24 h of presentation to the hospital and had at least one measured acetaminophen concentration were included. Prediction of initial acetaminophen concentrations using only population-based parameter estimates resulted in a percent mean error (%ME) and percent mean absolute error (%MAE) of 9.3 and 42.2, respectively. Using only the initial concentration as feedback, the Bayesian forecasting model accurately predicted the second acetaminophen concentration (%ME = 4.0, %MAE = 23.6). The Bayesian model also accurately predicted all concentrations within 8 h of the ingestion (%ME = 10.6, %MAE = 24.0). The prediction of concentrations between 2 to 4 h and 4 to 4.5 h after ingestion with only population-based parameter estimates resulted in %ME of 17.0 and 13.2, respectively, and %MAE of 36.5 and 35.1, respectively. Our data suggests that acetaminophen serum concentrations occurring within the first 4.5 h after ingestion can be reliably predicted by the set of population-based parameter estimates evaluated. Once a single acetaminophen concentration is available, the Bayesian forecasting model can accurately predict subsequent concentrations within the first 8 h after an acetaminophen ingestion.

Delayed toxic acetaminophen level after initial four hour nontoxic level

Antidotal therapy for acetaminophen poisoning is routinely based on a single acetaminophen level obtained four or more hours after ingestion. Some experts recommend additional acetaminophen levels if there are coingestants. This case report describes a 20-year-old woman who ingested acetaminophen 13 g, propoxyphene napsylate 2 g and naproxen sodium 3.75 g. A 4.5 h acetaminophen level was 83.5 mg/L (nontoxic). A 6.75 h acetaminophen level was 124.6 mg/L (toxic). The patient was treated with N-acetylcysteine and recovered without sequelae. This is the first published report of a delayed toxic acetaminophen level occurring after an initial nontoxic level. Although rare, the possibility of a delayed peak acetaminophen level merits consideration, particularly with coingestions that delay gastric emptying.

Acetaminophen ingestion in childhood--cost and relative risk of alternative referral strategies

Acetaminophen is the pharmaceutical most frequently ingested by small children. Although past research has allowed the safe management of 90% of these ingestions at home, several thousand are still referred to emergency departments annually. With the goal of further reducing the number of unnecessary referrals, the risk/benefit considerations of alternate referral strategies were analyzed. In a retrospective poison center chart review study from 11 centers, the records of children between the ages 1 and 6 years who acutely ingested acetaminophen and were referred to a hospital for determination of serum acetaminophen concentration in 1986 and 1987 were identified using the database of the American Association of Poison Control Centers. Risk of hepatic injury was assigned on the basis of the Rumack-Matthew acetaminophen toxicity nomogram. The cohort was stratified in terms of the amount ingested and whether a pediatric or adult preparation was ingested. The direct cost of an evaluation was estimated from four centers. Sensitivity, specificity and direct cost of each risk identification strategy were calculated. Eight hundred sixty six of 2091 patients had a timed serum acetaminophen concentration recorded. Of these, three patients had results in the "probable risk" area of the nomogram. A referral reduction strategy which would refer only children who ingest 200 mg/kg or more of an adult preparation could eliminate 82% of referrals without missing any of these "probable risk" patients. Six other children were determined to have serum acetaminophen concentrations in an area of the nomogram labeled "possible risk". No referral reduction strategy explored identified all of these patients. The average charge for an emergency department evaluation in 1992 was $272.00. These data suggest that children less than six years of age who ingest pediatric acetaminophen products other than those from packages containing greater than 30 tablets or who ingest less than 200 mg/kg of an adult preparation may be safely managed at home without referral to a hospital. This strategy would result in significant cost savings and prevent unnecessary inconvenience to many patients and families.

Potential misuse of ipecac

STUDY OBJECTIVE

To evaluate the use of ipecac by health care professionals.

DESIGN

A descriptive case series based on a one-year review of all calls to a poison center.

SETTING

A university hospital-affiliated regional poison center.

INTERVENTIONS

The use of ipecac was judged appropriate or inappropriate based on the consensus of three professionals associated with the poison center using predetermined contraindications.

MEASUREMENTS AND MAIN RESULTS

In 20% of cases in which ipecac was used, its use was inappropriate. The most common inappropriate situation was that too much time had elapsed from the time of ingestion. Among adults the most common contraindication was the ingestion of a substance known to cause altered mental status. Among children, the most common contraindication was the ingestion of a nontoxic substance or amount of substance. The poison center recommended ipecac inappropriately less often than emergency departments and usually in children ingesting a nontoxic substance. EDs recommended ipecac inappropriately with a broader range of contraindications and more often in adults.

CONCLUSION

Ipecac has potentially adverse consequences and should not be used reflexively. Providers of emergency care should be educated about possible contraindications to its use.

Transport management of the patient with acute poisoning

Poisoning in children is a common clinical problem encountered by pediatricians, general practitioners, and emergency room physicians. Poisoning in children less than 5 years of age is usually accidental, whereas, in young adults, any disparity between expected history and clinical findings should suggest poisoning. It is imperative that the treating physician expeditiously recognize, begin treating, and plan to transfer, when indicated, by specialized pediatric transport team the critically ill poisoned child to a tertiary care facility.

Failure of N-acetylcysteine to reduce alpha amanitin toxicity

Acetaminophen undergoes toxic conversion in the liver to a free-radical intermediary which binds to glutathione. N-Acetylcysteine acts as a glutathione precursor when natural stores are depleted, and is an effective antidote for acetaminophen overdose. Mushrooms containing amatoxins (such as Amanita phalloides) may undergo similar toxic conversion. However, in our amatoxin-poisoned mouse model, N-acetylcysteine (1.2 g kg-1) produced no change in survival or hepatic enzyme elevation compared to control animals. We conclude that N-acetylcysteine has no clinical role in the treatment of Amanita phalloides ingestion.

Anaphylactoid reaction to intravenous acetylcysteine associated with electrocardiographic abnormalities

OBJECTIVE

To review the potential for anaphylactoid reactions to intravenously administered acetylcysteine when used in the treatment of acetaminophen overdose. This case is unique in that electrocardiographic changes, including ST segment depression and T-wave inversion were associated with the episode and complicated the diagnosis.

DATA SOURCES

Reference articles and letters are identified in the text.

DATA SYNTHESIS

Intravenous administration of acetylcysteine has been used in the treatment of acetaminophen overdose. This route may be considered in some clinical situations where oral therapy is complicated. Anaphylactoid reactions, including cutaneous eruptions, flushing, chest pain, tachycardia, and fever have been reported in up to three percent of patients receiving intravenous acetylcysteine. The nature of these reactions and evidence concerning their etiology suggest a histamine-release phenomenon. Response to intervention with antihistamines and the safety of further acetylcysteine administration are discussed.

CONCLUSIONS

This case illustrates a variant anaphylactoid reaction to intravenously administered acetylcysteine and emphasizes the need for practitioners to consider the potential for these reactions prior to initiation of therapy and indicates appropriate treatment of these reactions.

Intravenous acetylcysteine in paracetamol induced fulminant hepatic failure: a prospective controlled trial

OBJECTIVE

To see whether intravenous acetylcysteine would improve outcome in patients with fulminant hepatic failure after paracetamol overdose.

DESIGN

A prospective randomised controlled study.

SETTING

The Institute of Liver Studies, King's College Hospital, London.

PATIENTS

50 consecutive patients (21 male) aged 16-60 with fulminant hepatic failure after paracetamol overdose who had not previously received acetylcysteine.

INTERVENTIONS

Conventional intensive liver care plus either acetylcysteine (25 patients) in the same dose regimen as used early after a paracetamol overdose, except that the infusion was continued until recovery from encephalopathy or death, or an equivalent volume of 5% dextrose (25 patients).

MAIN OUTCOME MEASURES

Survival; incidence of cerebral oedema, renal failure, and hypotension requiring inotropic support; liver function as assessed by prolongation of the prothrombin time; and degree of encephalopathy.

RESULTS

The rate of survival was significantly higher in the acetylcysteine treated group than in the controls (48% (12/25 patients) v 20% (5/25); p = 0.037, 95% confidence interval for difference in proportions surviving 3% to 53%). Acetylcysteine treated patients had a lower incidence of cerebral oedema (40% (10/25) v 68% (17/25); p = 0.047, 95% confidence interval for difference in incidence 2% to 54%), and fewer developed hypotension requiring inotropic support (48% (12/25) v 80% (20/25); p = 0.018, 95% confidence interval 7% to 57%). Rates of deterioration and recovery of liver function, however, were similar in the two groups. No adverse reactions to acetylcysteine were seen.

CONCLUSIONS

Acetylcysteine is safe and effective in fulminant hepatic failure after paracetamol overdose.

Acetaminophen overdose: a 48-hour intravenous N-acetylcysteine treatment protocol

STUDY OBJECTIVE

To determine the safety and efficacy of a 48-hour IV N-acetylcysteine (IV NAC) treatment protocol for acute acetaminophen overdose.

DESIGN

Nonrandomized trial open to all eligible patients.

SETTING

Multicenter; hospitals included moderate- and high-volume private, university, and municipal hospitals in urban and suburban settings.

TYPE OF PARTICIPANTS

Two hundred twenty-three patients were entered. Of these, 179 met inclusion criteria: acute acetaminophen overdose, plasma acetaminophen concentration above the treatment nomogram line, treatment with IV NAC according to the protocol, and sufficient data to determine outcome.

INTERVENTIONS

IV NAC treatment consisted of a loading dose of 140 mg/kg followed by 12 doses of 70 mg/kg every four hours.

MEASUREMENTS AND MAIN RESULTS

Patients were grouped for analysis according to risk group based on the initial plasma acetaminophen concentration. Hepatotoxicity (aspartate aminotransferase or alanine aminotransferase of more than 1,000 IU/L) developed in 10% (five of 50) of patients at "probable risk" when IV NAC was started within ten hours of acetaminophen ingestion and in 27.1% (23 of 85) when therapy was begun after ten to 24 hours. Among "high-risk" patients first treated 16 to 24 hours after overdose, hepatotoxicity occurred in 57.9% (11 of 19). There were two deaths (two of 179, 1.1%). Adverse reactions resulting from NAC occurred in 32 of 223 cases (14.3%), consisting in 29 of 32 patients (91% of reactions) of transient, patchy, skin erythema or mild urticaria during the loading dose that did not require discontinuation of therapy.

CONCLUSION

This 48-hour IV NAC protocol is safe and effective antidotal therapy for acetaminophen overdose. Based on available data, it is equal to 72-hour oral and 20-hour IV treatment protocols when started early and superior to the 20-hour IV regimen when treatment is delayed. Further study will be required to determine its relative efficacy in the high-risk patient treated very late.

Activated charcoal and acetylcysteine absorption: issues in interpreting pharmacokinetic data

Studies determining the effects of activated charcoal on drug absorption frequently use area under the plasma drug concentration versus time curve or drug and metabolite recovery in the urine as endpoints. The considerations in using these endpoints is presented using studies that have evaluated the effects of activated charcoal on acetylcysteine absorption. Acetylcysteine's pharmacokinetics, quantitation of plasma concentrations, and the lack of an identifiable pharmacokinetic-pharmacodynamic relationship all contribute to the difficulties in determining whether activated charcoal inhibits the oral absorption of acetylcysteine, or alters acetylcysteine's efficacy in treating acetaminophen overdoses. The results of these studies should be interpreted cautiously, with consideration of internal and external study validity.

Acetaminophen induced pancreatitis

This is the fourth reported case of acute pancreatitis associated with acetaminophen overdose. The patient had ingested the smallest amount of acetaminophen (9.75-13 g) that has been reported to produce acute pancreatitis. This patient also suffered liver and renal impairment and developed an ileus and ascites. Despite late therapy and laboratory tests that indicated a poor prognosis the patient made a complete recovery without sequelae.

Clinical evaluation of an acetaminophen meter for the rapid diagnosis of acetaminophen intoxication

STUDY OBJECTIVES

To test the accuracy of a newly developed meter that determines serum acetaminophen concentration after a 30-second analysis of one drop of whole blood.

DESIGN

Sixty-six blood samples from patients with known or suspected drug overdose were analyzed for the presence of acetaminophen. In all cases determination of serum acetaminophen concentration was performed simultaneously with the meter and by a reference laboratory.

SETTING

Eligible patients were those who presented during a nine-month period to the emergency departments of two tertiary care hospitals (including a pediatric hospital).

RESULTS

Thirty-one specimens had a laboratory-confirmed detectable acetaminophen concentration. The meter identified these toxic specimens in all cases; there were no false-negatives (sensitivity, 100%). Among the 35 specimens not containing acetaminophen, the meter invariably confirmed a nondetectable serum acetaminophen concentration (specificity, 100%). Acetaminophen measurements by the meter correlated strongly with laboratory determinations (r = .985, P less than .001). Repeated testing of one specimen documented the precision and reproducibility of the meter's analysis; mean coefficient of variation was .08 in measuring toxic acetaminophen concentrations. Drug coingestion had no significant effect on the accuracy of the meter. Instrument accuracy was maintained after more than 100 uses without recalibration.

CONCLUSIONS

This meter identifies the possibility of rapid and accurate determinations of serum acetaminophen concentration. The instrument is ideally suited for patients with acetaminophen poisoning in whom expeditious and appropriate administration of antidotal therapy is desired.

A comparative prospective study of self-poisoned patients in Trondheim, Norway between 1978 and 1987: epidemiology and clinical data

1. In a prospective study of patients hospitalized for deliberate self-poisoning between 1978 and 1987 the number of admissions increased from 303 to 425. The annual incidence increased significantly for both women (P less than 0.05) and men (P less than 0.01). The mean age decreased significantly in the male group (P less than 0.05), but increased in the female group (P less than 0.05). 2. The median latency time for patients presenting at the hospital was short; 3.7 h in 1978 and 2.9 h in 1987. 3. There was a significant reduction in the percentage using barbiturates (9% in 1978 and 1% in 1987; P less than 0.001) and the use of benzodiazepines increased (18% in 1978 and 32% in 1987; P less than 0.05). The percentage of unconscious patients did not change significantly. 4. In 1987 N-acetyl-cysteine was the most frequently used antidote. Physostigmine has almost been abandoned since 1978. 5. Significantly more patients were hypotensive in 1978: 24% vs 11% in 1987; (P less than 0.001) and significantly less patients needed treatment in the central intensive care unit (2% in 1987 and 5% in 1978; P less than 0.05). Complications were few (8-10%) and the mortality low (approximately 1%) in both years studied. 6. The mean duration of hospitalization in 1978 was 65 h vs 30 h in 1987, (P less than 0.001).

Value of rapid screening for acetaminophen in all patients with intentional drug overdose

We performed a prospective study to determine the incidence of missed, potentially toxic acetaminophen poisoning in all patients with any type of intentional drug ingestion presenting to two large, county hospital emergency departments. Of 486 patients with drug ingestion seen during a five-month period, 114 (23.5%) were suspected of having ingested acetaminophen. Of these, 71 (62.3%) had insignificant acetaminophen levels (false-positive history). Of the 365 patients who were not suspected of having acetaminophen ingestion, seven patients (1.9%) were found to have elevated levels on rapid screening (false-negative history). Of these, only one patient had a potentially hepatotoxic level. We conclude that the incidence of missed, potentially serious acetaminophen overdose is very low in our study population.

Efficacy of charcoal cathartic versus ipecac in reducing serum acetaminophen in a simulated overdose

The traditional role of gastric emptying as the initial step in the management of the poisoned patient has recently been questioned; immediate activated charcoal administration has been recommended by some. In the setting of acetaminophen overdose, ipecac-induced emesis may interfere with subsequent oral antidotal therapy. Therefore, we conducted a study to compare the efficacy of initial therapy with ipecac with therapy with activated charcoal-cathartic in a simulated acetaminophen overdosage. Ten healthy volunteers participated in a randomized, crossover trial. Subjects ingested 3.0 g acetaminophen, followed by either no intervention, 30 mL syrup of ipecac, or 50 g activated charcoal-sorbitol solution at one hour. Serial acetaminophen levels were determined at intervals over eight hours. Both interventions significantly reduced the area under the curve compared with control (P less than .05). When comparing ipecac with activated charcoal-cathartic, no significant difference was noted among these groups.

Effect of N-acetylcysteine on the antiproliferative action of X-rays or bleomycin in cultured human lung tumor cells

N-Acetylcysteine is currently being considered as a possible selective protector against pulmonary toxicity resulting from X-rays or chemotherapeutic treatment, but its clinical application awaits evidence that it does not interfere with the efficient killing of tumor cells. The capacity of N-acetylcysteine to protect against the antitumor activity of X-rays and of bleomycin was evaluated in a clonogenic cell-survival assay using SW-1573 human squamous lung carcinoma cells as a tumor model. Using the highest non-toxic dose of N-acetylcysteine (incubation for 2 days in the continuous presence of 10 mM) no effect on clonogenic cell killing by X-rays or bleomycin treatment could be detected, even though a twofold enhancement of endogenous glutathione was effectuated. Our data thus indicate that clinically relevant concentrations of N-acetylcysteine are incapable of protecting tumor cells against clonogenic killing by X-rays and by bleomycin.

Efficacy of oral N-acetylcysteine in the treatment of acetaminophen overdose. Analysis of the national multicenter study (1976 to 1985)

During the investigational use of oral N-acetylcysteine as an antidote for poisoning with acetaminophen, 11,195 cases of suspected acetaminophen overdose were reported. We describe the outcomes of 2540 patients with acetaminophen ingestions treated with a loading dose of 140 mg of oral N-acetylcysteine per kilogram of body weight, followed four hours later by 70 mg per kilogram given every four hours for an additional 17 doses. Patients were categorized for analysis on the basis of initial plasma acetaminophen concentrations and the interval between ingestion and treatment. Hepatotoxicity developed in 6.1 percent of patients at probable risk when N-acetylcysteine was started within 10 hours of acetaminophen ingestion and in 26.4 percent of such patients when therapy was begun 10 to 24 hours after ingestion. Among patients at high risk who were treated 16 to 24 hours after an acetaminophen overdose, hepatotoxicity developed in 41 percent--a rate lower than that among historical controls. When given within eight hours of acetaminophen ingestion, N-acetylcysteine was protective regardless of the initial plasma acetaminophen concentration. There was no difference in outcome whether N-acetylcysteine was started zero to four or four to eight hours after ingestion, but efficacy decreased with further delay. There were 11 deaths among the 2540 patients (0.43 percent); in the nine fatal cases in which aminotransferase was measured before treatment, values were elevated before N-acetylcysteine was started. No deaths were clearly caused by acetaminophen among patients in whom N-acetylcysteine therapy was begun within 16 hours. We conclude that N-acetylcysteine treatment should be started within eight hours of an acetaminophen overdose, but that treatment is still indicated at least as late as 24 hours after ingestion. On the basis of available data, the 72-hour regimen of oral N-acetylcysteine is as effective as the 20-hour intravenous regimen described previously, and it may be superior when treatment is delayed.

The relationship between plasma ibuprofen concentrations and toxicity in acute ibuprofen overdose

1. The information available from the literature and from a prospective survey of ibuprofen overdose being undertaken by the London centre of the National Poisons Information Service (NPIS) was examined utilizing the Generalized Linear Interactive Modelling (GLIM) statistical computing package. 2. This confirmed that timed ibuprofen plasma concentrations were related to the symptoms of tachycardia, dizziness, tinnitus, ocular symptoms and coma/stupor as well as to reversible renal impairment and plasma hepatic enzyme elevation. 3. The best model of the relationship between symptomatic toxicity and timed ibuprofen plasma concentrations, was an exponential equation in time. Because of the lack of specificity or sensitivity in this model, and absence of demonstrable clinical advantages from its application, we do not recommend its use as a guide to predict toxicity. 4. However analysis of a larger information base utilizing similar methodology could, by increasing the statistical power of the resultant model, provide a useful means of predicting ibuprofen toxicity. 5. A previously postulated relationship between post-ingestion ibuprofen plasma concentrations and toxicity was not confirmed.

Glutathione redox pathway and reperfusion injury. Effect of N-acetylcysteine on infarct size and ventricular function

Glutathione peroxidase is an important enzyme in the degradative cascade of reactive oxygen free radicals. N-Acetylcysteine (NAC) is a low molecular weight compound that has been used clinically to replenish glutathione. To assess the role of the glutathione redox pathway on reperfusion injury, 23 animals underwent 90 minutes of proximal left anterior descending coronary artery occlusion followed by 24 hours of reperfusion with the administration of NAC (n = 11) or saline (n = 12) beginning 30 minutes into occlusion and continuing for 3 hours after reperfusion. Regional ventricular function was measured with contrast ventriculography, and regional myocardial blood flow was determined with microspheres. At 24 hours, the area at risk was defined in vivo with Monastral Blue, and the area of necrosis was defined by incubation in triphenyltetrazolium. Biopsies were taken from the ischemic and nonischemic zones to determine levels of total glutathione, superoxide dismutase and glutathione peroxidase activity, and reactivity to thiobarbituric acid, an index of lipid peroxidation. The rate-pressure product and myocardial blood flow were similar in the two groups throughout the study. No significant differences were noted in infarct size expressed as a percentage of the area at risk (28.6 +/- 5.3% vs. 36.6 +/- 6.0%) and of the total left ventricle (14.4 +/- 3.2% vs. 16.5 +/- 3.1%), and no differences were noted between the two groups on examination of the ischemic subendocardium by light and electron microscopy. Both groups exhibited similar degrees of dyskinesis during occlusion; however, treated animals showed significant improvement in regional radial shortening at 3 hours (3.4 +/- 2.4% vs. -2.4 +/- 2.1%, p less than 0.02) and 24 hours (9.2 +/- 2.2% vs. -2.5 +/- 6.3%, p less than 0.001) after reperfusion. No differences were present in total glutathione, thiobarbituric acid reactivity, or superoxide dismutase and glutathione peroxidase activity in the ischemic zones of the two groups. This study suggests that N-acetylcysteine treatment before reperfusion may reduce myocardial stunning but does not limit myocyte death after reperfusion.

Subacute acetaminophen overdose after incremental dosing

A case of acetaminophen poisoning following the ingestion of 26 g of acetaminophen by incremental dosing over a 25-h period is reported. At presentation, seven h after the last ingestion, the patient experienced hematemesis, the acetaminophen level was 150 micrograms/mL, and the SGOT was normal. The patient recovered uneventfully following N-acetylcysteine therapy. A review of the pharmacology and toxicity of acetaminophen is discussed. The case illustrates the problems of judging hepatotoxic potential in a multiple-dose acetaminophen ingestion and describes the successful use of N-acetylcysteine in a patient with a "subacute" acetaminophen overdose.

N-acetylcysteine inhibits human neutrophil and monocyte chemotaxis and oxidative metabolism

The effect of N-acetylcysteine (NAC) on human neutrophil and monocyte cell viability, chemotaxis, oxygen consumption and chemiluminescence was studied. It was found that NAC at concentrations higher than 3 X 10(-2) M resulted in neutrophil and monocyte cytotoxicity. The studies on the effect of NAC on neutrophil and monocyte chemotaxis showed that NAC inhibited chemotaxis of both cell types in a concentration dependent manner. NAC at 3 X 10(-2) M inhibited chemotaxis of both cell types by about 50% and at 10(-1) M inhibited PMN chemotaxis by 95% and MNL chemotaxis by 85%. The studies on the effect of NAC on neutrophil chemiluminescence demonstrated that NAC at concentrations of 1.5 X 10(-2) M, or higher, inhibited the response of the activated cells totally. When pH adjusted NAC or Mucomyst was used the inhibition was observed with higher concentrations of the drug (1.5 X 10(-1) M). NAC exhibited a similar pattern of inhibition on monocyte chemiluminescence response. These findings demonstrate that NAC, at concentrations obtainable in vivo by inhalation, impairs the chemotaxis and generation of oxygen radicals by human phagocytic cells. This property of NAC could have important implications concerning the prevention of tissue damage caused by these cells in inflammatory areas.

Effect of oral N-acetylcysteine administration on human blood neutrophil and monocyte function

N-acetylcysteine (NAC) is known to be a scavenger of free oxygen radicals, and recent in vitro studies have demonstrated that it is also able to inhibit leukocyte function. The clinical significance of these effects is, however, not known. In this study we have measured the effect on human blood neutrophil and monocyte function of a single 400 mg dose of NAC administered orally. Administration of NAC to ten healthy volunteers resulted in significant reduction of neutrophil chemiluminescence response following activation by opsonized zymosan as compared to four non-treated persons acting as controls. No effect was observed on the chemotaxis of either cell type or on monocyte chemiluminescence response. These findings suggest that NAC may be beneficial in clinical conditions like cystic fibrosis, where tissue damage may be a consequence of the effects of increased release of toxic oxygen radicals and proteolytic enzymes.

Cimetidine protection against alpha-amanitin hepatotoxicity in mice: a potential model for the treatment of Amanita phalloides poisoning

The ingestion of the mushroom Amanita phalloides is associated with hepatic necrosis appearing clinically two to three days after ingestion. The mechanism of this toxicity is unknown, and no reliable antidote is available. Because of the similarity of Amanita poisoning to other toxins affecting cytochrome P450, we investigated the use of cimetidine (as a P450 cytochrome inhibitor) as an antidote against a primary toxin of the mushroom alpha-amanitin. Mice injected with alpha-amanitin and given cimetidine either prophylactically or within six hours showed histologic protection from the hepatic damage seen in control mice. Control animals displayed significant mitochondrial changes when examined by electron-microscopy, while the mitochondria of the cimetidine-treated animals were preserved, suggesting a possible site for toxin action. Further trials will be necessary before treatment of human cases with cimetidine is indicated.

Prevention and reversal of nitrate tolerance in patients with congestive heart failure

To evaluate possible mechanisms underlying the development of nitrate tolerance, we treated 35 patients who had severe chronic heart failure with a prolonged (48-hour) intravenous infusion of nitroglycerin (6.4 micrograms per kilogram of body weight per minute) given either continuously or intermittently (12-hour infusions separated by intervals of 12 hours). Intravenous nitroglycerin produced immediate hemodynamic benefits in all patients, but the magnitude of this improvement was greatly diminished after 48 hours of continuous therapy with the drug. This attenuation was accompanied by cross-tolerance to oral isosorbide dinitrate and by an increase in heart rate, plasma renin activity, and body weight. In contrast, intermittent therapy with intravenous nitroglycerin was not associated with a loss of hemodynamic efficacy or cross-tolerance to oral nitrates and was not accompanied by changes in neurohormonal activity or body weight. In eight patients in whom nitrate tolerance developed during continuous intravenous therapy, the administration of the sulfhydryl-containing compound N-acetylcysteine (200 mg per kilogram orally) restored the hemodynamic state toward that observed at the start of the infusion of nitroglycerin (partial reversal of tolerance). In contrast, N-acetylcysteine had little hemodynamic effect in patients who were not receiving nitroglycerin. These data support the hypothesis that neurohormonal activation and depletion of sulfhydryl groups may interact to cause the loss of hemodynamic efficacy that occurs during prolonged treatment with intravenous nitroglycerin in patients with heart failure. Evaluation of the suggested role of sulfhydryl depletion in the development of tolerance will, however, require direct studies of vascular tissue.

Role of reactive oxygen intermediates in the hepatotoxicity of endotoxin

Administration of endotoxin (2.5 micrograms/mouse, iv) to Corynebacterium parvum-pretreated (14 days earlier, 1 mg/mouse, i.v.) mice caused a rapid (90 min) decrease in liver cytochrome P450-dependent drug metabolism and an elevation of serum transaminase. The time course of the priming effect of C. parvum suggested that macrophages might be responsible for this sensitization to endotoxin. The antioxidant N-acetylcysteine (500 mg/kg) effectively protected against this depression of liver drug metabolism, thus supporting the hypothesis that liver macrophage-generated free radicals might mediate this hepatotoxic effect of endotoxin.

Prediction of acetaminophen level from clinical history of overdose using a pharmacokinetic model

A retrospective study was undertaken to determine the accuracy of predicting acetaminophen levels using the pharmacokinetic equation for first-order absorption and elimination of a single oral ingestion, (Formula: see text) Forty-four acute adult acetaminophen overdoses were studied during a 22-month period. Eighty levels drawn from 0 to 16 hours after ingestion were evaluated. To standardize the data, only first levels drawn in patients without prior spontaneous or ipecac-induced vomiting were analyzed (n = 26). Of these 26 levels, eight (31%) were drawn from 0 to two hours after ingestion, eight (31%) from two to four hours, and ten (38%) from four to 16 hours, with correlations of 0.59, 0.85, and 0.98, respectively. To determine the accuracy of predicting four-hour levels, five patients with first levels drawn at four hours, prior to vomiting, were evaluated. Substituting appropriate constants, the condensed equation, Cp4h = (0.59) (mg/kg dose), was used to predict the four-hour level (r = 0.99). Preliminary data suggest the ability to accurately predict four-hour acetaminophen levels from ingestion history alone using pharmacokinetic equations.

Effects of ethanol ingestion on the metabolism of a hepatotoxic dose of paracetamol in mice

After administration to mice of a hepatotoxic dose of paracetamol (400 mg/kg body wt, p.o.) peak plasma concentrations of the drug and its glucuronide were approximately 900 microM around one hour. Corresponding levels of the sulphate, mercapturate and cysteine conjugates were approximately 100, 35 and 20 microM, respectively. Urinary excretion accounted for 55% of the administered drug 31 h after dosing. Of this total, 64.7% was paracetamol glucuronide, 17.9% paracetamol cysteine, 10.4% paracetamol sulphate, 0.5% paracetamol mercapturate and 6.5% unchanged drug. One hour after acute ethanol administration (3 g/kg, p.o., concomitantly with paracetamol) plasma levels of the glucuronide, cysteine and mercapturate conjugates were decreased by approximately 50%. There were reductions in the urinary excretion of the glucuronide (-13%) and cysteine conjugates (-24%), but increases in the amounts of mercapturate (+52%), sulphate +11%) and unchanged drug (+81%). Chronic ethanol ingestion (15 g/kg per d for 28 d) caused a transient initial increase in plasma paracetamol cysteine (+32%) and mercapturate (+41%) concentrations, but the only substantial change in urinary excretion was a 29% increase in the amount of paracetamol glucuronide. After chronic ethanol consumption, acute ethanol administration had a transient inhibitory effect on paracetamol mono-oxygenation, but glucuronidation was unaffected (as judged by plasma concentrations). Only paracetamol mercapturate excretion was substantially affected (+64%).

Acetaminophen overdose in children and adolescents

Ingestion of acetaminophen by young children and adolescents is common. Most children under the age of 6 who have ingested pediatric products can be safely managed at home. Children under the age of 6 who have taken a significant ingestion should be evaluated with a plasma level 4 or more hours after ingestion and, if toxic, treated with the antidote NAC prior to 16 hours postingestion. Less than 5 per cent of children under the age of 6 with toxic plasma levels will develop transient hepatic abnormalities. Adolescents who use acetaminophen in a suicidal or manipulative attempt should be seen and evaluated with a plasma acetaminophen level 4 or more hours postingestion. If the level is in the potentially toxic range on the nomogram, they should be treated prior to 16 hours postingestion with the antidote NAC. All patients should be evaluated for the possibility of other drugs or ingestants, especially if there is a change in the sensorium early in the course. The expected course of events in a patient with a toxic level of acetaminophen in the plasma is to have nausea, vomiting, and diaphoresis the first 24 hours. Following this, the patient should feel better but may begin to develop abnormalities of SGOT, SGPT, bilirubin, and prothrombin. Toxic patients will have peak enzyme levels at 72 to 96 hours. Over 99 per cent of patients will recover to normal values by 7 to 8 days postingestion. Long-term sequelae are not known.

Analysis of factors responsible for continuing mortality after paracetamol overdose

To determine reasons for the continuing mortality in patients taking a paracetamol overdose, the presentation, drug ingestion history, patient background, use of antidote (N-acetylcysteine and methionine), clinical course and outcome were determined in 247 patients treated at King's College Hospital in 1982 and 1983. Patients (147) were referred from other centres because of severe liver damage and 100 were local patients seen in the accident and emergency department. Survival in the local patients was 100% and, for those with severe liver damage, 49 and 63% (1982 and 1983 values). Delay in initial presentation to hospital was a major factor in determination of an adverse outcome, with a median delay of 30 h in the referred patients and 8 h in the local cases. Such a delay precluded administration of antidote to the majority of patients in the referred group, but in 11 cases where antidote could have been given a full course was not provided and all 11 patients died. Included among these were four patients in whom the serum paracetamol concentration was in the 'non-toxic' range. One patient with a chronic alcohol-drinking history (greater than 200 g/day) received N-acetylcysteine at 12 h but died from liver failure. However, in the complete series prior alcohol consumption was not associated with a significantly worse prognosis and simultaneous ingestion of alcohol with paracetamol had no effect on outcome. The concomitant ingestion of dextropropoxyphene caused an early and marked impairment of consciousness unrelated to any hepatotoxicity but, in three cases where dextropropoxyphene combinations were used, death occurred subsequently from liver failure.