Repeated supratherapeutic acetaminophen ingestion (RSI) is an ingestion of acetaminophen at dosages higher than those recommended for extended periods of time. The risk of hepatotoxicity and the recommendations for treatment of acute acetaminophen ingestion (i.e., the Rumack-Matthew nomogram) do not apply to patients with RSI. Therefore, obtain the following information to guide acetylcysteine treatment for RSI:
- Acetaminophen serum or plasma concentrations. A reported history of the quantity of acetaminophen ingested is often inaccurate and is not a reliable guide to therapy.
- Laboratory tests to monitor hepatic and renal function and electrolyte and fluid balance: AST, ALT, bilirubin, INR, creatinine, BUN, blood glucose, and electrolytes.
For specific acetylcysteine dosage and administration information in patients with RSI, consider contacting your regional poison center at 1-800-222-1222, or alternatively, a special health professional assistance line for acetaminophen overdose at 1-800-525-6115.
Injection: 200 mg/mL (6 grams of acetylcysteine in 30 mL) in a single-dose vial.
Acetylcysteine Injection is contraindicated in patients with a previous hypersensitivity reaction to acetylcysteine [see Warnings and Precautions (5.1) ].
Serious acute hypersensitivity reactions during acetylcysteine administration including rash, hypotension, wheezing, and/or shortness of breath, have been observed in patients receiving intravenous acetylcysteine for acetaminophen overdose and occurred soon after initiation of the infusion [see Adverse Reactions (6.1) ]. If a severe hypersensitivity reaction occurs, immediately stop the infusion of acetylcysteine and initiate appropriate treatment.
One patient with asthma developed bronchospasm and died after intravenous administration of acetylcysteine. Acetylcysteine should be used with caution in patients with asthma, or where there is a history of bronchospasm. Patients with asthma should be closely monitored during initiation of acetylcysteine therapy and throughout acetylcysteine therapy.
Acute flushing and erythema of the skin may occur in patients receiving acetylcysteine intravenously. These reactions usually occur 30 to 60 minutes after initiating the infusion and often resolve spontaneously despite continued infusion of acetylcysteine. If a reaction to acetylcysteine involves more than simply flushing and erythema of the skin, it should be treated as a hypersensitivity reaction.
Management of less severe hypersensitivity reactions should be based upon the severity of the reaction and include temporary interruption of the infusion and/or administration of antihistaminic drugs. The acetylcysteine infusion may be carefully restarted after treatment of the hypersensitivity symptoms has been initiated; however, if the hypersensitivity reaction returns upon re-initiation of treatment or increases in severity, acetylcysteine should be discontinued and alternative patient management should be considered.
The total volume of acetylcysteine administered should be adjusted for patients less than 40 kg and for those requiring fluid restriction. To avoid fluid overload, the volume of diluent should be reduced as needed [see Dosage and Administration (2) ]. If volume is not adjusted fluid overload can occur, potentially resulting in hyponatremia, seizure and death.
Intravenous administration of acetylcysteine can cause fluid overload, potentially resulting in hyponatremia, seizure and death. To avoid fluid overload, use the recommended dilution shown in Tables 2, 3 and 4 [see Dosage and Administration (2.4) ].
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.
In the literature the most frequently reported adverse reactions attributed to intravenous acetylcysteine administration were rash, urticaria and pruritus. The frequency of adverse reactions has been reported to be between 0.2% and 21%, and they most commonly occur during the initial loading dose of acetylcysteine.
Loading Dose/Infusion Rate Study
In a randomized, open-label, multi-center clinical study conducted in Australia in patients with acetaminophen poisoning, the rates of hypersensitivity reactions between a 15-minute and 60-minute intravenous infusion for the 150 mg/kg loading dose of acetylcysteine were compared.
The incidence of drug-related adverse reactions occurring within the first 2 hours following acetylcysteine administration is presented in Table 5. Overall, 17% of patients developed an acute hypersensitivity reaction (18% in the 15-minute infusion group; 14% in the 60-minute infusion group) [see Warnings and Precautions (5.1), Clinical Studies (14)].
Unkn=Unknown; NOS = not other specified
|Number of Patients||n=109||n=71|
|Cardiac disorders||5 (5%)||2 (3%)|
|Tachycardia NOS||4 (4%)||1 (1%)||2 (3%)|
|Gastrointestinal disorders||16 (15%)||7 (10%)|
|Nausea||1 (1%)||6 (6%)||1 (1%)||1 (1%)|
|Vomiting NOS||2 (2%)||11 (10%)||2 (3%)||4 (6%)|
|Immune System Disorders||20 (18%)||10 (14%)|
|Hypersensitivity reaction||2 (2%)||6 (6%)||11 (10%)||1 (1%)||4 (6%)||5 (7%)||1 (1%)|
|Respiratory, thoracic and mediastinal disorders||2 (2%)||2 (3%)|
|Throat tightness||1 (1%)|
|Skin & subcutaneous tissue disorders||6 (6%)||5 (7%)|
|Pruritus||1 (1%)||2 (3%)|
|Rash NOS||3 (3%)||2 (2%)||3 (4%)|
|Vascular disorders||2 (2%)||3 (4%)|
|Flushing||1 (1%)||1 (1%)||2 (3%)||1 (1%)|
A large multi-center study was performed in Canada where data were collected from patients who were treated with intravenous acetylcysteine for acetaminophen overdose between 1980 and 2005. This study evaluated 4,709 adult cases and 1,905 pediatric cases. The incidence of hypersensitivity reactions in adult (overall incidence 8%) and pediatric (overall incidence 10%) patients is presented in Tables 6 and 7.
* Respiratory symptoms are defined as presence of any of the following: cough, wheezing, stridor, shortness of breath, chest tightness, respiratory distress, or bronchospasm.
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