Population pharmacokinetic analysis of acetaminophen overdose with immediate release, extended release and modified release formulations

OBJECTIVES

The introduction of delayed release formulations of acetaminophen (APAP) has created concern about the role of formulation in overdose. We examined the APAP overdose pharmacokinetic (PK) profiles to assess the role of dose, coingestants and formulation: immediate release (IR), extended release (ER), and modified release (MR) on APAP pharmacokinetic measures.

METHODS

We collected by-subject APAP PK data: subject description, timed blood APAP concentrations, dose, and coingestants. We sought both overdose and randomized controlled trials (RCTs) for supratherapeutic doses involving ER or MR formulations. Data analysis and simulation used the non-linear mixed-effects modeling program NONMEM-version 7.4.

RESULTS

The final dataset comprised 3,033 [APAP] from 356 subjects and 15 sources including 3 RCTs (179 subjects receiving IR, 122 ER, 65 MR). The final population PK (PopPK) model was a linear 2-compartment model with first-order (oral) absorption. Covariate relationships included: APAP absorption rate and bioavailability decreased with increased oral dose (p < 0.00005) for all 3 formulations (MR > ER > IR). Post hoc analyses showed opioid coingestant increased exposure (area under the curve, AUC) by factor of 1.6. Simulations of 100 g vs 10 g doses for IR, ER and MR showed overdose of the ER formulation exhibits slower absorption and lower C_max, overall exposure (AUC) is less than 80% of an equivalent dose of IR acetaminophen. The overall exposure for the MR formulation is less than 70% of an equivalent dose of IR.

CONCLUSIONS

Acetaminophen ER and MR formulations have slower absorption and decreased bioavailability leading to a lower C_max and later T_max than the IR formulation. These results have potential clinical implications because delayed absorption could confound use of the Rumack-Matthew nomogram by underestimating the severity of ingestion early in the course of treatment.

Delayed increase in serum acetaminophen concentration after ingestion of a combination medications: a case report

Acetaminophen is absorbed rapidly after oral intake, and serum concentration peaks within 4 hours. The Rumack–Matthew (RM) nomogram is widely used to identify the potential risk of liver dysfunction. However, the RM nomogram was intended for use only when a single agent was ingested. We report the case of a patient with overdose ingestion of an over-the-counter combination cold medication that contained acetaminophen, where the patient’s serum concentration increased over time. Over-the-counter combination cold medications are designed to relieve cold symptoms. However, the possibility that other agents that were present in the drug may change gastrointestinal kinetics should also be considered. The risk of liver dysfunction cannot be accurately determined from a single serum acetaminophen concentration measurement. Because of the risk of a delayed increase in the serum acetaminophen concentration, monitoring for liver dysfunction and developing a treatment strategy that includes N-acetylcysteine are required. This case report is targeted to clinical physicians who treat patients with acetaminophen overdose resulting from ingestion of multiple agents, and it reviews points of consideration when using the RM nomogram in acute intoxication.

Adverse Drug Reactions in the Intensive Care Unit

Adverse drug reactions (ADRs) are undesirable effects of medications used in normal doses [1]. ADRs can occur during treatment in an intensive care unit (ICU) or result in ICU admissions. A meta-analysis of 4139 studies suggests the incidence of ADRs among hospitalized patients is 17% [2]. Because of underreporting and misdiagnosis, the incidence of ADRs may be much higher and has been reported to be as high as 36% [3]. Critically ill patients are at especially high risk because of medical complexity, numerous high-alert medications, complex and often challenging drug dosing and medication regimens, and opportunity for error related to the distractions of the ICU environment [4]. Table 1 summarizes the ADRs included in this chapter.

Overdose with modified-release paracetamol (Panadol Osteo®) presenting to a metropolitan emergency medicine network: a case series

BACKGROUND

There are currently no large cases series documenting poisoning with paracetamol modified-release (Panadol Osteo®, GlaxoSmithKline, Sydney, NSW, Australia). Management guidelines recommend at least two serum paracetamol concentrations 4 h apart and initiating treatment with N-acetylcysteine (NAC) if more than 10 g is ingested.

OBJECTIVE

To describe a cohort of Panadol Osteo® poisoning and determine if the management of identified cases was consistent with existing guidelines.

METHOD

Descriptive retrospective case series presenting to a metropolitan hospital network with paracetamol poisoning from October 2009 to September 2013.

RESULTS

There were 42 cases of Panadol Osteo® poisoning identified. Twenty-nine patients (median ingested dose 19 950 mg) were treated with NAC, of which 27 were acute single ingestions. Of NAC-treated patients, 85% (23/27) had an initial serum paracetamol concentration that was above the nomogram line. However, 15% (4/27) had an initial non-toxic concentration that later increased above the line. In 14 untreated patients (median ingested dose 7980 mg), one was an unrecognised late line-crosser with initial non-toxic serum paracetamol concentration. Only 43% (6/14) had a repeat paracetamol concentration measured. Three patients had a 4 h paracetamol >500 μmol/L. Late line-crossing was seen in the NAC-treated group at this level. In two untreated patients, NAC should have been commenced on the reported dose.

CONCLUSION

Most patients presenting with Panadol Osteo® poisoning requiring NAC treatment had an initial serum paracetamol concentration indicating need for treatment. A small number of late treatment nomogram line-crossers was seen on repeat paracetamol estimation. The current guideline for Panadol Osteo® poisoning would have detected all cases requiring NAC treatment.

Unexpected late rise in plasma acetaminophen concentrations with change in risk stratification in acute acetaminophen overdoses

BACKGROUND

The acetaminophen risk analysis nomogram is used to predict hepatotoxicity risk in acute acetaminophen overdose based on a single plasma acetaminophen concentration (PAC) measured between 4 and 24 h after ingestion. There are case reports of patients with acute overdoses of acetaminophen combination products in whom a toxic PAC occurred later after an initial non-toxic PAC at approximately 4 h.

OBJECTIVES

The objective was to describe patients who had an initial non-toxic PAC and a subsequent toxic PAC.

METHODS

A poison center's database was searched for records in which patients were administered N-acetylcysteine. Cases were included if they involved an acute overdose of an acetaminophen-containing product with at least 2 plottable PACs, the first of which was obtained at least 4 h after ingestion and was below the treatment line on the nomogram with a subsequent toxic PAC. Data were analyzed for doses, timed PACs, specific acetaminophen preparation, coingestants, activated charcoal administration, and clinical effects.

RESULTS

Twenty patients were included. Thirteen patients ingested combination products. All patients experienced vomiting, neurologic, or cardiovascular effects at presentation or before obtaining the second PAC. Two patients developed hepatotoxicity, one of which died from the complications of acetaminophen-induced hepatotoxicity.

CONCLUSION

The nomogram fails to predict toxicity based on a single PAC in a small subset of patients.