Comparative pharmacokinetics of Panadol Extend and immediate-release paracetamol in a simulated overdose model

Population pharmacokinetics of immediate-release and modified-release paracetamol and its major metabolites in a supratherapeutic dosing study

OBJECTIVES

Overdose with paracetamol modified-release (MR) formulation, a bilayer tablet containing 69% slow-release component, has been increasing since its introduction to the market. However, little evidence exists for the management of MR paracetamol overdose. We aimed to develop a population pharmacokinetic (PK) model for immediate-release (IR) and MR paracetamol and its major metabolism, and quantitatively understand the formulation difference in toxicity assessment based on the nomogram line.

METHODS

Data from a cross-over study design in nine healthy volunteers administered a single supratherapeutic oral dose (80 mg/kg) of either IR and MR paracetamol were available from a published study. Plasma concentrations for paracetamol and its metabolites glucuronide (APAPG) and sulfate conjugate (APAPS) for both formulations were measured and analysed with population pharmacokinetic (PK) method using NONMEM. Toxicity in both formulations was assessed by comparing the simulated paracetamol concentrations under different paracetamol dose levels with the 150 mg/L nomograms. The difference in the assessment was compared between the two formulations.

RESULTS

Paracetamol concentrations for the IR formulation were described with a two-compartment model with first-order input and a lag time. The delayed time-course of MR paracetamol concentrations was best captured by a parallel absorption model in which the slow-release component was a serial zero-order then the first-order process. The formation of APAPG was linear, while APAPS concentrations were best fitted by a Michaelis-Menten process. The relative bioavailability of MR paracetamol compared to IR (FMR/IR) was estimated as 0.81. The simulated probability of making different toxicity assessments based on nomogram line was increased with dose levels and was as high as 14.6% after 22 g IR or MR paracetamol ingested.

CONCLUSIONS

A joint parent-metabolite model to describe time-course profiles of both IR and MR paracetamol and its metabolites APAPG and APAPS concentrations was developed. Simulations from the model showed that toxicity assessment based on the 150 mg/L nomograms is not suitable in MR paracetamol overdoses.

Bioequivalence and Safety of Twice-Daily Sustained-Release Paracetamol (Acetaminophen) Compared With 3- and 4-Times-Daily Paracetamol: A Repeat-Dose, Crossover Pharmacokinetic Study in Healthy Volunteers

Twice-daily sustained-release (SR) paracetamol (acetaminophen) offers convenient administration to chronic users. This study investigated at steady state (during the last 24 hours of a 3-day dosing period) the pharmacokinetics, bioequivalence, and safety of twice-daily SR paracetamol compared with extended-release (ER) and immediate-release (IR) paracetamol. In this open-label, randomized, multidose, 3-way crossover study, 28 healthy subjects received paracetamol SR (2 × 1000 mg twice daily), ER (2 × 665 mg 3 times daily), and IR (2 × 500 mg 4 times daily). At steady state, twice-daily SR paracetamol was bioequivalent to ER and IR paracetamol. The 90% confidence intervals for the ratios of geometric means were within the acceptance interval for SR/ER paracetamol (AUC_0-t , 0.973-1.033; AUC_0-24 , 0.974-1.034; AUC_0-∞ , 0.948-1.011; C_max , 1.082-1.212; C_av , 1.011-1.106) and SR/IR paracetamol (AUC_0-t , 0.969-1.029; AUC_0-24 , 0.968-1.027; AUC_0-∞ , 0.963-1.026; C_max , 0.902-1.010; C_av , 1.004-1.098). Given twice daily, the SR formulation demonstrated SR properties as expected. Mean time at or above a 4 μg/mL plasma concentration of paracetamol from 2 daily doses of the SR formulation was significantly longer than that from 4 daily doses of IR paracetamol. SR formulation also had a greater T_max , a longer half-life, and lower C_min compared with ER and IR paracetamol. All formulations were well tolerated.

A novel approach for estimating ingested dose associated with paracetamol overdose

AIM

In cases of paracetamol (acetaminophen, APAP) overdose, an accurate estimate of tissue-specific paracetamol pharmacokinetics (PK) and ingested dose can offer health care providers important information for the individualized treatment and follow-up of affected patients. Here a novel methodology is presented to make such estimates using a standard serum paracetamol measurement and a computational framework.

METHODS

The core component of the computational framework was a physiologically-based pharmacokinetic (PBPK) model developed and evaluated using an extensive set of human PK data. Bayesian inference was used for parameter and dose estimation, allowing the incorporation of inter-study variability, and facilitating the calculation of uncertainty in model outputs.

RESULTS

Simulations of paracetamol time course concentrations in the blood were in close agreement with experimental data under a wide range of dosing conditions. Also, predictions of administered dose showed good agreement with a large collection of clinical and emergency setting PK data over a broad dose range. In addition to dose estimation, the platform was applied for the determination of optimal blood sampling times for dose reconstruction and quantitation of the potential role of paracetamol conjugate measurement on dose estimation.

CONCLUSIONS

Current therapies for paracetamol overdose rely on a generic methodology involving the use of a clinical nomogram. By using the computational framework developed in this study, serum sample data, and the individual patient's anthropometric and physiological information, personalized serum and liver pharmacokinetic profiles and dose estimate could be generated to help inform an individualized overdose treatment and follow-up plan.

Interindividual variation in gene expression responses and metabolite formation in acetaminophen-exposed primary human hepatocytes

Acetaminophen (APAP) is a readily available over-the-counter drug and is one of the most commonly used analgesics/antipyretics worldwide. Large interindividual variation in susceptibility toward APAP-induced liver failure has been reported. However, the exact underlying factors causing this variability in susceptibility are still largely unknown. The aim of this study was to better understand this variability in response to APAP by evaluating interindividual differences in gene expression changes and APAP metabolite formation in primary human hepatocytes (PHH) from several donors (n = 5) exposed in vitro to a non-toxic to toxic APAP dose range. To evaluate interindividual variation, gene expression data/levels of metabolites were plotted against APAP dose/donor. The correlation in APAP dose response between donors was calculated by comparing data points from one donor to the data points of all other donors using a Pearson-based correlation analysis. From that, a correlation score/donor for each gene/metabolite was defined, representing the similarity of the omics response to APAP in PHH of a particular donor to all other donors. The top 1 % highest variable genes were selected for further evaluation using gene set overrepresentation analysis. The biological processes in which the genes with high interindividual variation in expression were involved include liver regeneration, inflammatory responses, mitochondrial stress responses, hepatocarcinogenesis, cell cycle, and drug efficacy. Additionally, the interindividual variation in the expression of these genes could be associated with the variability in expression levels of hydroxyl/methoxy-APAP and C8H13O5N-APAP-glucuronide. The before-mentioned metabolites or their derivatives have also been reported in blood of humans exposed to therapeutic APAP doses. Possibly these findings can contribute to elucidating the causative factors of interindividual susceptibility toward APAP.

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.

Application of physiologically based pharmacokinetic modeling to predict acetaminophen metabolism and pharmacokinetics in children

Acetaminophen (APAP) is a widely used analgesic and antipyretic drug that undergoes extensive phase I and II metabolism. To better understand the kinetics of this process and to characterize the dynamic changes in metabolism and pharmacokinetics (PK) between children and adults, we developed a physiologically based PK (PBPK) model for APAP integrating in silico, in vitro, and in vivo PK data into a single model. The model was developed and qualified for adults and subsequently expanded for application in children by accounting for maturational changes from birth. Once developed and qualified, it was able to predict clinical PK data in neonates (0–28 days), infants (29 days to <2 years), children (2 to <12 years), and adolescents (12–17 years) following intravenous and orally administered APAP. This approach represents a general strategy for projecting drug exposure in children, in the absence of pediatric PK information, using previous drug- and system-specific information of adults and children through PBPK modeling.

A novel paracetamol 1,000 mg sustained release formulation vs conventional paracetamol 500 mg formulation in patients with fever and pain: a randomized noninferiority trial

OBJECTIVE

To compare the efficacy and safety of newly developed paracetamol 1,000 mg sustained release (SR) tablets (test product) with conventional paracetamol 500 mg tablets (reference product) in patients with fever and pain.

DESIGN

An open label, multicentric, comparative, randomized, noninferiority trial.

METHODOLOGY

Eligible patient, as per predefined inclusion and exclusion criteria, were randomized to receive either one tablet of test product twice daily or one tablet of reference product four times a day for 3 consecutive days. Primary efficacy parameter (an antipyretic activity) was measured through recording changes in body temperature while secondary efficacy parameter (an analgesic activity) was measured by recording changes in visual analog scale (VAS) from the baseline. Safety assessment was done by recording adverse drug reactions occurred during treatment period. Analysis of variance was used for the statistical evaluation of data.

RESULTS

Of 500 randomized patients, 249 were received paracetamol 1,000 mg SR tablets (Group-I), and 247 were received conventional paracetamol 500 mg tablets (Group-II). Group-I reported temperature reduction from 101.35 ± 1.23°F to 98.80 ± 0.72°F while temperature reduction in Group-II was from 101.42 ± 1.33°F to 98.9 ± 0.85°F. Group-I reported reduction in mean VAS was from 6.16 ± 2.37 to 1.44 ± 1.70 in comparison to Group-II from 5.97 ± 2.45 to 1.38 ± 1.78. No significant adverse reactions were observed in either group.

CONCLUSION

Both the formulations of paracetamol were clinically and statically equivalent. Paracetamol 1,000 mg SR formulation is noninferior to conventional paracetamol 500 mg tablets.

Guidelines for the management of paracetamol poisoning in Australia and New Zealand--explanation and elaboration. A consensus statement from clinical toxicologists consulting to the Australasian poisons information centres

Paracetamol is involved in a large proportion of accidental paediatric exposures and deliberate self-poisoning cases, although subsequent hepatic failure and death are both uncommon outcomes. The optimal management of most patients with paracetamol overdose is usually straightforward. However, several differing nomograms and varying recommendations regarding potential risk factors for hepatic injury introduce complexity. In order to reconcile management advice with current Australasian clinical toxicology practice, revised guidelines have been developed by a panel of clinical toxicologists consulting to the poisons information centres in Australia and New Zealand using a workshop and consultative process. This article summarises the rationale for the recommendations made in these new guidelines.

Acetaminophen hepatotoxicity

Acetaminophen is a commonly used antipyretic and analgesic agent. It is safe when taken at therapeutic doses; however, overdose can lead to serious and even fatal hepatotoxicity. The initial metabolic and biochemical events leading to toxicity have been well described, but the precise mechanism of cell injury and death is unknown. Prompt recognition of overdose, aggressive management, and administration of N-acetylcysteine can minimize hepatotoxicity and prevent liver failure and death. Liver transplantation can be lifesaving for those who develop acute liver failure.