Clinical pharmacokinetics of paracetamol

What dose of paracetamol for older people?

Paracetamol, on its own or in combination with other analgesics, is widely used to treat pain associated with acute and chronic conditions. It is considered safe enough to have a general sales licence (GSL) for use by "adults, elderly and children over 16 years" and has few listed cautions or contraindications.1,2 However, recently the effectiveness and safety of paracetamol for some conditions have been challenged, 3,4 and there are published case reports of liver failure associated with therapeutic doses.5-9 Here, we review the use of paracetamol, its pharmacokinetics, the mechanisms by which it can cause liver damage and consider whether frail older people are at greater risk of adverse effects. We also discuss if dose reduction should be considered in some circumstances.

An Evidence-Based Opioid-Free Anesthetic Technique to Manage Perioperative and Periprocedural Pain

Background

The epidemic of opioid abuse is increasing, and the number of deaths secondary to opioid overdose is also increasing. Recent attention has focused on opioid prescribing and management of chronic pain. However, opioid use in perioperative and periprocedural patients, whether they have chronic pain or exhibit new persistent opioid abuse after a procedure, has received little attention.

Methods

We present an evidence-based technique that combines subanesthetic infusions of lidocaine and dexmedetomidine supplemented with other intravenous agents and a low dose of inhaled anesthetic.

Results

Based on evidence of drug action and interaction, an opioid-free anesthetic can be delivered successfully. We present the cases of 2 patients in whom the opioid-free anesthetic technique was used with a successful outcome, adequate pain management, and avoidance of opioid drugs.

Conclusion

This anesthetic prescription can be useful for opioid-naïve patients as well as for patients with chronic pain that is managed with opioids.

Acetaminophen (APAP or N-Acetyl-p-Aminophenol) and Acute Liver Failure

Acetaminophen (APAP) is the leading cause of acute liver failure (ALF), although the worldwide frequency is variable. APAP hepatotoxicity develops either following intentional overdose or unintentional ingestion (therapeutic misadventure) in the background of several factors, such as concomitant use of alcohol and certain medications that facilitate the formation of reactive and toxic metabolites. Spontaneous survival is more common in APAP-induced ALF compared with non-APAP etiologies. N-acetylcysteine is recommended for all patients with APAP-induced ALF and it reduces mortality. Liver transplantation should be offered early to those who are unlikely to survive based on described prognostic criteria.

Impact of medication on protein and amino acid metabolism in the elderly: the sulfur amino acid and paracetamol case

The optimisation of nutritional support for the growing number of older individuals does not usually take into account medication. Paracetamol (acetaminophen; APAP) is the first intention treatment of chronic pain that is highly prevalent and persistent in the elderly. Detoxification of APAP occurs in the liver and utilises sulfate and glutathione (GSH), both of which are issued from cysteine (Cys), a conditionally indispensable amino acid. The detoxification-induced siphoning of Cys could reduce the availability of Cys for skeletal muscle. Consequently, APAP could worsen sarcopenia, an important component of the frailty syndrome leading to dependency. The present review provides the rationale for the potential pro-sarcopenic effect of APAP then recent results concerning the effect of chronic APAP treatment on muscle mass and metabolism are discussed. The principal findings are that chronic treatments with doses of APAP comparable with the maximum posology for humans can increase the requirement for sulfur amino acids (SAA), reduce Cys availability for muscle, reduce muscle protein synthesis and aggravate sarcopenia in animals. One clinical study is in favour of an enhanced SAA requirement in the older individual under chronic treatment with APAP. Few clinical studies investigated the effect of chronic treatment with APAP combined with exercise, in nutritional conditions that probably did not affect Cys and GSH homeostasis. Whether APAP can aggravate sarcopenia in older individuals with low protein intake remains to be tested. If true, nutritional strategies based on enhancing Cys supply could be of prime interest to cut down the pro-sarcopenic effect of chronic treatment with APAP.

Molecular Adsorbent Recirculating System Treatment Can Reduce Blood Levels of N-Acetylcysteine in Patients With Acetaminophen Overdose: Case Reports

BACKGROUND

Acetaminophen poisoning continues to be a major cause of liver failure that can lead to liver transplantation. N-acetylcysteine (NAC) is the cornerstone of treatment. Some authors use a Molecular Adsorbent Recirculating System (MARS) system in acetaminophen poisoning. It is reported that the MARS system eliminates acetaminophen more efficiently than conventional dialysis. It is theoretically possible that treatment with MARS administered after NAC will increase the effectiveness of treatment.

CASE REPORTS

The first patient, a woman of 14 years old, presented blood levels of 112 mg/dL 12 hours after ingestion of 15 g of acetaminophen. Treatment with NAC was initiated. At 17 and 23 hours after ingestion, blood levels were 23.5 μg/mL and 5.9 μg/mL, respectively. The second patient, a woman of 28 years old, presented blood levels of 115 mg/dL 4 hours after ingestion of 40 g of acetaminophen. Treatment with NAC was initiated. At 14 and 23 hours after ingestion, blood levels were 15.8 μg/mL and <2 μg/mL, respectively. In both patients, we performed MARS after completing treatment with NAC, and after the first session, blood levels were below the lower limit of detection (≤2 μg/mL).

DISCUSSION

The correct timing of MARS to avoid interactions with the administered dose of NAC in acetaminophen overdose is essential so as to not impair the effectiveness of this treatment. These considerations in the management of this entity help in the resolution of liver failure, thus avoiding the need for a liver transplant.

Simultaneous determination of acetaminophen and oxycodone in human plasma by LC-MS/MS and its application to a pharmacokinetic study

A simple and rapid liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed and validated for simultaneous determination of acetaminophen and oxycodone in human plasma. Acetaminophen-d4 and oxycodone-d3 were used as internal standards. The challenge encountered in the method development that the high plasma concentration level of acetaminophen made the MS response saturated while the desired lower limit of quantification (LLOQ) for oxycodone was hard to reach was well solved. The analytes were extracted by protein precipitation using acetonitrile. The matrix effect of the analytes was avoided by chromatographic separation using a hydrophilic C₁₈ column coupled with gradient elution. Multiple reaction monitoring in positive ion mode was performed on tandem mass spectrometer employing electrospray ion source. The calibration curves were linear over the concentration ranges of 40.0–8000 ng/mL and 0.200–40.0 ng/mL for acetaminophen and oxycodone, respectively. This method, which could contribute to high throughput analysis and better clinical drug monitoring, was successfully applied to a pharmacokinetic study in healthy Chinese volunteers.

Acute acetaminophen ingestion improves performance and muscle activation during maximal intermittent knee extensor exercise

Aim

Acetaminophen is a commonly used medicine for pain relief and emerging evidence suggests that it may improve endurance exercise performance. This study investigated some of the physiological mechanisms by which acute acetaminophen ingestion might blunt muscle fatigue development.

Methods

Thirteen active males completed 60 × 3 s maximum voluntary contractions (MVC) of the knee extensors with each contraction separated by a 2 s passive recovery period. This protocol was completed 60 min after ingesting 1 g of maltodextrin (placebo) or 1 g of acetaminophen on two separate visits. Peripheral nerve stimulation was administered every 6th contraction for assessment of neuromuscular fatigue development, with the critical torque (CT), which reflects the maximal sustainable rate of oxidative metabolism, taken as the mean torque over the last 12 contractions. Surface electromyography was recorded continuously as a measure of muscle activation.

Results

Mean torque (61 ± 11 vs. 58 ± 14% pre-exercise MVC) and CT (44 ± 13 vs. 40 ± 15% pre-exercise MVC) were greater in the acetaminophen trial compared to placebo (both P < 0.05). Voluntary activation and potentiated twitch declined at a similar rate in both conditions (P > 0.05). However, the decline in electromyography amplitude was attenuated in the acetaminophen trial, with electromyography amplitude being greater compared to placebo from 210 s onwards (P < 0.05).

Conclusion

These findings indicate that acute acetaminophen ingestion might be ergogenic by increasing CT and preserving muscle activation during high-intensity exercise.

Electronic supplementary material

The online version of this article (10.1007/s00421-017-3794-7) contains supplementary material, which is available to authorized users.

Conjugation of nitrated acetaminophen to Der p1 amplifies peripheral blood monocyte response to Der p1

BACKGROUND

An association of acetaminophen use and asthma was observed in the International Study of Asthma and Allergies in Childhood study. However there are no clear mechanisms to explain an association between acetaminophen use and immunologic pathology. In acidic conditions like those in the stomach and inflamed airway, tyrosine residues are nitrated by nitrous and peroxynitrous acids. The resulting nitrotyrosine is structurally similar to 2,4-dinitrophenol and 2,4-dinitrochlorobenzene, known haptens that enhance immune responses by covalently binding proteins. Nitrated acetaminophen shares similar molecular structure.

OBJECTIVE

We hypothesized the acetaminophen phenol ring undergoes nitration under acidic conditions, producing 3-nitro-acetaminophen which augments allergic responses by acting as a hapten for environmental allergens.

METHODS

3-nitro-acetaminophen was formed from acetaminophen in the presence of acidified nitrite, purified by high performance liquid chromatography, and assayed by gas-chromatography mass spectrometry. Purified 3-nitro-acetaminophen was reacted with Dermatophagoides pteronyssinus (Der p1) and analyzed by mass spectrometry to identify the modification site. Human peripheral blood mononuclear cells proliferation response was measured in response to 3-nitro-acetaminophen and to 3-nitro-acetaminophen-modified Der p1.

RESULTS

Acetaminophen was modified by nitrous acid forming 3-nitro-acetaminophen over a range of different acidic conditions consistent with airway inflammation and stomach acidity. The Der p1 protein-hapten adduct creation was confirmed by liquid chromatography-mass spectrometry proteomics modifying cysteine 132. Peripheral blood mononuclear cells exposed to 3-nitro-acetaminophen-modified Der p1 had increased proliferation and cytokine production compared to acetaminophen and Der p1 alone (n = 7; p < 0.05).

CONCLUSION

These data suggests 3-nitro-acetaminophen formation and reaction with Der p1 provides a mechanism by which stomach acid or infection-induced low airway pH in patients could enhance the allergic response to proteins such as Der p1.

Supra-Therapeutic Oral Paracetamol Overdose in Adults: An Update for the Dental Team

Paracetamol (acetaminophen) is a commonly used analgesic; its 'over the counter' availability, low cost and popularity amongst patients often make it the first choice for dental pain. It is in this that its potential toxicity, made more complicated by the ever extending range of paracetamol-containing products, make the understanding of this medication key to the safe management of patients presenting to surgery with dental pain. Clinical relevance: The purpose of this article is to supply dental practitioners with the knowledge to manage patients who present having taken an oral supra-therapeutic paracetamol overdose. Consideration is given to those patients who can be treated safely in primary care and to those who require transfer to Accident and Emergency (A&E).

Quantification of Acetaminophen and Its Metabolites in Plasma Using UPLC-MS: Doors Open to Therapeutic Drug Monitoring in Special Patient Populations

BACKGROUND

Acetaminophen (APAP, paracetamol) is the most commonly used drug for pain and fever in both the United States and Europe and is considered safe when used at registered dosages. Nevertheless, differences between specific populations lead to remarkable changes in exposure to potentially toxic metabolites. Furthermore, extended knowledge is required on metabolite formation after intoxication, to optimize antidote treatment. Therefore, the authors aimed to develop and validate a quick and easy analytical method for simultaneous quantification of APAP, APAP-glucuronide, APAP-sulfate, APAP-cysteine, APAP-glutathione, APAP-mercapturate, and protein-derived APAP-cysteine in human plasma by ultraperformance liquid chromatography-electrospray ionization-tandem mass spectrometry.

METHODS

The internal standard was APAP-D4 for all analytes. Chromatographic separation was achieved with a reversed-phase Acquity ultraperformance liquid chromatography HSS T3 column with a runtime of only 4.5 minutes per injected sample. Gradient elution was performed with a mobile phase consisting of ammonium acetate, formic acid in Milli-Q ultrapure water or in methanol at flow rate of 0.4 mL/minute.

RESULTS

A plasma volume of only 10 μL was required to achieve both adequate accuracy and precision. Calibration curves of all 6 analytes were linear. All analytes were stable for at least 48 hours in the autosampler; the high quality control of APAP-glutathione was stable for 24 hours. The method was validated according to the U.S. Food and Drug Administration guidelines.

CONCLUSIONS

This method allows quantification of APAP and 6 metabolites, which serves purposes for research, as well as therapeutic drug monitoring. The advantage of this method is the combination of minimal injection volume, a short runtime, an easy sample preparation method, and the ability to quantify APAP and all 6 metabolites.

Dietary supplementation with cysteine prevents adverse metabolic outcomes of repeated cures with paracetamol in old rats

Cysteine (Cys), a conditionally indispensable amino acid, is required for the detoxification of paracetamol (acetaminophen, N-acetyl-para-aminophenol, 4-hydroxy-acetanilide, APAP), a drug of widespread use in older persons. We recently reported that repeated APAP cures could worsen sarcopenia in old rats, likely to be due to the impairment of Cys/GSH homoeostasis. The aim of the study was to evaluate whether a dietary Cys supplementation during APAP cures could improve Cys/GSH homoeostasis and thus preserve skeletal muscle. Male 21·5-month-old Wistar rats received three 2-week-long cures of APAP (1 % of diet) alone or with extra Cys (0·5 % of diet), intercalated with washout periods of 2 weeks (APAP and APAP-Cys groups, respectively). They were compared with untreated control rats (CT group). CT and APAP-Cys groups were pair-fed to the APAP group. Dietary Cys supplementation was efficient to prevent increase in liver mass (P<0·0001), decrease in liver GSH (P<0·0001), increase in blood GSH concentration (P<0·0001), and to some extent, decrease in plasma free Cys concentration (P<0·05), all induced by repeated APAP cures. The addition of Cys to APAP cures decreased plasma alanine transaminase (P<0·05), the fractional synthesis rate of liver proteins (P<0·01), and increased masses of extensor digitorum longus (P<0·01), and soleus (P<0·05), compared with the APAP group. Cys supplementation prevented alteration in Cys/GSH homoeostasis and increased some muscle masses in old rats under repeated cures with a non-toxic dose of APAP.

Male urinary paracetamol and semen quality

The endocrine-disrupting properties of paracetamol have been previously demonstrated in rodent studies of abnormal sperm morphology and diminished testosterone production, in addition to epidemiologic studies of diminished couple fecundity. In this study, we examined the relationship between paracetamol and its metabolite p-aminophenol quantified in a single spot urine and semen quality among 501 male partners of couples planning for pregnancy. Men provided a urine specimen and two fresh semen samples collected approximately one month apart and underwent 24-h analysis for 35 semen quality parameters. Paracetamol and p-aminophenol were quantified in urine by ultra-high-performance liquid chromatography coupled with an electrospray triple quadrupole mass spectrometry. The relationship between natural-log-transformed urinary paracetamol and p-aminophenol rescaled by their standard deviation and 21 Box-Cox-transformed, 14 non-transformed semen parameters was assessed using linear mixed-effects models. The median concentrations (IQR) of urinary paracetamol and p-aminophenol were 15.5 ng/mL (5.44, 73.5) and 978 ng/mL (500, 1596), respectively. Following adjustment for creatinine and age, a 1-standard deviation increase in log-transformed urinary paracetamol was associated with a reduction in beat cross-frequency and an increase in DNA fragmentation [β (95% CI): -0.59 Hz (-1.16, -0.03) and 0.05% (0.01, 0.09), respectively]. These findings were corroborated in models of categorical chemical concentrations; higher concentrations of paracetamol remained associated with reduced beat cross-frequency and increased DNA fragmentation. A 1-standard deviation increase in log-transformed urinary p-aminophenol was associated with a reduction in sperm head area [β (95% CI): -0.1 μm2 (-0.18, -0.02) and width -0.02 μm (-0.04, -0.01)]. However, only the association with sperm head area remained statistically significant in models of p-aminophenol quartiles. Our findings suggest that adult male urinary paracetamol is associated with sperm motility and DNA fragmentation, while the metabolite, p-aminophenol, is predominantly associated with sperm head morphometry.

Exposure to acetaminophen and all its metabolites upon 10, 15, and 20 mg/kg intravenous acetaminophen in very-preterm infants

BackgroundExposure to acetaminophen and its metabolites in very-preterm infants is partly unknown. We investigated the exposure to acetaminophen and its metabolites upon 10, 15, or 20 mg/kg intravenous acetaminophen in preterm infants.MethodsIn a randomized trial, 59 preterm infants (24-32 weeks' gestational age, postnatal age <1 week) received 10, 15, or 20 mg/kg acetaminophen intravenously. Plasma concentrations of acetaminophen and its metabolites (glucuronide, sulfate, cysteine, mercapturate, and glutathione) were determined in 293 blood samples. Area under the plasma concentration-time curves (AUC_0-500 min) was related to dose and gestational age.ResultsBetween 10 and 20 mg/kg dose, median AUCs of acetaminophen, glucuronide, sulfate, and cysteine increased significantly resulting in unchanged ratios of AUC of metabolite to acetaminophen. The AUC ratio of glucuronide to acetaminophen increased with gestational age, that of sulfate decreased, and the ratio of cysteine and mercapturate remained unchanged.ConclusionWe found a gestational-age-dependent increase in glucuronidation but no evidence for saturation of a specific pathway as there was a proportional increase in exposure of acetaminophen and all metabolites. Compared with adults, very low exposure to glucuronide but higher exposure to sulfate, cysteine, and mercapturate metabolites was found, of which the relevance is not yet known.

Morbidly Obese Patients Exhibit Increased CYP2E1-Mediated Oxidation of Acetaminophen

Introduction

Acetaminophen (paracetamol) is mainly metabolized via glucuronidation and sulphation, while the minor pathway through cytochrome P450 (CYP) 2E1 is held responsible for hepatotoxicity. In obese patients, CYP2E1 activity is reported to be induced, thereby potentially worsening the safety profile of acetaminophen. The aim of this study was to determine the pharmacokinetics of acetaminophen and its metabolites (glucuronide, sulphate, cysteine and mercapturate) in morbidly obese and non-obese patients.

Methods

Twenty morbidly obese patients (with a median total body weight [TBW] of 140.1 kg [range 106–193.1 kg] and body mass index [BMI] of 45.1 kg/m² [40–55.2 kg/m²]) and eight non-obese patients (with a TBW of 69.4 kg [53.4–91.7] and BMI of 21.8 kg/m² [19.4–27.4]) received 2 g of intravenous acetaminophen. Fifteen blood samples were collected per patient. Population pharmacokinetic modelling was performed using NONMEM.

Results

In morbidly obese patients, the median area under the plasma concentration–time curve from 0 to 8 h (AUC_0–8h) of acetaminophen was significantly smaller (P = 0.009), while the AUC_0–8h ratios of the glucuronide, sulphate and cysteine metabolites to acetaminophen were significantly higher (P = 0.043, 0.004 and 0.010, respectively). In the model, acetaminophen CYP2E1-mediated clearance (cysteine and mercapturate) increased with lean body weight [LBW] (population mean [relative standard error] 0.0185 L/min [15 %], P < 0.01). Moreover, accelerated formation of the cysteine and mercapturate metabolites was found with increasing LBW (P < 0.001). Glucuronidation clearance (0.219 L/min [5 %]) and sulphation clearance (0.0646 L/min [6 %]) also increased with LBW (P < 0.001).

Conclusion

Obesity leads to lower acetaminophen concentrations and earlier and higher peak concentrations of acetaminophen cysteine and mercapturate. While a higher dose may be anticipated to achieve adequate acetaminophen concentrations, the increased CYP2E1-mediated pathway may preclude this dose adjustment.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-015-0357-0) contains supplementary material, which is available to authorized users.

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.

Paracetamol (acetaminophen) for chronic non-cancer pain in children and adolescents

BACKGROUND

Pain is a common feature of childhood and adolescence around the world, and for many young people, that pain is chronic. The World Health Organization guidelines for pharmacological treatments for children's persisting pain acknowledge that pain in children is a major public health concern of high significance in most parts of the world. While in the past, pain was largely dismissed and was frequently left untreated, views on children's pain have changed over time, and relief of pain is now seen as important.We designed a suite of seven reviews on chronic non-cancer pain and cancer pain (looking at antidepressants, antiepileptic drugs, non-steroidal anti-inflammatory drugs, opioids, and paracetamol as priority areas) in order to review the evidence for children's pain utilising pharmacological interventions in children and adolescents.As the leading cause of morbidity in children and adolescents in the world today, chronic disease (and its associated pain) is a major health concern. Chronic pain (lasting three months or longer) can arise in the paediatric population in a variety of pathophysiological classifications: nociceptive, neuropathic, idiopathic, visceral, nerve damage pain, chronic musculoskeletal pain, and chronic abdominal pain, and other unknown reasons.Paracetamol (acetaminophen) is one of the most widely used analgesics in both adults and children. The recommended dosage in the UK, Europe, Australia, and the USA for children and adolescents is generally 10 to 15 mg/kg every four to six hours, with specific age ranges from 60 mg (6 to 12 months old) up to 500 to 1000 mg (over 12 years old). Paracetamol is the only recommended analgesic for children under 3 months of age. Paracetamol has been proven to be safe in appropriate and controlled dosages, however potential adverse effects of paracetamol if overdosed or overused in children include liver and kidney failure.

OBJECTIVES

To assess the analgesic efficacy and adverse events of paracetamol (acetaminophen) used to treat chronic non-cancer pain in children and adolescents aged between birth and 17 years, in any setting.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) via the Cochrane Register of Studies Online, MEDLINE via Ovid, and Embase via Ovid from inception to 6 September 2016. We also searched the reference lists of retrieved studies and reviews, and searched online clinical trial registries.

SELECTION CRITERIA

Randomised controlled trials, with or without blinding, of any dose and any route, treating chronic non-cancer pain in children and adolescents, comparing paracetamol with placebo or an active comparator.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for eligibility. We planned to use dichotomous data to calculate risk ratio and numbers needed to treat, using standard methods where data were available. We assessed GRADE (Grading of Recommendations Assessment, Development and Evaluation) and planned to create a 'Summary of findings' table.

MAIN RESULTS

No studies were eligible for inclusion in this review. We rated the quality of the evidence as very low. We downgraded the quality of evidence by three levels due to the lack of data reported for any outcome.

AUTHORS' CONCLUSIONS

There was no evidence from randomised controlled trials to support or refute the use of paracetamol (acetaminophen) to treat chronic non-cancer pain in children and adolescents. We are unable to comment about efficacy or harm from the use of paracetamol to treat chronic non-cancer pain in children and adolescents.We know from adult randomised controlled trials that paracetamol, can be effective, in certain doses, and in certain pain conditions (not always chronic).This means that no conclusions could be made about efficacy or harm in the use of paracetamol (acetaminophen) to treat chronic non-cancer pain in children and adolescents.

Pharmacokinetic Study of Intravenous Acetaminophen Administered to Critically Ill Multiple-Trauma Patients at the Usual Dosage and a New Proposal for Administration

The pharmacokinetic profile of intravenous acetaminophen administered to critically ill multiple-trauma patients was studied after 4 consecutive doses of 1 g every 6 hours. Eleven blood samples were taken (predose and 15, 30, 45, 60, 90, 120, 180, 240, 300, and 360 minutes postdose), and urine was collected (during 6-hour intervals between doses) to determine serum and urine acetaminophen concentrations. These were used to calculate the following pharmacokinetic parameters: maximum and minimum concentrations, terminal half-life, area under serum concentration-time curve from 0 to 6 hours, mean residence time, volume of distribution, and serum and renal clearance of acetaminophen. Daily doses of acetaminophen required to obtain steady-state minimum (bolus dosing) and average plasma concentrations (continuous infusion) of 10 μg/mL were calculated (10 μg/mL is the presumed lower limit of the analgesic range). Data are expressed as median [interquartile range]. Twenty-two patients were studied, mostly young (age 44 [34-64] years) males (68%), not obese (weight 78 [70-84] kg). Acetaminophen concentrations and pharmacokinetic parameters were these: maximum concentration 33.6 [25.7-38.7] μg/mL and minimum concentration 0.5 [0.2-2.3] μg/mL, all values below 10 μg/mL and 8 below the detection limit; half-life 1.2 [1.0-1.9] hours; area under the curve for 6 hours 34.7 [29.7-52.7] μg·h/mL; mean residence time 1.8 [1.3-2.6] hours; steady-state volume of distribution 50.8 [42.5-66.5] L; and serum and renal clearance 28.8 [18.9-33.7] L/h and 15 [11-19] mL/min, respectively. Theoretically, daily doses for a steady-state minimum concentration of 10 μg/mL would be 12.2 [7.8-16.4] g/day (166 [112-202] mg/[kg·day]); for an average steady-state concentration of 10 μg/mL, they would be 6.9 [4.5-8.1] g/day (91 [59-111] mg/[kg·day]). In conclusion, administration of acetaminophen at the recommended dosage of 1 g per 6 hours to critically ill multiple-trauma patients yields serum concentrations below 10 μg/mL due to increased elimination. To reach the 10 μg/mL target, and from a strictly pharmacokinetic point of view, continuous infusion may be more feasible than bolus dosing. Such a change in dosing strategy requires appropriate, pharmacokinetic-pharmacodynamic and specific safety study.

A high susceptibility to redox imbalance of the transmissible stages of Plasmodium falciparum revealed with a luciferase-based mature gametocyte assay

The goal to prevent Plasmodium falciparum transmission from humans to mosquitoes requires the identification of targetable metabolic processes in the mature (stage V) gametocytes, the sexual stages circulating in the bloodstream. This task is complicated by the apparently low metabolism of these cells, which renders them refractory to most antimalarial inhibitors and constrains the development of specific and sensitive cell-based assays. Here, we identify and functionally characterize the regulatory regions of the P. falciparum gene PF3D7_1234700, encoding a CPW-WPC protein and named here Upregulated in Late Gametocytes (ULG8), which we have leveraged to express reporter genes in mature male and female gametocytes. Using transgenic parasites containing a pfULG8-luciferase cassette, we investigated the susceptibility of stage V gametocytes to compounds specifically affecting redox metabolism. Our results reveal a high sensitivity of mature gametocytes to the glutathione reductase inhibitor and redox cycler drug methylene blue (MB). Using isobologram analysis, we find that a concomitant inhibition of the parasite enzyme glucose-6-phosphate dehydrogenase-6-phosphogluconolactonase, a key component of NADPH synthesis, potently synergizes MB activity. These data suggest that redox metabolism and detoxification activity play an unsuspected yet vital role in stage V gametocytes, rendering these cells exquisitely sensitive to decreases in NADPH concentration.

Management of Acute Hepatotoxicity Including Medical Agents and Liver Support Systems

Drug-induced liver injury (DILI) can be predictable or idiosyncratic and has an estimated incidence of approximately 20 cases per 100,000 persons per year. DILI is a common cause of acute liver failure in the United States. No accurate tests for diagnosing DILI exist, and its diagnosis is based on exclusion of other conditions. Managing DILI includes discontinuing the suspected causative agent and in selected cases administering an antidote. Liver support systems are used for long-term support or as a bridge to transplantation and are effective for improving encephalopathy, hyperbilirubinemia, and other liver-related conditions, but whether they improve survival remains uncertain.

The 100 most influential publications in paracetamol poisoning treatment: a bibliometric analysis of human studies

BACKGROUND

Analysis of the most influential publications within paracetamol poisoning treatment can be helpful in recognizing main and novel treatment issues within the field of toxicology. The current study was performed to recognize and describe the most highly cited articles related to paracetamol poisoning treatment.

METHODS

The 100 most highly cited articles in paracetamol poisoning treatment were identified from the Scopus database in November 2015. All eligible articles were read for basic information, including total number of citations, average citations per year, authors' names, journal name, impact factors, document types and countries of authors of publications.

RESULTS

The median number of citations was 75 (interquartile range 56-137). These publications were published between 1974 and 2013. The average number of years since publication was 17.6 years, and 45 of the publications were from the 2000s. A significant, modest positive correlation was found between years since publication and the number of citations among the top 100 cited articles (r = 0.316; p = 0.001). A total of 55 journals published these 100 most cited articles. Nine documents were published in Clinical Toxicology, whereas eight documents were published in Annals of Emergency Medicine. Citations per year since publication for the top 100 most-cited articles ranged from 1.5 to 42.6 and had a mean of 8.5 citations per year and a median of 5.9 with an interquartile range of 3.75-10.35. In relation to the origin of the research publications, they were from 8 countries. The USA had the largest number of articles, 47, followed by the UK and Australia with 38 and nine articles respectively.

CONCLUSIONS

This study is the first bibliometric assessment of the top 100 cited articles in toxicology literature. Interest in paracetamol poisoning as a serious clinical problem continues to grow. Research published in high-impact journals and from high income countries is most likely to be cited in published paracetamol research.

Urinary paracetamol and time-to-pregnancy

STUDY QUESTION

Is preconception urinary paracetamol (acetaminophen) associated with time-to-pregnancy (TTP)?

SUMMARY ANSWER

Higher urinary paracetamol concentrations among male partners were associated with a longer TTP.

WHAT IS KNOWN ALREADY

Paracetamol is a commonly used analgesic among women and men of all ages. As metabolites of select chemicals used in the manufacturing of polyurethane foam, dyes and various industrial products, as well as a common medicinal product, paracetamol and its primary metabolite p-aminophenol, are ubiquitous in the environment. Studies investigating the relationship between adult urinary concentrations of paracetamol and TTP are lacking.

STUDY DESIGN, SIZE, DURATION

This prospective cohort included 501 couples discontinuing contraception for the purposes of attempting conception during the years 2005-2009 and residing in Michigan or Texas, USA.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Total urinary paracetamol, its metabolite para-aminophenol (p-aminophenol), and a summary measure of both urinary biomarkers were quantified by ultra-performance liquid chromatography coupled with an electrospray triple quadrupole mass spectrometry (UPLC-ESI-MS/MS). Female partners used the Clearblue® digital home test to confirm pregnancy. Cox's proportional odds models for discrete survival time were used to estimate fecundability odds ratios (FORs) and 95% confidence intervals (CIs), adjusting for age, body mass index (BMI), urinary creatinine, preconception smoking status, race/ethnicity and household income. Models were further adjusted for hypothyroidism and hypertension as an attempt to account for possible indications of paracetamol medication use. FOR estimates <1.0 denote a longer TTP (diminished fecundity). Models were performed to examine urinary concentrations of paracetamol as a continuous and variable or categorized into quartiles. In light of TTP being a couple-dependent outcome, models were first performed for females and males, modeled separately, and then modeled for couples with each partner's concentrations being adjusted for the other.

MAIN RESULTS AND THE ROLE OF CHANCE

Among the 501 enrolled couples, 347 (69%) had an human chorionic gonadotrophin confirmed pregnancy. Urinary concentrations of paracetamol were lowest among females and males who achieved pregnancy and p-aminophenol concentrations were lowest among those not achieving pregnancy. Urinary paracetamol concentrations were higher among female than male partners (Median = 26.6 and 13.2 ng/ml, respectively; P < 0.0001). After adjustment for age, BMI, urinary creatinine, preconception smoking status, race/ethnicity and household income, the highest quartile of male urinary paracetamol was associated with a longer TTP [FOR = 0.67; 95% CI = (0.47, 0.95)]. This association remained after adjustment for chronic health conditions, hypothyroidism and hypertension and female partner's urinary paracetamol concentration [FOR = 0.65; 95% CI = (0.45, 0.94)]. No associations were observed between female or male partners' urinary concentrations of paracetamol or of its metabolite p-aminophenol when urinary concentrations were modeled continuously.

LIMITATIONS, REASONS FOR CAUTION

Only a single spot urine was available for analysis despite the short-lived nature of paracetamol. Additionally, participants were not asked to provide information on indication of use for paracetamol medications; any underlying conditions for the paracetamol use would have been potential confounders.

WIDER IMPLICATIONS OF THE FINDINGS

If corroborated with more robust studies, findings from our exploratory analysis may have both clinical and public health relevance among reproductive aged individuals, including those trying for pregnancy, given the prevalent use of paracetamol/acetaminophen medications and the ubiquitous nature of paracetamol in the environment.

STUDY FUNDING/COMPETING INTERESTS

This research was supported by the National Institutes of Health, Intramural Research Program, and Eunice Kennedy Shriver National Institute of Child Health and Human Development (contracts N01-HD-3-3355; N01-HD-3-3356; NOH-HD-3-3358; HHSN27500001/HHSN27500001). None of the authors have any conflicts to declare.

Validation of the paracetamol absorption test for measuring gastric tube emptying in esophagectomized patients versus gold standard scintigraphy

OBJECTIVE

Scintigraphy is the gold standard for objective measurement of delayed gastric tube emptying after esophagectomy. The aim of this pilot study is to validate, by reference to scintigraphy, the paracetamol absorption test for measuring gastric tube emptying in esophagectomized patients.

MATERIAL AND METHODS

The paracetamol absorption test and scintigraphy were performed simultaneously in 13 patients who had undergone an esophagectomy with gastric tube reconstruction. Emptying was calculated for both methods and compared. Post-esophagectomy symptoms and quality of life (QoL) were assessed by European Organization on Research and Treatment of Cancer questionnaires.

RESULTS

Mean time to 50% emptying was 17 min measured with the paracetamol absorption test and 23 min with scintigraphy. For time to 25% emptying, Bland-Altman calculation gave a bias of 1.6 min and 95% limits of agreement (LoA) of -6.3 to 9.5 min. For time to 50% emptying, there was one outlier resulting in a bias of -6.33 min and 95% LoA of -36.4 to 23.8 min. For time to 75% emptying, bias was -11.6 min and 95% LoA of -38.5 to 15.4 min. Post-esophagectomy symptoms were similar to those reported previously, and QoL was comparable to the general Swedish population.

CONCLUSIONS

There was reasonably close correlation between the paracetamol absorption test and scintigraphy for time to 25% and 50% emptying, except for one outlier. For time to 75% emptying the methods were in less accordance. The results indicate that the paracetamol absorption test may be a useful screening tool for identifying delayed gastric tube emptying in this patient group.

Pharmacokinetic properties of intramuscular versus oral syrup paracetamol in Plasmodium falciparum malaria

Background

Fever is an inherent symptom of malaria in both adults and children. Paracetamol (acetaminophen) is the recommended antipyretic as it is inexpensive, widely available and has a good safety profile, but patients may not be able to take the oral drug reliably. A comparison between the pharmacokinetics of oral syrup and intramuscular paracetamol given to patients with acute falciparum malaria and high body temperature was performed.

Methods

A randomized, open-label, two-treatment, crossover, pharmacokinetic study of paracetamol dosed orally and intramuscularly was conducted. Twenty-one adult patients with uncomplicated falciparum malaria were randomized to receive a single 600 mg dose of paracetamol either as syrup or intramuscular injection on day 0 followed by a single dose administered by the alternative route on day 1. Paracetamol plasma concentrations were quantified frequently and modelled simultaneously using nonlinear mixed-effects modelling. The final population pharmacokinetic model was used for dose optimization simulations. Relationships between paracetamol concentrations with temperature and parasite half-life were investigated using linear and non-linear regression analyses.

Results

The population pharmacokinetic properties of paracetamol were best described by a two-compartment disposition model, with zero-order and first-order absorption for intramuscular and oral syrup administration, respectively. The relative bioavailability of oral syrup was 84.4 % (95 % CI 68.2–95.1 %) compared to intramuscular administration. Dosing simulations showed that 1000 mg of intramuscular or oral syrup administered six-hourly reached therapeutic steady state concentrations for antipyresis, but more favourable concentration–time profiles were achieved with a loading dose of 1500 mg, followed by a 1000 mg maintenance dose. This ensured that maximum therapeutic concentrations were reached rapidly during the first 6 h. No significant relationships between paracetamol concentrations and temperature or parasite half-life were found.

Conclusions

Paracetamol plasma concentrations after oral syrup and intramuscular administration in patients with acute falciparum malaria were described successfully by a two-compartment disposition model. Relative oral bioavailability compared to intramuscular dosing was estimated as 84.4 % (95 % CI 68.2–95.1 %). Dosing simulations showed that a loading dose followed by six-hourly dosing intervals reduced the time delay to reach therapeutic drug levels after both routes of administration. The safety and efficacy of loading dose paracetamol antipyretic regimens now needs to be established in larger studies.

Therapeutic drug monitoring in dried blood spots using liquid microjunction surface sampling and high resolution mass spectrometry

Dried blood spots (DBS) are a versatile and stable tool for direct clinical blood analysis. We demonstrate the utility of liquid microjunction surface sampling technology in combination with an Orbitrap mass spectrometer for direct quantification of multiple drugs in DBS.

Paracetamol pharmacokinetics and metabolism in young women

Background

There is relevant between individual variability in paracetamol clearance in young women. In this pooled study, we focused on the population pharmacokinetic profile of intravenous paracetamol metabolism and its covariates in young women.

Methods

Population PK parameters using non-linear mixed effect modelling were estimated in a pooled dataset of plasma and urine PK studies in 69 young women [47 at delivery, 8/47 again 10–15 weeks after delivery (early postpartum), and 7/8 again 1 year after delivery (late postpartum), 22 healthy female volunteers with or without oral contraceptives].

Results

Population PK parameters were estimated based on 815 plasma samples and 101 urine collections. Compared to healthy female volunteers (reference group) not on oral contraceptives, being at delivery was the most significant covariate for clearance to paracetamol glucuronide (Factor = 2.03), while women in early postpartum had decreased paracetamol glucuronidation clearance (Factor = 0.55). Women on contraceptives showed increased paracetamol glucuronidation clearance (Factor = 1.46). The oestradiol level did not further affect this model. Being at delivery did not prove significant for clearance to paracetamol sulphate, but was higher in pregnant women who delivered preterm (<37 weeks, Factor = 1.34) compared to term delivery and non-pregnant women. Finally, clearance of unchanged paracetamol was dependent on urine flow rate.

Conclusions

Compared to healthy female volunteers not on oral contraceptives, urine paracetamol glucuronidation elimination in young women is affected by pregnancy (higher), early postpartum (lower) or exposure to oral contraceptives (higher), resulting in at least a two fold variability in paracetamol clearance in young women.

Semimechanistic model describing gastric emptying and glucose absorption in healthy subjects and patients with type 2 diabetes

The integrated glucose-insulin (IGI) model is a previously published semimechanistic model that describes plasma glucose and insulin concentrations after glucose challenges. The aim of this work was to use knowledge of physiology to improve the IGI model's description of glucose absorption and gastric emptying after tests with varying glucose doses. The developed model's performance was compared to empirical models. To develop our model, data from oral and intravenous glucose challenges in patients with type 2 diabetes and healthy control subjects were used together with present knowledge of small intestinal transit time, glucose inhibition of gastric emptying, and saturable absorption of glucose over the epithelium to improve the description of gastric emptying and glucose absorption in the IGI model. Duodenal glucose was found to inhibit gastric emptying. The performance of the saturable glucose absorption was superior to linear absorption regardless of the gastric emptying model applied. The semiphysiological model developed performed better than previously published empirical models and allows better understanding of the mechanisms underlying glucose absorption. In conclusion, our new model provides a better description and improves the understanding of dynamic glucose tests involving oral glucose.

Pharmaceutical Removal from Synthetic Wastewater Using Heterogeneous - Photocatalyst

Compound Parabolic Collecting Reactor (CPCR) was designed and used for the heterogeneous-photocatalytic treatment process. Sunray was act as an economically and ecologically sensible light source. The photocatalytic degradation of paracetamol in the synthetic wastewater by using titanium dioxide (TiO2) was investigated. The experimental results show that the paracetamol removal rates were very high and nearly equal (97.2% to 99.7%) at pH 4-7 and TiO2 concentration of 0.5-1 g/L. This implies that the photocatalytic degradation rate of paracetamol is not affected by pH range in this study as the electrostatic interaction between the TiO2 and paracetamol is not able to be developed unless a wider range of pH is set. Furthermore, the concentration of TiO2 of 0.5 g/L is too high to treat the concentration of 10 mg/L of paracetamol. Further research is needed in order to identify the optimum pH condition and a suitable correlation of concentration between TiO2 and paracetamol. Finally, the results proved that the heterogeneous-photocatalyst treatment method which associated with the application of CPCR and solar energy is able to eliminate the paracetamol from the synthetic wastewater.

Changing the Management of Paracetamol Poisoning

PURPOSE

The management of paracetamol poisoning was revolutionized after use of acetylcysteine in the 1970s. The protocol used, 3 weight-related infusions, requires almost 24 hours in hospital. It is associated with adverse events in treated patients, particularly anaphylactoid reactions and vomiting. Present treatment nomograms were based on a small series of untreated patients: only 5 of 22 (23%) and 6 of 25 (24%) between the 100 to 200 mg/L and 200 to 300 mg/L nomogram lines, respectively, developed liver injury (alanine transaminase >1000 IU/L). Many patients treated today are unlikely to be at actual risk for major hepatotoxicity. This article discusses the background to future prospects in this area.

METHODS

The history behind approaches to the use of acetylcysteine is presented briefly. The rationale for, and key findings of, a new 12-hour antidote regimen for paracetamol poisoning are detailed. Newer markers of hepatotoxicity, such as miR-122, HMGB1, and necrosis K18, which predict patients at risk more reliably and earlier than existing tests, are discussed.

FINDINGS

A 2-phase 12-hour acetylcysteine infusion protocol (100 mg/kg over 2 hours: 200 mg/kg over 10 hours) was studied in a formal factorial design against the traditional 3-phase 20.25-hour infusion protocol, with and without pretreatment with ondansetron or placebo. The 12-hour regimen was associated with very significant reductions in anaphylactoid reactions (odds ratio = 0.23; 95% CI, 0.12-0.43; P < 0.0001) and vomiting (odds ratio = 0.37; 95% CI, 0.18-0.79; P = .003) compared with the 20.25-hour infusion protocol. There were few withdrawals from the clinical trial, indicating the feasibility of conducting such studies in Europe.

IMPLICATIONS

Novel proteomic markers are better than existing standard tests (alanine transaminase and international normalized ratio) early in the course of paracetamol poisoning. Together with these new biomarkers of hepatotoxicity, a 12-hour acetylcysteine protocol offers clinicians and patients the possibility for better targeting of therapy, fewer adverse effects, a simpler dosing regimen, and shorter hospital stay.

Favipiravir inhibits acetaminophen sulfate formation but minimally affects systemic pharmacokinetics of acetaminophen

Aims

The antiviral agent favipiravir is likely to be co-prescribed with acetaminophen (paracetamol). The present study evaluated the possiblility of a pharmacokinetic interaction between favipiravir and acetaminophen, in vitro and in vivo.

Methods

The effect of favipivir on the transformation of acetaminophen to its glucuronide and sulfate metabolites was studied using a pooled human hepatic S9 fraction in vitro. The effect of acute and extended adminstration of favipiravir on the pharmacokinetics of acetaminophen and metabolites was evaluated in human volunteers.

Results

Favipiravir inhibited the in vitro formation of acetaminophen sulfate, but not acetaminophen glucuronide. In human volunteers, both acute (1 day) and extended (6 days) administration of favipiravir slightly but significantly increased (by about 20 %) systemic exposure to acetaminophen (total AUC), whereas C_max was not significantly changed. AUC for acetaminophen glucuronide was increased by 23 to 35 % above control by favipiravir, while AUC for acetaminophen sulfate was reduced by about 20 % compared to control. Urinary excretion of acetaminophen sulfate was likewise reduced to 44 to 65 % of control values during favipiravir co-administration, while excretion of acetaminophen glucuronide increased to 17 to 32 % above control.

Conclusion

Favipiravir inhibits acetaminophen sulfate formation in vitro and in vivo. However the increase in systemic exposure to acetaminophen due to favipiravir co-administration, though statistically significant, is small in magnitude and unlikely to be of clinical importance.

Acetaminophen: old drug, new issues

INTRODUCTION

The purpose of this review was to discuss new issues related to safety, labeling, dosing, and a better understanding of the analgesic effect of acetaminophen.

METHODS

The MEDLINE, Embase, Cochrane, and PubMed databases were searched. Additionally, the bibliography of all relevant articles and textbooks were manually searched. Two reviewers independently selected the relevant articles.

RESULTS

Concerns about acetaminophen overdose and related liver failure have led the US Food and Drug Administration to mandate new labeling on acetaminophen packaging. In addition, large-scale epidemiologic studies increasingly report evidence for second-generation adverse effects of acetaminophen. Prenatal exposure to acetaminophen is associated with neurodevelopmental and behavioral disorders. Recent studies also suggest that acetaminophen is a hormone disrupter (ie, it interferes with sex and thyroid hormone function essential for normal brain development) and thus may not be considered a safe drug during pregnancy. Finally, emerging evidence suggests that although the predominant mechanism by which acetaminophen exerts its therapeutic effect is by inhibition of cyclooxygenase, multiple other mechanisms also contribute to its analgesic effect.

CONCLUSIONS

Available evidence suggests that indiscriminate usage of this drug is not warranted. and its administration to a pregnant patient should be considered with great caution.

UV-induced photocatalytic degradation of aqueous acetaminophen: the role of adsorption and reaction kinetics

Nanostructured titania supported on activated carbon (AC), termed as integrated photocatalytic adsorbents (IPCAs), were prepared by ultrasonication and investigated for the photocatalytic degradation of acetaminophen (AMP), a common analgesic and antipyretic drug. The IPCAs showed high affinity towards AMP (in dark adsorption studies), with the amount adsorbed proportional to the TiO2 content; the highest adsorption was at 10 wt% TiO2. Equilibrium isotherm studies showed that the adsorption followed the Langmuir model, indicating the dependence of the reaction on an initial adsorption step, with maximum adsorption capacity of 28.4 mg/g for 10 % TiO2 IPCA. The effects of initial pH, catalyst amount and initial AMP concentration on the photocatalytic degradation rates were studied. Generally, the AMP photodegradation activity of the IPCAs was better than that of bare TiO2. Kinetic studies on the photocatalytic degradation of AMP under UV suggest that the degradation followed Langmuir-Hinshelwood (L-H) kinetics, with an adsorption rate constant (K) that was considerably higher than the photocatalytic rate constant (k r), indicating that the photocatalysis of AMP is the rate-determining step during the adsorption/photocatalysis process.

Concurrent Use of Conventional Drugs with Chinese Herbal Products in Taiwan: A Population-based Study

The increased use of Chinese herbal products (CHPs) worldwide has raised the concern of herb-drug interactions. The aim of this study was to determine the prevalence and utilization patterns of concurrent use of conventional drugs and CHPs in Taiwan. The usage and frequency of services in the co-prescription of a CHP and a conventional drug were evaluated. Subjects were recruited from a simple random sample of 1,000,000 subjects from over 22 million beneficiaries of the National Health Insurance in 2007. The logistic regression method was employed to estimate the odds ratios (ORs) for the co-prescription of a CHP and a conventional drug (CH + D) and a conventional drug alone (D-alone). The prevalence of the CH + D was 14.1%. Females, regular salary earners, and elderly (65 years and above) were more likely to consume a CHP and a conventional drug concurrently. Painkillers, especially acetaminophen, and anti-cough medicines were the top two conventional drugs that were most frequently co-prescribed with a CHP. Anti-cough medication is the most common conventional drug co-prescribed with CHP, after painkillers. We recommend that safety issues be investigated in future research and integrating both healthcare technologies may be beneficial for the overall health and quality of life of patients.

Estradiol and weight are covariates of paracetamol clearance in young women

AIM

Paracetamol clearance differs between pregnant and non-pregnant women and between women with or without specific oral contraceptives (OCs). However, an association between female sex hormones and paracetamol clearance has never been explored.

METHODS

In total, 49 women at delivery, 8 female control subjects without OC use, historical data of 14 women taking OCs, and 15 postpartum observations with and without OCs were pooled to explore covariates of paracetamol clearance. All received a single intravenous 2-gram paracetamol dose, and blood samples were collected up to 6 h after dosing. High-performance liquid chromatography was used to quantify paracetamol. The area under the curve to time infinity (AUC0-∞) was determined and clearance (l/h·m(2)) was calculated by dose/ AUC0-∞. In addition, estradiol and progesterone were quantified by ELISA with electro-chemiluminescence.

RESULTS

Median paracetamol clearance at delivery was significantly higher when compared to postpartum or non-pregnant women (11.9 vs. 6.42 and 8.4 l/h·m(2), at least p < 0.05), while an association between paracetamol clearance and estradiol was observed (R = 0.494, p < 0.0001). In non-pregnant subjects, there was no impact of OC exposure on paracetamol clearance. Multiple regression revealed a linear association (Radj = 0.41, p < 0.001) between paracetamol clearance and weight (p = 0.0462) and estradiol (p < 0.0001).

CONCLUSION

Estradiol and weight in part explain the variation in paracetamol clearance in young women.

Acetaminophen-related hepatotoxicity

Acetaminophen (APAP) is the leading worldwide cause of drug overdose and acute liver failure (ALF). Single overdose ingestion and therapeutic misadventure may cause hepatotoxicity. Several factors, such as concomitant alcohol use or abuse, concurrent medications, genetic factors, and nutritional status, can influence the susceptibility and severity of APAP hepatotoxicity. Early manifestations of APAP hepatotoxicity are nonspecific, but require prompt recognition by physicians. Patients with repeated overdose tend to present late, and in such hepatotoxicity may have already evolved. N-acetylcysteine is a very effective antidote when giving within 8 hours, and is also recommended after a presentation of hepatotoxicity and ALF. The prognosis of patients with APAP-induced ALF is better than other causes of ALF. Liver transplantation should be offered to those who are unlikely to survive.

Reading between the (guide)lines--the KDIGO practice guideline on acute kidney injury in the individual patient

The KDIGO guidelines for acute kidney injury (AKI) are designed to assist health-care providers around the world in managing patients with AKI. Clinical guidelines are intended to help the clinician make an informed decision based on review of the currently available evidence. Due to the generic nature of guidelines, it is sometimes difficult to translate a guideline for a particular individual patient who may have specific clinical circumstances. To illustrate this point, we have discussed the interpretation of the KDIGO guideline in patients who have subtleties in their clinical presentation, which may make treatment decisions less than straightforward.

The pharmacokinetic profile of intravenous paracetamol in adult patients undergoing major abdominal surgery

BACKGROUND

Intravenous (IV) paracetamol is commonly used in the postoperative period for the treatment of mild to moderate pain. The main pathways for paracetamol metabolism are glucuronidation, sulfation, and oxidation, accounting for approximately 55%, 30%, and 10% of urinary metabolites, respectively. The aim of this study was to describe the pharmacokinetics of IV paracetamol and its metabolites in adult patients after major abdominal surgery.

METHODS

Twenty patients were given 1 g of paracetamol by IV infusion at induction of anesthesia (Interval 1) and every 6 hours thereafter, with the final dose given at 48-72 hours (Interval 2). Plasma and urine samples were collected for up to 8 hours after infusion for both intervals. The samples were analyzed by high-performance liquid chromatography to determine the amount of paracetamol and its metabolites. The data were modeled in Phoenix WinNonlin using a user-defined ASCII parent-metabolite model with linear disposition, to obtain the estimates for volume of distribution, metabolic and urinary clearance.

RESULTS

Mean (95% confidence interval) metabolic clearance to paracetamol glucuronide increased from 0.06 (0.05-0.08) to 0.14 (0.11-0.18) L · h⁻¹ · kg⁻¹, P value <0.001 and urinary clearance increased from 0.08 (0.07-0.09) to 0.14 (0.10-0.17) L · h⁻¹ · kg⁻¹, P value 0.002. The mean (95% confidence interval) volume of distribution of paracetamol increased from 0.17 (0.12-0.21) to 0.43 (0.27-0.59) L · kg⁻¹, P value 0.032.

CONCLUSIONS

After major abdominal surgery, there were apparent increases in the metabolic conversion to paracetamol glucuronide and its urinary clearance suggesting potential induction of paracetamol glucuronidation.

A review of acetaminophen poisoning

Acetaminophen poisoning remains one of the more common drugs taken in overdose with potentially fatal consequences. Early recognition and prompt treatment with N-acetylcysteine can prevent hepatic injury. With acute overdose, the Rumack-Matthew nomogram is a useful tool to assess risk and guide management. Equally common to acute overdose is the repeated use of excessive amounts of acetaminophen. Simultaneous ingestion of several different acetaminophen-containing products may result in excessive dosage. These patients also benefit from N-acetylcysteine. Standard courses of N-acetylcysteine may need to be extended in patients with persistently elevated plasma concentrations of acetaminophen or with signs of hepatic injury.