Clinical pharmacokinetics of paracetamol

Kinetics of phosphate absorption in lactating dairy cows after enteral administration of sodium phosphate or calcium phosphate salts

Hypophosphataemia is frequently encountered in dairy cows during early lactation. Although supplementation of P is generally recommended, controversy exists over the suitability of oral P supplementation in animals with decreased or absent rumen motility. Since the effects of transruminal P absorption and the reticular groove reflex on the absorption kinetics of P are not well understood, it is unclear in how far treatment efficacy of oral P supplementation is affected by decreased rumen motility. Phosphate absorption was studied in six phosphate-depleted dairy cows fitted with rumen cannulas and treated with test solutions containing either NaH2PO4 or CaHPO4 with acetaminophen. Each animal was treated orally, intraruminally and intra-abomasally in randomised order. Absorption kinetics of P were studied and compared with the absorption kinetics of acetaminophen, a marker substance only absorbed from the small intestine. Intra-abomasal treatment with NaH2PO4 resulted in the most rapid and highest peaks in plasma inorganic P (Pi) concentration. Oral and intraruminal administration of NaH2PO4 resulted in similar increases in plasma Pi concentration from 4 to 7 h in both groups. Treatment with NaH2PO4 caused more pronounced peaks in plasma Pi concentration compared with CaHPO4. Neither transruminal P absorption nor the reticular groove reflex affected P absorption kinetics as determined by comparing plasma concentration–time curves of P and acetaminophen after administration of 1M-phosphate salt solutions. It is concluded that oral treatment with NaH2PO4 but not CaHPO4 is effective in supplementing P in hypophosphataemic cows with adequate rumen motility. Decreased rumen motility is likely to hamper the efficacy of oral phosphate treatment.

Pharmacokinetics of an Oral Drug (Acetaminophen) Administered at Various Times in Relation to Subcutaneous Injection of Exenatide (Exendin-4) in Healthy Subjects

Exenatide is an incretin mimetic with potential glucoregulatory activity in type 2 diabetes. This randomized, single-blind, placebo-controlled 6-way crossover study assessed exenatide's effect on acetaminophen pharmacokinetics. Of 40 randomized healthy subjects, 39 completed the study. On the placebo day, acetaminophen (1000 mg) was ingested and placebo injected subcutaneously at 0 hours. On exenatide days, acetaminophen was ingested at -1, 0, +1, +2, and +4 hours, relative to the 10 mug exenatide injected subcutaneously at 0 hours. With exenatide injection, mean plasma acetaminophen AUC(0-12 h) values were reduced by 11% to 24% (vs placebo). Peak plasma acetaminophen concentrations were similar for the -1-hour and placebo groups and reduced by 37% to 56% at other times. The most frequent adverse events were generally mild to moderate nausea and vomiting. Exenatide treatment concurrent with or preceding acetaminophen ingestion slowed acetaminophen absorption but had minimal effect on the extent of absorption.

Role of electrostatic potential in the in silico prediction of molecular bioactivation and mutagenesis

Electrostatic potential (ESP) is a useful physicochemical property of a molecule that provides insights into inter- and intramolecular associations, as well as prediction of likely sites of electrophilic and nucleophilic metabolic attack. Knowledge of sites of metabolic attack is of paramount importance in DMPK research since drugs frequently fail in clinical trials due to the formation of bioactivated metabolites which are often difficult to measure experimentally due to their reactive nature and relatively short half-lives. Computational chemistry methods have proven invaluable in recent years as a means to predict and study bioactivated metabolites without the need for chemical syntheses, or testing on experimental animals. Additional molecular properties (heat of formation, heat of solvation and E(LUMO) - E(HOMO)) are discussed in this paper as complementary indicators of the behavior of metabolites in vivo. Five diverse examples are presented (acetaminophen, aniline/phenylamines, imidacloprid, nefazodone and vinyl chloride) which illustrate the utility of this multidimensional approach in predicting bioactivation, and in each case the predicted data agreed with experimental data described in the scientific literature. A further example of the usefulness of calculating ESP, in combination with the molecular properties mentioned above, is provided by an examination of the use of these parameters in providing an explanation for the sites of nucleophilic attack of the nucleic acid cytosine. Exploration of sites of nucleophilic attack of nucleic acids is important as adducts of DNA have the potential to result in mutagenesis.

The biochemistry of acetaminophen hepatotoxicity and rescue: a mathematical model

BACKGROUND

Acetaminophen (N-acetyl-para-aminophenol) is the most widely used over-the-counter or prescription painkiller in the world. Acetaminophen is metabolized in the liver where a toxic byproduct is produced that can be removed by conjugation with glutathione. Acetaminophen overdoses, either accidental or intentional, are the leading cause of acute liver failure in the United States, accounting for 56,000 emergency room visits per year. The standard treatment for overdose is N-acetyl-cysteine (NAC), which is given to stimulate the production of glutathione.

METHODS

We have created a mathematical model for acetaminophen transport and metabolism including the following compartments: gut, plasma, liver, tissue, urine. In the liver compartment the metabolism of acetaminophen includes sulfation, glucoronidation, conjugation with glutathione, production of the toxic metabolite, and liver damage, taking biochemical parameters from the literature whenever possible. This model is then connected to a previously constructed model of glutathione metabolism.

RESULTS

We show that our model accurately reproduces published clinical and experimental data on the dose-dependent time course of acetaminophen in the plasma, the accumulation of acetaminophen and its metabolites in the urine, and the depletion of glutathione caused by conjugation with the toxic product. We use the model to study the extent of liver damage caused by overdoses or by chronic use of therapeutic doses, and the effects of polymorphisms in glucoronidation enzymes. We use the model to study the depletion of glutathione and the effect of the size and timing of N-acetyl-cysteine doses given as an antidote. Our model accurately predicts patient death or recovery depending on size of APAP overdose and time of treatment.

CONCLUSIONS

The mathematical model provides a new tool for studying the effects of various doses of acetaminophen on the liver metabolism of acetaminophen and glutathione. It can be used to study how the metabolism of acetaminophen depends on the expression level of liver enzymes. Finally, it can be used to predict patient metabolic and physiological responses to APAP doses and different NAC dosing strategies.

Simultaneous LC-MS/MS quantitation of acetaminophen and its glucuronide and sulfate metabolites in human dried blood spot samples collected by subjects in a pilot clinical study

BACKGROUND

In support of a pilot clinical trial using acetaminophen as the model compound to assess dried blood spot (DBS) sampling as the method for clinical pharmacokinetic sample collection, a novel sensitive LC-MS/MS method was developed and validated for the simultaneous determination of acetaminophen and its major metabolites, acetaminophen glucuronide and sulfate, in human DBS samples collected by subjects via fingerprick.

RESULTS

The validated assay dynamic range was from 50.0 to 5000 ng/ml for each compound using a 1/8´´ (3-mm) disc punched from a DBS sample. Baseline separation of the three analytes was achieved to eliminate the possible impact of insource fragmentation of the conjugated metabolites on the analysis of the parent. The overall extraction efficiency was from 61.3 to 78.8% for the three analytes by direct extraction using methanol.

CONCLUSION

The validated method was successfully implemented in the pilot clinical study with the obtained pharmacokinetic parameters in agreement with the values reported in literature.

A generalisation of T-optimality for discriminating between competing models with an application to pharmacokinetic studies

The T-optimality criterion is used in optimal design to derive designs for model selection. To set up the method, it is required that one of the models is considered to be true. We term this local T-optimality. In this work, we propose a generalisation of T-optimality (termed robust T-optimality) that relaxes the requirement that one of the candidate models is set as true. We then show an application to a nonlinear mixed effects model with two candidate non-nested models and combine robust T-optimality with robust D-optimality. Optimal design under local T-optimality was found to provide adequate power when the a priori assumed true model was the true model but poor power if the a priori assumed true model was not the true model. The robust T-optimality method provided adequate power irrespective of which model was true. The robust T-optimality method appears to have useful properties for nonlinear models, where both the parameter values and model structure are required to be known a priori, and the most likely model that would be applied to any new experiment is not known with certainty.

Therapeutic paracetamol treatment in older persons induces dietary and metabolic modifications related to sulfur amino acids

Sulfur amino acids are determinant for the detoxification of paracetamol (N-acetyl-p-aminophenol) through sulfate and glutathione conjugations. Long-term paracetamol treatment is common in the elderly, despite a potential cysteine/glutathione deficiency. Detoxification could occur at the expense of anti-oxidative defenses and whole body protein stores in elderly. We tested how older persons satisfy the extra demand in sulfur amino acids induced by long-term paracetamol treatment, focusing on metabolic and nutritional aspects. Effects of 3 g/day paracetamol for 14 days on fasting blood glutathione, plasma amino acids and sulfate, urinary paracetamol metabolites, and urinary metabolomic were studied in independently living older persons (five women, five men, mean (±SEM) age 74 ± 1 years). Dietary intakes were recorded before and at the end of the treatment and ingested sulfur amino acids were evaluated. Fasting blood glutathione, plasma amino acids, and sulfate were unchanged. Urinary nitrogen excretion supported a preservation of whole body proteins, but large-scale urinary metabolomic analysis revealed an oxidation of some sulfur-containing compounds. Dietary protein intake was 13% higher at the end than before paracetamol treatment. Final sulfur amino acid intake reached 37 mg/kg/day. The increase in sulfur amino acid intake corresponded to half of the sulfur excreted in urinary paracetamol conjugates. In conclusion, older persons accommodated to long-term paracetamol treatment by increasing dietary protein intake without any mobilization of body proteins, but with decreased anti-oxidative defenses. The extra demand in sulfur amino acids led to a consumption far above the corresponding population-safe recommendation.

Prenatal paracetamol exposure and risk of wheeze at preschool age

AIM

To analyse the association between prenatal paracetamol exposure and preschool wheeze.

METHODS

Data were obtained from a prospective, longitudinal study of a cohort of children born in the region of western Sweden in 2003; 8176 families were randomly selected. The parents answered questionnaires at 6 and 12 months and at 4.5 years of age. The response rate was 55%, i.e. 4496 of the 5398 questionnaires distributed at 4.5 years (83%). Inhaled corticosteroid (ICS) treated wheeze during the last year was regarded as a proxy for doctor-diagnosed asthma. Episodic viral wheeze was defined as wheezing only with viral infections and multiple-trigger wheeze as wheezing also in between infections.

RESULTS

In the multivariate analysis, the risk of ICS-treated wheeze was increased by paracetamol (OR 1.6; 95% CI 1.01-2.6). Within the ICS-treated group, the effect was significant for multiple-trigger wheeze (OR 2.4; 1.2-4.8) but not for episodic viral wheeze (OR 1.1; 0.5-2.3).

CONCLUSION

Prenatal paracetamol exposure was an independent risk factor for ICS-treated wheeze at preschool age, especially among children with ICS-treated multiple-trigger wheeze. Although the analysis adjusted for e.g. maternal asthma and antibiotic use, the possibility of residual confounding by maternal indication (respiratory illness) should be acknowledged.

Effect of prenatal exposure to fine particulate matter and intake of Paracetamol (Acetaminophen) in pregnancy on eczema occurrence in early childhood

The goal of the study was to test the hypothesis that prenatal Paracetamol exposure increases the risk of developing eczema in early childhood and that this association may be stronger in children who are exposed in fetal period to higher concentrations of fine particulate matter (PM2.5). The study sample consisted of 322 women recruited from January 2001 to February 2004 in the Krakow inner city area who gave birth to term babies and completed 5-year follow-up. Paracetamol use in pregnancy was collected by interviews and prenatal personal exposure to PM2.5 over 48 h was measured in recruited women in the second trimester of pregnancy. After delivery, every three months in the first 24 months of the newborn's life and every 6 months later, a detailed standardized face-to-face interview on the infant's health was administered to each mother by trained interviewers. During the interviews at each of the study periods after birth, a history of eczema was recorded. The incident rate ratio (IRR) for frequency of eczema events over the follow-up was estimated from the Poisson regression model and the overall effect of main exposure variables on eczema was assessed by odds ratios (ORs) by the logistic model. The estimated relative risk of eczema occurring whenever in the follow-up was related significantly neither with prenatal Paracetamol nor higher PM2.5 exposure, however, their joint effect was significant (OR interaction term=6.04; 95%CI: 1.04-35.16). Of potential confounders considered in the analysis only damp/moldy home significantly increased the risk of eczema (OR=1.53; 95%CI: 1.14-2.05). In contrast, there was an inverse significant association between the presence of older siblings and eczema (OR=0.55; 95%CI: 0.35-0.84). The joint effect of the main exposure variables significantly increased frequency of eczema events (IRR=1.78, 95%CI: 1.22-2.61). In conclusion, the findings of the study suggest that Paracetamol use by mothers in pregnancy is not an independent risk factor for eczema in children, however, even very small doses of Paracetamol taken in pregnancy may contribute to the occurrence of allergic symptoms in early childhood if there is prenatal co-exposure to higher airborne fine particulate matter.

Reduced exposure of imatinib after coadministration with acetaminophen in mice

Purpose:

Imatinib is an efficacious drug against chronic myeloid leukemia (CML) and gastrointestinal stromal tumor (GIST) due to selective inhibition of c-KIT and BCR-ABL kinases. It presents almost complete bioavailability, is eliminated via P450-mediated metabolism and is well tolerated. However, a few severe drug-drug interactions have been reported in cancer patients taking acetaminophen.

Materials and Methods:

Male ICR mice were given 100 mg/kg single dose of imatinib orally or imatinib 100 mg/kg (orally) coadministered with acetaminophen intraperitoneally (700 mg/kg). Mice were euthanized at predetermined time points, blood samples collected, and imatinib plasma concentration measured by HPLC.

Results:

Imatinib AUC_0-12 was 27.04 ± 0.38 mg·h/ml, C_max was 7.21 ± 0.99 mg/ml and elimination half-life was 2.3 hours. Acetaminophen affected the imatinib disposition profile: AUC_0-12 and C_max decreased 56% and 59%, respectively and a longer half-life was observed (5.6 hours).

Conclusions:

The study shows a pharmacokinetic interaction between acetaminophen and imatinib which may render further human studies necessary if both drugs are administered concurrently to cancer patients.

A randomized, controlled trial validates a peripheral supra-additive antihyperalgesic effect of a paracetamol-ketorolac combination

The combination of paracetamol with non-steroidal anti-inflammatory drugs (NSAIDs) is widely used; however, the nature and mechanism of their interaction are still debated. A double-blind, pharmacokinetic/pharmacodynamic, randomized, cross-over, placebo-controlled study was carried out in human healthy volunteers. The aim was to explore the existence of a positive interaction between paracetamol 1 g and ketorolac 20 mg administered intravenously on experimental pain models in human beings. The effects of the paracetamol-ketotolac combination were compared with similar doses of respective single analgesic and to placebo on the sunburn model (UVB-induced inflammation), cold pain tolerance and the nociceptive flexion reflex. The kinetics of the plasma concentrations of paracetamol and ketorolac were measured using 2D-liquid chromatography-mass spectrometry. Thirteen volunteers were screened, and 11 completed the study. Ketorolac significantly decreased primary hyperalgesia to heat stimuli compared with paracetamol (p < 0.014). The combination performed better than paracetamol (p < 0.001) and placebo (p < 0.042), increasing heat pain threshold by 1.5°C. The combination radically reduced primary hyperalgesia to mechanical stimulation (39%) compared with placebo (p < 0.002) and single agents (paracetamol p < 0.024 and ketorolac p < 0.032). The combination also reduced, slightly although significantly, the intensity of pain (10%) for the cold pressor test (versus placebo: p < 0.012, paracetamol: p < 0.019 and ketorolac p < 0.004). None of the treatments significantly affected the central models of pain at this dosage level. No pharmacokinetic interactions were observed. These results suggest a supra-additive pharmacodynamic interaction between paracetamol and ketorolac in an inflammatory pain model. The mechanism of this interaction could mainly rely on a peripheral contribution of paracetamol to the effect of NSAIDs.

New marker for paracetamol poisoning-revolution or evolution?

There is a pressing need for new biomarkers that can improve the care of patients with paracetamol poisoning, a common clinical problem. In this issue of Clinical Toxicology a new marker is proposed that has a number of attractive properties. This commentary discusses the use of biomarkers in the context of the management of paracetamol-induced liver injury. New biomarkers should allow better triage and management of & "at risk" patients.

The pharmacokinetic profile of a novel fixed-dose combination tablet of ibuprofen and paracetamol

Background

Ibuprofen and paracetamol differ in their mode of action and related therapeutic effects, suggesting that combined administration may offer improved analgesia. Reported here are the results of two studies on the pharmacokinetic properties of a novel ibuprofen (200 mg) and paracetamol (500 mg) fixed-dose combination tablet.

Methods

Both studies were open-label, randomised studies in healthy volunteers: Study 1 was a four-way crossover, single-dose study; Study 2 was a two-way cross-over, repeat-dose study.

Results

Pharmacokinetic parameters for ibuprofen and paracetamol were similar for the combination and monotherapy tablets (values falling within the 80% to 125% acceptable bioequivalence range) except for the rate of absorption of paracetamol from the combination (t_max), which was significantly faster compared with monotherapy (median difference 10 minutes; p < 0.05). Mean plasma concentrations of both drugs were higher, earlier, following administration of the combination tablet compared with monotherapy. Mean plasma levels at 10 and 20 minutes were 6.64 μg.mL^-1 and 16.81 μg.mL^-1, respectively, for ibuprofen from the combination, compared with 0.58 μg.mL^-1 and 9.00 μg.mL^-1, respectively, for monotherapy. For paracetamol, mean plasma levels at 10 and 20 minutes were 5.43 μg.mL^-1 and 14.54 μg.mL^-1, respectively, for the combination compared with 0.33 μg.mL^-1 and 9.19 μg.mL^-1, respectively, for monotherapy. The rate of absorption of both ibuprofen and paracetamol was significantly delayed when the combination tablet was administered in the fed versus fasted state; median delay was 25 minutes for ibuprofen (p > 0.05) and 55 minutes for paracetamol (p < 0.001). The pharmacokinetic parameters were comparable irrespective of whether the combination tablet was given twice or three times daily; systemic exposure was, however, approximately 1.4 times greater for both drugs when given three times daily.

Conclusions

Administration of ibuprofen and paracetamol in a fixed-dose combination tablet does not significantly alter the pharmacokinetic profiles of either drug, except for enhancing the rate of paracetamol absorption, offering potential therapeutic benefits in relation to the onset of analgesia. Concentrations of both drugs reached previously reported therapeutic levels when the combination tablet was administrated in the fed or fasted state. Three times daily dosing may offer enhanced therapeutic effect for longer than twice daily dosing.

Paracetamol for intravenous use in medium--and intensive care patients: pharmacokinetics and tolerance

PURPOSE

We studied the pharmacokinetics of paracetamol and determine the incidence of hypotension after intravenous administration in medium- (MCU) and intensive care (ICU) patients.

METHODS

All patients on the ICU/MCU starting with paracetamol i.v. were included, yielding 38 patients. Blood samples were collected at predetermined time points to determine paracetamol serum concentration. The number of patients with a clinically relevant reduction in systolic blood pressure (SBP) and the number of patients that needed intervention to regain an acceptable blood pressure level were assessed.

RESULTS

Overall, pharmacokinetic data were roughly comparable with earlier publications, but differences were noted in the subgroup ICU patients. Also, there was a trend to a larger peak serum concentration (p = 0.052) and a significantly smaller volume of distribution (p = 0.033) in MCU patients compared with ICU patients. Twenty-two percent (22%) and 33% of patients had a clinically relevant reduction in systolic blood pressure (SBP) 15 and 30 min after start of paracetamol infusion, respectively. In six patients (16%), an intervention was needed to correct blood pressure. Overall, SBP was significantly reduced at T = 15 min and 30 min postinfusion (p < 0.003 at both time points) when compared with SBP at the start of paracetamol infusion.

CONCLUSIONS

Further research on differences in paracetamol pharmacokinetics between ICU and MCU patients is warranted, as these differences might result in differences in efficacy. Furthermore, administration of paracetamol i.v. as potential cause of hypotension in the critically ill patient must not be overlooked.

Late extensive intravenous administration of N-acetylcysteine can reverse hepatic failure in acetaminophen overdose

Acetaminophen is a commonly used analgesic and has been shown to be a main cause of drug-induced liver failure. N-acetylcysteine (NAC) should be employed as the antidote in case of acetaminophen poisoning within the first 8-10 hours. Oral administration of NAC is universally recommended and due to the adverse effects, the intravenous administration of the agent is reserved for patients with oral intolerance and severe complications. We here report an 18-year-old man with severe liver failure due to a huge ingestion of acetaminophen, who was taken into the Loghman Hakim Hospital Poison Center 72 hours after attempted suicide. Regarding the poor prognostic clues as his level of consciousness and impaired liver functions, an extensive intravenous regimen of NAC was started. The patient survived the condition with an additional intravenous administration of NAC past the first 72 hours of treatment. We discuss that even in late phases of intoxication; high-dose intravenous NAC can serve a substantial improvement.

Pharmacometabonomic identification of a significant host-microbiome metabolic interaction affecting human drug metabolism

We provide a demonstration in humans of the principle of pharmacometabonomics by showing a clear connection between an individual's metabolic phenotype, in the form of a predose urinary metabolite profile, and the metabolic fate of a standard dose of the widely used analgesic acetaminophen. Predose and postdose urinary metabolite profiles were determined by (1)H NMR spectroscopy. The predose spectra were statistically analyzed in relation to drug metabolite excretion to detect predose biomarkers of drug fate and a human-gut microbiome cometabolite predictor was identified. Thus, we found that individuals having high predose urinary levels of p-cresol sulfate had low postdose urinary ratios of acetaminophen sulfate to acetaminophen glucuronide. We conclude that, in individuals with high bacterially mediated p-cresol generation, competitive O-sulfonation of p-cresol reduces the effective systemic capacity to sulfonate acetaminophen. Given that acetaminophen is such a widely used and seemingly well-understood drug, this finding provides a clear demonstration of the immense potential and power of the pharmacometabonomic approach. However, we expect many other sulfonation reactions to be similarly affected by competition with p-cresol and our finding also has important implications for certain diseases as well as for the variable responses induced by many different drugs and xenobiotics. We propose that assessing the effects of microbiome activity should be an integral part of pharmaceutical development and of personalized health care. Furthermore, we envisage that gut bacterial populations might be deliberately manipulated to improve drug efficacy and to reduce adverse drug reactions.

Metabolic profiling and population screening of analgesic usage in nuclear magnetic resonance spectroscopy-based large-scale epidemiologic studies

The application of a (1)H nuclear magnetic resonance (NMR) spectroscopy-based screening method for determining the use of two widely available analgesics (acetaminophen and ibuprofen) in epidemiologic studies has been investigated. We used samples and data from the cross-sectional INTERMAP Study involving participants from Japan (n = 1145), China (n = 839), U.K. (n = 501), and the U.S. (n = 2195). An orthogonal projection to latent structures discriminant analysis (OPLS-DA) algorithm with an incorporated Monte Carlo resampling function was applied to the NMR data set to determine which spectra contained analgesic metabolites. OPLS-DA preprocessing parameters (normalization, bin width, scaling, and input parameters) were assessed systematically to identify an optimal acetaminophen prediction model. Subsets of INTERMAP spectra were examined to verify and validate the presence/absence of acetaminophen/ibuprofen based on known chemical shift and coupling patterns. The optimized and validated acetaminophen model correctly predicted 98.2%, and the ibuprofen model correctly predicted 99.0% of the urine specimens containing these drug metabolites. The acetaminophen and ibuprofen models were subsequently used to predict the presence/absence of these drug metabolites for the remaining INTERMAP specimens. The acetaminophen model identified 415 out of 8436 spectra as containing acetaminophen metabolite signals while the ibuprofen model identified 245 out of 8604 spectra as containing ibuprofen metabolite signals from the global data set after excluding samples used to construct the prediction models. The NMR-based metabolic screening strategy provides a new objective approach for evaluation of self-reported medication data and is extendable to other aspects of population xenometabolome profiling.

Effect of repeated administration with subtoxic doses of acetaminophen to rats on enterohepatic recirculation of a subsequent toxic dose

Development of resistance to toxic effects of acetaminophen (APAP) was reported in rodents and humans, though the mechanism is only partially understood. We examined in rats the effect of administration with subtoxic daily doses (0.2, 0.3, and 0.6g/kg, i.p.) of APAP on enterohepatic recirculation and liver toxicity of a subsequent i.p. toxic dose of 1g/kg, given 24h after APAP pre-treatment. APAP and its major metabolite APAP-glucuronide (APAP-Glu) were determined in bile, urine, serum and liver homogenate. APAP pre-treatment was not toxic, as determined by serum markers of liver damage and neither induced oxidative stress as demonstrated by assessment of ROS generation in liver or glutathione species in liver and bile. APAP pre-treatment induced a partial shift from biliary to urinary elimination of APAP-Glu after administration with the toxic dose, and decreased hepatic content and increased serum content of this conjugate, consistent with a marked up-regulation of its basolateral transporter Mrp3 relative to apical Mrp2. Preferential secretion of APAP-glu into blood decreased enterohepatic recirculation of APAP, thus attenuating liver exposition to the intact drug, as demonstrated 6h after administration with the toxic dose. The beneficial effect of interfering the enterohepatic recirculation was alternatively tested in animals receiving activated charcoal by gavage to adsorb APAP of biliary origin. The data indicated decreased liver APAP content and glutathione consumption. We conclude that selective up-regulation of Mrp3 expression by APAP pre-treatment may contribute to development of resistance to APAP hepatotoxicity, at least in part by decreasing its enterohepatic recirculation.

A New Predictor of Toxicity Following Acetaminophen Overdose Based on Pretreatment Exposure

INTRODUCTION

Despite extensive clinical experience, no dose-response curve exists for acetaminophen toxicity in man. The absence of accurate toxicodynamics has hampered efforts to optimize patient therapy and to identify risk modifiers following overdose. We set out to parameterize both the degree and duration of pretreatment exposure into a single, continuous measure of exposure, which will serve as the x-axis of an eventual dose-response curve.

METHODS

The model was constructed from pharmacokinetic first principles, using as inputs the vertical distance above the Rumack-Matthew nomogram line (expressed as the equivalent serum acetaminophen concentration 4 h after ingestion) and the delay to antidote therapy (tNAC). A no-effect dose ([APAP]threshold) and lag time (ti) were assumed.

RESULTS

The area under the serum acetaminophen concentration vs. time curve bounded by [APAP]threshold, ti and tNAC represents our proposed time-weighted measure of exposure. We demonstrate that this non-negative area estimates the cellular burden of toxic adducts formed following overdose. This measure is also easily calculated at patient presentation using clinical data and allows for both declining serum acetaminophen concentrations and variable delays to antidote therapy.

DISCUSSION

We describe a new, pharmacokinetically based measure of exposure following acute acetaminophen overdose treated with N-acetylcysteine. Using this measure should enhance the analysis of nonexperimental clinical data and permit more accurate characterization of acetaminophen toxicodynamics. Ultimately, this approach may facilitate progress on many of the long-standing controversies regarding acetaminophen toxicity in man.

Effects of mitemcinal (GM-611), an orally active erythromycin-derived prokinetic agent, on delayed gastric emptying and postprandial glucose in a new minipig model of diabetes

AIMS

This study was conducted to evaluate the suitability of a new minipig model for investigating aspects of diabetes such as delayed gastric emptying and glucose metabolism abnormalities, and to test the effects of mitemcinal (GM-611), an orally active erythromycin-derived motilin receptor agonist, on gastric emptying and postprandial glucose in normal and diabetic minipigs.

METHODS AND RESULTS

Intravenous injection of 300 mg/kg streptozotocin (STZ) to 5-week-old minipigs induced moderate hyperglycemia (about 200 mg/dl) for >80 weeks without insulin treatment. Decreased insulin production (P<.05), increased area under the glucose curve (P<.05), and slower glucose disappearance (P<.05) were demonstrated, and there was no severe inhibition of body weight gain, liver failure, or renal failure. Gastric emptying was significantly delayed in diabetic minipigs (P<.05) at 80 weeks, but not at 40 weeks, post-STZ. Oral administration of mitemcinal (5 mg/kg) at 80 weeks accelerated gastric emptying and induced a similar postprandial glucose profile in normal and diabetic minipigs with delayed gastric emptying.

CONCLUSIONS

The new diabetic minipig model showed suitability for investigating diabetes, gastric emptying, and plasma glucose excursions. Since delayed gastric emptying and irregular plasma glucose excursions are characteristic of diabetic gastroparesis, the accelerating and regulating effects of mitemcinal on this model add to the existing evidence that mitemcinal is likely to be useful for treating diabetic gastroparesis.

Use of over-the-counter analgesics in patients with chronic liver disease: physicians' recommendations

BACKGROUND

Over-the-counter analgesics (OTCAs), principally paracetamol (acetaminophen)-containing compounds and NSAIDs, are commonly used medications. Guidelines for the use of these agents in patients with chronic liver disease (CLD) are not available, despite the possibility that such patients may be more susceptible to the effects of an adverse reaction. Notwithstanding the lack of guidelines for healthcare providers, patients are often counselled to modify their use of these drugs. Therefore, the primary aim of this study was to assess healthcare providers' recommendations on how OTCAs should be used by patients with CLD.

METHODS

An 11-question web-based survey was distributed via email to healthcare providers participating in four healthcare networks in the US, to determine what recommendations they make to patients with cirrhosis (compensated and decompensated) and chronic hepatitis regarding the use of paracetamol and NSAIDs. Healthcare providers were also queried about the recommendations they make to patients with cirrhosis regarding pain control, and on the use of paracetamol for patients who consume alcohol daily.

RESULTS

Overall, a 12% response rate was obtained. Internal medicine, family practice, paediatrics, and gastroenterology were the most represented practice types. Recommendations against the use of NSAIDs were significantly less common than recommendations against paracetamol use, in cases of both compensated and decompensated cirrhosis (p = 0.001). Non-gastroenterologists and non-primary care physicians were the least likely to recommend against NSAID use (p = 0.001), while gastroenterologists were the least likely to recommend against paracetamol in these patients (p = 0.001). It was the recommendation of most respondents that OTCAs should be avoided in patients with cirrhosis, and that paracetamol should be avoided or its dose reduced in the setting of daily alcohol use.

CONCLUSIONS

Significant variability exists among healthcare providers on their recommendations for OTCA use in the setting of chronic liver disease. Non-gastroenterologists are more likely to recommend against the use of paracetamol than NSAIDs, and patients with chronic liver disease may be under-treated for pain.

The poisoned child in the pediatric intensive care unit

Acutely poisoned children remain a common problem facing pediatricians working in acute care medicine in the United States and worldwide. The management of such children continues to be challenging, and their care has evolved throughout the years. The concept of gastric decontamination in acute poisoning has significantly changed over the past 10 years, and many of the previously used techniques have been abandoned or fallen out of favor for lack of evidence to their benefit or unacceptable serious risks and side effects. Supportive care continues to be the cornerstone in managing most poisoned children. Only a few patients benefit from antidotes or specific interventions.

Adverse drug interactions involving common prescription and over-the-counter analgesic agents

BACKGROUND

Eight analgesic preparations with approved indications for acute pain were among the top 200 drugs prescribed in the United States in 2006. In addition, an estimated 36 million Americans use over-the-counter (OTC) analgesics daily. Given this volume of use, it is not surprising that a number of drug interactions involving analgesic drugs have been reported.

OBJECTIVES

This article examines the pharmacologic factors that enhance the clinical relevance of potential drug interactions and reviews the literature on drug interactions involving the most commonly used analgesic preparations in the United States.

METHODS

A PubMed search was conducted for English-language articles published between January 1967 and July 2007. Among the search terms were drug interactions, acetaminophen, aspirin, ibuprofen, naproxen, celecoxib, NSAIDs, hydrocodone, oxycodone, codeine, tramadol, OTC analgesics, alcohol, ethanol, antihypertensive drugs, methotrexate, warfarin, SSRIs, paroxetine, fluoxetine, sertraline, citalopram, serotonin syndrome, MAOIs, and overdose. Controlled clinical trials, case-control studies, and case reports were included in the review.

RESULTS

A number of case reports and well-controlled clinical trials were identified that provided evidence of the relatively well known drug-drug interactions between prescription/OTC NSAIDs and alcohol, antihypertensive drugs, high-dose methotrexate, and lithium, as well as between frequently prescribed narcotics and other central nervous system depressants. In contrast, the ability of recent alcohol ingestion to exacerbate the hepatotoxic potential of therapeutic doses of acetaminophen is not supported by either case reports or clinical research. Use of ibuprofen according to OTC guidelines in patients taking cardioprotective doses of aspirin does not appear to interfere with aspirin's antiplatelet activity, whereas chronic prescription use of ibuprofen and other NSAIDs may interfere. Low-dose aspirin intake appears to abolish the gastroprotective effects of cyclooxygenase-2-selective inhibitors, including celecoxib. There is evidence of other less well known and potentially clinically significant drug-drug interactions, including the ability of selective serotonin reuptake inhibitors to inhibit the analgesic activity of tramadol and codeine through inhibition of their metabolic activation, to induce serotonin syndrome when used chronically in the presence of high doses of tramadol through synergistic serotonergic action, and to increase the potential for gastrointestinal bleeding associated with NSAID therapy through additive or supra-additive antiplatelet activity.

CONCLUSIONS

Considering the widespread use of analgesic agents, the overall incidence of serious drug-drug interactions involving these agents has been relatively low. The most serious interactions usually involved other interacting drugs with low therapeutic indices or chronic and/or high-dose use of an analgesic and the interacting drug.

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.

Acute Fatal Acetaminophen Overdose Without Liver Necrosis

Two unusual cases of suicidal overdose of acetaminophen (paracetamol) without the usual extensive centrilobular necrosis of the liver are reported. Both cases were subjected to comprehensive drug screening by immunoassay, and a combination of gas chromatography with mass spectrometry, nitrogen detection, and electron capture detection. Acetaminophen was detected in both cases. No other drugs were detected in case #1, and only a small amount of olanzapine (<0.1 mg/L) was detected in case #2. No anatomical cause of death was identified in either case. If untreated, the normal outcome of a large acetaminophen overdose would be massive hepatic necrosis with delayed death and low blood and tissue acetaminophen concentrations. In contrast, particularly high postmortem acetaminophen concentrations were measured in both our cases with little hepatic tissue damage. For case #1, femoral blood acetaminophen 1280 mg/L, vitreous 878 mg/L, and liver 729 mg/kg; in case #2, cardiac blood 1220 mg/L, vitreous 779 mg/L, liver 3260 mg/kg, and gastric 11,500 mg/500 g. Acetaminophen was measured using high performance liquid chromatography with UV detection (254 nm) using 3-hydroxyacetanilide as the internal standard. The very high concentrations of acetaminophen is these cases but relatively little hepatic damage suggests an alternative, possibly cardiac, mechanism of death.

Pharmacokinetics of an oral drug (acetaminophen) administered at various times relative to subcutaneous injection of pramlintide in subjects with type 2 diabetes

Pramlintide, an adjunct treatment to mealtime insulin for patients with type 2 and type 1 diabetes, aids glycemic control by suppressing postprandial glucagon secretion, slowing gastric emptying, and enhancing satiety. Because gastric emptying affects oral medication absorption, this placebo-controlled, single-blind, crossover study examined the absorption of 1000 mg of acetaminophen elixir administered -2, -1, 0, +1, and +2 hours relative to pramlintide (120 microg) or 0 hours relative to placebo in 24 patients with type 2 diabetes. When acetaminophen administration occurred 0, +1, or +2 hours relative to pramlintide, the maximum observed plasma concentration of acetaminophen decreased 14% to 29%, and time to maximum observed plasma concentration increased by 0.8 to 1.2 hours compared with administration 0 hours relative to placebo. Pramlintide treatment slowed but did not alter the extent of acetaminophen absorption (area under the concentration-time curve). No serious adverse events or withdrawals were reported. Oral agents should be administered at least 1 hour before or 2 hours after pramlintide injection if rapid onset of action is required for efficacy.

Safety and pharmacokinetics of paracetamol following intravenous administration of 5 g during the first 24 h with a 2-g starting dose

Intravenous (i.v.) paracetamol is used as 1-g infusions with a maximal daily dose of 4 g/day. However, a higher initial analgesic dose could be of interest in the immediate postoperative period when the pain is maximal. The purpose of the present study was to determine in healthy subjects the safety and the pharmacokinetics of i.v. paracetamol, starting with a 2-g dose, followed by 1-g doses every 6 h, leading to a total of 5 g the first 24 h. This was an open-label, single-sequence study. The paracetamol pharmacokinetic profile was assessed in 26 subjects after both the 2-g starting dose and the 1-g doses. Safety, especially hepatotoxicity, was evaluated up to 72 h after the initial 2-g dose. Following the first 15-min i.v. administration of paracetamol 2 g, plasma concentrations ranged from 67.9+/-21.8 mug/ml (peak plasma concentration (C(max)) at the end of infusion) to 6.2+/-2.3 mug/ml (trough plasma concentration (C(min)) measured just before the next infusion) without any C(max) in the toxic range for any subject. After the repeated 1-g infusions, the plasma concentrations were approximately 35% lower than that measured after 2 g, showing the absence of accumulation. No clinical adverse events related to the drug administration nor clinically relevant changes in laboratory parameters, including biochemical signs of hepatotoxicity, were reported. After i.v. administration of paracetamol 2-g starting dose and 5 g during the first 24 h, the pharmacokinetics of paracetamol remain unchanged, with concentrations far below the toxic threshold. Overall, these results demonstrate that the i.v. administration of a 2-g starting dose of paracetamol, followed by three i.v. administrations of 1 g during the first 24 h is safe in healthy subjects.

Detection of urinary drug metabolite (xenometabolome) signatures in molecular epidemiology studies via statistical total correlation (NMR) spectroscopy

Western populations use prescription and nonprescription drugs extensively, but large-scale population usage is rarely assessed objectively in epidemiological studies. Here we apply statistical methods to characterize structural pathway connectivities of metabolites of commonly used drugs detected routinely in 1H NMR spectra of urine in a human population study. 1H NMR spectra were measured for two groups of urine samples obtained from U.S. participants in a known population study. The novel application of a statistical total correlation spectroscopy (STOCSY) approach enabled rapid identification of the major and certain minor drug metabolites in common use in the population, in particular, from acetaminophen and ibuprofen metabolites. This work shows that statistical connectivities between drug metabolites can be established in routine "high-throughput" NMR screening of human samples from participants who have randomly self-administered drugs. This approach should be of value in considering interpopulation patterns of drug metabolism in epidemiological and pharmacogenetic studies.

High-amylose carboxymethyl starch matrices for oral sustained drug-release: In vitro and in vivo evaluation

High-amylose corn starch, that contains 70% of amylose chains and 30% of amylopectin, has been used to obtain substituted amylose (SA) polymers. Tablets have been prepared by direct compression, i.e. dry mixing of drug and SA, followed by compression, which is the easiest way to manufacture an oral dosage form. Until now, their controlled-release properties have been assessed only by an in vitro dissolution test. Amylose-based polymers are normally subject to biodegradation by alpha-amylase enzymes present in the gastrointestinal tract, but matrix systems show no significant degradation of tablets by alpha-amylase in vitro. High-amylose sodium carboxymethyl starch (HASCA) is an interesting excipient for sustained drug-release in solid oral dosage forms. In addition to the easy manufacture of tablets by direct compression, the results show that in vitro drug-release from an optimized HASCA formulation is not affected by either acidic pH value or acidic medium residence time. In addition, a compressed blend of HASCA with an optimized quantity of sodium chloride provides a pharmaceutical sustained-release tablet with improved integrity for oral administration. In vivo studies demonstrate extended drug absorption, showing that the matrix tablets do not disintegrate immediately. Nevertheless, acetaminophen does not seem to be the most appropriate drug for this type of formulation.

A matched patient-sibling study on the usage of paracetamol and the subsequent development of allergy and asthma

A number of studies have suggested that intake of paracetamol during pregnancy and during the first months of life is associated with an increased risk of childhood asthma. We aimed to determine the association between paracetamol usage during pregnancy and the first 6 months of life, and childhood allergy (i.e. positive skin prick tests), allergic asthma, and asthma, using a matched patient-sibling study comparing patients with allergic asthma with their healthy siblings without any symptoms of allergic diseases. Allergy in patients and their siblings was determined by skin prick tests. Children having at least one positive skin prick test were considered to be allergic. Intake of paracetamol was assessed by standardized, interviewer-administered, questionnaire. Nineteen pairs of allergic asthma patients vs. non-allergic siblings were compared to determine the risk factors for allergic asthma, while 15 pairs of allergic asthma patients vs. allergic siblings were compared to determine the risk factors for asthma. Moreover, 33 pairs of allergic asthma patients vs. non-asthmatic siblings (with and without allergy) were compared to determine the risk factors for asthma. In addition, 17 allergic siblings (without asthma) were compared with 19 non-allergic siblings (without asthma) to determine the risk factors for allergy. Usage of paracetamol during pregnancy was associated with allergic asthma (p = 0.03). Furthermore, usage of paracetamol between birth and 6 months of age, and between 4 and 6 months of age, was also found to be associated with non-allergic asthma (p = 0.008 and p = 0.03 respectively). Usage of paracetamol during pregnancy and during the early months of life may play a role in the development of allergic and non-allergic asthma in children. However, due to obvious ethical reasons, direct evidence for this association (i.e. a double-blind, prospective study) is not available.

Glucuronidation in the chimpanzee (Pan troglodytes): studies with acetaminophen, oestradiol and morphine

The chimpanzee has recently been characterized as a surrogate for oxidative drug metabolism in humans and as a pharmacokinetic model for the selection of drug candidates. In the current study, the glucuronidation of acetaminophen, morphine and oestradiol was evaluated in the chimpanzee to extend the characterization of this important animal model. Following oral administration of acetaminophen (600 mg) to chimpanzees (n=2), pharmacokinetics were comparable with previously reported human values, namely mean oral clearance 0.91 vs. 0.62+/-0.05 l h-1 kg-1, apparent volume of distribution 2.29 vs. 1.65+/-0.25 l kg-1, and half-life 1.86 vs. 1.89+/-7h, for chimpanzee vs. human, respectively. Urinary excretions (percentage of dose) of acetaminophen, acetaminophen glucuronide and acetaminophen sulfate were also similar between chimpanzees and humans, namely 2.3 vs. 5.0, 63.1 vs. 54.7, and 25.0 vs. 32.3%, respectively. Acetaminophen, oestradiol and morphine glucuronide formation kinetics were investigated using chimpanzee (n=2) and pooled human liver microsomes (n=10). V(max) (app) and K(m)(app) (or S(50)(app)) for acetaminophen glucuronide, morphine 3- and 6-glucuronide, and oestradiol 3- and 17-glucuronide formation were comparable in both species. Eadie-Hofstee plots of oestradiol 3-glucuronide formation in chimpanzee microsomes were characteristic of autoactivation kinetics. Western immunoblot analysis of chimpanzee liver microsomes revealed a single immunoreactive band when probed with anti-human UGT1A1, anti-human UGT1A6, and anti-human UGT2B7. Taken collectively, these data demonstrate similar glucuronidation characteristics in chimpanzees and humans.

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

BACKGROUND

Panadol Extend is a modified-release paracetamol formulation in which each 665 mg tablet contains 69% slow-release and 31% immediate-release paracetamol. There are no data on Panadol Extend pharmacokinetics in overdose. It is unknown whether the paracetamol treatment nomogram can be used to make decisions regarding the toxicity of this product in overdose.

OBJECTIVE

To compare the pharmacokinetics of Panadol Extend and immediate-release paracetamol (APAP-IR) in simulated overdose model in healthy volunteers.

METHODS

Cross-over study using a dose of 90 mg/kg ideal body weight of Panadol Extend or APAP-IR in seven healthy volunteers. Serum paracetamol concentrations were measured over 12 h. Maximal paracetamol concentration (Cmax), time to Cmax (Tmax), area under the curve (AUC) and elimination half-life (t(1/2)) were compared.

RESULTS

Mean paracetamol dose was 73 mg/kg actual body weight. Panadol Extend produced lower Cmax (0.208 mmol/L +/- 0.02 vs 0.48 mmol/L +/- 0.02, P = 0.0001) and AUC(0-12 h) when compared with APAP-IR. Tmax was delayed with Panadol Extend (2.83 h +/- 0.26 vs 0.94 h +/- 0.17, P = 0.0001). Absorption was complete in all subjects by 4 h post ingestion in both study arms. Elimination t(1/2) was 1.69 +/- 0.09 h for APAP-IR and 1.65 +/- 0.13 h for Panadol Extend (not significant).

CONCLUSIONS

Reductions in Panadol Extend Cmax and AUC(0-12 h) might be related to elimination occurring during the absorption phase. In this model of Panadol Extend moderate overdose, Tmax was significantly delayed. In larger overdoses, time to peak paracetamol levels might be further delayed, because of continuing absorption from the formulation. Therefore, the paracetamol treatment nomogram might not reliably predict hepatotoxicity from Panadol Extend if paracetamol levels are measured too early.

Reduction of paracetamol metabolism after hepatic resection

INTRODUCTION

Paracetamol is often used as an analgesic following hepatic resection. During liver resection, vascular clamping is carried out to reduce blood loss. Previous studies have described transient postoperative rises in serum aminotransferase levels and decreases in prothrombin time and factor V levels. We have examined paracetamol metabolism after liver resection.

METHODS

A prospective observational study was performed. All patients undergoing liver resection were included. Propacetamol was given every 6 h. Blood samples for plasma paracetamol concentrations were collected before, 1 h after the end of the first injection (T1), just before the second injection (6 h: T6), and just before the fifth injection (24 h: T24).

RESULTS

37 patients were recruited. 13 had hepatic vascular exclusion (HVE group), 13 had portal triad clamping (PTC group) and 11 had abdominal surgery with no liver resection (NLR group: control group). At T6, the plasma paracetamol concentration in the HVE group was significantly higher than in the NLR groups; at T24, this concentration was significantly higher in the HVE group than in the NLR and PTC groups, and was higher in the PTC group than in the NLR group. Prothrombin time and factor V was significantly lower in the HVE group than in the PTC group on the first postoperative day.

DISCUSSION

This study showed a reduction of paracetamol metabolism in the liver resection group with significantly increased paracetamol levels. However, the maximum mean plasma concentration reached was not clinically or toxicologically significant. For these reasons, we cannot suggest that paracetamol should or should not be avoided in patients undergoing liver resection.

Hyperbaric oxygen reduces acetaminophen toxicity and increases HIF-1alpha expression

OBJECTIVES

To investigate the effect of hyperbaric oxygen (HBO2) on acetaminophen (APAP)-induced hepatotoxicity. The authors further evaluated the effects of APAP poisoning and HBO2 on the expression and function of hypoxia-inducible factor 1-alpha (HIF-1alpha) in an effort to further describe the mechanisms of APAP-induced hepatotoxicity. In vitro assays were performed to better understand the effects of HBO2 on HIF-1alpha function.

METHODS

In vivo, four groups of C57BL/6 mice were treated as follows: APAP only, APAP followed by HBO2, HBO2 only, and untreated shams. Plasma alanine aminotransferase activity was measured, and hepatic HIF-1alpha induction was determined by Western blot. In vitro, cultured HEP G2 hepatocytes were exposed to HBO2, hypoxia (2.5% O2), or normoxia. HIF-1alpha DNA-binding and transcriptional activity were assessed.

RESULTS

Alanine aminotransferase activity was reduced in the APAP+HBO2 group (2,606 IU/L +/- 4,080; vs. APAP: 6,743 +/- 3,397, p = 0.01 at 6 hours). APAP-only, HBO2-only, and APAP+HBO2 treatments all increased HIF-1alpha expression relative to shams (p = 0.02, p = 0.02, and p < 0.01, respectively). HBO2 increased HIF-1alpha DNA binding 5.7 (+/- 1.2)-fold relative to controls (p < 0.01); however, a parallel increase in HIF functional transcriptional activity did not occur.

CONCLUSIONS

Hyperbaric oxygen reduced early APAP-induced hepatocellular injury. APAP poisoning increases HIF-1alpha protein levels and functional activity. HBO2 increases HIF-1alpha protein levels and DNA binding without a corresponding increase in transcriptional activity.

In vitro inhibitory effects of non-steroidal anti-inflammatory drugs on 4-methylumbelliferone glucuronidation in recombinant human UDP-glucuronosyltransferase 1A9--potent inhibition by niflumic acid

The inhibitory potencies of non-steroidal anti-inflammatory drugs (NSAIDs) on UDP-glucuronosyltransferase (UGT) 1A9 activity were investigated in recombinant human UGT1A9 using 4-methylumbelliferone (4-MU) as a substrate for glucuronidation. 4-MU glucuronidation (4-MUG) showed Michaelis-Menten kinetics with a Km value of 6.7 microM. The inhibitory effects of the following seven NSAIDs were investigated: acetaminophen, diclofenac, diflunisal, indomethacin, ketoprofen, naproxen and niflumic acid. Niflumic acid had the most potent inhibitory effect on 4-MUG with an IC50 value of 0.0341 microM. The IC50 values of diflunisal, diclofenac and indomethacin were 1.31, 24.2, and 34.1 microM, respectively, while acetaminophen, ketoprofen and naproxen showed less potent inhibition. Niflumic acid, diflunisal, diclofenac and indomethacin inhibited 4-MUG competitively with Ki values of 0.0275, 0.710, 53.3 and 69.9 microM, respectively, being similar to each IC50 value. In conclusion, of the seven NSAIDs investigated, niflumic acid was the most potent inhibitor of recombinant UGT1A9 via 4-MUG in a competitive manner.