Mechanistic and Quantitative Understanding of Pharmacokinetics in Zebrafish Larvae through Nanoscale Blood Sampling and Metabolite Modeling of Paracetamol.

Zebrafish larvae are increasingly used for pharmacological research, but internal drug exposure is often not measured. Understanding pharmacokinetics is necessary for reliable translation of pharmacological results to higher vertebrates, including humans. Quantification of drug clearance and distribution requires measurements of blood concentrations. Additionally, measuring drug metabolites is of importance to understand clearance in this model organism mechanistically. We therefore mechanistically studied and quantified pharmacokinetics in zebrafish larvae, and compared this to higher vertebrates, using paracetamol (acetaminophen) as a paradigm compound. A method was developed to sample blood from zebrafish larvae 5 days post fertilization. Blood concentrations of paracetamol and its major metabolites, paracetamol-glucuronide and paracetamol-sulfate, were measured. Blood concentration data were combined with measured amounts in larval homogenates and excreted amounts and simultaneously analyzed through nonlinear mixed-effects modeling, quantifying absolute clearance and distribution volume. Blood sampling from zebrafish larvae was most successful from the posterior cardinal vein, with a median volume (interquartile range) of 1.12 nl (0.676-1.66 nl) per blood sample. Samples were pooled (n = 15-35) to reach measurable levels. Paracetamol blood concentrations at steady state were only 10% of the external paracetamol concentration. Paracetamol-sulfate was the major metabolite, and its formation was quantified using a time-dependent metabolic formation rate. Absolute clearance and distribution volume correlated well with reported values in higher vertebrates, including humans. Based on blood concentrations and advanced data analysis, the mechanistic and quantitative understanding of paracetamol pharmacokinetics in zebrafish larvae has been established. This will improve the translational value of this vertebrate model organism in drug discovery and development. SIGNIFICANCE STATEMENT: In early phases of drug development, new compounds are increasingly screened in zebrafish larvae, but the internal drug exposure is often not taken into consideration. We developed innovative experimental and computational methods, including a blood-sampling technique, to measure the paradigm drug paracetamol (acetaminophen) and its major metabolites and quantify pharmacokinetics (absorption, distribution, elimination) in zebrafish larvae of 5 days post fertilization with a total volume of only 300 nl. These parameter values were scaled to higher vertebrates, including humans.

An ultra-rapid drug screening method for acetaminophen in blood serum based on probe electrospray ionization-tandem mass spectrometry.

Poisoning incidents caused by drugs, accidental ingestion of poisons, attempted suicide, homicide, and exposure to toxic compounds occur frequently every year across the globe. This raises the need to rapidly identify toxic agents in poisoned patients in a clinical emergency setting. In addition, determining drug/poison concentration is undoubtedly necessary to arrive at a toxicological treatment plan. The purpose of this study was to develop an ultra-rapid drug screening method for the clinical treatment of poisoning. Probe electrospray ionization (PESI), one of the ambient ionization techniques, is able to detect compounds from various biological materials almost directly. We applied the PESI technique to the rapid detection of acetaminophen (APAP). Blood serum samples were diluted 100-fold with 10 mM ammonium formate/ethanol (1:1 v/v) solution including deuterium-labeled internal standards (IS; APAP-d4). Only 10 µL of the diluted sample was used for measurement. The tandem mass spectrometer (MS/MS) equipped with a PESI was used in selected reaction monitoring mode for the quantitation of APAP; the measurement time was only 18 s. Transitions were set at 152 > 110 for quantitation, 152 > 65 for qualifier, and 156 > 114 for IS (APAP-d4). All measurements were conducted in positive mode. The calibration curve (1/x2) was linear over the range of 1.56-200 µg/mL (r2 = 0.998), and the limit of detection and quantitation were 0.37 µg/mL and 1.56 µg/mL, respectively. The accuracy (bias) and precision (RSD%) of the method were within an acceptable range (-0.15-2.8% and 2.3-6.1%, respectively) and matrix effect at 3 concentrations (95.1-104%) indicated that PESI-MS/MS is only slightly affected by matrices. In real forensic cases, quantitative values of APAP determined by the PESI-MS/MS were almost identical to those determined by the liquid chromatography-MS/MS method. Since PESI-MS/MS is a simple, reliable, and rapid determination method for toxic agents with virtually no need for blood serum pre-treatment, it would be highly suitable for poisoning cases in clinical emergency settings. In the future, a method for simultaneous rapid determination of multiple toxic agents will be developed.

The effect of modulated electro-hyperthermia on the pharmacokinetic properties of nefopam in healthy volunteers: A randomised, single-dose, crossover open-label study.

PURPOSE: Nefopam is a widely available analgesic for the management of pain. The aim of this study was to reveal the effect of regional hyperthermia of the abdominal area on the pharmacokinetics of nefopam. MATERIALS AND METHODS: A randomised, single-dose, crossover, open-label study was conducted to reveal the effect of hyperthermia using modulated electro-hyperthermia on the pharmacokinetics of nefopam. The pharmacokinetics of orally administered nefopam without hyperthermia was studied in 12 healthy volunteers and then 7 days later they were treated with nefopam plus modulated electro-hyperthermia to the abdominal area for 1 h. Blood samples were collected up to 24 h after the drug administration. From the blood concentration-time curve, the maxinum plasma concentration (C(max)), time to C(max) (T(max)) and the area under the curve (AUC) were obtained. The safety and tolerability of these treatments were also assessed. RESULTS: The geometric mean ratios (GMRs) ((nefopam + modulated electro-hyperthermia)/nefopam) and the associated 90% confidence intervals (CIs) for C(max), AUC(last) and AUC(inf) were 1.2804 (1.1155∼1.4696), 1.0512 (0.9555∼1.1566) and 1.0612 (0.9528∼1.1819), respectively. The increase in C(max) was statistically significant, and T(max) was significantly shortened. CONCLUSIONS: The significant increase in C(max) and decrease in T(max) indicated that modulated electro-hyperthermia increased the absorption of the orally administered nefopam, thereby transitionally increasing the blood concentration of the drug. The AUC is an important parameter that contributes to the therapeutic effect of drugs. The lack of significant change in AUC suggests that modulated electro-hyperthermia may increases the absorption of orally administered drugs without increasing the systemic adverse effect of the drugs.

Glucosamine enhances paracetamol bioavailability by reducing its metabolism.

Paracetamol has an extensive first-pass metabolism that highly affects its bioavailability (BA); thus, dose may be repeated several times a day in order to have longer efficacy. However, hepatotoxicity may arise because of paracetamol metabolism. Therefore, this project aimed to increase paracetamol BA in rats by glucosamine (GlcN). At GlcN-paracetamol racemic mixture ratio of 4:1 and paracetamol dose of 10 mg/kg, paracetamol area under the curve (AUC) and maximum concentration (Cmax ) were significantly increased by 99% and 66%, respectively (p < 0.05). Furthermore, paracetamol AUC and Cmax levels were increased by 165% and 88% in rats prefed with GlcN for 2 days (p < 0.001). Moreover, GlcN significantly reduced phase Ι and phase I/ΙΙ metabolic reactions in liver homogenate by 48% and 54%, respectively. Furthermore, GlcN molecule was found to possess a good in silico binding mode into the CYP2E1 active site-forming bidentate hydrogen bonding with the Thr303 side chain. Finally, serum ALT and AST levels of rats-administered high doses of paracetamol were significantly reduced when rats were prefed with GlcN (p < 0.01). In conclusion, GlcN can increase the relative BA of paracetamol through reducing its metabolism. This phenomenon is associated with reduction in hepatocytes injury following ingestion of high doses of paracetamol.

Interaction between different extracts of Hypericum perforatum L. from Serbia and pentobarbital, diazepam and paracetamol.

Herb-drug interactions are an important safety concern and this study was conducted regarding the interaction between the natural top-selling antidepressant remedy Hypericum perforatum (Hypericaceae) and conventional drugs. This study examined the influence of acute pretreatment with different extracts of Hypericum perforatum from Serbia on pentobarbital-induced sleeping time, impairment of motor coordination caused by diazepam and paracetamol pharmacokinetics in mice. Ethanolic extract, aqueous extract, infusion, tablet and capsule of Hypericum perforatum were used in this experiment. The profile of Hypericum perforatum extracts as well as paracetamol plasma concentration was determined using RP-HPLC analysis. By quantitative HPLC analysis of active principles, it has been proven that Hypericum perforatum ethanolic extract has the largest content of naphtodianthrones: hypericin (57.77 µg/mL) and pseudohypericin (155.38 µg/mL). Pretreatment with ethanolic extract of Hypericum perforatum potentiated the hypnotic effect of pentobarbital and impairment of motor coordination caused by diazepam to the greatest extent and also increased paracetamol plasma concentration in comparison to the control group. These results were in correlation with naphtodianthrone concentrations. The obtained results have shown a considerable influence of Hypericum perforatum on pentobarbital and diazepam pharmacodynamics and paracetamol pharmacokinetics.

Antinociceptive curcuminoid, KMS4034, effects on inflammatory and neuropathic pain likely via modulating TRPV1 in mice.

BACKGROUND: Curcumin, the active ingredient of turmeric (Curcuma longa), has a wide range of beneficial effects including anti-inflammation and analgesia. However, poor bioavailability of curcumin hinders its clinical application. To overcome this limitation, we modified the structure of curcumin and synthesized new derivatives with favourable pharmacokinetic profiles. Recently, curcumin has been shown to have an antagonizing effect on transient receptor potential vanilloid type 1 (TRPV1) ion channels. We investigated the antinociceptive activity of KMS4034 which had the most favourable pharmacokinetics among the tested curcumin derivatives. METHODS: To evaluate the mechanism of the antinociceptive effects of KMS4034, capsaicin (I(CAP))- and heat (I(heat))-induced currents in TRPV1 expressing HEK293 cells were observed after the application of KMS4034. Nociceptive behavioural measurement using the hot-plate test, formalin test, and chronic constriction injury (CCI) model were evaluated in mice. Also, calcitonin gene-related peptide (CGRP) was stained immunohistochemically in the L4/5 dorsal horns in mice with neuropathic pain. RESULTS: I(CAP) (P<0.01) and I(heat) (P<0.05) of TRPV1 were significantly blocked by 10 µM KMS4034. Behaviourally, noticeable antinociceptive effects after 10 mg kg(-1) of KMS4034 treatment were observed in the first (P<0.05) and second phases (P<0.05) of the formalin and hot-plate tests. The mechanical threshold of CCI mice treated with 10 mg kg(-1) KMS4034 was significantly increased compared with control. Immunohistochemical CGRP expression was decreased in the lamina I-II of the lumbar dorsal horns in KMS4034-treated CCI mice compared with the control (P<0.05). CONCLUSIONS: KMS4034 may be an effective analgesic for various pain conditions.

Chlorogenic acid differentially affects postprandial glucose and glucose-dependent insulinotropic polypeptide response in rats.

Regular coffee consumption significantly lowers the risk of type 2 diabetes (T2D). Coffee contains thousands of compounds; however, the specific component(s) responsible for this reduced risk is unknown. Chlorogenic acids (CGA) found in brewed coffee inhibit intestinal glucose uptake in vitro. The objective of this study was to elucidate the mechanisms by which CGA acts to mediate blood glucose response in vivo. Conscious, unrestrained, male Sprague-Dawley rats were chronically catheterized and gavage-fed a standardized meal (59% carbohydrate, 25% fat, 12% protein), administered with or without CGA (120 mg·kg(-1)), in a randomized crossover design separated by a 3-day washout period. Acetaminophen was co-administered to assess the effects of CGA on gastric emptying. The incretins glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) were measured. GLP-1 response in the presence of glucose and CGA was further examined, using the human colon cell line NCI-H716. Total area under the curve (AUC) for blood glucose was significantly attenuated in rats fed CGA (p < 0.05). Despite this, no differences in plasma insulin or nonesterified fatty acids were observed, and gastric emptying was not altered. Plasma GIP response was blunted in rats fed CGA, with a lower peak concentration and AUC up to 180 min postprandially (p < 0.05). There were no changes in GLP-1 secretion in either the in vivo or in vitro study. In conclusion, CGA treatment resulted in beneficial effects on blood glucose response, with alterations seen in GIP concentrations. Given the widespread consumption and availability of coffee, CGA may be a viable prevention tool for T2D.

In situ gelling xyloglucan/alginate liquid formulation for oral sustained drug delivery to dysphagic patients.

BACKGROUND: The oral administration of liquid dosage forms of suitable consistency and with sustained release characteristics may provide a means of improving the compliance of geriatric patients who experience difficulties in swallowing conventional solid dosage forms. AIM: We have designed and evaluated liquid preparations for administration to dysphagic patients, composed of aqueous mixtures of xyloglucan, which has thermally reversible gelation characteristics, and sodium alginate, which has ion-responsive gelation characteristics. METHOD: The gelation and in vitro and in vivo release characteristics of liquid formulations containing appropriate concentrations of xyloglucan and sodium alginate with mannuronate/guluronate ratios of either 0.5 or 0.8 were assessed. RESULTS: Aqueous mixtures of 1.5% xyloglucan and 0.5% alginate had suitable viscosities for ease of swallowing and appropriate gelation temperatures (approximately 33 degrees C) to ensure in situ gelation following oral administration. The in vitro release of paracetamol at pH 5.0 from gels formed by these formulations and also by a 1.5% xyloglucan solution was diffusion-controlled. Plasma levels of paracetamol after oral administration to gastric-acidity controlled rats (pH 5) of a solution containing 1.5% xyloglucan/0.5% alginate showed that a more sustained release was achieved from the gels formed by the in situ gelation of this formulation compared with that of a 1.5% xyloglucan solution. Visual observation of the contents of the rat stomach after oral administration showed that the inclusion of alginate in the xyloglucan solutions was effective in reducing gel erosion, so sustaining drug release. CONCLUSIONS: Liquid formulations of xyloglucan and sodium alginate in appropriate proportions are of suitable consistency for ease of administration to dysphagic patients and form gels in situ in the rat stomach capable of sustaining the release of paracetamol over a 6-hour period.

GC/MS analysis of an herbal dietary supplement containing ephedrine.

An unconscious 20-year-old female was admitted to hospital with a heart rate of 164, a blood pressure of 132/90 mmHg, and hypokalemia. "Triage" urine screening tests were negative on arrival and 12 h later. The next day, her SGOT and SGPT levels rose remarkably; however, on the third day, the patient regained consciousness. Two Japanese OTC drugs and an American herbal dietary supplement ("7th heaven") were found in her room. The supplement and the patient's samples were analyzed using GC/MS. Ephedrine (2.32 mg/g) and caffeine (17.96 mg/g) were detected in the supplement and in the patient's serum (0.627 mg/L, 383 mg/L, respectively), as well as acetaminophen, bromvalerylurea, and etenzamide, which are constituents of the OTC drugs. The serum ephedrine concentration was above the therapeutic level but did not reach the fatal level. The acetaminophen concentration was sufficient to cause liver damage. Although a prescription is necessary to obtain products containing ephedrine in Japan, this patient had no prescription. Thus, how the patient obtained the drug and the amount ingested were unclear. Information about acquisition of drugs via the Internet or magazine advertisements is constantly changing and unreliable. Thus, it is indispensable to analyze unfamiliar supplements found with patients.

Dose-dependent effects of smoked cannabis on capsaicin-induced pain and hyperalgesia in healthy volunteers.

BACKGROUND: Although the preclinical literature suggests that cannabinoids produce antinociception and antihyperalgesic effects, efficacy in the human pain state remains unclear. Using a human experimental pain model, the authors hypothesized that inhaled cannabis would reduce the pain and hyperalgesia induced by intradermal capsaicin. METHODS: In a randomized, double-blinded, placebo-controlled, crossover trial in 15 healthy volunteers, the authors evaluated concentration-response effects of low-, medium-, and high-dose smoked cannabis (respectively 2%, 4%, and 8% 9-delta-tetrahydrocannabinol by weight) on pain and cutaneous hyperalgesia induced by intradermal capsaicin. Capsaicin was injected into opposite forearms 5 and 45 min after drug exposure, and pain, hyperalgesia, tetrahydrocannabinol plasma levels, and side effects were assessed. RESULTS: Five minutes after cannabis exposure, there was no effect on capsaicin-induced pain at any dose. By 45 min after cannabis exposure, however, there was a significant decrease in capsaicin-induced pain with the medium dose and a significant increase in capsaicin-induced pain with the high dose. There was no effect seen with the low dose, nor was there an effect on the area of hyperalgesia at any dose. Significant negative correlations between pain perception and plasma delta-9-tetrahydrocannabinol levels were found after adjusting for the overall dose effects. There was no significant difference in performance on the neuropsychological tests. CONCLUSIONS: This study suggests that there is a window of modest analgesia for smoked cannabis, with lower doses decreasing pain and higher doses increasing pain.

Hypokalaemia following paracetamol overdose in two teenage girls.

We report on two teenage girls presenting following significant paracetamol overdoses (>28 g paracetamol). Both presented within 4 h of the overdose and both were treated with N-acetylcysteine, in accordance with the National Poisons Information Service protocol. Within 8 h of presentation both had developed significant hypokalaemia with serum potassium concentrations <3.0 mmol/L and were treated with intravenous potassium chloride. Potassium concentrations returned to within reference limits (>3.5 mmol/L) after commencing potassium chloride supplementation. An audit of potassium concentrations in 254 patients presenting with significant paracetamol overdose (paracetamol >0.5 mmol/L) admitted through four A&E departments in the West of Scotland showed a significant decline in mean serum potassium from 3.9 mmol/L on admission to 3.6 mmol/L (P = <0.001) over the next 36 h. The mechanism for this hypokalaemia in these two individuals is unclear, however regular monitoring of potassium is advocated in such patients during their initial treatment.

Interaction between traditional Chinese medicine and Western medicine in rats--In-Chen-How and acetaminophen.

The purpose of this study is to evaluate the interaction effects of In-Chen-How (Artemisia capillaries Thunb.) on the pharmacokinetics of acetaminophen and on liver microsomal cytochrome P450 enzyme activity in rats. The rats were divided into control group (n = 8) without In-Chen-How and the pretreated group (n = 8) administered with In-Chen-How (approximately 1.0 mL x kg(-1), according to weight) for 5 consecutive days. Rats in the control group received water simultaneously. Each rat was then given acetaminophen. The pharmacokinetic parameters of acetaminophen of the two groups were significantly different. In the In-Chen-How pretreated group, the maximum concentration of acetaminophen and the area under the plasma concentration-time curve were reduced about 58.4%, 56.7% and 55.4%. To further explain the results, liver microsomal suspensions were obtained from rats that were randomly divided into control and In-Chen-How pretreated group. The levels of CYP1A2 and CYP2E1 in hepatic microsomal protein from pretreated group were increased as compared to that from the control group. It indicated that In-Chen-How can stimulate the activity of CYP isozymes. The changes in the pharmacokinetics of acetaminophen resulting from the administration of In-Chen-How are related to an increase in metabolic activity of CYP1A2 and CYP2E1.

The analgesic effect of oral delta-9-tetrahydrocannabinol (THC), morphine, and a THC-morphine combination in healthy subjects under experimental pain conditions.

From folk medicine and anecdotal reports it is known that Cannabis may reduce pain. In animal studies it has been shown that delta-9-tetrahydrocannabinol (THC) has antinociceptive effects or potentiates the antinociceptive effect of morphine. The aim of this study was to measure the analgesic effect of THC, morphine, and a THC-morphine combination (THC-morphine) in humans using experimental pain models. THC (20 mg), morphine (30 mg), THC-morphine (20 mg THC+30 mg morphine), or placebo were given orally and as single doses. Twelve healthy volunteers were included in the randomized, placebo-controlled, double-blinded, crossover study. The experimental pain tests (order randomized) were heat, cold, pressure, single and repeated transcutaneous electrical stimulation. Additionally, reaction time, side-effects (visual analog scales), and vital functions were monitored. For the pharmacokinetic profiling, blood samples were collected. THC did not significantly reduce pain. In the cold and heat tests it even produced hyperalgesia, which was completely neutralized by THC-morphine. A slight additive analgesic effect could be observed for THC-morphine in the electrical stimulation test. No analgesic effect resulted in the pressure and heat test, neither with THC nor THC-morphine. Psychotropic and somatic side-effects (sleepiness, euphoria, anxiety, confusion, nausea, dizziness, etc.) were common, but usually mild.

Phosphatidylcholine association increases the anti-inflammatory and analgesic activity of ibuprofen in acute and chronic rodent models of joint inflammation: relationship to alterations in bioavailability and cyclooxygenase-inhibitory potency.

We investigated whether chemical association of phosphatidylcholine (PC) to ibuprofen enhances the anti-inflammatory/analgesic activity of the nonsteroidal anti-inflammatory drug (NSAID) and whether any change in therapeutic action is due to alterations in drug bioavailability and cyclooxygenase (COX) inhibitory activity. Acute/chronic joint inflammation was induced in rats, by injection of Complete Freund's Adjuvant. In the acute study, rats were administered saline, ibuprofen, or PC-ibuprofen (at NSAID doses of 10, 25, and 50 mg/kg), and 2 h later the pain threshold of the affected joint to pressure was measured. PC-ibuprofen increased the pain threshold at all NSAID doses, whereas unmodified ibuprofen demonstrated analgesic activity at only the highest dose. In the chronic study, we investigated the effects of saline, PC-ibuprofen, and ibuprofen (administered at 15 and 25 mg/kg/day) on ankle thickness and pain threshold, and demonstrated that PC-ibuprofen had significantly greater anti-inflammatory and analgesic activity than ibuprofen, over a 30- to 60-day period. PC association resulted in reduced uptake (decreased Cmax), a modest increase in the area under the curve, and a longer t(1/2) of ibuprofen. We also demonstrated that PC-ibuprofen was a comparable or a more effective inhibitor of both 6-keto-prostaglandin F1alpha concentration of fluid collected from tissue in and around the inflamed stifle joint, and COX-2 activity in activated human umbilical vein endothelial cells. In conclusion, we have demonstrated that PC association results in increases in ibuprofen's anti-inflammatory and analgesic activity in rodent models of acute and chronic joint inflammation, and this effect may relate to alterations in drug bioavailability and COX-inhibitory potency.

Plasma paracetamol concentrations and pharmacokinetics following rectal administration in neonates and young infants.

BACKGROUND: Despite widespread use in children pharmacokinetic data about paracetamol are relatively scarce, not the least in the youngest age groups. This study aimed to describe plasma paracetamol concentrations and pharmacokinetics of a single rectal paracetamol dose in neonates and young infants. METHODS: Perioperatively, 17 neonates and infants < or =160 days of age received one rectal paracetamol dose (mean 23.9 mg/kg (+/-4.2 mg/kg)). Blood samples were drawn at 60, 120, 180, 240, 300 and 360 min, according to the infants' weights. Plasma paracetamol concentrations were measured by a Colorometric Assay, Ectachem Clinical Chemistry Slides (Johnson & Johnson Clinical Diagsnostics). RESULTS: The plasma paracetamol concentrations were mainly below the therapeutic (i.e. antipyretic) range of 66-132 micromol/l and did not exceed 160 micromol/l in any infant. The mean maximum plasma concentration (Cmax) was 72.4 micromol/l (+/-33.5 micromol/l) and the time to Cmax, i.e. the mean Tmax was 102.4 min (_+59.1 min). The mean "apparent" terminal half-life (n=10) was 243.6 min (+/-114.1 min). CONCLUSION: The absorption of rectal paracetamol (mean dose 23.9 mg/kg, +/-4.2mg/kg) in young infants <160 days is variable and often prolonged and achieves mainly subtherapeutic plasma concentrations.

The effect of diazepam in the recovery of rabbits from acute acetaminophen intoxication.

We have recently shown that diazepam can reduce mortality of acute iron overdose in rats. The mechanism for that effect is not yet defined. Our objective in the present study was to assess whether diazepam can similarly reduce mortality of experimental acute acetaminophen intoxication. Survival of rabbits was compared among four groups receiving 3 g/kg (body weight) of acetaminophen (LD40) orally each, followed by: 1) nothing (group I), 2) one oral dose of 140 mg/kg N-acetylcystein (NAC) an hour later (group II), 3) intramuscular injection of 7 mg/kg diazepam (group III), 4) intramuscular injection of 7 mg/kg diazepam and one oral dose of 140 mg/kg NAC an hour later (group IV). 37.5% of rabbits in group I died after 16 hours, whereas none of the rabbits in group III died, (p = 0.04). No animal died during the 96-hour observation period in groups II and IV. Two and four hours post drug administration, acetaminophen plasma concentrations (APC) were significantly lower among rabbits in group III than in group I (p = 0.0007 and 0.01, respectively) and significantly lower among rabbits in group IV than in those in group II (p<0.0001 and p = 0.03, respectively). Acetaminophen plasma concentrations 2 hours after drug administration were also significantly lower among rabbits in group III than in those in group II (p = 0.0002). Seven and 24 hours after dosage, APC tended to be higher among rabbits in group III than in those in group I, but not significantly so. Administration of diazepam without NAC did not prevent liver and renal dysfunction. We conclude that early administration of diazepam in acute experimental acetaminophen overdose in rabbits reduced APC and mortality, probably by slowing intestinal motility, which resulted in delayed acetaminophen absorption from the gastrointestinal tract.

Pharmacokinetic study on acetaminophen: interaction with a Chinese medicine.

To know the influences of a Chinese traditional medicine (KAKKONTO) on the metabolism of acetaminophen (APAP), we have carried out pharmacokinetic studies on APAP under KAKKONTO coadministration in humans and rats. In humans, the pharmacokinetic parameters were calculated from the blood APAP concentration-time curves of each volunteer. The parameters did not show any significant differences between the KAKKONTO-coadministration group (group K) and the APAP-administration group (group A). KAKKONTO, when given at two different doses, did not show any significant effects on blood APAP level. In rats, the blood APAP level was significantly higher than that of group A (p < 0.01) only in the 100 mg/kg of group K at 0.25 h after APAP administration. There were no other significant differences.

The effect of caffeine on the pharmacokinetics of acetaminophen in man.

The influence of caffeine (60 mg) was studied on the pharmacokinetic characteristics of acetaminophen (500 mg single dose) in ten healthy male human volunteers in a complete cross-over design. A high-performance liquid chromatography (HPLC) method was used to analyse serum drug concentrations. Caffeine caused a highly significant (p < 0.01) increase in AUC and AUMC, a significant (p < 0.05) increase in Cmax, and a significant (p < 0.05) decrease in clearance (C1/F) of acetaminophen. We conclude that caffeine taken in doses commonly available commercially or in a cup of coffee can significantly potentiate the therapeutic potential of acetaminophen in man.