Pharmacokinetic study of 4'-acetamidophenyl-2-(5'-p-toluyl-1'-methylpyrrole)acetate in the rat

A pharmacokinetic study has been performed on a new non-steroidal anti-inflammatory drug, AU-8001 (4'-acetamidophenyl-2-(5'-p-toluyl-1'-methylpyrrole)acetate, CAS 82239-77-8) in the rat, following intravenous (10 mg/kg) and oral (50 mg/kg) administrations. The new molecule constitutes a prodrug of paracetamol and tolmetin. Compartmental and non-compartmental treatment of experimental data lead to the same conclusions. After intravenous administration, the rapid hydrolysis of the ester function of the molecule causes a short transit of the prodrug in the organism and the rapid attainment of maximum plasmatic levels of metabolites. After oral administration, the prodrug shows flip-flop behaviour in which the absorption constant rate is the limiting factor and is responsible for the slow bioconversion of the substance. The bioavailability of the prodrug is incomplete and, according to the urinary excretion data, a fraction of the dose reaches the blood stream in the form of metabolites. AU-8001, however, in spite of its limited bioavailability, is a model prodrug which could be used to prolong the activity of the original drugs.

An evaluation of gastric emptying times in pregnancy and the puerperium

In a controlled study, gastric emptying was measured during the three trimesters of pregnancy and after delivery, using an indirect paracetamol absorption technique. The peak plasma paracetamol concentration, time to reach the peak, and the area under the plasma paracetamol concentration-time curve, were determined. As compared to nonpregnant controls, there were no significant differences in the gastric emptying times of women in the three trimesters of pregnancy and of mothers from 18 h after delivery onwards. Gastric emptying was significantly delayed in mothers within 2 h after delivery (p < 0.01); median (range) values of peak paracetamol concentration, time to reach the peak and the area under the paracetamol concentration-time curve for this group were 12.5 (0.2-30.5) mg.l-1, 120 (30-120) min and 3.8 (0.1-16.6) mg.l-1 x h respectively, and 20.8 (8.6-64.5) mg.l-1, 40 (10-120) min and 13.5 (5.5-28.8) mg.l-1 x h respectively, for the nonpregnant control group (p < 0.01). Repeated measurements of gastric emptying in these women on the second postpartum day showed no significant delay.

HPLC of folinic acid diastereoisomers and 5-methyltetrahydrofolate in plasma

We present a rapid, sensitive, and automated HPLC method with direct resolution of l-folinic acid (l-FA), d-folinic acid (d-FA), and 5-methyltetrahydrofolate (5MTHF) from plasma samples. Plasma (500 microL) is first extracted on solid phase (RP-18 cartridge). The dI-FA peak is collected on-line from a reversed-phase column (RP-8, 119 x 2 mm, 4 microns: HPLC 1) and then automatically loaded onto a chiral stationary phase (human serum albumin, 150 x 4.6 mm, 7 microns: HPLC 2). The same mobile phase flows in both systems (0.2 mol/L Na2HPO4:1-propanol, 98:2, pH 6.2). HPLC 1 allows quantification of 5MTHF by absorption at 313 nm; HPLC 2, the quantification of l-FA and d-FA by electrochemical detection in the oxidation mode (total run time 18 min). Recoveries are > 80%. CVs for intra- and interassay reproducibilities are < 5% and 15%, respectively. Linearity of the response (0.1-1 mumol/L and 1-50 mumol/L, r = 0.99, P < 0.01) is satisfactory. The sensitivity limit is 50 nmol/L for 5MTHF and 20 nmol/L for l-FA and d-FA. This assay is substantially improved over existing methods regarding feasibility and is being used in pharmacokinetic investigations in cancer patients.

Biotransformation and toxicity of acetaminophen in congenic RHA rats with or without a hereditary deficiency in bilirubin UDP-glucuronosyltransferase

Acetaminophen is eliminated primarily by glucuronidation, thereby avoiding cytochrome P450-catalyzed bioactivation to a toxic reactive intermediate. Previous studies have shown that UDP-glucuronosyltransferase-deficient Gunn rats are more susceptible to acetaminophen toxicity than normal Wistar controls, from which the Gunn strain was derived. However, the Gunn and Wistar strains are not congenic, and differences in toxicologic susceptibility could be due in part to genetic differences other than UDP-glucuronosyltransferase activity. Accordingly, acetaminophen (750 mg/kg, ip) was administered to congenic RHA rats with normal (homozygous, RHA/++), moderately deficient (heterozygous, RHA/j+), and severely deficient (homozygous jaundiced, RHA/jj) activities of bilirubin UDP-glucuronosyltransferase. Acetaminophen metabolites were measured by high-performance liquid chromatography and production of the acetaminophen glucuronide conjugate was quantified by the area under plasma concentration-time curve (AUC) from 0 to 2 hr, standardized by the AUC value for acetaminophen in the same animal (glucuronidation ratio = AUC acetaminophen glucuronide/AUC acetaminophen). The 0- to 2-hr time period for AUC calculations was necessitated by the accumulation at later time points of glucuronide and sulfate conjugates in the plasma of animals experiencing severe nephrotoxicity. Acetaminophen bioactivation was quantified by the 24-hr urinary recovery of glutathione-derived conjugates. Hepatotoxicity and nephrotoxicity were assessed respectively by the peak concentrations of plasma alanine aminotransferase (ALT) and blood urea nitrogen (BUN). Glucuronidation of acetaminophen in RHA/jj rats (0.065 +/- 0.005) (mean +/- SE) was reduced 63% compared to the RHA/++ controls (0.17 +/- 0.01) (p < 0.05). RHA/jj rats demonstrated respective 230- and 7-fold increases in the peak plasma concentrations of ALT (17144 +/- 1014 vs 75 +/- 10) and BUN (128 +/- 23 vs 18.4 +/- 0.2) compared to congenic normal controls (RHA/++) (p < 0.05). Heterozygous animals (RHA/j+) demonstrated intermediary toxicity for both parameters (ALT = 2029 +/- 1581, BUN = 41 +/- 16, p < 0.05). Decreased glucuronide production correlated with elevations in ALT (r = -0.86, p < 0.001), while increased acetaminophen bioactivation correlated directly with both elevated ALT (r = 0.93, p < 0.001) and BUN (r = 0.83, p = 0.001). These results using congenic controls demonstrate that the enhanced susceptibility of UDP-glucuronosyltransferase-deficient rats to acetaminophen toxicity is due to decreased glucuronidation resulting in enhanced bioactivation, rather than to other unappreciated genetic differences.

Laboratory evaluation of the Glucocard blood glucose test meter

The Glucocard (Kyoto Daiichi Kagaku) blood glucose meter is designed for self-monitoring of blood glucose concentrations in capillary blood through use of an electrochemical test strip. Evaluated in this laboratory, the Glucocard had CVs of 4.6%, 6.6%, and 3.5% at blood glucose concentrations of 2.4, 4.1, and 18.9 mmol/L, respectively. The meter's response varied linearly with blood glucose concentration between 2.2 and 27.8 mmol/L. Hemolysis, urate, ascorbate, and acetaminophen interfered by > 5%. Different hematocrits, in the range 0.20-0.70, did not affect the measured glucose concentration. Comparison with glucose results measured in whole blood with a NOVA Stat Profile 5 instrument yielded the following: Glucocard = 0.898 NOVA--0.184 (r = 0.995). The main advantages of the Glucocard are its small sample volume (5 microL), wide linear range, and fully automated sample-handling steps, which reduce user-related variability.

Hepatotoxicity from paracetamol self-poisoning in western Sydney: a continuing challenge

OBJECTIVE

To determine the annual incidence of admissions for paracetamol overdosage in the years 1985 to 1990, morbidity and mortality rates, predictors of poor prognosis and the most appropriate use of N-acetylcysteine (NAC).

DESIGN

A retrospective review of case records of all patients with a discharge diagnosis of paracetamol overdosage.

SETTING

A 900-bed tertiary referral teaching hospital in western Sydney with a busy accident and emergency department.

PATIENTS

306 patient records were reviewed and details of the overdose and admission were recorded.

INTERVENTIONS

NAC infusion in patients with possible paracetamol hepatotoxicity.

MAIN OUTCOME MEASURES

Blood paracetamol levels; elevated alanine aminotransferase levels; prolonged prothrombin time; severe liver injury; and NAC side effects.

RESULTS

Annual admission rate was constant at circa 55 per annum. Female to male ratio was 2:1. Predictors of liver injury included paracetamol dose over 10 g, presentation more than 10 hours after the overdose and chronic ingestion of more than 80 g alcohol per day. There were no deaths. Fifty-five patients (18%) had toxic paracetamol levels, 51% received treatment with NAC, including 40% of those with non-toxic levels, and 11% of those treated with NAC experienced side effects.

CONCLUSION

Paracetamol overdosage continues to be a significant cause of hospital admissions in western Sydney. Severe hepatic damage occurs infrequently and the prognosis for liver injury, when it occurs, is good. Treatment with NAC should be reserved for patients with definite indications for the drug.

Tolerance and pharmacokinetics of propacetamol, a paracetamol formulation for intravenous use

In 12 healthy volunteers, paracetamol pharmacokinetics were compared following administration of 1 g propacetamol HCl given intravenously over a 15-min period and 500 mg paracetamol given orally. Mean +/- SD total AUC (microgram/ml.h) following the iv formulation was significantly (P < 0.01) greater than following oral paracetamol (25.53 +/- 4.27 vs 21.04 +/- 4.49) corresponding to a mean oral bioavailability of paracetamol of 82.2 +/- 9.4%. Between 1 and 2 h after administration, paracetamol plasma concentrations became very similar following both formulations. In another study, 2 g propacetamol HCl was given both as a 15-min infusion and as a 2-min bolus injection to six healthy volunteers. Contrary to mild to moderate local discomfort experienced during the 2-min bolus injection, the 15-min infusion was well tolerated without any complaints reported.

Plasma and cerebrospinal fluid concentrations of paracetamol after a single intravenous dose of propacetamol

Since the antipyretic and probably the analgesic effects of paracetamol are, at least in part, centrally mediated, its plasma and cerebrospinal fluid (CSF) concentrations were measured in 43 patients with nerve-root compression pain. Each subject was given a short i.v. infusion of 2 g propacetamol, a prodrug which is hydrolysed to paracetamol within 7 min. Single blood and CSF samples were drawn concomitantly in each patient at intervals between 20 min and 12 h. Maximum CSF drug concentrations were observed at the 4th hour, subsequent concentrations exceeding those in plasma. The elimination half-life of paracetamol calculated from pooled data was shorter in plasma (2.4 h) than in CSF (3.2 h). The time-course of paracetamol in CSF may parallel that of analgesic effect.

Acetaminophen and ibuprofen: fever control and overdose

Fever has been recognized as a sign of disease for centuries. Health care professionals and parents frequently search for new methods of pediatric fever control. Current research suggests that prostaglandins play an important role in fever production. As antipyretics, both acetaminophen and ibuprofen are effective in fever reduction by inhibiting prostaglandin synthesis. In this article, the pathophysiology of fever is discussed as a foundation for understanding fever management. The metabolic pathways of both agents are compared as they relate to fever control; the common side effects and nursing management for acute overdoses are discussed.

Normal chromosomal aberration frequencies in peripheral lymphocytes of healthy human volunteers exposed to a maximum daily dose of paracetamol in a double blind trial

Paracetamol (acetaminophen) has been examined for mutagenic potential in numerous studies: gene mutation tests consistently gave negative results while in vitro chromosomal aberration tests showed equally consistently positive effects. In vivo studies for chromosome breaking activity gave clearly negative, equivocal or weakly positive results. In particular two reports have indicated that human volunteers taking a maximum daily dose of paracetamol (3 x 1000 mg over 8 h) exhibited significantly elevated frequencies of chromatid breaks in their peripheral lymphocytes 24 h later. In the one study evaluating the time course, levels returned to normal between 3 and 7 days later. We performed a carefully controlled double-blind study in which volunteers were pre-screened for normal liver function, they all were non-smoking and their diet and environmental exposures were controlled during the study. Cell-cycle kinetics were monitored and paralleled and a placebo group was included. Although a larger number of cells than in the other studies was analysed we were unable to reproduce their findings. No significant increases in structural chromosome aberrations (CA) were found either when the paracetamol group (male, female or both) post-dosing values were compared with pre-dosing values, or when treated groups at any sampling time were compared with the placebo groups. There was not even any evidence that individuals responded to the clastogenic potential of paracetamol or that a group response may have been masked by non-responders. In conjunction with the recently published results of the NTP bioassay, showing no carcinogenic activity in mice and no carcinogenic activity in rats except an increase of mononuclear cell leukaemia in female rats which is of doubtful relevance, the study presented here argues that paracetamol does not pose an unacceptable (if any) genotoxic/carcinogenic risk to man.

The influence of different types of breakfast on the absorption of paracetamol among members of an ethnic group

It is well known that food influences the absorption and therapeutic efficacy of many drugs. In this study, the influence of three different types of breakfast, on the absorption of paracetamol was studied in a South African ethnic population group (Tswanas). The results indicated that breakfasts with a high fat content delayed the absorption of paracetamol to the largest extent while breakfasts with a high carbohydrate content delayed the absorption of paracetamol to a lesser extent.

Gastric emptying after minor gynaecological surgery. The effect of anaesthetic technique

Gastric emptying was measured using the paracetamol absorption method in 30 patients immediately after a general anaesthetic for minor gynaecological surgery and in 10 female controls. Anaesthesia was induced with either propofol alone, propofol and alfentanil (4.5 micrograms.kg-1) or propofol and fentanyl (1.4 micrograms.kg-1) and maintained with intermittent propofol and 66% nitrous oxide in oxygen. Gastric emptying was delayed significantly in all patient groups when compared with volunteers. However, the delay in gastric emptying was similar in the three patient groups.

Plasma concentration of paracetamol and its major metabolites after p.o. dosing with paracetamol or concurrent administration of paracetamol and its N-acetyl-DL-methionine ester in mice

1. Single doses of paracetamol 400 (PAR 400) and 800 mg/kg (PAR 800), SUR 2647 combination (free paracetamol + paracetamol-N-acetyl-DL-methionate, paracetamol/methionine ratio 2:1) equivalent to PAR 400 (SURc 400) and PAR 800 (SURc 800) were given p.o. to male Bom:NMRI mice. 2. The objective was to compare the plasma concentrations of free paracetamol and the major metabolites paracetamol-sulphate and paracetamol-glucuronide for a 6 hr period after each test drug. 3. There was no significant difference between PAR 400 and SURc 400 with respect to plasma paracetamol, paracetamol-glucuronide and paracetamol-sulphate concentration with the exception of lower plasma paracetamol concentration (P less than 0.03) at 3 hr following PAR 400. 4. There was no significant difference between PAR 800 and SURc 800 with respect to plasma paracetamol, paracetamol-glucuronide and paracetamol-sulphate concentrations with the exception of lower plasma paracetamol-glucuronide concentration (P less than 0.03) at 4 hr after dosing following SURc 800. 5. Combining free paracetamol and its methionine ester does not seem to alter the pattern of plasma paracetamol, paracetamol-glucuronide and paracetamol-sulphate compared to equal doses of free paracetamol alone after p.o. administration of toxic doses to male Bom:NMRI mice.

Analgesic efficacy of immediate and sustained release paracetamol and plasma concentration of paracetamol. Double blind, placebo-controlled evaluation using painful laser stimulation

The analgesic efficacy of single doses of immediate release paracetamol 500 mg and 1000 mg, sustained release paracetamol 2000 mg, and placebo was evaluated over a 12 h period in 10 healthy volunteers. The efficacy was related to the concurrent plasma concentrations of paracetamol. Experimental pain was induced by brief cutaneous application of argon laser pulses, and the analgesic effect was assessed as change in pricking pain threshold. Both 0.5 g and 1.0 g immediate release paracetamol had an analgesic effect superior to that of placebo from 1 to 5 h after administration. Peak analgesia was reached after 2 h. No difference was found in the analgesic effect of the two dosages. Sustained release paracetamol was not significantly superior to placebo at any time. The plasma concentration of paracetamol had peaked in the 1 h sample after of the immediate release tablet. The peak plasma concentration was reached 3-4 h after 2.0 g sustained release paracetamol. It is not known why the sustained release formulation did not produce any detectable analgesia. It is proposed, that the rate of increase in the plasma concentration of paracetamol might be important in the alleviation of acute (laser-induced) pain.

Single-dose pharmacokinetics of ibuprofen and acetaminophen in febrile children

The disposition of antipyretic drugs is central to the understanding of their action in children. Accordingly, the authors measured plasma levels of acetaminophen and ibuprofen in 153 febrile children for 6 hours after a single dose of either acetaminophen (12.5 mg/kg) or ibuprofen (5 or 10 mg/kg). Cmax occurred about 2 1/2 hours before maximum antipyresis, when plasma acetaminophen or ibuprofen was 25 to 50% less than Cmax. Most plasma level data fit a one-compartment open model, and this suggests a pharmacodynamic basis for the observed lag between Cmax and maximum antipyretic response. Plasma levels (and AUCO----infinity) of ibuprofen 10 mg/kg were less than expected for a two-fold increase in dose. For acetaminophen, the tlag was less than ibuprofen, Ka was more than ibuprofen, and beta was less than ibuprofen. The ibuprofen beta was not dose dependent, but the Vd was dose and model dependent. In contrast, ibuprofen Clp was dose and model independent. Acetaminophen pharmacokinetics were similar to those previously reported. Initial temperature, race, gender, prior medications, or diagnosis did not confound the results for ibuprofen or acetaminophen. Accordingly, a pharmacodynamic basis is a more likely explanation for the initial temperature effects found previously for antipyretic drugs in children. Ibuprofen (5 and 10 mg/kg) AUCO-----infinity was higher in the older (greater than or equal to 2.5 yrs) children and the Vd and Clp were lower in the older children, when discriminated by age or pharmacokinetic parameters. The observed dose dependency of AUCO----infinity and the effect of age on ibuprofen disposition must be considered if pharmacokinetic interpretations are used to develop the antipyretic dose of ibuprofen in children.

Optimal patient position for transport and initial management of toxic ingestions

STUDY OBJECTIVES

Many factors influence the rate of gastric emptying and therefore the rate of drug absorption in the orally poisoned patient. Limited studies have evaluated the effect of body position on the rate of gastric emptying of radiographically marked foods and contrast media, but effects on drug absorption have not been studied previously. Our hypothesis was that body position would have an effect on the rate of drug absorption in an oral overdose model.

DESIGN

A blinded, within-subjects (crossover) design.

PARTICIPANTS

Six male and six female healthy, adult volunteer subjects with no concurrent drug use or medications affecting gastrointestinal function.

INTERVENTIONS

Five body positions commonly used in prehospital and emergency department settings were examined: left lateral decubitus, right lateral decubitus, supine, prone, and sitting. All were performed by all subjects in random order with a three-day washout phase between trials. To simulate an acute overdose, fasted subjects ingested 80 mg/kg acetaminophen in the form of 160-mg pediatric tablets. Each subject then remained in the body position for that trial for two hours. Acetaminophen levels were obtained at 15-minute intervals, and a two-hour area under the curve (AUC) was calculated for each subject trial to represent total drug absorption during each study period. Investigators were blinded to all results until all trials were completed.

MEASUREMENTS AND MAIN RESULTS

All subjects completed the study. Group mean drug absorption as represented by two-hour AUC (mg.L.min) was calculated for each body position. AUC for left lateral decubitus (6,006 +/- 2,614) was lowest but did not significantly differ from that for supine (6,649 +/- 2,761). Both were significantly less than those for prone (7,432 +/- 1,809), right lateral decubitus (8,950 +/- 1,405), and sitting (8,608 +/- 1,725) positions (P less than .05 by one-way analysis of variance and follow-up paired t tests).

CONCLUSION

Initial drug absorption as determined by two-hour AUC was lowest in the left lateral decubitus position. Although the difference between the left lateral decubitus and supine positions did not reach statistical significance, both left lateral decubitus and supine were significantly lower than three other common patient body positions tested. Because the left lateral decubitus position has other advantages (eg, prevention of aspiration) in addition to minimizing drug absorption, we recommend that orally poisoned patients be placed in the left lateral decubitus position for prehospital and initial ED management.

No effect of cisapride on paracetamol absorption after oral simultaneous administration

We have measured the effect of oral cisapride on paracetamol absorption in 12 healthy volunteers in a double-blind placebo-controlled study. Volunteers received paracetamol plus placebo, paracetamol plus cisapride 10 mg and paracetamol plus cisapride 20 mg. Mean plasma paracetamol AUC at 60 min were 1070, 1051 and 1031 micrograms.min.ml-1 and maximum paracetamol concentrations were 31.5, 29.3 and 27.4 micrograms.ml-1 respectively (no significant differences). There was no difference also in time to maximum paracetamol concentration [median (range) 30 (15-120), 30 (15-90) and 30 (15-60) min, respectively]. .

An improved model of acetaminophen-induced fulminant hepatic failure in dogs

We have established an improved model of fulminant hepatic failure in dogs. Buthionine sulfoximine is used to inactivate glutathione synthesis, and small increments of acetaminophen are given intravenously to maintain the plasma level at approximately 200 micrograms/ml for 20 hr. This regimen produces severe liver injury along with many of the features seen in humans with acetaminophen poisoning. The first sign of impending liver failure is hypoglycemia. This occurs about 15 hr into the experiment and requires treatment with a continuous infusion of glucose. Between 15 and 20 hr, serum ALT activity begins to rise, indicating the onset of liver necrosis. Over the following 15 to 20 hr ALT activity continues to rise and is accompanied by an increase in bilirubin, a prolongation of the prothrombin time and the development of fetor hepaticus. Thirty to 48 hr after the initial acetaminophen dose, the animals begin to exhibit symptoms of encephalopathy and progress from lethargy to the inability to maintain posture and then coma, seizures and death. Liver biopsy specimens obtained at several stages throughout the study showed progressive necrosis, ultimately resulting in the complete destruction of zones 2 and 3.

Decreased glucuronidation and increased bioactivation of acetaminophen in Gilbert's syndrome

Gilbert's syndrome occurs in 5%-7% of the human population and is caused by an inherited deficiency in the glucuronidation of endogenous bilirubin, resulting in its accumulation and jaundice. The authors of the present study have previously shown that rats with a similar deficiency in bilirubin glucuronidation (Gunn rats) had reduced glucuronidation and enhanced susceptibility to the toxicity of the widely used analgesic, acetaminophen. Acetaminophen is eliminated primarily by glucuronidation, which prevents its cytochrome P-450-catalysed bioactivation to a hepatotoxic reactive intermediate. The purpose of this study was to determine whether people with Gilbert's syndrome had reduced glucuronidation and enhanced bioactivation of acetaminophen. Therefore, the biotransformation of acetaminophen, 20 mg/kg IV, was investigated in six subjects with Gilbert's syndrome (total bilirubin, 41 +/- 6 mumol/L; mean +/- SE) and six normal controls (total bilirubin, 11 +/- 2 mumol/L; P less than 0.01). Formation of the acetaminophen glucuronide conjugate measured by high-performance liquid chromatography was quantified by the ratio of the area under the plasma concentration-time curve (AUC) from 0 to 2 hours for the acetaminophen glucuronide divided by the AUC for acetaminophen. Acetaminophen bioactivation was quantified by the molar percentage of acetaminophen excreted in the urine during 24 hours as glutathione-derived conjugates (cysteine and mercapturic acid). Acetaminophen glucuronide formation in subjects with Gilbert's syndrome was 31% lower than that in normal controls (0.27 +/- 0.05 vs. 0.39 +/- 0.03; P less than 0.05), and bioactivation was 1.7-fold higher (3.5% +/- 0.4% vs. 2.1% +/- 0.3%; P less than 0.05). One control subject with normal bilirubin glucuronidation had substantially decreased acetaminophen glucuronide formation (0.20) and enhanced bioactivation (4.8%). Among all subjects, glucuronidation correlated inversely with bioactivation (r = -0.84; P less than 0.001), indicating that a decrease in a major pathway of elimination can shunt more drug through the toxifying route. Thus, a deficiency in bilirubin UDP-glucuronosyltransferase, evidenced by jaundice, can be paralleled by a deficiency in glucuronidation of other compounds. In these cases, jaundice can be a phenotypic determinant of enhanced acetaminophen bioactivation. On the other hand, some people with normal bilirubin glucuronidation may have a deficiency in the glucuronidation of acetaminophen; these people are not easily recognized.(ABSTRACT TRUNCATED AT 400 WORDS)

Determination of paracetamol and its four major metabolites in mouse plasma by reversed-phase ion-pair high-performance liquid chromatography

A reversed-phase ion-pair high-performance liquid chromatographic method has been used for the separation of paracetamol and its four major metabolites (glucuronide, sulphate, cysteine and mercapturate conjugates) in mouse plasma samples. An ODS column was used and the mobile phase consisted of an aqueous solution of 0.01 M tetrabutylammonium chloride and 0.01 M Tris buffered to pH 5.0 with phosphoric acid, with methanol as the organic solvent. The gradient elution started with 30% methanol. After a delay of 0.5 min the methanol concentration was increased linearly to 75% over 7.5 min. The column was returned to the initial conditions after a delay of 1 min. A methanol solution of theophylline was added to the mouse plasma sample, centrifuged and immediately injected into the chromatographic system. The advantages of this method include good and rapid separation (last metabolite detected at 6.86 min), well resolved peaks, only a small amount of sample required for assay, adequate precision (no coefficient of variation was greater than 10% for paracetamol metabolites) and a high sensitivity (particularly for unchanged paracetamol and the cysteine conjugate).

Oral amino acids and gastric emptying: an investigation of the mechanism of levodopa-induced gastric stasis

To investigate possible mechanisms of levodopa-induced gastric stasis, we have studied the effect of other amino acids on gastric emptying. The large neutral amino acid tryptophan delays gastric emptying in the dog at molar concentrations below those required to stimulate duodenal osmoreceptors. In healthy volunteers, we have shown that neither tryptophan nor the small neutral amino acid glycine delayed gastric emptying when given in concentrations similar to those of levodopa which produce gastric stasis. The study suggests that levodopa does not inhibit gastric emptying by an effect on duodenal amino acid receptors or via osmoreceptors.

Gastric emptying in healthy volunteers after multiple doses of levodopa

1. Oral levodopa frequently produces an episodic delay in gastric emptying which leads to multiple peak concentrations of the drug in plasma. We have studied the effects of multiple dosing of levodopa on gastric emptying and levodopa absorption in eight healthy young volunteers in a randomised two-way cross-over study. 2. The plasma concentration-time curves for levodopa were measured after three oral doses of 125 mg given at 2 h intervals and compared with the concentration-time curve for levodopa following administration of two doses of placebo and a single oral dose of 125 mg. 3. A low incidence of multiple peak plasma concentrations of levodopa was detected after all doses of levodopa. The area under the plasma concentration-time curves (AUC) for the final dose of levodopa (150.8 +/- 22.0 micrograms ml-1 min) was lower than for the two preceding doses (205.7 +/- 41.8 and 199.5 +/- 51.8 micrograms ml-1 min) but not different from that of the single dose given at the same time of day (141.7 +/- 29.1 micrograms ml-1 min). This indicates that the lower AUC of the final dose of levodopa was related to the time of administration and not a result of the two preceding doses. 4. The absence of any significant effects of preceding doses of levodopa on gastric emptying was confirmed a) by co-administration of soluble paracetamol, as a marker of gastric emptying, with the second dose of levodopa or placebo and b) by co-administration of radiolabelled DTPA and gamma-camera imaging with the final dose of levodopa on the multiple dosing day and the single dose of levodopa on the placebo day.(ABSTRACT TRUNCATED AT 250 WORDS)

Paracetamol metabolism after general anaesthesia

Paracetamol metabolism was compared between nine patients after general anaesthesia and nine healthy volunteers. Each subject received 1.5 g of paracetamol orally, and paracetamol concentrations in venous blood were measured by HPLC at intervals over 12 h. Urine samples collected over 24 h were analysed by HPLC for cysteine, mercapturic acid, sulphate and glucuronide metabolites. There were no significant differences in the area under the concentration-time curve for paracetamol, or plasma half-life. Statistically significant differences were observed in the median percentages of unchanged paracetamol (volunteers 2.9%, patients 2.0%) and mercapturic acid (volunteers 4.5%, patients 6.5%) excreted in 24 h. The percentage of sulphate excreted was significantly lower in the 8-24-h period, although there was no difference over the total 24 h.