Gastric emptying in the postpartum period

We measured gastric emptying, using the technique of paracetamol absorption, in eight women on their first and third postpartum day. Gastric emptying was rapid and there was no difference between the first and third day in the time to peak plasma concentration of paracetamol. Six women returned after six weeks for a further study. Gastric emptying was still rapid but the metabolism of paracetamol appeared to be slower than that found during the immediate postpartum period. These findings suggest that fluid fasting guidelines in patients more than one day postpartum need not be different from those in non-pregnant patients.

Postmortem absorption of drugs and ethanol from aspirated vomitus--an experimental model

Using human cadavers an experimental model was developed to simulate the agonal aspiration of drug- and alcohol-laden vomitus. By needle puncture, an acidified (N/20 HCl) 60-ml slurry of drugs (paracetamol 3.25 g, dextropropoxyphene 325 mg) and ethanol 3% w/v was introduced into the trachea. After 48 h undisturbed at room temperature, blood samples were obtained from ten sites. Ethanol and drug concentrations were highest in the pulmonary vessels in all five cases studied. Pulmonary vein mean ethanol was 58 mg% (range 13-130), paracetamol 969 mg/l (range 284-1934), propoxyphene 70 mg/l (range 11-168). Pulmonary artery mean ethanol was 53 mg% (range 10-98), paracetamol 476 mg/l (range 141-882), propoxyphene 29 mg/l (range 7.6-80). Ethanol and drug concentrations in aortic blood were higher than in the left heart and concentrations in the superior vena cava were higher than in the right heart, suggesting direct diffusion into these vessels rather than diffusion via the pulmonary and cardiac blood. Potential interpretive problems arising from this phenomenon can be avoided by using femoral vein blood for quantitative toxicological analysis.

Acetaminophen overdose: a 48-hour intravenous N-acetylcysteine treatment protocol

STUDY OBJECTIVE

To determine the safety and efficacy of a 48-hour IV N-acetylcysteine (IV NAC) treatment protocol for acute acetaminophen overdose.

DESIGN

Nonrandomized trial open to all eligible patients.

SETTING

Multicenter; hospitals included moderate- and high-volume private, university, and municipal hospitals in urban and suburban settings.

TYPE OF PARTICIPANTS

Two hundred twenty-three patients were entered. Of these, 179 met inclusion criteria: acute acetaminophen overdose, plasma acetaminophen concentration above the treatment nomogram line, treatment with IV NAC according to the protocol, and sufficient data to determine outcome.

INTERVENTIONS

IV NAC treatment consisted of a loading dose of 140 mg/kg followed by 12 doses of 70 mg/kg every four hours.

MEASUREMENTS AND MAIN RESULTS

Patients were grouped for analysis according to risk group based on the initial plasma acetaminophen concentration. Hepatotoxicity (aspartate aminotransferase or alanine aminotransferase of more than 1,000 IU/L) developed in 10% (five of 50) of patients at "probable risk" when IV NAC was started within ten hours of acetaminophen ingestion and in 27.1% (23 of 85) when therapy was begun after ten to 24 hours. Among "high-risk" patients first treated 16 to 24 hours after overdose, hepatotoxicity occurred in 57.9% (11 of 19). There were two deaths (two of 179, 1.1%). Adverse reactions resulting from NAC occurred in 32 of 223 cases (14.3%), consisting in 29 of 32 patients (91% of reactions) of transient, patchy, skin erythema or mild urticaria during the loading dose that did not require discontinuation of therapy.

CONCLUSION

This 48-hour IV NAC protocol is safe and effective antidotal therapy for acetaminophen overdose. Based on available data, it is equal to 72-hour oral and 20-hour IV treatment protocols when started early and superior to the 20-hour IV regimen when treatment is delayed. Further study will be required to determine its relative efficacy in the high-risk patient treated very late.

Simulated acetaminophen overdose: pharmacokinetics and effectiveness of activated charcoal

STUDY OBJECTIVE

To determine the absorption rate of a supratherapeutic dose of acetaminophen elixir and compare the effect of activated charcoal (AC) given at different time intervals on preventing acetaminophen absorption.

DESIGN

Randomized, nonblinded, crossover controlled study.

SETTING

A certified regional poison control center.

PARTICIPANTS

Ten healthy, adult male volunteers from 21 to 39 years old.

INTERVENTIONS

Each subject received 5 g acetaminophen (elixir) on four occasions: a control phase plus 30 g of AC administered 15, 30, or 120 minutes after acetaminophen. Serum acetaminophen levels were obtained during the control phase only, and 24-hour urine collections were obtained during all four phases.

MEASUREMENTS AND MAIN RESULTS

The highest serum acetaminophen levels were measured 1.4 +/- 0.52 hours after ingestion, and absorption was 97% complete by a mean of 2.05 hours. The administration of AC at 15, 30, and 120 minutes after acetaminophen reduced urinary recovery of acetaminophen and metabolites by 48%, 44%, and 33%, respectively.

CONCLUSION

AC significantly reduces urinary recovery but not absorption of acetaminophen when administered two hours after acetaminophen elixir.

Effects of paracetamol and aspirin on neural activity of joint mechanonociceptors in adjuvant arthritis

1. The effects of paracetamol and lysine acetylsalicylate (L-AS) on high-threshold mechanonociceptors have been investigated by recording neural activity from the inflamed ankle joint in anaesthetized rats with mild adjuvant-induced monoarthritis. 2. Paracetamol (50 mg kg-1, i.v.) and L-AS (100 mg kg-1, i.v., equivalent to 50 mg kg-1 aspirin) both caused a maximal reduction of about 40% in mechanically-evoked discharge and of 30% in ongoing (spontaneous) activity by about 15 min after the injection: a second dose of either drug did not have any significant additional effect on discharge. 3. The prostanoid IP receptor agonist, cicaprost (0.1-0.5 micrograms), increased both mechanically-evoked and ongoing discharge to pre-paracetamol levels when injected close-arterially 30-50 min after paracetamol, whereas prostaglandin E2 (PGE2) was relatively ineffective at restoring activity. 4. The results suggest that prostacyclin (PGI2) contributes to the sensitization of high-threshold joint mechanonociceptors in adjuvant-induced monoarthritis, and that paracetamol and L-AS both act to reduce discharge by inhibiting the synthesis of prostacyclin in the joint capsule. 5. Paracetamol has a direct peripheral action affecting joint capsule mechanonociceptors in rat adjuvant-induced arthritis which is very similar to that of the soluble aspirin preparation, L-AS. These findings, together with the existing literature concerning the anti-arthritic effects of paracetamol, are relevant to the treatment of chronic inflammatory disorders such as rheumatoid arthritis.

Lack of effect of paracetamol on the pharmacokinetics of indomethacin and paracetamol in humans

Paracetamol is an analgetic drug with additive effect if combined with indomethacin. In rat experiments, paracetamol has been shown to be gastro-protective, and in animal experiments, indomethacin blood levels decreased during combined treatment with paracetamol. The kinetic effect of paracetamol on indomethacin has been investigated in ten healthy volunteers. The mean area under the indomethacin plasma concentration curve AUC 0-alpha was 10.4 +/- 4.21 micrograms/mL x hr and did not change during combined paracetamol treatment (11.0 +/- 3.24 micrograms/mL x hr NS). Paracetamol levels were unchanged. In this study, no evidence was found that paracetamol can alter the pharmacokinetics of indomethacin in humans.

Gastric emptying following Colles' fracture

There are few complications associated with intravenous regional anaesthesia but convulsions with loss of consciousness induced by local anaesthetic toxicity may result in pulmonary aspiration. In many hospitals, patients are fasted prior to the procedure although such a delay would be of little value if gastric emptying was inhibited following painful injury. Utilizing the kinetics of paracetamol absorption, we investigated the rate of gastric emptying in patients sustaining a Colles' fracture within the previous 4 h. Post-manipulation control values were obtained at their first out-patient attendance. There was no statistically significant difference in the rate of gastric emptying. Since gastric emptying is not delayed by a recent Colles' fracture, the simple precaution of fasting patients prior to intravenous regional anaesthesia should reduce the risk of pulmonary aspiration.

Mechanized toxicological serum tests in screening hospitalized patients

A spectrum of quantitative and qualitative methods was adapted to the RA-1000/RA-XT selective analyser for the purpose of excluding or detecting common types of intoxication in the emergency laboratory of our primary care community hospital. Ethanol and salicylates (measured photometrically) and acetaminophen (measured immunologically by EMIT tox) were quantitatively analysed in serum. immunological group tests (EMIT tox) for barbiturates, benzodiazepines, tricyclic antidepressants and related compounds were used for qualitative analysis. Well established clinical chemical methods (aspartarte aminotransferase, alanine aminotransferase, creatine kinase, pseudocholinesterase, glucose and lactate) were applied to the serum samples using the same selective analyser. Within and between run precision, accuracy, recovery and detection ranges (linearity) fulfilled the recommendations of forefield toxicological analysis for all methods. Ethanol (g/l), measured photometrically with the RA-1000 analyser, agreed with the reference method (headspace gas-chromatography) with a correlation coefficient greater than 0.99 (y = 0.06 + 0.98x). Acetaminophen and salicylates showed correlation coefficients greater than 0.94 and greater than 0.99, when compared with manual colorimetric procedures (acetaminophen (mg/l): y = -3.22 + 0.896x; salicylates (mg/l): y = -2.1 + 1x). Qualitative group tests for barbiturates, benzodiazepines and tricyclic antidepressants measured with the RA-1000 analyser were in good agreement with the EMIT single test procedure. The ranges of the quantitative methods allowed quantification of analytes from therapeutic (non-toxic) to very high levels in undiluted samples (ethanol 0.05 up to 4 g/l; salicylates 32 up to 1200 mg/l and acetaminophen 1.9 up to 200 mg/l). The low detection limits of the qualitative tests allowed the recognition of compounds in plasma that were present in low concentrations and/or displayed only minor reactivity with the antibodies provided by the EMIT tox test kits. As a consequence, decision limits for all three group tests in serum were lowered to near the detection limit: (table: see text) For quantitative tests the lower limits of quantification were: (table: see text) The working reagents were stable for at least 14 days at 4-8 degrees C. Calibration curves were stable over the expiration period of reconstituted original reagents (6-12 weeks), also when working reagents were prepared in aliquots from stored reconstituted reagents. Application of the newly adapted programme to serum samples of nearly two hundred patients showed it to be suitable for screening patients in which intoxication is suspected or needs to be excluded.

Combined assay for phenacetin and paracetamol in plasma using capillary column gas chromatography-negative-ion mass spectrometry

A gas chromatographic-mass spectrometric assay has been developed for the measurement of phenacetin and its major metabolite paracetamol in plasma. Phenacetin and unconjugated paracetamol are analysed in a single chromatographic run while total paracetamol is measured separately after enzymatic hydrolysis. The two compounds, and the deuterated analogues used as internal standards, are analysed as their trifluoroacetyl derivatives and the mass spectrometer is operated in the electron-capture negative-ion chemical ionisation mode. The negative-ion mass spectra of the derivatives contain fragment ions, formed by loss of an acetyl group from the respective molecular ions, which are the base peaks in the spectra. When these ions are specifically monitored, amounts of derivative equivalent to 1 pg of parent compound can be detected. This allowed the development of an assay for phenacetin, unconjugated paracetamol and total paracetamol in plasma having a precision of 2.6, 1.4 and 2.4%, respectively, and preliminary results for a subject given a 100-mg oral dose of phenacetin are reported.

The influence of rectal cisapride on morphine-induced gastric stasis

The effect of a new formulation of the gastric prokinetic agent cispride on opioid-induced gastric stasis was investigated. Forty patients were randomly allocated to one of four therapies administered as premedication; group A, placebo suppositories only; group B, placebo suppositories and intramuscular morphine 10 mg; group C, rectal cisapride 30 mg and intramuscular morphine 10 mg and group D, rectal cisapride 60 mg and intramuscular morphine 10 mg. Gastric emptying was assessed from the small bowel absorption of paracetamol following oral absorption. The kinetics of the suppository formulation were determined from venous blood samples. Rectal cisapride in the two doses used did not prevent opioid-induced gastric stasis. This may reflect an inability of this formulation to produce adequate plasma concentrations.

Stimulatory effect of N-[4-[2-(dimethylamino)-ethoxy] benzyl]-3,4-dimethoxybenzamide hydrochloride (HSR-803) on normal and delayed gastrointestinal propulsion

To estimate the effect of a new gastroprokinetic agent, N-[4-[2-(dimethylamino)ethoxy]benzyl]-3,4-dimethoxybenzamide hydrochloride (HSR-803), on non-ulcer dyspepsia, the influence of HSR-803 on gastrointestinal propulsion was assayed in dogs, rats and mice in comparison with some gastroprokinetic agents. HSR-803 (30 mg/kg, p.o.) significantly enhanced gastric emptying in dogs, and it significantly improved the delayed gastric emptying induced by dopamine (0.4 mg/kg, i.p.) and morphine (1 mg/kg, s.c.) in rats. Metoclopramide (30 mg/kg, p.o.) also significantly restored the dopamine-induced delay, but at a dose of 10 mg/kg, p.o., it enhanced the morphine-induced delay in gastric emptying in rats. HSR-803 (10-100 mg/kg, p.o.) increased small intestinal transit in mice in a dose-dependent manner, and the effect was abolished by atropine (0.3 mg/kg, i.p.). Metoclopramide also increased small intestinal transit, but domperidone and cisapride had no effect. In delayed small intestinal transit in mice, HSR-803 (10-100 mg/kg, p.o.) improved the morphine (0.3 mg/kg, s.c.)-induced delay in a dose-dependent manner. In conclusion, because of the promotion of normal and delayed gastrointestinal propulsion, HSR-803 seems to be a promising gastroprokinetic agent for the treatment of non-ulcer dyspepsia. The action of HSR-803 is likely to be exerted through cholinergic stimulation.

Effect of cisapride on gastric emptying in diabetic patients without gastrointestinal symptoms

The long-team effects of cisapride on gastric emptying and hormonal interaction in diabetic patients without gastrointestinal symptoms was evaluated. Gastric emptying was determined by the N-acetyl-p-amino-phenol (APAP) method before and after cisapride treatment. Gastric emptying improved significantly, from 5.95 to 8.04 micrograms/ml, after 6 weeks of treatment. Plasma concentrations of immunoreactive insulin (IRI), after 30 and 45 minutes in the gastric emptying test, increased significantly after treatment. It appeared that improvement of gastric emptying after loading with cisapride might be related to improved insulin secretion in diabetic patients without subjective symptoms of gastroparesis.

Gastric emptying in pregnancy

The rate of gastric emptying in pregnancy was measured indirectly using the rate of paracetamol absorption in four groups of 15 patients: non-pregnant controls, first trimester patients presenting for termination of pregnancy, second trimester patients presenting for prostaglandin termination of pregnancy, and patients presenting for elective Caesarean section. All patients were fasted for 6 h and then received paracetamol tablets 1.5 g orally with water 50 ml. Blood samples were taken at 15-min intervals for 120 min and analysed for paracetamol concentration. There was no significant difference between the groups in the maximum concentration and time to maximum concentration (ANOVA). The AUC was reduced for the first trimester group at 60 and 120 min (P less than 0.05). No significant delay in gastric emptying was demonstrated in any of the three trimesters of pregnancy compared with the control group.

Protective effect of pregnenolone-16 alpha-carbonitrile on acetaminophen-induced hepatotoxicity in hamsters

Overdosage of acetaminophen (AA) is known to produce acute liver toxicity in both humans and laboratory animals. Hamsters are especially sensitive to the hepatotoxic effect of AA. In the present study, hamsters pretreated with pregnenolone-16 alpha-carbonitrile (PCN; 75 mg/kg, ip, daily for 4 days) were given a single dose of AA (350-1200 mg/kg, ip) and liver function was determined 24 hr later. Serum activities of alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) as well as histopathology were used as indices of hepatotoxicity. PCN pretreatment decreased AA-induced mortality. PCN dramatically decreased ALT (93-97%) and SDH (63-98%) activities relative to control values from hamsters treated with AA alone, and remarkably decreased hepatic centrilobular necrosis produced by AA. To investigate the mechanism of this protective effect, the biliary and urinary excretion of AA metabolites were measured for 1 hr after administration of AA (150 mg/kg, iv) in bile-duct-cannulated hamsters. PCN pretreatment resulted in increased urinary and biliary excretion of AA-glucuronide and decreased biliary excretion of AA-glutathione. Microsomes from PCN-pretreated hamsters produced less benzoquinoneimine intermediate than controls, as determined by the formation of AA-glutathione. In addition, hepatic UDP-glucuronic acid and UDP-glucuronosyltransferase were significantly increased in PCN-pretreated hamsters. In conclusion, PCN pretreatment protected against AA-induced hepatotoxicity. The mechanism of this protection appears to be due to decreased formation of the reactive metabolite by the cytochrome P450 pathway, and an increased detoxication by enhanced glucuronidation of AA.

Failure of physicians to recognize acetaminophen hepatotoxicity in chronic alcoholics

We encountered six alcoholic patients with severe acetaminophen hepatotoxicity during a 2-year period. All patients had marked elevations of aminotransferases and sometimes remarkably high prothrombin times at, or shortly after, presentation. In five of six cases the diagnosis was missed by the physicians initially caring for the patient. The apparent reasons for the missed diagnosis were insufficient history regarding the use of acetaminophen, an inappropriate reliance on blood acetaminophen levels, and lack of knowledge regarding typical aminotransferase elevations in alcoholic hepatitis vs acetaminophen toxicity. The initial clinical presentation of acetaminophen hepatotoxicity in chronic alcoholics is easily recognized clinically and is distinct from acetaminophen hepatotoxicity in suicide ingestions and from alcoholic hepatitis. Internists and other physicians should be aware of this entity and rely on the clinical picture and the history of acetaminophen use to confirm the diagnosis.

The effect of malaria infection on paracetamol disposition in the rat

The effect of Plasmodium berghei infection, a rodent malarial model, on the disposition of paracetamol (50 mg/kg, i.v.) was investigated in rats. Malaria infection (MI) resulted in a significant decrease in clearance (control: 21.6 +/- 5.5 vs test: 11.8 +/- 2.9 mL/min/kg, P less than 0.005) with no change in volume of distribution and a significant prolongation of the elimination half-life (control: 30.7 +/- 6.3 vs 53.3 +/- 12.1 min, P less than 0.005) of paracetamol in malaria infected rats. These changes were not related to the severity of MI. Malaria infection also decreased biliary clearance of paracetamol (64%) but not its glucuronide and sulphate conjugates in the bile compared with controls. In addition, glutathione conjugates were not detected in bile samples of malaria infected rats. These data suggest that important pathways of drug detoxification may be compromised by MI in a relatively selective fashion and the relevance of these findings to the clinical use of drugs eliminated by these pathways merits further study.

Pharmacokinetics of acetaminophen, antipyrine, and salicylic acid in the lactating and nursing rabbit, with model predictions of milk to serum concentration ratios and neonatal dose

The rabbit was utilized for examining the pharmacokinetics of three compounds (acetaminophen, AC; antipyrine, AN; and salicylic acid, SA) in nursing adults and their suckling offspring and for assessing the ability of a diffusional model to predict milk to serum drug concentration ratios (M/S) from in vitro experiments. AC, AN, and SA serum concentration time profiles declined monoexponentially for both adults and their pups. The mean systemic clearance (Cls) for AC in the adults and pups was 16.1 and 13.7 ml/min/kg, respectively. The mean half-lives of AC (t1/2) were 25.5 and 33.3 min in the adult and pup groups, respectively. AN declined in parallel for adult rabbits and an older group of suckling pups (23-25 days old). In a younger group of pups (18-21 days old) it declined with a longer t1/2 (97.5, 95.1, and 347.6 min in the adults, older pups, and younger pups, respectively). The mean AN Cls in the adults, the older pups, and the younger pups was 5.34, 6.30, and 1.91 ml/min/kg, respectively. The time course of SA was prolonged in the suckling pups (t1/2 of 633 min in the pups vs 78.7 min in the adult). The mean Cls values in the adults and the pups were 1.05 and 0.27 ml/min/kg, respectively. The mean systemic clearance of unbound drug (Clu) for SA was 11.2 ml/min/kg in the adults and 0.92 ml/min/kg in the pups. The serum protein binding of AC and AN was limited, whereas the mean free fraction for SA was 9.7% in adult serum and 32.5% in pup serum. AC and AN in milk paralleled serum drug profiles; a time lag was noted for milk SA. M/S ratios were determined in vivo (M/Sobs; AN = 0.885, AC = 0.580, and SA = 0.125) using area under the milk and serum concentration time profiles. Predicted M/S values (M/Spred; AN = 0.779, AC = 0.578, and SA = 0.085) were calculated from in vitro measurements of the unbound fractions of drug in skim milk and serum, the skim to whole milk drug concentration ratio, milk and serum pH, and the pKa of the model compound. Mean values for M/Sobs were highly correlated with M/Spred values (r2 = 0.976) when the present data were combined with previous data for propranolol, phenobarbital, phenytoin, and diazepam (Fleishaker, J.C., and McNamara, P.J., J. Pharmacol. Exp. Ther. 244, 919, 1988). These results support the usefulness of the diffusional model for predicting M/S in vivo, provided that the distributional process is governed by passive diffusion.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparison of serum and saliva paracetamol concentrations

The relationship between serum and saliva paracetamol concentrations was investigated in twenty healthy volunteers. The plasma and saliva drug concentrations showed a significant correlation (r = 0.67). However the agreement between the two methods of measurement was poor with limits of agreement of -15.3 mg l-1 to +15.9 mg l-1 with mean sample values of 19.2 and 19.5 mg l-1 for plasma and saliva, respectively.

Central analgesic effect of acetaminophen but not of aspirin

The central nervous system effect of acetaminophen (paracetamol) and acetylsalicylic acid was investigated in healthy volunteers according to a crossover, double-blind, and placebo-controlled design. Ten subjects received, by intravenous route, a placebo, 1 gm acetaminophen, and 1 gm acetylsalicylic acid. Analgesia was assessed by measurement of the subjective pain threshold and the objective nociceptive flexion reflex threshold in response to selective transcutaneous electrical stimulations. A close correlation was observed between subjective and objective pain thresholds. Acetaminophen increased both thresholds for more than 4 hours (24% and 23% of baseline value at 120 minutes, respectively; p less than 0.001, ANOVA). In contrast, acetylsalicylic acid had no noticeable effect on either threshold. These findings show that acetaminophen-induced analgesia is centrally mediated, in contrast to aspirin. The time delay between plasma concentration kinetics and acetaminophen analgesic effect is another argument in favor of its direct action on the central nervous system.

In vivo microdialysis sampling for pharmacokinetic investigations

In vivo microdialysis sampling coupled to liquid chromatography was used to study acetaminophen disposition in anesthetized rats. The pharmacokinetics of acetaminophen and its sulfate and glucuronide metabolites were determined using both microdialysis sampling and collection of whole blood. For microdialysis, samples were continuously collected for over 5 hr without fluid loss using a single experimental animal. Microdialysis sampling directly assesses the free drug concentration in blood. The pharmacokinetic results obtained with microdialysis sampling were the same as those obtained from blood collection. The administration of heparin, necessary when collecting blood samples, was found to double the elimination half-life of acetaminophen. Microdialysis sampling is a powerful tool for pharmacokinetic studies, providing accurate and precise pharmacokinetic data.

A comparison of the hypoalgesic effect of paracetamol in slow-release and plain tablets on laser-induced pain

1. In a double-blind, three way, cross-over study 15 volunteers received plain paracetamol tablets 1000 mg every 6th hour, paracetamol slow-release tablets 2000 mg every 12th hour, and placebo. Steady state conditions were established over a 5 day period preceding each test session. 2. Plain paracetamol was given twice in the 12h test session, initially and after 6 h, and the slow-release formulation was given once at the start of the session. 3. Hypoalgesia, measured by experimentally laser-induced pain (pain threshold), and plasma concentrations of paracetamol were measured hourly for 12 h. 4. Both formulations of paracetamol were significantly superior (P = 0.0003) to placebo, but not difference in analgesic efficacy was found between the two regimens.

Pharmacokinetic consequences of spaceflight

Spaceflight induces a wide range of physiological and biochemical changes, including disruption of gastrointestinal (GI) function, fluid and electrolyte balance, circulatory dynamics, and organ blood flow, as well as hormonal and metabolic perturbations. Any of these changes can influence the pharmacokinetics and pharmacodynamics of in-flight medication. That spaceflight may alter bioavailability was proposed when drugs prescribed to alleviate space motion sickness (SMS) had little therapeutic effect. Characterization of the pharmacokinetic and/or pharmacodynamic behavior of operationally critical medications is crucial for their effective use in flight; as a first step, we sought to determine whether drugs administered in space actually reach the site of action at concentrations sufficient to elicit the therapeutic response.

The influence of disulfiram on acetaminophen metabolism in man

1. Acetaminophen clearance and its partial clearance to its major metabolites has been determined before and after 5 days treatment with the anti-alcohol abuse agent disulfiram (200 mg daily). The study was conducted in 10 subjects, five without liver disease and five with alcoholic cirrhosis of the liver. Acetaminophen was given i.v. at a dose of 500 mg. Plasma samples were obtained up to 8 h after injection and urine collected for 24 h. 2. Across all subjects acetaminophen plasma clearance was reduced from 0.249 +/- 0.061 to 0.217 +/- 0.066 l/min after disulfiram treatment (mean +/- SD, P less than 0.05). Thus no change in acetaminophen dosage would be required in patients treated with disulfiram. 3. The partial clearance of acetaminophen to its glucuronide, sulphate and glutathione derivatives (i.e. cysteine and N-acetyl cysteine) was not significantly changed by disulfiram treatment. Thus it seems unlikely that the previously observed protective effects of disulfiram against acetaminophen-induced hepatotoxicity in animals due to inhibition of metabolism will be seen in man.

Inhibition of the metabolism of paracetamol by isoniazid

1. The effect of isoniazid given daily for 7 days on paracetamol (acetaminophen) kinetics and metabolism was studied in 10 healthy volunteers. Paracetamol, 500 mg, was given before isoniazid, on day 7 of isoniazid administration, and 2 days after the last dose of isoniazid. 2. On day 7, isoniazid markedly inhibited the formation clearance of the glutathione and catechol metabolites by 69.7% and 62.2%, respectively. Total paracetamol clearance was lowered by 15.2%. There was no effect of isoniazid on the non-oxidative pathways of paracetamol elimination. 3. Two days after isoniazid was discontinued, paracetamol metabolism had returned to pre-isoniazid values.