Lack of effect of influenza vaccine on the pharmacokinetics of antipyrine, alprazolam, paracetamol (acetaminophen) and lorazepam

31 healthy male (n = 17) and female (n = 14) volunteers, aged 20 to 45 years, were divided into 4 groups and received on 3 separate occasions either: paracetamol (acetaminophen) 650mg intravenously (n = 9); alprazolam 1mg orally (n = 7); antipyrine (phenazone) 1g intravenously (n = 8); or lorazepam 2mg intravenously (n = 7). Doses were administered prior to influenza vaccine (0.5ml, intramuscularly) and at 7 and 21 days post-vaccination. The overall differences among the 3 trials in clearance of antipyrine were of borderline significance (p less than 0.0611), with a trend towards reduced clearance in both of the post-vaccination trials. There were no overall differences observed in the elimination half-life of antipyrine, nor were there significant differences between trials in cumulative urinary excretion or fractional recovery of intact antipyrine, 4-hydroxyantipyrine, norantipyrine, or 3-hydroxymethyl antipyrine. For paracetamol and alprazolam, there were no significant differences among the 3 trials in any of the kinetic variables. The elimination half-life of lorazepam varied significantly among trials, but differences were small and not systematic. Lorazepam clearance did not vary significantly among trials. Thus, clearance of drugs which undergo hepatic conjugative reactions such as glucuronidation and sulphation are unlikely to be affected by the coadministration of influenza vaccine. Furthermore, not all drugs which are biotransformed by hepatic microsomal oxidation necessarily have impaired clearance due to coadministration of influenza vaccine.     

Effects of acetylsalicylic acid and paracetamol alone and in combination on prostanoid synthesis in man.

1. The present study was designed to investigate the effects of acetylsalicylic acid and paracetamol given separately and in combination on total body and renal PGE2 synthesis in healthy volunteers. 2. In a randomized four-way cross-over study eleven female volunteers received for two consecutive days 3 g day-1 acetylsalicylic acid or 3 g day-1 paracetamol or a combination of 1.5 g day-1 acetylsalicylic acid and 1.5 g day-1 paracetamol, or 1.5 g day-1 acetylsalicylic acid separated by washout phases of at least 5 days. Urinary excretion of the major urinary metabolite of PGE2 (PGE-MUM), PGE2 and creatinine clearance were measured before and on day 2 of each treatment period. Compliance was tested by measuring metabolites of the two drugs in urine. 3. Paracetamol did not reduce urinary excretion of PGE2 whereas both dosages of acetylsalicylic acid caused a significant reduction. 4. The combination of both drugs did not reduce PGE2 excretion more than acetylsalicylic acid alone. 5. All four drug schedules reduced urinary excretion of PGE-MUM significantly.     

Gastric erosions induced by analgesic drug mixtures in the rat.

Gastric erosions after oral administration of analgesics separately and in admixture have been examined in adult rats. After administration of acetylsalicylic acid (aspirin), phenacetin, paracetamol and caffeine as single drugs, gastric erosions were only observed with aspirin. The combination of aspirin with phenacetin did not change, that of aspirin with caffeine significantly increased, and aspirin with paracetamol significantly decreased the incidence of gastric lesions compared with aspirin alone. The results for aspirin with paracetamol did not differ from those for the vehicle. Addition of caffeine to the combination of aspirin and phenacetin caused a significant increase in erosions, but when given with aspirin and paracetamol no erosions occurred. The mechanisms underlying the effects of these drugs on aspirin-induced erosions are discussed.     

Gastric erosions induced by analgesic drug mixtures in the rat

Gastric erosions after oral administration of analgesics separately and in admixture have been examined in adult rats. After administration of acetylsalicylic acid (aspirin), phenacetin, paracetamol and caffeine as single drugs, gastric erosions were only observed with aspirin. The combination of aspirin with phenacetin did not change, that of aspirin with caffeine significantly increased, and aspirin with paracetamol significantly decreased the incidence of gastric lesions compared with aspirin alone. The results for aspirin with paracetamol did not differ from those for the vehicle. Addition of caffeine to the combination of aspirin and phenacetin caused a significant increase in erosions, but when given with aspirin and paracetamol no erosions occurred. The mechanisms underlying the effects of these drugs on aspirin-induced erosions are discussed.     

A pharmacokinetic study of paracetamol in Thai β-thalassemia/HbE patients

Background

Thalassemia may alter the pharmacokinetics of several drugs in thalassemic patients. Paracetamol is a commonly used analgesic and antipyretic drug which is extensively metabolized in the liver via glucuronidation. The aim of this study was to compare the pharmacokinetics of paracetamol (PCM) and its metabolites [paracetamol glucuronide (PCM-G), paracetamol sulfate (PCM-S), and paracetamol cysteine (PCM-C)] in 16 patients with 16 normal subjects.

Method

Following an overnight fast, a single dose of paracetamol (1,000 mg of Tylenol®) was given and blood samples were obtained at predose, 0.5, 1, 1.5, 2, 3, 4, 5, 7, and 9 h after dosing for determination of the plasma levels of PCM and its metabolites by high-performance liquid chromatography.

Results

There was no significant difference in maximum concentration of PCM between groups. However, a significantly shorter elimination half-life of PCM was observed in the thalassemic subjects (p<0.001). Total apparent clearance of PCM was significantly faster in thalassemic subjects (p<0.01) while the apparent volume of distribution of PCM did not change. The area under the concentration time curve (AUC_0->∞) of PCM-G and PCM-S increased in thalassemic subjects (p<0.05) whereas this parameter for PCM-C was slightly lower in the patients. The half-lives of PCM metabolites were significantly shorter (p<0.01) in thalassemic subjects.

Conclusion

The results indicate that the elimination of PCM and its metabolites in thalassemic subjects is faster than that in normal subjects. Our pharmacokinetic data provide additional evidence that plasma PCM-G is higher in thalassemic patients with hyperbilirubinemia, which could be a casual relationship in regulating the UDP-glucuronosyltransferase expression.     

Drug adsorption to charcoals and anionic binding resins

1. The in-vitro binding of four drugs with differing physiochemical properties to two commercial charcoal preparations and two anionic binding resins was studied at 37 degrees C and pH 7.4. 2. The two charcoal preparations (Carbomix and Medicoal) behaved similarly and adsorbed metoclopramide and antipyrine to a greater degree than warfarin or paracetamol. 3. Cholestyramine had a significantly greater maximum adsorption capacity (K2) for warfarin and significantly lower adsorption capacity for paracetamol and metoclopramide than did the charcoals. 4. Colestipol behaved similarly but also bound metoclopramide to a significantly greater extent than did either cholestyramine or charcoal and antipyrine to a significantly lesser extent than did Carbomix. 5. There appeared to be no consistent relationship between the maximum adsorption capacity of the adsorbents for the drugs tested and the physicochemical properties of those drugs (e.g. basic or acidic structure, pKa or molecular weight).     

A single blind controlled comparison of tramadol/paracetamol combination and paracetamol in hand and foot surgery. A prospective study

The objective of this study was to compare the efficacy and effectiveness between an analgesic combination of tramadol/paracetamol (37.5+325 mg), and paracetamol monotherapy (1000 mg) for acute postoperative pain after hand and foot surgery. The study design was a single blind randomized controlled trial. A total of 114 patients who underwent hand and foot surgery under brachial plexus block were randomized to receive either paracetamol monotherapy (group P, n=57) or tramadol/paracetamol (group TP, n=57) postoperatively. The number of patients who required an extra-dose of analgesic pain score, and adverse affects were compared between the two groups. Analgesic requirement was significantly lower in those in the TP group when compared with the P group. In the TP group, the pain score after surgery was significantly lower than in the P group. Adverse effects did not significantly differ between the two groups. There were no serious adverse events in either group. The association of tramadol and paracetamol appears to have more efficacy when compared with paracetamol monotherapy for acute postoperative pain after hand and foot surgery.     

Orphenadrine citrate increases and prolongs the antinociceptive effects of paracetamol in mice

Orphenadrine, a muscle relaxant with antinociceptive effects, was shown to increase and prolong the antinociceptive effects of paracetamol in mice. Both in the increasing temperature hot plate test and in the formalin test, a combination of the two drugs showed a significantly improved effect compared to either of the drugs alone. The time course of the effects was tested in the increasing temperature hot plate test. The group treated with the drug combination showed a prolonged effect compared to both single drug treated groups, the effect lasting longer than 120 min. for the combination and about 80 min. for the single drugs. Orphenadrine and paracetamol increased antinociception even when orphenadrine was injected 90 min. after paracetamol, which by that time did not exert antinociceptive effects by itself. Thus the combination of orphenadrine and paracetamol enhances the antinociceptive effect of either drug in mice.     

The role of sulphate conjugation in the metabolism and disposition of oral and intravenous paracetamol in man.

The effects of paracetamol dose (5 and 20 mg/kg) and route of administration (intravenous and oral) on the urinary excretion of paracetamol and its glucuronide, sulphate, cysteine and mercapturic acid conjugates were studied in five healthy subjects. The fractional urinary excretion of unchanged paracetamol and its conjugates was independent of the route of administration at both dose levels, suggesting that the gastrointestinal tract is not an important site for paracetamol metabolism. The percentage of the dose excreted as the sulphate conjugate was significantly higher after 5 than after 20 mg/kg (37.7% and 33.3% respectively) and this is consistent with saturation of sulphate conjugation. No significant effect of paracetamol dose upon the area under the plasma concentration-time curve (AUC), corrected for dose, was found for the sulphate or glucuronide conjugates. The total plasma clearance of paracetamol and the renal clearance of the sulphate conjugate were significantly higher after the 5 than the 20 mg/kg dose (331 +/- 42 ml/min and 295 +/- 48 ml/min; 273 +/- 74 ml/min and 205 +/- 46 ml/min respectively). The oral systemic availability of paracetamol was 80% and independent of dose.     

Comparison of the pharmacokinetic profiles of soluble aspirin and solid paracetamol tablets in fed and fasted volunteers

The aim of this study was to investigate the absorption of popular preparations of two common analgesics--soluble aspirin and solid paracetamol tablets. An open, randomised, crossover study design was used to compare the pharmacokinetic parameters of soluble aspirin and solid paracetamol tablets in 16 healthy, male volunteers from the University of the Witwatersrand, South Africa, in both fed and fasted states. Plasma concentrations of paracetamol, aspirin and salicylic acid were measured. It was found that the rate of absorption was significantly faster for soluble aspirin than for solid paracetamol, regardless of fed or fasting state, considering time to maximum concentration (p < 0.01), time to first quantifiable concentrations (p < 0.05) and absorption rate (p < 0.01). Absorption rate was significantly affected by food for both soluble aspirin (p = 0.028) and for solid paracetamol (p = 0.0003). Time to maximum concentration was not significantly affected by food for soluble aspirin (p = 0.17) but significantly lengthened for solid paracetamol (p = 0.0003). The extent of absorption was affected by food in terms of maximum concentration for both drugs (p = 0.0001), with a reduction of 49% in the fed state for solid paracetamol compared to 18% for soluble aspirin, the difference between the drugs being statistically significant (p = 0.0024). The overall bioavailability of soluble aspirin was unaffected by food and the bioavailability of salicylic acid was increased in the fed state, whereas that of solid paracetamol was lowered in the fed state. Greater inter-individual variation was seen in paracetamol concentrations compared with aspirin or salicylic acid levels. In conclusion, these results show that the absorption of soluble aspirin is largely unaffected by food, whereas, in the same volunteers, the absorption of solid paracetamol tablets is greatly affected. In some volunteers, maximum plasma concentrations of paracetamol following food did not reach levels previously reported to be required for effective analgesia, and this may have implications for pain relief in some individuals. The practice in some individuals of taking aspirin tablets after food to minimise potential gastric disturbance should not affect the level of analgesia.     

Salivary secretion of paracetamol in man

Plasma and saliva paracetamol levels were measured by HPLC in ten healthy volunteers who took a therapeutic dose after an overnight fast. Salivary levels of the drug were consistently and significantly higher than those in plasma for the first 50 min after oral ingestion, but saliva and plasma levels correlated closely during the elimination phase. There was a highly significant correlation between the AUC 0-alpha calculated from saliva and plasma paracetamol concentration-time curves. The elevated saliva/plasma ratio for the first 50 min was not due to loss of paracetamol from plasma during sample preparation, binding to plasma protein or adsorption to the buccal mucosa. Administration of probenecid in an attempt to block possible active secretion of paracetamol into saliva did not significantly alter the saliva/plasma concentration ratio for the first 50 min, but did significantly reduce this ratio in the time period 125-360 min. The experimental data conformed to a recently proposed model in which elevated saliva/plasma ratios during the early stages following oral ingestion were related to ongoing absorption into the arterial system.     

Paracetamol and metabolite pharmacokinetics in infants

BACKGROUND: Data concerning metabolism of paracetamol in infants are scant. Previous studies have examined urinary metabolite recovery rates after a single dose of paracetamol in either neonates (<6 weeks) or children (3-9 years). There are no studies investigating infants. METHODS: Infants ( n=47) undergoing major craniofacial surgery were given paracetamol 19-45 mg/kg 6-, 8-, or 12-hourly as either elixir or suppository formulation for postoperative analgesia, after a loading dose of 33-59 mg/kg rectally during the operation. Serum was assayed for paracetamol concentration in 40 of these infants at 5, 8, 11, 14, 17 and 20 h postoperatively. Urine samples were collected every 3 h for 24 h in 15 of these infants. The clearances of paracetamol to glucuronide and sulphate metabolites as well as the urinary clearance of unmetabolised paracetamol were estimated using non-linear, mixed-effects models. RESULTS: Mean (+/-SD) age and weight of the patients were 11.8+/-2.5 months and 9.1+/-1.9 kg. Clearances of paracetamol to paracetamol-glucuronide (%CV) and to paracetamol-sulphate were 6.6 (11.5) l/h and 7.5 (11.5) l/h respectively, standardised to a 70-kg person using allometric "1/4 power" models. Glucuronide formation clearance, but not sulphate formation, was related to age and increased with age from a predicted value in a neonate of 2.73 l/h/70 kg to a mature value of 6.6 l/h/70 kg with a maturation half-life of 8.09 months. Urine clearance of paracetamol-glucuronide, paracetamol-sulphate and unchanged paracetamol (%CV) were, respectively, 2.65, 3.03 and 0.55 (28) l/h/70 kg. The urine clearance of unchanged paracetamol and metabolites was related to urine volume flow rate. Clearance attributable to pathways other than these measured in urine was not identifiable. The glucuronide/sulphate formation clearance ratio was 0.69 at 12 months of age. Sulphate metabolism contributed 50% towards paracetamol clearance. CONCLUSION: Glucuronide formation clearance increases with age in the infant age range but sulphate formation does not. Renal clearance of paracetamol and its metabolites increases with urine flow rate. This and other studies show that paracetamol metabolism to glucuronide appears to be similar in infants and children, but in adults is increased in comparison with children. Oxidative pathways were undetectable in this infant study and may explain, in part, the reduced incidence of hepatotoxicity in infants.     

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.     

Patterns of regular drug use in Spanish childbearing women: changes elicited by pregnancy

Objective: To determine drug use in Spanish women before pregnancy and from conception to the awareness of pregnancy (early period of pregnancy, EPP), as well as to analyse attitudinal changes when pregnancy was planned or known. Methods: Trained gynaecologists used a structured questionnaire to collect demographic and obstetric characteristics, histories of regular drug taking before pregnancy, attitudes towards drug taking during pregnancy and current drug use in the EPP. Women were interviewed at their first antenatal visit during the first trimester. Results: Two hundred and seventy-two women were included (mean age 29.3 years and 66.3 days of gestation). Before pregnancy, 24% regularly took drugs, 70% of them more than twice a week; a significantly higher frequency was found in those receiving public antenatal care and in those who had had less education. In 39% of women, awareness of pregnancy did not change their attitudes towards regular drug use. Among those who decided to suppress their regular drug intake, 58% did so when their pregnancy was confirmed and 42% when they planned it. In women who planned their pregnancy, 30.1% stopped when they tried to become pregnant. However, 62% of all women took drugs during the EPP. In private antenatal care significantly more drugs were taken per patient. By the 168 women 278 compounds were consumed during the EPP: 40% were analgesics (mainly paracetamol and acetylsalicylic acid) and 25% were digestive and metabolic drugs (mainly antacids and laxatives). Drugs were often used more than twice a week, particularly in women receiving public antenatal care and in those who had had less education. Conclusion: Drug taking is common in Spanish women of childbearing age, and many of those in our study did not decide to stop during the EPP. Few women avoid drugs when planning a pregnancy. Therefore, gynaecologists must advise against drug taking in patients who wish to become pregnant and suggest that unnecessary drug use be avoided when the pregnancy is already diagnosed. Received: 17 February 1998 / Accepted in revised form: 20 May 1998     

Paracetamol elimination in patients with non-insulin dependent diabetes mellitus.

The pharmacokinetics and metabolism of an intravenous dose (500 mg) of paracetamol were studied in a group of non-insulin dependent diabetic patients (n = 10) and in a group of healthy control subjects (n = 9). Paracetamol clearance, half-life and the partial clearance to paracetamol glucuronide were not significantly different, but the partial clearance to paracetamol sulphate was significantly reduced (62 +/- 18 vs 86 +/- 17 ml h-1 kg-1 (mean +/- s.d.)) and the renal clearance of paracetamol was significantly increased (56 +/- 20 vs 22 +/- 6 ml h-1 kg-1 (mean +/- s.d.)) in the non-insulin dependent diabetic patients, compared with the control group.     

Pilot study of the antipyretic and analgesic activity of nimesulide paediatric suppositories.

The object of this study was the preliminary evaluation, in paediatric patients, of the analgesic and antipyretic effect of nimesulide given rectally. Nimesulide was studied in comparison with paracetamol, according to a double-blind technique. Forty-eight hospitalized children with fever or pain, between 1 and 8 years old, were included. The drugs were administered with a flexible posology (1 to 4 suppositories/day with an interval between administrations of at least 6 h). Monitoring of symptom intensity was scheduled in the 6 hours after each administration. At the end of the therapy the physician expressed a global judgement on the drug. Both treatments resulted in a significant decrease in body temperature at the 1 h observation. From the second hour onward, a more rapid tendency to temperature normalization was observed with nimesulide than with paracetamol. Repeated measurements with ANOVA did not show significant differences between treatments but the physicians' overall judgements were significantly more favourable to the nimesulide than to the paracetamol antipyretic activity. Good analgesic activity, favouring a rapid decrease in the painful symptomatology, was observed in both groups. No differences were found in the analgesic activity of the treatments, although in this case the clinical evidence was more favourable to paracetamol. Both drugs were very well tolerated.     

Comparison of paracetamol metabolism in young adult and elderly males

Summary Paracetamol metabolism was compared in groups of young adult (mean age 20.8 years) and elderly (mean 79.3 years) males.Apparent oral clearance and half-life and partial metabolic clearances to the glucuronide and glutathione-derived conjugates of paracetamol were not significantly different between the two groups. However, the partial metabolic clearance to paracetamol sulphate was 23.1% lower and renal clearance of unchanged drug was 42.9% lower in the elderly compared to the young adults.Despite the decreased clearance by these pathways, reduction in paracetamol dosage should not be necessary in the elderly.     

The effect of propranolol on paracetamol metabolism in man.

Ten healthy volunteers were treated for 4 days with 160 mg propranolol HCl and placebo in random order. At the end of each treatment salivary antipyrine kinetics and the plasma kinetics and urinary excretion of paracetamol and its major metabolites were measured following a 1500 mg oral dose. Propranolol prolonged the half-life of antipyrine by 11 +/- 5% (mean +/- s.e. mean) and lowered its clearance by 14 +/- 3% (P less than 0.05). Propranolol increased the half-life of paracetamol by 25 +/- 12% (P less than 0.05) and lowered its clearance by 14 +/- 3% (P less than 0.05). Propranolol decreased the partial clearance of paracetamol to its cysteine and mercapturate derivatives by 16 +/- 3% (P less than 0.05) and 32 +/- 7% (P less than 0.05), respectively. The partial clearance to the glucuronide conjugate was decreased by 27 +/- 6% (P less than 0.05), whereas that to sulphate was not changed significantly. Propranolol inhibits paracetamol metabolism predominantly through inhibition of the oxidation and glucuronidation pathways.     

Guaifenesin enhances the analgesic potency of paracetamol in mice

AIM OF INVESTIGATION: Guaifenesin is used as an expectorant and it has been reported to possess muscle relaxant and sedative activity. Guaifenesin has been used as a component of composite OTC analgesics containing paracetamol for many years. The aim of our study was to ascertain effects of guaifenesin on paracetamol analgesic activity and locomotor performance. METHODS: Antinociceptive efficacy was tested in mice using an acetic acid (0.7%) writhing test. Locomotor performance was tested in rota-rod test and activity cage. All drugs were given orally and tested in mice. RESULTS: In combination with a subeffective dose of guaifenesin (200 mg/kg), the ED(50) for paracetamol in the writhing test was significantly lower (82.2 mg/kg) than that of paracetamol administered alone (233.7 mg/kg). Guaifenesin alone did not show an analgesic effect. Guaifenesin did not produce statistically significant locomotor impairment in the rota-rod test at doses enhancing analgesic activity of paracetamol, although there was a trend for decreased locomotor activity in activity cage. CONCLUSION: The present results indicate that guaifenesin may enhance analgesic activity of paracetamol.