Dose-dependent Inhibition of Platelet Function by Acetaminophen in Healthy Volunteers

Does Early Neonatal Thrombocytopenia Affect Ductal Therapeutic Response to Acetaminophen in Preterm Neonates?

OBJECTIVE

Perinatal thrombocytopenia has been shown to affect responsiveness to therapeutic ductal closure with cyclooxygenase (COX) inhibitors. This has not been studied in responsiveness to acetaminophen, which has less effect on platelet function. The objective of this study was to evaluate whether thrombocytopenia affects ductal responsiveness to acetaminophen.

STUDY DESIGN

This study was a retrospective review of preterm neonates <1,500 g. Echocardiograms were performed within the first week of life; if ductal status was found to be hemodynamically significant, infants were treated with acetaminophen.

RESULTS

We studied 254 infants. Fifty-seven of these (22%) had a hemodynamically significant patent ductus arteriosus (hsPDA) and were treated with acetaminophen. Forty (70%) of those treated responded with ductal closure after one to two courses of acetaminophen. Seventeen infants were considered nonresponsive, requiring the addition of ibuprofen and/or surgical ligation. Sixty seven of the 254 infants (26%) developed moderate thrombocytopenia (platelets <100,000) within the first 10 days of life, more within the hsPDA group (54 vs. 18% p < 0.001); however, no differences in platelet-related parameters were observed between those who did and did not respond to acetaminophen treatment when comparing infants with hsPDA. Twenty-six of the 67 thrombocytopenic infants were already thrombocytopenic prior to acetaminophen treatment, and 19 of these 26 (73%) with pretreatment thrombocytopenia responded to acetaminophen treatment-with the overall response rate of 70%.

CONCLUSIONS

This study is the first to document that, in contrast to the COX inhibitors, there is no association between early neonatal thrombocytopenia and ductal therapeutic responsiveness to acetaminophen.

KEY POINTS

· Perinatal thrombocytopenia affects ductal closure with COX inhibitors.. · In contrast to the COX inhibitors, acetaminophen responsiveness is not affected by thrombocytopenia.. · Acetaminophen can be recommended to close hsPDA in the presence of thrombocytopenia..

Common Medications Which Should Be Stopped Prior to Platelet-Rich Plasma Injection

Osteoarthritis (OA) is an extremely prevalent joint condition in the United States, affecting over 30 million people [...]

A Systematic Review on the Effect of Common Medications on Platelet Count and Function: Which Medications Should Be Stopped Before Getting a Platelet-Rich Plasma Injection?

Background:

Platelet-rich plasma (PRP) exerts its effect through the release of growth factors and cytokines from the platelet concentrate. Certain medications may affect platelet count or function, resulting in decreased efficacy of PRP injections.

Purpose:

To systematically review the literature regarding common medications and their effects on platelets to establish guidelines for which medications should be stopped before obtaining a PRP injection.

Study Design:

Systematic review; Level of evidence, 2.

Methods:

This review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. A search for studies assessing the effect of common medications on platelet count or platelet function was performed of the PubMed, Cochrane Library, Web of Science, and OpenGrey databases. Inclusion criteria were as follows: drug studied was aspirin, acetaminophen, a nonsteroidal anti-inflammatory drug (NSAID), a statin, or gabapentin; human participants; and article in the English language. Risk of bias was assessed using the Cochrane Risk of Bias tool and the Risk of Bias in Non-randomised Studies—of Interventions tool.

Results:

A total of 1711 studies were identified through the initial search, with 20 studies meeting all inclusion criteria. No studies involving gabapentin met all inclusion criteria. Patients treated with aspirin (268 patients) or acetaminophen (13 patients) showed a significant decrease in platelet aggregation. Statin therapy (73 patients) did not result in a significant decrease in platelet aggregation. Patients who took NSAIDs (172 patients) demonstrated significantly decreased platelet aggregation only when treated with nonselective formulations. Those treated with cyclooxygenase (COX)-2–selective NSAIDs showed no significant difference in platelet aggregation. Treatment with aspirin, acetaminophen, statins, or NSAIDs did not lead to a significant decrease in platelet count.

Conclusion:

Aspirin, acetaminophen, and nonselective NSAIDs should be considered for suspension before a PRP injection because of their potential to diminish the effects of the injection. COX-2–selective NSAIDs and statins do not need to be withheld before a PRP injection.

COVID-19 Medical and Pharmacological Management in the European Countries Compared to Italy: An Overview

(1) Background: Italy accounts for more than 150,000 deaths due to the COVID-19 pandemic, leading the top rank in SARS-CoV-2-caused deceases in Europe. A survey on the different ways by which the COVID-19 pandemic emergency was managed in the foreign European countries compared to Italy is the purpose of this paper. (2) Methods: A literature search and various mathematical algorithms to approach a rank scoring scale were used to describe in detail the different approaches used by European countries to manage the COVID-19 pandemic emergency. (3) Results: The study showed that Italy stands at the bottom ranking for COVID-19 management due to its high mortality rate. Possible causes of the observed huge numbers of hospitalization and deaths were (a) the demographic composition of the European country; (b) its decentralized healthcare system organization; (c) the role of correct pharmacology in the early stages before hospitalization. Post-mortem examinations were of paramount importance to elucidate the etiopathogenesis of COVID-19 and to tailor a suitable and proper therapy in the early symptomatic stages of COVID-19, preventing hospitalization. (4) Conclusions: Factors such as the significant impact on elderly people, the public health organization prevalently state-owned and represented mainly by hospitals, and criticism of the home therapy approach toward SARS-CoV-2-infected people, may have concurred in increasing the number of COVID-19 deaths in Italy.

Thromboelastography in the setting of acetaminophen-induced hepatotoxicity

BACKGROUND

Severe acetaminophen (APAP) poisoning can result in fulminant hepatic failure and abnormal tests of coagulation. Although the international normalized ratio (INR) may be elevated, the actual hemostatic status of patients with APAP-induced hepatotoxicity is unknown. Few studies exist investigating the clinical use of thromboelastography (TEG) to evaluate the hemostatic status in the setting of APAP-induced hepatotoxicity.

METHODS

We performed a retrospective review of patients who were admitted for APAP toxicity and received TEG testing at a single transplant center.

RESULTS

Nine patients had detectable APAP concentrations and exhibited elevated aspartate and alanine aminotransferase activities. Seven had thrombocytopenia. TEG revealed a decreased median alpha angle and maximum amplitude but other values were within the normal reference range.

DISCUSSION

Based on our study of APAP-induced hepatotoxicity, TEG showed a decreased rate of fibrin formation and cross-linking, as well as reduced clot strength. These findings suggest that patients with APAP-induced hepatotoxicity and thrombocytopenia have a theoretically increased bleeding risk as demonstrated by both elevated INR and abnormal TEG values. However, these TEG findings are more likely related to thrombocytopenia rather than directly to APAP-induced hepatotoxicity. Further studies should be performed to elucidate the potential role of TEG in various stages of APAP-induced hepatotoxicity.

Home pharmacological therapy in early COVID-19 to prevent hospitalization and reduce mortality: Time for a suitable proposal

The COVID‐19 pandemic is a highly dramatic concern for mankind. In Italy, the pandemic exerted its major impact throughout the period of February to June 2020. To date, the awkward amount of more than 134,000 deaths has been reported. Yet, post‐mortem autopsy was performed on a very modest number of patients who died from COVID‐19 infection, leading to a first confirmation of an immune‐thrombosis of the lungs as the major COVID‐19 pathogenesis, likewise for SARS. Since then (June–August 2020), no targeted early therapy considering this pathogenetic issue was approached. The patients treated with early anti‐inflammatory, anti‐platelet, anticoagulant and antibiotic therapy confirmed that COVID‐19 was an endothelial inflammation with immuno‐thrombosis. Patients not treated or scarcely treated with the most proper and appropriate therapy and in the earliest, increased the hospitalization rate in the intensive care units and also mortality, due to immune‐thrombosis from the pulmonary capillary district and alveoli. The disease causes widespread endothelial inflammation, which can induce damage to various organs and systems. Therapy must be targeted in this consideration, and in this review, we demonstrate how early anti‐inflammatory therapy may treat endothelia inflammation and immune‐thrombosis caused by COVID‐19, by using drugs we are going to recommend in this paper.

Synergism between oral paracetamol and nefopam in a murine model of postoperative pain

BACKGROUND

The use of paracetamol or nefopam for postoperative pain control is limited by the need of high doses associated with unwanted effects. Previous works suggest positive interactions between both compounds that may be exploited to obtain potentiation of antinociception.

METHODS

Mechanical and heat antinociception induced by oral doses of paracetamol, nefopam or their combination was studied by isobolographic analysis in a murine model of postsurgical pain. The effective doses that produced 50% antinociception (ED₅₀ ) were calculated from the log dose-response curves for each compound. Subsequently, the effects of ED_8.7 s, ED_12.5 s, ED_17.5 s and ED₃₅ s of nefopam and paracetamol combined were assessed.

RESULTS

Oral paracetamol induced dose-dependent relief of postoperative sensitivity and showed higher efficacy reducing mechanical hypersensitivity (ED₅₀ 177.3 ± 15.4 mg/kg) than heat hyperalgesia (ED₅₀ 278.6 ± 43 mg/kg). Oral nefopam induced dose-dependent antinociception with similar efficacy for mechanical and heat hypersensitivity (ED₅₀ s 5.42 ± 0.81 vs. 5.83 ± 0.72). Combinations of increasing isoeffective doses revealed that combined ED_17.5 s (85.76 mg/kg paracetamol and 1.9 mg/kg nefopam) and ED₃₅ s (132.67 mg/kg and 3.73 mg/kg) showed synergistic effects leading to 75% and 90% mechanical antinociception, respectively. These mixtures were defined by interaction indexes of 0.43 and 0.41 and ratios 45:1 and 35:1 paracetamol:nefopam, respectively. The same combinations showed additive effects for the inhibition of incisional thermal hyperalgesia.

CONCLUSIONS AND LIMITATIONS

This work describes a synergistic antinociceptive interaction between low doses of nefopam and paracetamol for the treatment of postoperative hypersensitivity to peripheral stimuli. The promising results obtained on reflexive nociceptive responses of young male mice subjected to plantar surgery highlight the interest of further research evaluating the effects of this mixture on the affective-motivational component of pain and in females and additional age groups. Confirmation of pain-relieving efficacy and safety of this oral combination clinically available in European and Asian countries could provide a useful tool for postsurgical pain management.

SIGNIFICANCE

Early postoperative pain is currently undertreated and has been recognized as a relevant source of chronic postsurgical pain. Oral efficient treatments could facilitate fast-track surgeries and patient recovery at home. Here, we identify in a mouse model of postoperative pain a potent synergistic oral combination consisting of low paracetamol and nefopam doses that provides relief of postsurgical hypersensitivity to mechanical and thermal stimuli. Oral multimodal paracetamol-nefopam mixtures represent a potential clinically available pharmacological strategy for the relief of incisional sensitivity and the promotion of patient recovery.

Frailty and Co-Prescribing of Potentially Interacting Drugs in New Users of Warfarin

Background

Warfarin is underutilised in frail older people because of the fear of bleeding complications. Drug interactions are an independent bleeding risk factor. However, the extent to which potential drug interactions are taken into account at warfarin therapy initiation in frail patients is not known.

Objective

The objective of this study was to investigate the use of potentially interacting drugs increasing the bleeding risk before and after warfarin initiation in frail and non-frail patients.

Methods

We conducted an observational study including inpatients aged ≥ 60 years initiated on warfarin in a tertiary hospital in Adelaide, South Australia. Frailty status was assessed with the Reported Edmonton Frail Scale. Medication charts were reviewed before and after warfarin initiation.

Results

In total, 151 patients (102 non-frail and 49 frail) were included. Before warfarin initiation, the use of clopidogrel and acetaminophen was more common in frail patients compared with non-frail patients (25.5% vs 10.2%, p = 0.0135, 63.8% vs 35.7% p = 0.0014, respectively). The use of non-steroidal anti-inflammatory drugs, 9.2% in non-frail patients and 6.4% in frail patients before warfarin initiation, was completely stopped after warfarin initiation in both groups. The use of antiplatelet drugs decreased from 56.1% in non-frail patients and 66.0 % in frail patients to 12.2% and 14.9%, respectively. Instead, the use of drugs affecting the metabolism of warfarin or vitamin K increased in both groups. No statistically significant difference was seen in the exposure to interacting drugs between study groups after warfarin initiation. Acetaminophen, senna glycosides and cytochrome P450 2C9 inhibiting drugs were the most common interacting drugs at discharge used in 49.0%, 18.4% and 20.4% of non-frail patients and 53.2%, 29.8% and 19.1% of frail patients, respectively.

Conclusions

The overall frequency of potential drug interactions was moderate and frail patients were not exposed to warfarin drug interactions more often than non-frail patients. Further studies in larger study populations are required to verify these results.

Electronic supplementary material

The online version of this article (10.1007/s40266-020-00755-0) contains supplementary material, which is available to authorized users.

Molecular and Mechanical Mechanisms Regulating Ductus Arteriosus Closure in Preterm Infants

Failure of ductus arteriosus closure after preterm birth is associated with significant morbidities. Ductal closure requires and is regulated by a complex interplay of molecular and mechanical mechanisms with underlying genetic factors. In utero patency of the ductus is maintained by low oxygen tension, high levels of prostaglandins, nitric oxide and carbon monoxide. After birth, ductal closure occurs first by functional closure, followed by anatomical remodeling. High oxygen tension and decreased prostaglandin levels mediated by numerous factors including potassium channels, endothelin-1, isoprostanes lead to the contraction of the ductus. Bradykinin and corticosteroids also induce ductal constriction by attenuating the sensitivity of the ductus to PGE2. Smooth muscle cells of the ductus can sense oxygen through a mitochondrial network by the role of Rho-kinase pathway which ends up with increased intracellular calcium levels and contraction of myosin light chains. Anatomical closure of the ductus is also complex with various mechanisms such as migration and proliferation of smooth muscle cells, extracellular matrix production, endothelial cell proliferation which mediate cushion formation with the interaction of blood cells. Regulation of vessel walls is affected by retinoic acid, TGF-β1, notch signaling, hyaluronan, fibronectin, chondroitin sulfate, elastin, and vascular endothelial cell growth factor (VEGF). Formation of the platelet plug facilitates luminal remodeling by the obstruction of the constricted ductal lumen. Vasa vasorum are more pronounced in the term ductus but are less active in the preterm ductus. More than 100 genes are effective in the prostaglandin pathway or in vascular smooth muscle development and structure may affect the patency of ductus. Hemodynamic changes after birth including fluid load and flow characteristics as well as shear forces within the ductus also stimulate closure. Current pharmacological treatment for the closure of a patent ductus is based on the blockage of the prostaglandin pathway mainly through COX or POX inhibition, albeit with some limitations and side effects. Further research for new agents aiming ductal closure should focus on a clear understanding of vascular biology of the ductus.

Paracetamol as a basic component of a modern approach to adequate perioperative analgesia

The problem of adequate perioperative anesthesia is one of the most pressing in the current health care system, given its medical, humanistic and socio-economic aspects. Currently, the standard of postoperative analgesia is multimodal analgesia (MMA). One of the major and required components of MMA is paracetamol, which has antipyretic and analgesic effects with limited peripheral anti-inflammatory activity. Most authors consider intravenous paracetamol as a base drug in a multimodal analgesia strategy for a variety of surgical interventions, which reduces the need for opioids and reduces the side effects of the latter, which in turn significantly affects the results of treatment and the length of hospital stay.Numerous studies in many countries have created a broad evidence base for the clinical use of this drug. Due to its pharmacokinetic and pharmacodynamic properties, it has been shown that intravenous paracetamol has several advantages over oral and rectal forms: early and more effective onset of analgesia and stable maintenance of the therapeutic dose of paracetamol are explained by the formation of a faster and higher peak in the concentration of the drug. The side effects of using paracetamol can be compared with placebo. The mechanism of action of the drug is different from the mechanism of action of NSAIDs, however, is still not fully understood. It may possibly involve inhibition of cyclooxygenase, cannabinoid, or nitric oxide pathways in the central nervous system. Intravenous paracetamol is a safe and effective first-line drug for the treatment of moderate pain in the perioperative period.

Not all (N)SAID and done: Effects of nonsteroidal anti-inflammatory drugs and paracetamol intake on platelets

Platelets are key mediators of hemostasis and thrombosis and can be inhibited by nonsteroidal anti-inflammatory drugs (NSAIDs). As a result, platelet donors are temporarily deferred from donating if they have recently taken NSAIDs such as aspirin or ibuprofen. Despite these measures, a proportion of platelet donations show exposure to these drugs; however, little is known about the effect of NSAIDs and their metabolites on platelet quality in vivo and during storage. In this review, the effect of NSAIDs on platelet function is summarized, with a focus on the widely consumed over-the-counter (OTC) medications aspirin, ibuprofen, and the non-NSAID paracetamol. Aspirin and ibuprofen have well-defined antiplatelet effects. In comparison, studies regarding the effect of paracetamol on platelets report variable findings. The timing and order of NSAID intake is important, as concurrent NSAID use can inhibit or potentiate platelet activation depending on the drug taken. NSAID deferral periods and maximum platelet shelf-life is set by each country and are revised regularly. Reduced donor deferral periods and longer platelet storage times may affect the quality of platelet products, and it is therefore important to identify the possible impact of NSAID intake on platelet quality before and after storage.

Pain Management After Surgical Tonsillectomy: Is There a Favorable Analgesic?

The aim of this study was to examine how ibuprofen and paracetamol prevent pain after cold-steel extracapsular tonsillectomy in children. Also, we examined the relation between age, gender, nausea, postoperative bleeding, antibiotic use, type of diet, and postoperative pain intensity and the type of administered analgesic. A prospective study was conducted on 147 children (95 males and 52 females, aged 7-17 years) who underwent tonsillectomy in the Clinical-Hospital Center "Dragiša Mišović" from January 1 to June 30, 2016. The degree of pain was measured using a visual analog scale (VAS). We did not observe any significant differences in postoperative nausea, hospitalization rate postoperative bleeding, and antibiotic use between the paracetamol and ibuprofen groups. A test of within-patient effects showed that VAS scores changed significantly during the postoperative follow-up period (P = .00), but there were no significant differences between the groups (P = .778). After 12 hours, 29.3% of the patients on paracetamol and 21.8% on ibuprofen were transferred to a soft diet; after 24 hours, 84.8% of the paracetamol group and 85.5% of the ibuprofen group were on a soft diet (χ² test, P < .05). There was a statistically significant correlation between VAS scores measured 4 hours after the surgery and the time of transference to the soft diet (Spearman ρ test, P < .001). The transfer to soft and normal diets was not significantly different between the 2 groups as assessed by the VAS scores (Pearson χ² test, P = .565).There is still no consensus on the most effective postoperative pain-control regiment after tonsillectomy. This study showed that satisfactory pain management was achieved equally with both paracetamol and ibuprofen.

A randomised, investigator-initiated, clinical trial of the effects of fentanyl on P2Y12-receptor inhibition in patients with ST-elevation myocardial infarction who are pre-treated with crushed ticagrelor: rationale and design of the Opioids aNd crushed Ticagrelor In Myocardial infarction Evaluation (ON-TIME 3) trial

Background

Fast and accurate platelet inhibition is an important therapeutic goal in the acute treatment of patients with ST-elevation myocardial infarction (STEMI). Platelet inhibitory effects induced by oral P2Y12-receptor antagonists are delayed in STEMI patients undergoing primary percutaneous coronary intervention (PCI) due to haemodynamic changes and delayed gastro-intestinal absorption. Concomitant use of opioids, although recommended in the American College of Cardiology/American Heart Association and European Society of Cardiology STEMI guidelines, further delays gastro-intestinal absorption. To date, trials investigating alternative analgesics in STEMI patients have been scarce. This trial aims to assess the feasibility of a novel drug strategy for treatment of STEMI patients with crushed ticagrelor in combination with paracetamol (acetaminophen) instead of opioids.

Hypothesis

STEMI patients who are pre-treated with crushed ticagrelor and paracetamol have a higher level of platelet inhibition after primary PCI than patients pre-treated with crushed ticagrelor and fentanyl.

Study design

The Opioids aNd crushed Ticagrelor In Myocardial infarction Evaluation (ON-TIME 3) trial is a randomised controlled trial designed to examine whether administration of paracetamol instead of fentanyl can optimise platelet inhibition in STEMI patients who are pre-treated with crushed ticagrelor in the ambulance. One hundred and ninety patients with STEMI will be randomised (1:1 fashion) to intravenous (IV) fentanyl or IV paracetamol. The primary endpoint is the level of platelet reactivity units measured immediately after primary PCI.

Summary

The ON-TIME 3 trial (NCT03400267) aims to achieve optimal platelet inhibition and pain relief in STEMI patients receiving crushed ticagrelor in the ambulance by investigating IV fentanyl and IV paracetamol as analgesics.

Comparative Safety and Efficacy of Two High Dose Regimens of Oral Paracetamol in Healthy Adults Undergoing Third Molar Surgery under Local Anaesthesia

This study compared the efficacy and safety of single oral doses of 60 mg/kg and 90 mg/kg paracetamol in fit young adult patients undergoing third molar extractions. The study was a randomised, blinded, crossover design on 20 young, fit adults. Paracetamol was administered 30 minutes prior to the surgical extraction of the teeth, which was done under intravenous sedation and local anaesthesia. There were no clinically or statistically significant differences in the pain scores between 60 mg/kg or 90 mg/kg doses until the intake of rescue analgesics. There was a reduction in factor VII activity with 90 mg/kg dose compared to 60 mg/kg dose. It may be concluded that the 90 mg/kg dose, though safe, does not offer any advantages over 60 mg/kg dose of paracetamol in young fit adults undergoing third molar surgery.

Effect profile of paracetamol, Δ9-THC and promethazine using an evoked pain test battery in healthy subjects

BACKGROUND

A battery of evoked pain tasks (PainCart) was developed to investigate the pharmacodynamic properties of novel analgesics in early-phase clinical research. As part of its clinical validation, compounds with different pharmacological mechanisms of actions are investigated. The aim was to investigate the analgesic effects of classic and nonclassic analgesics compared to a sedating negative control in a randomized placebo-controlled crossover study in 24 healthy volunteers using the PainCart.

METHODS

The PainCart consisted of pain tasks eliciting electrical, pressure, heat, cold and inflammatory pain. Subjective scales for cognitive functioning and psychotomimetic effects were included. Subjects were administered each of the following oral treatments: paracetamol (1000 mg), Δ9-THC (10 mg), promethazine (50 mg) or matching placebo. Pharmacodynamic measurements were performed at baseline and repeated up to 10 h postdose.

RESULTS

Paracetamol did not show a significant reduction in pain sensation or subjective cognitive functioning compared to placebo. Promethazine induced a statistically significant reduction in PTT for cold pressor and pressure stimulation. Furthermore, reduced subjective alertness was observed. Δ9-THC showed a statistically significant decrease in PTT for electrical and pressure stimulation. Δ9-THC also demonstrated subjective effects, including changes in alertness and calmness, as well as feeling high and psychotomimetic effects.

CONCLUSIONS

This study found a decreased pain tolerance due to Δ9-THC and promethazine, or lack thereof, using an evoked pain task battery. Pain thresholds following paracetamol administration remained unchanged, which may be due to insufficient statistical power. We showed that pain thresholds determined using this pain test battery are not driven by sedation.

SIGNIFICANCE

The multimodal battery of evoked pain tasks utilized in this study may play an important role in early-phase clinical drug development. This battery of pain tasks is not sensitive to the effects of sedation alone, and thus suitable to investigate the analgesic potential of novel analgesic compounds.

NF-κB signaling pathway as target for antiplatelet activity

In different nucleated cells, NF-κB has long been considered a prototypical proinflammatory signaling pathway with the expression of proinflammatory genes. Although platelets lack a nucleus, a number of functional transcription factors are involved in activated platelets, such as NF-κB. In platelet activation NF-κB regulation events include IKKβ phosphorylation, IκBα degradation, and p65 phosphorylation. Multiple pathways contribute to platelet activation and NF-κB is a common pathway in this activation. Therefore, in platelet activation the modulation of NF-κB pathway could be a potential new target in the treatment of inflammation-related vascular disease therapy (antiplatelet and antithrombotic activities).

Acetaminophen, nonsteroidal anti-inflammatory drugs, and cyclooxygenase-2 selective inhibitors: an update

SUMMARY

Plastic and cosmetic surgery is often performed as an ambulatory procedure, and pain is often mild to moderate. Good pain relief is central to patient comfort and satisfaction. Analgesics used should ensure rapid onset and adequate pain relief lasting a sufficiently long duration with minimal or no side effects. Acetaminophen is well tolerated by patients, efficacious, and associated with only minor side effects, when used in the minimal effective doses. Nonsteroidal anti-inflammatory drugs (NSAIDs) are more efficacious, having lower numbers needed to treat compared with acetaminophen, but have several side effects and contraindications. However, when used in the correct doses in healthy patients, NSAIDs are excellent for pain management with one caveat that there is an increased risk for oozing or bleeding. In contrast, cyclooxygenase inhibitors (Coxibs) are equally efficacious as NSAIDs but have the added advantage that they have minimal or no effect on platelet function, and therefore, the risk for bleeding complications is minimal. However, there has been some concern about the risk of vascular events in patients with ischemic heart disease, specifically when using Coxibs, but even some NSAIDs, for example, diclofenac. In conclusion, acetaminophen should be given postoperatively to all patients undergoing plastic surgical procedures. For patients undergoing moderately invasive surgery, the addition of Coxibs to acetaminophen would be an advantage except in the patient with ischemic heart disease where NSAIDs could have a place in management of pain. Side effects and contraindications of NSAIDs, however, restrict their use to the healthy patient with mild comorbidities.

Co-Prescribing of Potentially Interacting Drugs during Warfarin Therapy - A Population-Based Register Study

We analysed the occurrence of co-prescribing of potentially interacting drugs during warfarin therapy in the community-dwelling population of Finland. We identified drugs having interaction potential with warfarin using the Swedish Finnish INteraction X-referencing drug-drug interaction database (SFINX) and obtained data on drug purchases from the nationwide Prescription Register. We defined warfarin users as persons purchasing warfarin in 2010 (n = 148,536) and followed them from their first prescription in 2010 until the end of the calendar year. Co-prescribing was defined as at least 1-day overlap between warfarin and interacting drug episodes. In addition, we identified persons who initiated warfarin therapy between 1 January 2007 and 30 September 2010 (n = 110,299) and followed these incident users for a 3-month period since warfarin initiation. Overall, 74.4% of warfarin users were co-prescribed interacting drugs. Co-prescribing covered 46.4% of the total person-years of warfarin exposure. Interacting drugs that should be avoided with warfarin were co-prescribed for 13.4% of warfarin users. The majority of the co-prescriptions were for drugs that are not contraindicated during warfarin therapy but require special consideration. Among incident users, 57.1% purchased potentially interacting drugs during the 3-month period after initiation, while 9.0% purchased interacting drugs that should be avoided with warfarin. To conclude, the occurrence of co-prescribing of potentially interacting drugs was high during warfarin therapy. Our findings highlight the importance of close monitoring of warfarin therapy and the need for further studies on the clinical consequences of co-prescribing of interacting drugs with warfarin.

The effect of paracetamol and tropisetron on pain: experimental studies and a review of published data

Experimental studies suggest that paracetamol-induced analgesia is mediated via central serotonergic pathways and attenuated by 5-HT3-antagonists. However, clinical studies do not support this, and 5-HT3-antagonists are expected to reduce pain by blocking the descending pronociceptive pathway. The current project tested whether tropisetron attenuates analgesia by paracetamol. Two randomized, double-blind, crossover studies with 18 healthy male volunteers in each were performed. Pain stimuli were cold water immersion (cold pressor test), contact heat pain (study 1) and electrical stimulation (study 2). In both studies, tropisetron 5 mg i.v. or saline was administered, followed by paracetamol 2 g i.v. 30 min. later. Individual changes in heat and cold pain intensity, cold pain tolerance and unpleasantness were recorded. The same thresholds were also expressed as scores (% of the individual score at baseline). Additionally, previously published findings on the effects of paracetamol and its interaction with 5HT3-antagonists in human experimental pain models were reviewed. After calculation of the sensory and pain scores (%), tropisetron seemed to amplify the analgesic action of paracetamol. Paracetamol 2 g i.v. did not show any statistically significant analgesia in thermal tests (study 1), or differences in sensory, pain detection or moderate pain thresholds of the electrical stimulus (study 2). As paracetamol did not have a measurable analgesic effect in these tests, no conclusions can be drawn about the interaction between paracetamol and tropisetron. However, tropisetron may have an analgesic effect of its own. Clinicians should not avoid using these drugs together, unless larger clinical studies indicate otherwise.

Does concomitant use of paracetamol potentiate the gastroduodenal mucosal injury associated with aspirin? A prospective, randomised, pilot study

BACKGROUND

Paracetamol is commonly prescribed for first-line symptomatic treatment in patients with osteoarthritis and aspirin is often co-administered for cardiovascular prophylaxis. It is not known if an interaction exists between aspirin and paracetamol in regards to gastroduodenal mucosal injury.

AIM

To investigate whether or not co-administered aspirin with paracetamol results in an increased rate of endoscopic gastroduodenal mucosal injury as compared to either agent alone.

METHODS

In this prospective, double-blind, randomised, three-arm, placebo- and active-controlled, parallel-group pilot study healthy adult subjects (18-75 years old) with a normal baseline trans-nasal oesophagogastroduodenoscopy (TN-EGD), received oral paracetamol 4000 mg q.d.s. (n = 21), aspirin 325 mg q.d.s. (n = 19) or paracetamol 4000 mg q.d.s. and aspirin 325 mg q.d.s. (n = 20). Upper gastrointestinal mucosal injury was evaluated after 7 days of treatment with TN-EGD.

RESULTS

The rate of gastric ulcers in subjects receiving paracetamol (0/21, 0%) alone or aspirin (3/19, 16%) or both (2/20, 10%) was not different. There were, however, significantly more subjects with one or more lesions (erosion or ulcer) per subject in the paracetamol and aspirin (16/20, 80%) treated subjects as compared to the aspirin (8/19, 42%, P < 0.001) or the paracetamol (3/21, 14%, P < 0.01) exposed subjects. The mean number of lesions per subject was also greater (7.9 vs. 0.7, P < 0.01) in those treated with aspirin and paracetamol compared to paracetamol alone.

CONCLUSIONS

Co-administration of paracetamol and aspirin was not associated with a significant difference in endoscopic ulcer rates compared to either drug alone. There was a strong signal for increased endoscopic erosions and ulcers in the combined group compared to either aspirin or paracetamol alone.

Clinical review: fever in septic ICU patients--friend or foe?

In recent years, fever control in critically ill patients by medications and/or external cooling has gained widespread use, notably in patients suffering from neurological injuries. Nevertheless, such a strategy in septic patients is not supported by relevant data. Indeed, in response to sepsis, experimental and clinical studies argue that fever plays a key role in increasing the clearance of microorganisms, the immune response and the heat shock response. Moreover, fever is a cornerstone diagnostic sign in clinical practice, which aids in early and appropriate therapy, and allows physicians to follow the infection course. After discussing the physiological aspects of fever production, the present review aims to delineate the advantages and drawbacks of fever in septic patients. Finally, the treatment of fever by pharmacological and/or physical means is discussed with regards to their drawbacks, which argues for their careful use in septic patients in the absence of clinical relevance.

What do we (not) know about how paracetamol (acetaminophen) works?

WHAT IS KNOWN AND BACKGROUND

Although paracetamol (acetaminophen), N-(4-Hydroxyphenyl)acetamide, is one of the world's most widely used analgesics, the mechanism by which it produces its analgesic effect is largely unknown. This lack is relevant because: (i) optimal pain treatment matches the analgesic mechanism to the (patho)physiology of the pain and (ii) modern drug discovery relies on an appropriate screening assay.

OBJECTIVE

To review the clinical profile and preclinical studies of paracetamol as means of gaining insight into its mechanism of analgesic action.

METHODS

A literature search was conducted of clinical and preclinical literature and the information obtained was organized and reviewed from the perspective of its contribution to an understanding of the mechanism of analgesic action of paracetamol.

RESULTS

Paracetamol's broad spectrum of analgesic and other pharmacological actions is presented, along with its multiple postulated mechanism(s) of action. No one mechanism has been definitively shown to account for its analgesic activity.

WHAT IS NEW AND CONCLUSION

Further research is needed to uncover the mechanism of analgesic action of paracetamol. The lack of this knowledge affects optimal clinical use and impedes drug discovery efforts.

Prevention of pain on injection of propofol: a comparison of lidocaine with different doses of paracetamol

BACKGROUND AND OBJECTIVE

The aim of this study was to compare the efficacy of pretreatment with paracetamol 0.5 mg kg(-1), 1 mg kg(-1), 2 mg kg(-1) and lidocaine 0.5 mg kg(-1) for prevention of propofol induced pain.

METHODS

In this double-blind, placebo-controlled study, 250 adult patients ASA I or II, scheduled to undergo elective surgery, were randomly assigned into five groups of 50 each. Group P0.5, group P1 and group P2 received 0.5, 1 and 2 mg kg(-1) paracetamol respectively; group L received 0.5 mg kg(-1) lidocaine; and the control group, group C, received isotonic saline pretreatment in the dorsum of the hand, followed by propofol 1 min later. A blinded researcher assessed the patient's pain level via a four-point scale.

RESULTS

There were no significant differences in patient characteristics among the groups. The incidence of propofol injection pain in all treatment groups was significantly lower than in the control group (P < 0.001). When the paracetamol 0.5 mg kg(-1) group was compared with both the paracetamol 1 mg kg(-1) group (P < 0.01) and the paracetamol 2 mg kg(-1) group (P < 0.001), significant differences were observed. In the lidocaine 0.5 mg kg(-1) group propofol injection pain was significantly reduced compared with the paracetamol 0.5 mg kg(-1) group (P < 0.01). However, in the paracetamol 2 mg kg(-1) group pain was more significantly reduced than in the lidocaine 0.5 mg kg(-1) group (P < 0.001). In the paracetamol 2 mg kg(-1) group the incidence of pain was significantly less than in paracetamol 1 mg kg(-1) group (P < 0.001).

CONCLUSION

When given as venous retention pretreatments 1 min before propofol, paracetamol 1 mg kg(-1) and lidocaine 0.5 mg kg(-1) were equally effective in attenuating pain during intravenous (i.v.) injection of propofol whereas pretreatment with paracetamol 2 mg kg(-1) was shown to be the most effective treatment.

Using pharmacokinetic principles to optimize pain therapy

Cyclo-oxygenase (COX) inhibitors are widely used to relieve musculoskeletal pain. These agents block the production of prostaglandins (PGs) at sites of inflammation by inhibiting the activity of two COX enzymes necessary for PG production and normal organ homeostasis. Inhibition of PG production at sites unrelated to pain is associated with adverse drug reactions (ADRs). The degree of analgesic efficacy, as well as the incidence and the localization of ADRs, are critically influenced by the pharmacokinetics (absorption, distribution and elimination) of these drugs. Ideally, sufficient and permanent inhibition of COX enzymes should be achieved in target tissues, with minimal ADRs. To minimize underdosing or overdosing, which result in therapeutic failure or ADRs, the COX inhibitor with the most appropriate pharmacokinetic properties should be selected on the basis of a thorough pharmacokinetic-pharmacodynamic analysis. In this Review, the pharmacokinetics of the prevailing COX inhibitors will be discussed and enigmatic aspects of these intensively used drugs will be considered.

Peri-operative use of paracetamol

This article is a review of the peri-operative use of paracetamol. It reviews the pharmacology of paracetamol, highlighting new information about the mechanism of action, and examines its therapeutic use in the peri-operative period, focusing on efficacy, route of administration, and the use of a loading dose to improve early postoperative analgesia.

Point-of-care platelet function tests: detection of platelet inhibition induced by nonopioid analgesic drugs

Detection of platelet inhibition is of clinical relevance in the preinterventional risk-benefit assessment in chronic low-back-pain patients scheduled for invasive pain therapy. We evaluated the sensitivity of various point-of-care platelet function tests for the detection of platelet inhibition induced by nonopioid analgesic drugs. After Institutional Review Board approval and informed consent, citrated whole blood from 40 patients with chronic unspecific low back pain was investigated before and 30 min after intravenous infusion of the study medication consisting of diclofenac 75 mg (plus orphenadrin 30 mg; Neodolpasse; Fresenius Kabi Austria GmbH, Austria), parecoxib 40 mg (Dynastat; Pharmacia Europe EEIG, UK), paracetamol 1 g (Perfalgan; Bieffe Medital S.P.A., Italy), or normal saline in a randomized, cross-over, double-blinded, placebo-controlled study. Platelet function was assessed using the PFA-100 platelet function analyzer and thromboelastometry, as well as impedance aggregometry (in the last 17 patients recruited after it became commercially available). Sensitivity for detecting diclofenac-induced platelet inhibition was 85% for the PFA-100 using epinephrine as agonist and 94% for arachidonic acid-induced impedance aggregometry. ADP-induced platelet function tests, as well as cytochalasin D-modified thromboelastometry were unreliable. All tests had a low incidence of false-positive test results after normal saline. Paracetamol and parecoxib had no significant platelet inhibiting effect. The PFA-100 using epinephrine as agonist and arachidonic acid-induced impedance aggregometry are recommended for the detection of cyclooxygenase-I-inhibiting effects of nonsteroidal anti-inflammatory drugs such as diclofenac. Our findings confirm that a single rescue dose of paracetamol and parecoxib has no antiplatelet effect.

Effect of 3 g of intravenous paracetamol on post-operative analgesia, platelet function and liver enzymes in patients undergoing tonsillectomy under local anaesthesia

BACKGROUND

Paracetamol is often given as an adjunctive analgesic to reduce opioid-related adverse effects but its optimal dose is unknown. We studied the analgesic effect and safety of a single 3-g intravenous (i.v.) dose of paracetamol in adults.

METHODS

One hundred and seven patients undergoing tonsillectomy under local anaesthesia were randomly allocated to receive i.v. 3 g of paracetamol, 75 mg of diclofenac or placebo prior to surgery. The consumption of post-operative morphine using a patient-controlled analgesia-device was quantified for 6 h. Platelet aggregation and the concentrations of paracetamol, liver aminotransferases, glutathione transferase alpha 1-1 (GSTA1-1) and thromboxane B(2) were measured.

RESULTS

During the first hours after surgery, both paracetamol and diclofenac reduced (P < 0.05) the consumption of morphine but had no effect thereafter. The values for the 6-h cumulative consumption of morphine in patients given paracetamol (18.7 +/- 13.8 mg), diclofenac (16.1 +/- 9.9 mg) and placebo (22.0 +/- 12.1 mg) did not differ. Paracetamol had no effect on platelet aggregation, which was impaired only by diclofenac in response to arachidonic acid (P < 0.005). Both paracetamol (P < 0.01) and diclofenac (P < 0.005) inhibited the release of thromboxane B(2) at 1 h but they did not affect serum aminotransferase and GSTA1-1 levels. One patient given paracetamol displayed a transient increase in GSTA1-1 and liver aminotransferases.

CONCLUSION

During the initial hours after tonsillectomy, the administration of 3 g of i.v. paracetamol and 75 mg of diclofenac reduced the consumption of morphine. Both drugs also reduced the release of thromboxane B(2) from activated platelets but only diclofenac had a negative effect on platelet aggregation. In sensitive individuals, large doses of paracetamol may disturb the hepatocellular integrity. We do not recommend the use of i.v. doses of paracetamol higher than 1 g.

Intravenous paracetamol is highly effective in pain treatment after tonsillectomy in adults

Tonsillectomy in adults is associated with significant postoperative pain. Intravenous paracetamol injection (Perfalgan) is marketed for the management of acute pain. This prospective placebo-controlled study was performed to evaluate the analgesic efficacy and safety of intravenous paracetamol in 76 adult patients undergoing elective standard bipolar diathermy tonsillectomy. After tonsillectomy was performed under general anesthesia, the patients were randomized to receive either intravenous paracetamol 1 g (Perfalgan) (n = 38) or 0.9% normal saline as a placebo (n = 38) at 6-h intervals. No other analgesic medication was permitted for postoperative pain during the study. Need for rescue analgesic during the first 24 h after surgery as well as all adverse events were recorded. The intravenous paracetamol group differed significantly from the placebo group regarding pain relief and median time to pethidine rescue. Intravenous paracetamol significantly reduced pethidine consumption over the 24-h period. The worst pain after surgery was also more severe in the placebo group than that in the paracetamol group. There was no significant difference between groups in the incidence of adverse events. Intravenous paracetamol administered regularly in adult patients with moderate to severe pain after tonsillectomy provided rapid and effective analgesia and was well tolerated.

Pain treatment and recovery after endoscopic sinus surgery

OBJECTIVES/HYPOTHESIS

Early recovery and pain management after endoscopic sinus surgery (ESS) are largely unexplored regardless of the large number of ESSs performed by otorhinolaryngologists. In the present study, we evaluated whether scheduled administration of acetaminophen (paracetamol) for pain management after ESS would allow faster recovery to normal daily activities compared with acetaminophen administered on an as needed basis.

STUDY DESIGN

Open, prospective, randomized, controlled clinical trial with two parallel groups.

METHODS

There were 78 patients who were undergoing ESS and were randomized into two groups. The "scheduled" group (n = 38) was instructed to take two acetaminophen 665 mg modified-release tablets three times a day during the first five postoperative days, whereas the "as needed" group (n = 40) was given instructions to use acetaminophen 665 mg tablets only on an as needed basis. Patients filled in a questionnaire at the follow-up visits on the 7th and 30th postoperative days. The main outcome measures were return to normal daily activities (primary endpoint) and pain during the first week after surgery and patients' satisfaction with pain management (secondary endpoints).

RESULTS

Patients returned to their normal daily activities in 8.8 (SD 4.8) days in the "scheduled" group versus in 10.3 (SD 7.0) days in the "as needed" group (mean difference 1.5; 95% CI of the difference -1.3 to 4.2; P = .29). In the "scheduled" group, the mean of worst pain was 3.4 (2.9) compared with 5.2 (3.0) in the "as needed" group on an 11-point scale (mean difference 1.7; 95% CI of the difference 0.4-5.2; P = .019). The patients in both groups were equally satisfied with pain management.

CONCLUSIONS

The present study suggests that patients recover in 9 to 10 days after ESS when provided with appropriate pain management. Our data indicate that by prescribing scheduled acetaminophen, postoperative pain after ESS can be controlled effectively without the need for opioid analgesics.

Acetaminophen (paracetamol) is a selective cyclooxygenase-2 inhibitor in man

For more than three decades, acetaminophen (INN, paracetamol) has been claimed to be devoid of significant inhibition of peripheral prostanoids. Meanwhile, attempts to explain its action by inhibition of a central cyclooxygenase (COX)-3 have been rejected. The fact that acetaminophen acts functionally as a selective COX-2 inhibitor led us to investigate the hypothesis of whether it works via preferential COX-2 blockade. Ex vivo COX inhibition and pharmacokinetics of acetaminophen were assessed in 5 volunteers receiving single 1000 mg doses orally. Coagulation-induced thromboxane B(2) and lipopolysaccharide-induced prostaglandin E(2) were measured ex vivo and in vitro in human whole blood as indices of COX-1 and COX-2 activity. In vitro, acetaminophen elicited a 4.4-fold selectivity toward COX-2 inhibition (IC(50)=113.7 micromol/L for COX-1; IC(50)=25.8 micromol/L for COX-2). Following oral administration of the drug, maximal ex vivo inhibitions were 56% (COX-1) and 83% (COX-2). Acetaminophen plasma concentrations remained above the in vitro IC(50) for COX-2 for at least 5 h postadministration. Ex vivo IC(50) values (COX-1: 105.2 micromol/L; COX-2: 26.3 micromol/L) of acetaminophen compared favorably with its in vitro IC(50) values. In contrast to previous concepts, acetaminophen inhibited COX-2 by more than 80%, i.e., to a degree comparable to nonsteroidal antiinflammatory drugs (NSAIDs) and selective COX-2 inhibitors. However, a >95% COX-1 blockade relevant for suppression of platelet function was not achieved. Our data may explain acetaminophen's analgesic and antiinflammatory action as well as its superior overall gastrointestinal safety profile compared with NSAIDs. In view of its substantial COX-2 inhibition, recently defined cardiovascular warnings for use of COX-2 inhibitors should also be considered for acetaminophen.

Acetaminophen, phenacetin and dipyrone do not modulate pressor responses to arachidonic Acid or to pressor agents

In contrast to nonsteroidal anti-inflammatory drugs (NSAIDs), the nonopioid analgesics phenacetin, acetaminophen and dipyrone exhibit weak anti-inflammatory properties. An explanation for this difference in pharmacologic activity was provided by the recent discovery of a new cyclooxygenase isoform, cyclooxygenase (COX)-3, that is reported to be inhibited by phenacetin, acetaminophen and dipyrone. However, COX-3 was found to be a spliced variant of COX-1 and renamed COX-1b. Although recent studies provide evidence for the existence of this new COX isoform, it is uncertain whether this COX-3 (COX-1b) isoform, or putative acetaminophen-sensitive pathway, plays a role in the generation of vasoactive prostaglandins. NSAIDs increase systemic blood pressure by inhibiting the formation of vasodilator prostanoids. Angiotensin II, norepinephrine and other vasoconstrictor agents have been reported to release prostaglandins. It is possible that this acetaminophen-sensitive pathway also modulates pressor responses to these vasoconstrictor agents. Therefore, the purpose of the present study was to determine whether this acetaminophen-sensitive pathway plays a role in the generation of vasoactive products of arachidonic acid or in the modulation of vasoconstrictor responses in the pulmonary and systemic vascular bed of the intact-chest rat. In the present study, the nonopioid analgesics did not attenuate changes in pulmonary or systemic arterial pressure in response to injections of the prostanoid precursor, arachidonic acid, to the thromboxane A(2) mimic, U46619, or to angiotensin II or norepinephrine. The results of the present study do not provide evidence in support of a role of a functional COX-3 (COX-1b) isoform, or an acetaminophen-sensitive pathway, in the generation of vasoactive prostanoids or in the modulation of responses to vasoconstrictor hormones in the intact-chest rat.

Update on the role of non-opioids for postoperative pain treatment

Non-opioids play an ever increasing role in the treatment of postoperative pain; either on their own for mild to moderate pain or in combination with other analgesic approaches, in particular opioids, as a component of multimodal analgesia. The analgesics paracetamol (acetaminophen) and dipyrone (metamizole) as well as compounds with an additional anti-inflammatory effect (non-selective non-steroidal anti-inflammatory drugs and selective cyclo-oxygenase-2 inhibitors) are used widely in the perioperative period. Paracetamol is gaining renewed interest in this setting due to its minimal adverse effects and recent availability in a parenteral preparation, but its benefits are insufficiently studied. Dipyrone continues to be used in many countries despite the ongoing debate on the incidence and relevance of its ability to cause agranulocytosis. Among the anti-inflammatory drugs, selective cyclo-oxygenase-2 inhibitors have the most supportive data for their beneficial effects as a component of multimodal analgesia and offer benefits with regard to their adverse effect profile.

Acetaminophen is Highly Effective in Pain Treatment After Endoscopic Sinus Surgery

OBJECTIVES/HYPOTHESIS

Endoscopic sinus surgery (ESS) is increasingly performed by otorhinolaryngologists. However, the early recovery and pain management after ESS is still largely unexplored. In the present study, we have evaluated the incidence and severity of pain and the efficacy and safety of acetaminophen (paracetamol) for pain management in patients undergoing ESS.

STUDY DESIGN

The authors conducted a prospective, double-blind, placebo-controlled clinical trial.

METHODS

Seventy-four patients with ESS were randomized to receive either 1 g intravenous acetaminophen (Perfalgan) (n = 36) or 0.9% normal saline as a placebo (n = 38) after ESS was performed under local anesthesia. No other analgesic medication was permitted during the study. Need for rescue analgesic during the first 4 hours after surgery as well as all adverse events were recorded.

RESULTS

Most patients, 27 of 38 (71%), in the placebo group needed rescue analgesics but significantly fewer patients in the acetaminophen group required rescue analgesia, i.e., only nine of 36 (25%) patients needed oxycodone. The worst pain after surgery was also more severe in the placebo group than that in the acetaminophen group. There was no significant difference between groups in the incidence of adverse events. The most common adverse events were vomiting, nausea, and headache.

CONCLUSIONS

ESS is associated with significant postoperative pain. Acetaminophen provides adequate pain relief in most patients who have undergone ESS. However, the analgesic efficacy of acetaminophen alone is insufficient in some patients, and hence all patients with ESS must be followed closely to identify those patients in need of more efficient analgesia during the early phase of recovery.

State of the art of paracetamol in acute pain therapy

PURPOSE OF REVIEW

This review highlights new insights into the mechanism of action of paracetamol (acetaminophen) and therapeutic schemes.

RECENT FINDINGS

Paracetamol, a centrally acting inhibitor of cyclooxygenases, has weak peripheral effects recently demonstrated. Paracetamol is nevertheless devoid of side effects commonly observed with the use of nonsteroidal anti-inflammatory drugs. Paracetamol is available by the oral, rectal, and, more recently, intravenous routes of administration. Paracetamol efficacy is surgical procedure dependent. The analgesic efficacy of a 2-g starting dose of intravenous paracetamol is superior to the recommended dose of 1 g in terms of magnitude and duration of analgesic effect. The usual scheme of administration (1 g every 6 hours) has a less than 10-mg sparing effect on 24-hour morphine consumption and consequently does not significantly reduce morphine side effects. The combination of nonsteroidal anti-inflammatory drugs and paracetamol is more effective than paracetamol alone, but the benefit is unclear when compared with nonsteroidal anti-inflammatory drugs used alone.

SUMMARY

Further studies are required to assess the opioid-sparing effect and complementary analgesic effect of new intravenous paracetamol therapeutic schemes.

Influence on platelet aggregation of i.v. parecoxib and acetaminophen in healthy volunteers

BACKGROUND

Acetaminophen (paracetamol) alone or in combination with other analgesics is widely used for postoperative analgesia. While acetaminophen and non-steroidal anti-inflammatory drugs inhibit platelet function, the cyclooxygenase-2 (COX-2) selectively inhibiting coxibs show no interference with platelet function. The authors studied the effect of a combination of i.v. parecoxib and acetaminophen on platelet function in healthy volunteers.

METHODS

Eighteen healthy, male volunteers (22-33 yr) received i.v. acetaminophen 1 g, parecoxib 40 mg+acetaminophen 1 g or placebo in a double-blind, crossover study. Platelet function was assessed by photometric aggregometry and by measuring the release of thromboxane B(2). Plasma acetaminophen concentrations were measured by high-performance liquid chromatography.

RESULTS

Platelet aggregation (median area under the curve) triggered with arachidonic acid 500 microM was 24.6, 3.9 and 4.2x10(3) area units (P=0.02, all groups) after placebo, acetaminophen and parecoxib+acetaminophen, respectively. Inhibition of platelet aggregation showed no difference between acetaminophen alone and the combination (P=0.82). Aggregation triggered with arachidonic acid 750 or 1000 microM, adenosine diphosphate (ADP) 1.5 or 3 microM, or epinephrine 5 microM showed no differences between the groups. Release of thromboxane B(2) in response to ADP was inhibited similarly by both acetaminophen and the combination. Plasma acetaminophen concentrations were similar after acetaminophen and the combination.

CONCLUSIONS

Acetaminophen and parecoxib showed no interaction in inhibiting platelet function. In combination they cause a mild degree of COX-1 inhibition corresponding to that of acetaminophen alone.