Analgesic effect of i.v. paracetamol: possible ceiling effect of paracetamol in postoperative pain

Efficacy and safety of intravenous acetaminophen (2 g/day) for reducing opioid consumption in Chinese adults after elective orthopedic surgery: A multicenter randomized controlled trial

Background: Acetaminophen is an important component of a multimodal analgesia strategy to reduce opioid consumption and pain intensity after an orthopedic surgery. The opioid-sparing efficacy of intravenous acetaminophen has been established at a daily dose of 4 g. However, it is still unclear for the daily dose of 2 g of acetaminophen, which is recommended by the China Food and Drug Administration Center for Drug Evaluation, in terms of its efficacy and safety.

Objectives: This study aimed to evaluate the efficacy and safety of intravenous acetaminophen at a daily dose of 2 g for reducing opioid consumption and pain intensity after orthopedic surgery.

Methods: In this multicenter, randomized, double-blind, placebo-controlled phase III trial, 235 patients who underwent orthopedic surgery were randomly assigned to receive intravenous acetaminophen 500 mg every 6 h or placebo. Postoperative morphine consumption, pain intensity at rest and during movement, and adverse events were analysed.

Results: For the mean (standard deviation) morphine consumption within 24 h after surgery, intravenous acetaminophen was superior to placebo both in the modified intention-to-treat analysis [8.7 (7.7) mg vs. 11.2 (9.2) mg] in the acetaminophen group and the placebo group, respectively. Difference in means: 2.5 mg; 95% confidence interval, 0.25 to 4.61; p = 0.030), and in the per-protocol analysis (8.3 (7.0) mg and 11.7 (9.9) mg in the acetaminophen group and the placebo group, respectively. Difference in means: 3.4 mg; 95% confidence interval: 1.05 to 5.77; p = 0.005). The two groups did not differ significantly in terms of pain intensity and adverse events.

Conclusion: Our results suggest that intravenous acetaminophen at a daily dose of 2 g can reduce morphine consumption by Chinese adults within the first 24 h after orthopedic surgery, but the extent of reduction is not clinically relevant.

Clinical Trial Registration: [ClinicalTrials.gov], identifier [NCT02811991].

Systematic Review of Systemic and Neuraxial Effects of Acetaminophen in Preclinical Models of Nociceptive Processing

Acetaminophen (APAP) in humans has robust effects with a high therapeutic index in altering postoperative and inflammatory pain states in clinical and experimental pain paradigms with no known abuse potential. This review considers the literature reflecting the preclinical actions of acetaminophen in a variety of pain models. Significant observations arising from this review are as follows: 1) acetaminophen has little effect upon acute nociceptive thresholds; 2) acetaminophen robustly reduces facilitated states as generated by mechanical and thermal hyperalgesic end points in mouse and rat models of carrageenan and complete Freund’s adjuvant evoked inflammation; 3) an antihyperalgesic effect is observed in models of facilitated processing with minimal inflammation (eg, phase II intraplantar formalin); and 4) potent anti-hyperpathic effects on the thermal hyperalgesia, mechanical and cold allodynia, allodynic thresholds in rat and mouse models of polyneuropathy and mononeuropathies and bone cancer pain. These results reflect a surprisingly robust drug effect upon a variety of facilitated states that clearly translate into a wide range of efficacy in preclinical models and to important end points in human therapy. The specific systems upon which acetaminophen may act based on targeted delivery suggest both a spinal and a supraspinal action. Review of current targets for this molecule excludes a role of cyclooxygenase inhibitor but includes effects that may be mediated through metabolites acting on the TRPV1 channel, or by effect upon cannabinoid and serotonin signaling. These findings suggest that the mode of action of acetaminophen, a drug with a long therapeutic history of utilization, has surprisingly robust effects on a variety of pain states in clinical patients and in preclinical models with a good therapeutic index, but in spite of its extensive use, its mechanisms of action are yet poorly understood.

The relationship between postoperative opioid consumption and the incidence of hypoxemic events following total hip arthroplasty: a post hoc analysis

Background

Postoperative opioid analgesia may cause respiratory depression. We assessed whether following total hip arthroplasty, placebo-adjusted reductions in morphine consumption at 48 hours with parecoxib (47.0%), propacetamol (35.1%) or parecoxib plus propacetamol (67.9%) translated into a reduction in hypoxemic events.

Methods

This was a post hoc analysis of a randomized, placebo-controlled, noninferiority study. Patients were randomly assigned to receive intravenous parecoxib (40 mg twice daily), propacetamol (2 g 4 times daily), parecoxib plus propacetamol (40 mg twice daily + 2 g 4 times daily) or placebo. Dose, date and time of morphine administration via patient-controlled analgesia were monitored throughout the study. In patients not receiving supplemental oxygen, peripheral blood oxygenation was assessed continuously for 48 hours after surgery. Hypoxemia was defined as peripheral oxygen saturation less than 90%. The times and oximeter readings of hypoxemic events were recorded. Pearson correlation coefficient was used to assess for correlations between cumulative morphine consumption at 48 hours and mean number of hypoxemic events.

Results

A significantly smaller proportion of patients who received the combined treatment with parecoxib and propacetamol had hypoxemia versus placebo (2.8% v. 13.2%, p < 0.05), and the mean number of hypoxemic events was significantly smaller for parecoxib (0.12), propacetamol (0.06) and parecoxib plus propacetamol (0.03) versus placebo (0.36; all p < 0.05). There was no correlation between the reduction in cumulative morphine consumption at 48 hours and the mean number of hypoxemic events in any treatment group (all p > 0.1).

Conclusion

Following total hip arthroplasty, a greater than 70% reduction in morphine consumption may be necessary to translate into a corresponding reduction in hypoxemic events.

Evidence review conducted for the AHRQ Safety Program for Improving Surgical Care and Recovery: focus on anesthesiology for gynecologic surgery

Enhanced recovery after surgery (ERAS) protocols for gynecologic (GYN) surgery are increasingly being reported and may be associated with superior outcomes, reduced length of hospital stay, and cost savings. The Agency for Healthcare Research and Quality, in partnership with the American College of Surgeons and the Johns Hopkins Medicine Armstrong Institute for Patient Safety and Quality, has developed the Safety Program for Improving Surgical Care and Recovery, which is a nationwide initiative to disseminate best practices in perioperative care to more than 750 hospitals across five major surgical service lines in a 5-year period. The program is designed to identify evidence-based process measures shown to prevent healthcare-associated conditions and hasten recovery after surgery, integrate those into a comprehensive service line-based pathway, and assist hospitals in program implementation. In conjunction with this effort, we have conducted an evidence review of the various anesthesia components which may influence outcomes and facilitate recovery after GYN surgery. A literature search was performed for each intervention, and the highest levels of available evidence were considered. Anesthesiology-related interventions for preoperative (carbohydrate loading/fasting, multimodal preanesthetic medications), intraoperative (standardized intraoperative pathway, regional anesthesia, protective ventilation strategies, fluid minimization) and postoperative (multimodal analgesia) phases of care are included. We have summarized the best available evidence to recommend the anesthetic components of care for ERAS for GYN surgery.

Effect of Capsaicin and Other Thermo-TRP Agonists on Thermoregulatory Processes in the American Cockroach

Capsaicin is known to activate heat receptor TRPV1 and induce changes in thermoregulatory processes of mammals. However, the mechanism by which capsaicin induces thermoregulatory responses in invertebrates is unknown. Insect thermoreceptors belong to the TRP receptors family, and are known to be activated not only by temperature, but also by other stimuli. In the following study, we evaluated the effects of different ligands that have been shown to activate (allyl isothiocyanate) or inhibit (camphor) heat receptors, as well as, activate (camphor) or inhibit (menthol and thymol) cold receptors in insects. Moreover, we decided to determine the effect of agonist (capsaicin) and antagonist (capsazepine) of mammalian heat receptor on the American cockroach's thermoregulatory processes. We observed that capsaicin induced the decrease of the head temperature of immobilized cockroaches. Moreover, the examined ligands induced preference for colder environments, when insects were allowed to choose the ambient temperature. Camphor exposure resulted in a preference for warm environments, but the changes in body temperature were not observed. The results suggest that capsaicin acts on the heat receptor in cockroaches and that TRP receptors are involved in cockroaches' thermosensation.

Patient-controlled Analgesia With Propacetamol-Fentanyl Mixture for Prevention of Postoperative Nausea and Vomiting in High-risk Patients Undergoing Spine Surgery: A Randomized Controlled Trial

BACKGROUND

This randomized trial evaluated the effect of intravenous patient-controlled analgesia (IV-PCA) based on fentanyl mixed with either propacetamol or an equivalent volume of normal saline on postoperative nausea and vomiting (PONV) in highly susceptible patients undergoing spinal surgery.

MATERIALS AND METHODS

One hundred eight nonsmoking female patients were randomly and evenly allocated to receive IV-PCA with either propacetamol (4 g) or normal saline mixed to fentanyl (20 μg/kg). Primary study outcome was PONV incidence at 24 hours postsurgery. Secondary outcomes were nausea severity, pain intensity (100-mm visual analog scale), use of rescue antiemetics and analgesics, patient satisfaction, and adverse events at 6, 12, and 24 hours postsurgery.

RESULTS

Postsurgery, the propacetamol versus normal saline group had lower PONV incidence at 24 hours (41% vs. 66%, P=0.011); pain intensity at rest and rescue analgesic requirements at 6 to 12 hours (30±15 vs. 41±19, P=0.008; and 25% vs. 49%, P=0.036, respectively) and at 12 to 24 hours (25±15 vs. 35±17, P=0.008; and 19% vs. 42%, P=0.044, respectively); and higher patient satisfaction score (6.4±1.4 vs. 5.7±1.8, P=0.028).

CONCLUSIONS

In patients undergoing spinal surgery and at risk of developing PONV, continuous IV-PCA based on propacetamol mixed to fentanyl, relative to fentanyl alone, effectively reduced the incidence of PONV, pain intensity at rest, and additional use of rescue analgesics with higher patient satisfaction.

Pharmacokinetic Study of Intravenous Acetaminophen Administered to Critically Ill Multiple-Trauma Patients at the Usual Dosage and a New Proposal for Administration

The pharmacokinetic profile of intravenous acetaminophen administered to critically ill multiple-trauma patients was studied after 4 consecutive doses of 1 g every 6 hours. Eleven blood samples were taken (predose and 15, 30, 45, 60, 90, 120, 180, 240, 300, and 360 minutes postdose), and urine was collected (during 6-hour intervals between doses) to determine serum and urine acetaminophen concentrations. These were used to calculate the following pharmacokinetic parameters: maximum and minimum concentrations, terminal half-life, area under serum concentration-time curve from 0 to 6 hours, mean residence time, volume of distribution, and serum and renal clearance of acetaminophen. Daily doses of acetaminophen required to obtain steady-state minimum (bolus dosing) and average plasma concentrations (continuous infusion) of 10 μg/mL were calculated (10 μg/mL is the presumed lower limit of the analgesic range). Data are expressed as median [interquartile range]. Twenty-two patients were studied, mostly young (age 44 [34-64] years) males (68%), not obese (weight 78 [70-84] kg). Acetaminophen concentrations and pharmacokinetic parameters were these: maximum concentration 33.6 [25.7-38.7] μg/mL and minimum concentration 0.5 [0.2-2.3] μg/mL, all values below 10 μg/mL and 8 below the detection limit; half-life 1.2 [1.0-1.9] hours; area under the curve for 6 hours 34.7 [29.7-52.7] μg·h/mL; mean residence time 1.8 [1.3-2.6] hours; steady-state volume of distribution 50.8 [42.5-66.5] L; and serum and renal clearance 28.8 [18.9-33.7] L/h and 15 [11-19] mL/min, respectively. Theoretically, daily doses for a steady-state minimum concentration of 10 μg/mL would be 12.2 [7.8-16.4] g/day (166 [112-202] mg/[kg·day]); for an average steady-state concentration of 10 μg/mL, they would be 6.9 [4.5-8.1] g/day (91 [59-111] mg/[kg·day]). In conclusion, administration of acetaminophen at the recommended dosage of 1 g per 6 hours to critically ill multiple-trauma patients yields serum concentrations below 10 μg/mL due to increased elimination. To reach the 10 μg/mL target, and from a strictly pharmacokinetic point of view, continuous infusion may be more feasible than bolus dosing. Such a change in dosing strategy requires appropriate, pharmacokinetic-pharmacodynamic and specific safety study.

Laparoscopic surgery: a narrative review of pharmacotherapy in pain management

Laparoscopic surgery is widespread, and an increasing number of surgeries are performed laparoscopically. Early pain after laparoscopy can be similar or even more severe than that after open surgery. Thus, proactive pain management should be provided. Pain after laparoscopic surgery is derived from multiple origins; therefore, a single agent is seldom sufficient. Pain is most effectively controlled by a multimodal, preventive analgesia approach, such as combining opioids with non-opioid analgesics and local anaesthetics. Wound and port site local anaesthetic injections decrease abdominal wall pain by 1-1.5 units on a 0-10 pain scale. Inflammatory pain and shoulder pain can be controlled by NSAIDs or corticosteroids. In some patient groups, adjuvant drugs, ketamine and α2-adrenergic agonists can be helpful, but evidence on gabapentinoids is conflicting. In the present review, the types of pain that need to be taken into account while planning pain management protocols and the wide range of analgesic options that have been assessed in laparoscopic surgery are critically assessed. Recommendations to the clinician will be made regarding how to manage acute pain and how to prevent persistent postoperative pain. It is important to identify patients at the highest risk for severe and prolonged post-operative pain, and to have a proactive strategy in place for these individuals.

Single dose intravenous paracetamol or intravenous propacetamol for postoperative pain

BACKGROUND

This is an updated version of the original Cochrane review published in Issue 10, 2011. Paracetamol (acetaminophen) is the most commonly prescribed analgesic for the treatment of acute pain. It may be administered orally, rectally, or intravenously. The efficacy and safety of intravenous (IV) formulations of paracetamol, IV paracetamol, and IV propacetamol (a prodrug that is metabolized to paracetamol), compared with placebo and other analgesics, is unclear.

OBJECTIVES

To assess the efficacy and safety of IV formulations of paracetamol for the treatment of postoperative pain in both adults and children.

SEARCH METHODS

We ran the search for the previous review in May 2010. For this update, we searched the Cochrane Central Register of Controlled Trials (CENTRAL 2016, Issue 1), MEDLINE (May 2010 to 16 February 2016), EMBASE (May 2010 to 16 February 2016), LILACS (2010 to 2016), a clinical trials registry, and reference lists of reviews for randomized controlled trials (RCTs) in any language and we retrieved articles.

SELECTION CRITERIA

Randomized, double-blind, placebo- or active-controlled single dose clinical trials of IV paracetamol or IV propacetamol for acute postoperative pain in adults or children.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data, which included demographic variables, type of surgery, interventions, efficacy, and adverse events. We contacted study authors for additional information. We graded each included study for methodological quality by assessing risk of bias and employed the GRADE approach to assess the overall quality of the evidence.

MAIN RESULTS

We included 75 studies (36 from the original review and 39 from our updated review) enrolling a total of 7200 participants.Among primary outcomes, 36% of participants receiving IV paracetamol/propacetamol experienced at least 50% pain relief over four hours compared with 16% of those receiving placebo (number needed to treat to benefit (NNT) = 5; 95% confidence interval (CI) 3.7 to 5.6, high quality evidence). The proportion of participants in IV paracetamol/propacetamol groups experiencing at least 50% pain relief diminished over six hours, as reflected in a higher NNT of 6 (4.6 to 7.1, moderate quality evidence). Mean pain intensity at four hours was similar when comparing IV paracetamol and placebo, but was seven points lower on a 0 to 100 visual analog scale (0 = no pain, 100 = worst pain imaginable, 95% CI -9 to -6, low quality evidence) in those receiving paracetamol at six hours.For secondary outcomes, participants receiving IV paracetamol/propacetamol required 26% less opioid over four hours and 16% less over six hours (moderate quality evidence) than those receiving placebo. However, this did not translate to a clinically meaningful reduction in opioid-induced adverse events.Meta-analysis of efficacy comparisons between IV paracetamol/propacetamol and active comparators (e.g., opioids or nonsteroidal anti-inflammatory drugs) were either not statistically significant, not clinically significant, or both.Adverse events occurred at similar rates with IV paracetamol or IV propacetamol and placebo. However, pain on infusion occurred more frequently in those receiving IV propacetamol versus placebo (23% versus 1%). Meta-analysis did not demonstrate clinically meaningful differences between IV paracetamol/propacetamol and active comparators for any adverse event.

AUTHORS' CONCLUSIONS

Since the last version of this review, we have found 39 new studies providing additional information. Most included studies evaluated adults only. We reanalyzed the data but the results did not substantially alter any of our previously published conclusions. This review provides high quality evidence that a single dose of either IV paracetamol or IV propacetamol provides around four hours of effective analgesia for about 36% of patients with acute postoperative pain. Low to very low quality evidence demonstrates that both formulations are associated with few adverse events, although patients receiving IV propacetamol have a higher incidence of pain on infusion than both placebo and IV paracetamol.

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.

Single-dose systemic acetaminophen to prevent postoperative pain: a meta-analysis of randomized controlled trials

OBJECTIVES

The effect of a single-dose systemic acetaminophen to treat postoperative pain has been previously quantified, but the effect of systemic acetaminophen to prevent postoperative pain is currently not well defined. The preventive analgesic effect of acetaminophen has yet to be quantified in a meta-analysis. The objective of the current investigation was to evaluate the effect of a single preventive dose of systemic acetaminophen on postoperative pain outcomes.

MATERIALS AND METHODS

A wide search was performed to identify randomized controlled trials that evaluated the effects of a single dose of systemic acetaminophen on pain outcomes in a large variety of surgical procedures. Meta-analysis was performed using a random-effect model.

RESULTS

Eleven randomized clinical trials evaluating 740 patients were included in the analysis. The weighted mean difference (95% confidence interval [CI]) of the combined effects favored acetaminophen over control for early pain at rest (≤4 h, -1.1 (-2.0 to -0.2)) and early pain at movement (24 h, -1.9 (-2.8 to -1.0)) Postoperative opioid consumption was decreased in the systemic acetaminophen group compared with control. Weighted mean difference (95% CI) of -9.7 (-13.0 to -6.4) mg morphine intravenous equivalents systemic acetaminophen also reduced postoperative nausea and vomiting compared with control, odds ratio (95% CI) of 0.25 (0.13 to 0.47), numbers needed to treat (95% CI)=3.3 (2.3 to 5.9).

DISCUSSION

Systemic acetaminophen, when used as a single-dose preventive regimen, is an effective intervention to reduce postoperative pain. It also reduces postoperative nausea and/or vomiting. Doses >1 g were not associated with greater reduction in pain outcomes.

The opioid rotation ratio of hydrocodone to strong opioids in cancer patients

PURPOSE

Cancer pain management guidelines recommend initial treatment with intermediate-strength analgesics such as hydrocodone and subsequent escalation to stronger opioids such as morphine. There are no published studies on the process of opioid rotation (OR) from hydrocodone to strong opioids in cancer patients. Our aim was to determine the opioid rotation ratio (ORR) of hydrocodone to morphine equivalent daily dose (MEDD) in cancer outpatients.

PATIENTS AND METHODS

We reviewed the records of consecutive patient visits at our supportive care center in 2011-2012 for OR from hydrocodone to stronger opioids. Data regarding demographics, Edmonton Symptom Assessment Scale (ESAS), and MEDD were collected from patients who returned for follow-up within 6 weeks. Linear regression analysis was used to estimate the ORR between hydrocodone and MEDD. Successful OR was defined as 2-point or 30% reduction in the pain score and continuation of the new opioid at follow-up.

RESULTS

Overall, 170 patients underwent OR from hydrocodone to stronger opioid. The median age was 59 years, and 81% had advanced cancer. The median time between OR and follow-up was 21 days. We found 53% had a successful OR with significant improvement in the ESAS pain and symptom distress scores. In 100 patients with complete OR and no worsening of pain at follow-up, the median ORR from hydrocodone to MEDD was 1.5 (quintiles 1-3: 0.9-2). The ORR was associated with hydrocodone dose (r = -.52; p < .0001) and was lower in patients receiving ≥40 mg of hydrocodone per day (p < .0001). The median ORR of hydrocodone to morphine was 1.5 (n = 44) and hydrocodone to oxycodone was 0.9 (n = 24).

CONCLUSION

The median ORR from hydrocodone to MEDD was 1.5 and varied according to hydrocodone dose.

Pediatric ambulatory anesthesia

Pediatric patients often undergo anesthesia for ambulatory procedures. This article discusses several common preoperative dilemmas, including whether to postpone anesthesia when a child has an upper respiratory infection, whether to test young women for pregnancy, which children require overnight admission for apnea monitoring, and the effectiveness of nonpharmacological techniques for reducing anxiety. Medication issues covered include the risks of anesthetic agents in children with undiagnosed weakness, the use of remifentanil for tracheal intubation, and perioperative dosing of rectal acetaminophen. The relative merits of caudal and dorsal penile nerve block for pain after circumcision are also discussed.

Pharmacokinetics of paracetamol and its metabolites in women at delivery and post-partum

AIM

A recent report on intravenous (i.v.) paracetamol pharmacokinetics (PK) showed a higher total clearance in women at delivery compared with non-pregnant women. To describe the paracetamol metabolic and elimination routes involved in this increase in clearance, we performed a population PK analysis in women at delivery and post-partum in which the different pathways were considered.

METHODS

Population PK parameters using non-linear mixed effect modelling were estimated in a two-period PK study in women to whom i.v. paracetamol (2 g loading dose followed by 1 g every 6 h up to 24 h) was administered immediately following Caesarean delivery and in a subgroup of the same women to whom single 2 g i.v.loading dose was administered 10-15 weeks post-partum.

RESULTS

Population PK analysis was performed based on 255 plasma and 71 urine samples collected in 39 women at delivery and in eight of these 39 women 12 weeks post-partum. Total clearance was higher in women at delivery compared with 12th post-partum week (21.1 vs. 11.7 l h⁻¹) due to higher clearances to paracetamol glucuronide (11.6 vs. 4.76 l h⁻¹), to oxidative metabolites (4.95 vs. 2.77 l h⁻¹) and of unchanged paracetamol (1.15 vs. 0.75 l h⁻¹). In contrast, there was no difference in clearance to paracetamol sulphate.

CONCLUSION

The increased total paracetamol clearance at delivery is caused by a disproportional increase in glucuronidation clearance and a proportional increase in clearance of unchanged paracetamol and in oxidation clearance, of which the latter may potentially limit further dose increase in this patient group.

The pharmacokinetic profile of intravenous paracetamol in adult patients undergoing major abdominal surgery

BACKGROUND

Intravenous (IV) paracetamol is commonly used in the postoperative period for the treatment of mild to moderate pain. The main pathways for paracetamol metabolism are glucuronidation, sulfation, and oxidation, accounting for approximately 55%, 30%, and 10% of urinary metabolites, respectively. The aim of this study was to describe the pharmacokinetics of IV paracetamol and its metabolites in adult patients after major abdominal surgery.

METHODS

Twenty patients were given 1 g of paracetamol by IV infusion at induction of anesthesia (Interval 1) and every 6 hours thereafter, with the final dose given at 48-72 hours (Interval 2). Plasma and urine samples were collected for up to 8 hours after infusion for both intervals. The samples were analyzed by high-performance liquid chromatography to determine the amount of paracetamol and its metabolites. The data were modeled in Phoenix WinNonlin using a user-defined ASCII parent-metabolite model with linear disposition, to obtain the estimates for volume of distribution, metabolic and urinary clearance.

RESULTS

Mean (95% confidence interval) metabolic clearance to paracetamol glucuronide increased from 0.06 (0.05-0.08) to 0.14 (0.11-0.18) L · h⁻¹ · kg⁻¹, P value <0.001 and urinary clearance increased from 0.08 (0.07-0.09) to 0.14 (0.10-0.17) L · h⁻¹ · kg⁻¹, P value 0.002. The mean (95% confidence interval) volume of distribution of paracetamol increased from 0.17 (0.12-0.21) to 0.43 (0.27-0.59) L · kg⁻¹, P value 0.032.

CONCLUSIONS

After major abdominal surgery, there were apparent increases in the metabolic conversion to paracetamol glucuronide and its urinary clearance suggesting potential induction of paracetamol glucuronidation.

Postoperative plasma paracetamol levels following oral or intravenous paracetamol administration: a double-blind randomised controlled trial

In day-case surgery paracetamol is commonly given orally preoperatively, or intravenously intraoperatively. In this double-blind randomised controlled trial we investigated which of these methods of administration achieved therapeutic plasma levels most effectively in the early postoperative period. Thirty patients undergoing day case arthroscopy of the knee were randomised to receive either 1.0 g oral paracetamol 30 to 60 minutes preoperatively (20 patients) or 1.0 g intravenous paracetamol intraoperatively (10 patients). Plasma paracetamol levels were measured 30 minutes after arrival in the recovery room. Secondary outcomes included postoperative pain scores, rescue analgesia requirements and duration of stay in the recovery room. All patients receiving the intravenous preparation had plasma levels above the analgesic level compared to less than half (7/20) in the oral group. Mean plasma paracetamol levels were 88.6 µmol/l for the intravenous group and 53.2 µmol/l for the oral group (P=0.0005). There were trends towards reduced rescue analgesia and duration of stay in the recovery room for the intravenous group although not reaching statistical significance. There was no difference in pain scores between groups. Intraoperative administration of 1.0 g of intravenous paracetamol more reliably achieved effective paracetamol levels in the early postoperative period compared to an equal dose given orally preoperatively. Only a minority of patients receiving the 1.0 g oral dose preoperatively had plasma levels in the therapeutic analgesic range.

Population pharmacokinetics of single-dose intravenous paracetamol in children

BACKGROUND

To determine the pharmacokinetics (PK) of a new i.v. formulation of paracetamol (Perfalgan) in children ≤15 yr of age.

METHODS

After obtaining written informed consent, children under 16 yr of age were recruited to this study. Blood samples were obtained at 0, 15, 30 min, 1, 2, 4, 6, and 8 h after administration of a weight-dependent dose of i.v. paracetamol. Paracetamol concentration was measured using a validated high-performance liquid chromatographic assay with ultraviolet detection method, with a lower limit of quantification (LLOQ) of 900 pg on column and an intra-day coefficient of variation of 14.3% at the LLOQ. Population PK analysis was performed by non-linear mixed-effect modelling using NONMEM.

RESULTS

One hundred and fifty-nine blood samples from 33 children aged 1.8-15 yr, weight 13.7-56 kg, were analysed. Data were best described by a two-compartment model. Only body weight as a covariate significantly improved the goodness of fit of the model. The final population models for paracetamol clearance (CL), V(1) (central volume of distribution), Q (inter-compartmental clearance), and V(2) (peripheral volume of distribution) were: 16.51×(WT/70)(0.75), 28.4×(WT/70), 11.32×(WT/70)(0.75), and 13.26×(WT/70), respectively (CL, Q in litres per hour, WT in kilograms, and V(1) and V(2) in litres).

CONCLUSIONS

In children aged 1.8-15 yr, the PK parameters for i.v. paracetamol were not influenced directly by age but were by total body weight and, using allometric size scaling, significantly affected the clearances (CL, Q) and volumes of distribution (V(1), V(2)).

Analgesic efficacy and safety of intravenous paracetamol (acetaminophen) administered as a 2 g starting dose following third molar surgery

BACKGROUND

The recommended dose for intravenous (IV) paracetamol injection in adults is 1g, however pharmacokinetic and pharmacodynamic findings suggest that a better analgesia could be obtained with a 2 g starting dose.

METHODS

A single-centre, randomised, double-blind, placebo-controlled, 3-parallel group study was performed to demonstrate the analgesic efficacy and safety of IV paracetamol 2 g. Following third molar surgery, patients reporting moderate to severe pain received a single 15-min infusion of either IV paracetamol 2 g, IV paracetamol 1g or placebo. Efficacy and safety were evaluated over 8 h. Laboratory tests were performed before and 48 h after drug administration.

RESULTS

Two hundred and ninety seven patients (132 = IV paracetamol 2g; 132 = IV paracetamol 1g; 33 = placebo) were randomised and completed the study. The summed pain relief over 6h (TOTPAR6) was significantly superior with IV paracetamol 2 g as compared to IV paracetamol 1g and placebo (p < 0.0001). Pain relief scores of IV paracetamol 2g were significantly superior to IV paracetamol 1g and to placebo from T30' to T8h (p < 0.0001). Median duration of analgesia was significantly longer following IV paracetamol 2 g compared to IV paracetamol 1g and placebo (p < 0.0001). Adverse events occurred with the same frequency in the 3 treatment groups. No clinically significant changes from baseline were observed for vital signs or laboratory tests.

CONCLUSION

The analgesic efficacy of a 2 g starting dose of IV paracetamol was superior over the recommended dose of 1g in terms of magnitude and duration of analgesic effect for postoperative pain following third molar surgery, with no significant difference between groups regarding safety.

Single dose intravenous propacetamol or intravenous paracetamol for postoperative pain

BACKGROUND

Paracetamol (acetaminophen) is the most commonly prescribed analgesic for the treatment of acute pain. It may be administered orally or intravenously. The efficacy and safety of intravenous (IV) formulations of paracetamol, IV paracetamol and IV propacetamol, compared with placebo and other analgesics, is unclear.

OBJECTIVES

To assess the efficacy and safety of IV formulations of paracetamol for treatment of postoperative pain in both adults and children.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 2), MEDLINE (1950 to May 2010), EMBASE (1980 to 2010, Week 18), LILACS (1992 to May 2010) and reference lists of retrieved articles.

SELECTION CRITERIA

Randomized, double-blind, placebo- or active-controlled single dose clinical trials of IV propacetamol or IV paracetamol for acute postoperative pain in adults or children.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the risk of bias and extracted data. We contacted study authors for additional information. We collected adverse event information from the studies.

MAIN RESULTS

Thirty-six studies (3896 participants) were included. Thirty-seven percent of participants receiving IV propacetamol/paracetamol experienced at least 50% pain relief over four hours compared with 16% of those receiving placebo (number needed to treat to benefit (NNT = 4.0; 95% confidence interval 3.5 to 4.8). The proportion of participants in IV propacetamol/paracetamol groups experiencing at least 50% pain relief diminished over six hours, as reflected in a higher NNT of 5.3 (4.2 to 6.7). Participants receiving IV propacetamol/paracetamol required 30% less opioid over four hours than those receiving placebo. However, this did not translate to a reduction in opioid-induced adverse events.Meta-analysis of efficacy comparisons between IV propacetamol/paracetamol and active comparators (opioids or nonsteroidal anti-inflammatories (NSAIDs)) were either not statistically significant, not clinically significant, or both.Adverse events occurred at similar rates with IV propacetamol or IV paracetamol and placebo. However, pain on infusion occurred more frequently in those receiving IV propacetamol versus placebo (23% versus 1%).Meta-analysis did not demonstrate statistically significant differences between IV propacetamol/paracetamol and active comparators for any adverse event except a reduction in the rate of hypotension versus NSAIDs and a reduction in the rate of gastrointestinal disorders versus opioids.

AUTHORS' CONCLUSIONS

A single dose of both IV propacetamol and IV paracetamol provides around four hours of effective analgesia for about 37% of patients with acute postoperative pain. Both formulations are associated with few adverse events, although patients receiving IV propacetamol have a higher incidence of pain on infusion than both placebo and IV paracetamol.

Continuous multimechanistic postoperative analgesia: a rationale for transitioning from intravenous acetaminophen and opioids to oral formulations

Good surgical outcomes depend in part on good pain relief, allowing for early mobilization, optimal recovery, and patient satisfaction. Postsurgical pain has multiple mechanisms, and multimechanistic approaches to postoperative analgesia are recommended and may be associated with improved pain relief, lowered opioid doses, and sometimes a lower rate of opioid-associated side effects. Acetaminophen (paracetamol) is a familiar agent for treating many types of pain, including postsurgical pain. Oral acetaminophen has been shown to be safe and effective in a variety of acute pain models. Combination products using a fixed-dose of acetaminophen and an opioid have also been effective in treating postsurgical pain. Combination products with acetaminophen have demonstrated an opioid-sparing effect, which inconsistently results in a reduced rate of opioid-associated side effects. Intravenous (IV) acetaminophen and an opioid analgesic administered in the perioperative period may be followed by an oral acetaminophen and opioid combination in the postoperative period. Transitioning from an IV acetaminophen and opioid formulation to a similar but oral formulation of the same drugs appears to be a reasonable step in that both analgesic therapies are known to be safe and effective. For postsurgical analgesia with any acetaminophen product, patient education is necessary to be sure that the patient does not concurrently take any over-the-counter products containing acetaminophen and accidentally exceed dose limits.

Single-dose intravenous paracetamol or propacetamol for prevention or treatment of postoperative pain: a systematic review and meta-analysis

Paracetamol is the most commonly prescribed analgesic for the treatment of acute pain. The efficacy and safety of i.v. formulations of paracetamol is unclear. We performed a systematic search (multiple databases, bibliographies, any language, to May 2010) for single-dose, randomized, controlled clinical trials of propacetamol or i.v. paracetamol for acute postoperative pain in adults or children. Thirty-six studies involving 3896 patients were included. For the primary outcome, 37% of patients (240/367) receiving propacetamol or i.v. paracetamol experienced at least 50% pain relief over 4 h compared with 16% (68/527) receiving placebo (number needed to treat=4.0; 95% confidence interval, 3.5-4.8). The proportion of patients in propacetamol or i.v. paracetamol groups experiencing at least 50% pain relief diminished over 6 h. Patients receiving propacetamol or paracetamol required 30% less opioid over 4 h and 16% less opioid over 6 h than those receiving placebo. However, this did not translate to a reduction in opioid-induced adverse events (AEs). Similar comparisons between propacetamol or i.v. paracetamol and active comparators were either not statistically significant, not clinically significant, or both. AEs occurred at similar rates with propacetamol or i.v. paracetamol and placebo. However, pain on infusion occurred more frequently in those receiving propacetamol compared with placebo (23% vs 1%). A single dose of either propacetamol or i.v. paracetamol provides around 4 h of effective analgesia for about 37% of patients with acute postoperative pain. Both formulations are associated with few AEs, although patients receiving propacetamol have a higher incidence of pain on infusion.

Paracetamol for intravenous use in medium--and intensive care patients: pharmacokinetics and tolerance

PURPOSE

We studied the pharmacokinetics of paracetamol and determine the incidence of hypotension after intravenous administration in medium- (MCU) and intensive care (ICU) patients.

METHODS

All patients on the ICU/MCU starting with paracetamol i.v. were included, yielding 38 patients. Blood samples were collected at predetermined time points to determine paracetamol serum concentration. The number of patients with a clinically relevant reduction in systolic blood pressure (SBP) and the number of patients that needed intervention to regain an acceptable blood pressure level were assessed.

RESULTS

Overall, pharmacokinetic data were roughly comparable with earlier publications, but differences were noted in the subgroup ICU patients. Also, there was a trend to a larger peak serum concentration (p = 0.052) and a significantly smaller volume of distribution (p = 0.033) in MCU patients compared with ICU patients. Twenty-two percent (22%) and 33% of patients had a clinically relevant reduction in systolic blood pressure (SBP) 15 and 30 min after start of paracetamol infusion, respectively. In six patients (16%), an intervention was needed to correct blood pressure. Overall, SBP was significantly reduced at T = 15 min and 30 min postinfusion (p < 0.003 at both time points) when compared with SBP at the start of paracetamol infusion.

CONCLUSIONS

Further research on differences in paracetamol pharmacokinetics between ICU and MCU patients is warranted, as these differences might result in differences in efficacy. Furthermore, administration of paracetamol i.v. as potential cause of hypotension in the critically ill patient must not be overlooked.

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.

Analgesic efficacy of intravenous paracetamol for outpatient fractional curettage: a randomised, controlled trial

OBJECTIVE

To determine the efficacy of intravenous (i.v.) paracetamol for decreasing pain associated with fractional curettage.

MATERIALS AND METHODS

This double-blind, randomised, placebo-controlled trial included 70 women who underwent fractional curettage. Patients were randomly assigned to receive i.v. infusion of either 1000 mg paracetamol (n = 36) or 0.9% normal saline as placebo (n = 34) prior to the procedure. The main outcome measure was the intensity of pain assessed by a 10-cm visual analogue scale. Pain scoring was performed at t(1) = prior to the procedure, t(2) = during the procedure and t(3) = 30 min after the procedure. Statistical analysis was performed using the Student's t-test, chi-squared and Pearson's correlation analysis.

RESULTS

The pain scores at t(2) and t(3) were significantly higher than the score at t(1) in both groups. There was no statistically significant difference between the pain scores at t(1), t(2) and t(3) among the two groups. Menopausal status had no effect on the pain scores and on the treatment outcome. The pain scores prior to the procedure were significantly higher in women with a history of endometrial curettage when compared with women who have no history.

CONCLUSIONS

Fractional curettage is associated with mild pain. We were unable to detect a significant difference in pain scores in patients undergoing fractional curettage when comparing the use of i.v. paracetamol with placebo. History of prior endometrial curettage seems to be a predictor of the basal pain scores at admission although it does not affect the pain intensity related to the procedure.

Supra-additive effects of tramadol and acetaminophen in a human pain model ☆

The combination of analgesic drugs with different pharmacological properties may show better efficacy with less side effects. Aim of this study was to examine the analgesic and antihyperalgesic properties of the weak opioid tramadol and the non-opioid acetaminophen, alone as well as in combination, in an experimental pain model in humans. After approval of the local Ethics Committee, 17 healthy volunteers were enrolled in this double-blind and placebo-controlled study in a cross-over design. Transcutaneous electrical stimulation at high current densities (29.6+/-16.2 mA) induced spontaneous acute pain (NRS=6 of 10) and distinct areas of hyperalgesia for painful mechanical stimuli (pinprick-hyperalgesia). Pain intensities as well as the extent of the areas of hyperalgesia were assessed before, during and 150 min after a 15 min lasting intravenous infusion of acetaminophen (650 mg), tramadol (75 mg), a combination of both (325 mg acetaminophen and 37.5mg tramadol), or saline 0.9%. Tramadol led to a maximum pain reduction of 11.7+/-4.2% with negligible antihyperalgesic properties. In contrast, acetaminophen led to a similar pain reduction (9.8+/-4.4%), but a sustained antihyperalgesic effect (34.5+/-14.0% reduction of hyperalgesic area). The combination of both analgesics at half doses led to a supra-additive pain reduction of 15.2+/-5.7% and an enhanced antihyperalgesic effect (41.1+/-14.3% reduction of hyperalgesic areas) as compared to single administration of acetaminophen. Our study provides first results on interactions of tramadol and acetaminophen on experimental pain and hyperalgesia in humans. Pharmacodynamic modeling combined with the isobolographic technique showed supra-additive effects of the combination of acetaminophen and tramadol concerning both, analgesia and antihyperalgesia. The results might act as a rationale for combining both analgesics.

Recent advances in the pharmacological management of pain

Pain is an unpleasant sensation that originates from ongoing or impending tissue damage. Management of different types of pain (acute, postoperative, inflammatory, neuropathic or cancer) is the most frequent issue encountered by clinicians and pharmacological therapy is the first line of approach for the treatment of pain. This review presents and discusses recent clinical advances regarding both the improvements in delivery of analgesic drugs and improvements in the design of analgesic molecules. The new modalities of administration of analgesics used in the clinic are reviewed, including skin patches, oral and mucosal sprays, transdermal delivery systems and intranasal administration. New insights are then presented on standard drugs used to relieve pain, such as opioids (including tramadol), NSAIDs including selective cyclo-oxygenase-2 inhibitors, paracetamol (acetaminophen), local anaesthetics and adjuvant analgesics such as antidepressants, anticonvulsants (gabapentin and pregabalin), cannabinoids, ketamine and others (e.g. nefopam). Although the understanding of pain mechanisms has improved significantly recently, much more is yet to be discovered and awaited. Broadening of our knowledge is needed to improve basic and clinical research in this field in order to better alleviate pain in millions of people.

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.

Safety and pharmacokinetics of paracetamol following intravenous administration of 5 g during the first 24 h with a 2-g starting dose

Intravenous (i.v.) paracetamol is used as 1-g infusions with a maximal daily dose of 4 g/day. However, a higher initial analgesic dose could be of interest in the immediate postoperative period when the pain is maximal. The purpose of the present study was to determine in healthy subjects the safety and the pharmacokinetics of i.v. paracetamol, starting with a 2-g dose, followed by 1-g doses every 6 h, leading to a total of 5 g the first 24 h. This was an open-label, single-sequence study. The paracetamol pharmacokinetic profile was assessed in 26 subjects after both the 2-g starting dose and the 1-g doses. Safety, especially hepatotoxicity, was evaluated up to 72 h after the initial 2-g dose. Following the first 15-min i.v. administration of paracetamol 2 g, plasma concentrations ranged from 67.9+/-21.8 mug/ml (peak plasma concentration (C(max)) at the end of infusion) to 6.2+/-2.3 mug/ml (trough plasma concentration (C(min)) measured just before the next infusion) without any C(max) in the toxic range for any subject. After the repeated 1-g infusions, the plasma concentrations were approximately 35% lower than that measured after 2 g, showing the absence of accumulation. No clinical adverse events related to the drug administration nor clinically relevant changes in laboratory parameters, including biochemical signs of hepatotoxicity, were reported. After i.v. administration of paracetamol 2-g starting dose and 5 g during the first 24 h, the pharmacokinetics of paracetamol remain unchanged, with concentrations far below the toxic threshold. Overall, these results demonstrate that the i.v. administration of a 2-g starting dose of paracetamol, followed by three i.v. administrations of 1 g during the first 24 h is safe in healthy subjects.

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.

Pharmacokinetics/Pharmacodynamics of Acetaminophen Analgesia in Japanese Patients with Chronic Pain

Acetaminophen (APAP) is a popular analgesic. In the present study, we characterized the pharmacokinetics and pharmacodynamics of APAP in the Japanese. Five healthy volunteers were administered 1000 mg of APAP orally. Five patients with chronic pain were administered the optimal oral dose of APAP ranging from 600 to 1000 mg to allow for an adequate analgesic effect. Plasma APAP and APAP metabolite concentrations were measured in the volunteers, plasma APAP concentrations and pain scores using a visual analog scale were measured in the patients with chronic pain. Patient data were fitted to a first-order absorption one-compartment model with delayed effects accounted for by an effect compartment. A sigmoid Emax model was used as the pharmacodynamic model. Acetaminophen-cysteine metabolites, which are conjugates of the toxic metabolite N-acetyl-p-benzoquinone-imine, were detected in the plasma at levels lower than 0.2 microg/ml, but no side effects were observed. The pharmacokinetic and pharmacodynamic parameter (mean+/-S.D.) estimates were as follows: clearance, 18.7+/-4.7 l/h; distribution volume, 30.9+/-6.8 l; absorption rate constant, 2.4+/-1.3 h(-1); rate constant for the elimination of APAP from the effect compartment, 1.3+/-0.5 h(-1); maximum pain relief score, 4.6+/-2.2 units; effect compartment concentration at 50% maximum, 2.0+/-1.2 microg/ml; and sigmoid factor, 1.3+/-0.7. These results suggest that these parameters can be used to determine an effective APAP dosage regimen for Japanese patients with chronic pain.

Intravenous acetaminophenvs oral ibuprofen in combination with morphine PCIA after Cesarean delivery

PURPOSE

To compare the effects of iv acetaminophen with those of oral ibuprofen with respect to postoperative pain control and morphine requirements in patients receiving morphine patient-controlled iv analgesia (PCIA) after Cesarean delivery.

METHODS

Forty-five term patients scheduled for Cesarean delivery were randomized to receive acetaminophen 1 g iv every six hours plus oral placebo (group A) or ibuprofen 400 mg po every six hours plus iv placebo (group I); the first dose of study drug was given 30 min preoperatively. Postoperatively, all patients received PCIA for 48 hr using morphine bolus dose 2 mg iv, lockout interval ten minutes, and no basal infusion. Visual analogue scale (VAS; 0 to 10) at rest and morphine requirements were recorded every hour for four hours then every four hours for a total of 48 hr postoperatively. Patient satisfaction was recorded on a ten-point scale (from 1 to 10) 48 hr postoperatively.

RESULTS

Visual analogue scale scores decreased similarly in both groups over time, however, there were no differences between groups at any time during the study period (estimated marginal means: 1.4 +/- SEM 0.2 vs 1.9 +/- SEM 0.2 for groups A and I, respectively, P = 0.124). Cumulative doses of postoperative morphine were 98 +/- 37 vs 93 +/- 33 mg for groups A and I, respectively (P = 0.628). Patient satisfaction with analgesia was high in both groups (9 +/- 1 vs 9 +/- 1, P = 0.93).

CONCLUSION

Intravenous acetaminophen is a reasonable alternative to oral ibuprofen as an adjunct to morphine patient-controlled analgesia after Cesarean delivery.

Intravenous acetaminophen reduced the use of opioids compared with oral administration after coronary artery bypass grafting

OBJECTIVE

The purpose of this study was to evaluate if intravenous acetaminophen compared to oral administration reduced the consumption of opioids and their side effects without an increase in pain during the stay in the intensive care unit (ICU).

DESIGN

Prospective, randomized study.

SETTING

An ICU in a university hospital.

PARTICIPANTS

Eighty patients with written informed consent undergoing coronary artery bypass grafting with cardiopulmonary bypass. Anesthesia was based on propofol and fentanyl combined with sevoflurane.

INTERVENTIONS

Patients were randomized to 2 groups: acetaminophen, 1 g every sixth hour during the postoperative period, either as tablets or intravenously after extubation.

MEASUREMENTS AND MAIN RESULTS

The amount of opioids administered during the study period was measured starting with acetaminophen administration during the stay in the ICU until 9 o'clock the following morning. Incidence of postoperative nausea and vomiting (PONV) was noted. Pain was evaluated with a visual analog scale (VAS) from 0 to 10. Three patients, 2 in the oral and 1 in the intravenous group, were excluded because of incomplete data. The intravenous group received less opioids than the orally treated group, 17.4 +/- 7.9 mg compared with 22.1 +/- 8.6 mg (p = 0.016). PONV incidence and VAS scores did not differ. During the first hours after extubation, 50 of 77 patients reported VAS scores >3 with no difference between groups.

CONCLUSIONS

Intravenous acetaminophen had a limited opioid-sparing effect when compared with oral administration after coronary artery bypass graft surgery. The opioid-sparing effect was not accompanied by any reduction in the incidence of PONV. The clinical significance of the opioid-sparing effect could therefore be questioned.

Characterization of inhibition of platelet function by paracetamol and its interaction with diclofenac in vitro

BACKGROUND

Paracetamol (acetaminophen) is an effective analgesic and a weak inhibitor of cyclo-oxygenase (COX). Clinically paracetamol is often used together with traditional NSAIDs, which are strong inhibitors of COX. We studied binding of paracetamol to COX and its action on platelet function together with diclofenac.

METHODS

Blood was collected from healthy donors and platelet function was assessed by photometric aggregometry, a platelet function analyser (PFA-100, Dade Behring, Deerfield, IL) and by measuring the release of thromboxane B(2) (TxB(2)), the stable metabolite of thromboxane A(2), after addition of paracetamol (10-80 microg ml(-1)). A concentration-inhibition relationship was established and the inhibition coefficient (K(i)) demonstrating 50% binding to COX was determined using a Schild-plot. Interaction of paracetamol (5-20 microg ml(-1)) and diclofenac (0.1-0.8 microg ml(-1)) was determined and an isobolographic analysis was performed.

RESULTS

Paracetamol added to platelet-rich plasma (PRP) caused a concentration-dependent inhibition of platelet function. Photometric aggregometry and TxB(2) release was significantly inhibited by paracetamol from 10 microg ml(-1) onwards. The PFA-100 closure time was significantly prolonged by paracetamol at a high concentration only. K(i) was 15.2 microg ml(-1) with a 95% confidence interval of 11.8-18.6 microg ml(-1). Inhibition of aggregation by diclofenac was augmented by paracetamol. Isobolographic analysis showed synergism.

CONCLUSIONS

The 95% confidence interval of K(i) equals the antipyretic plasma concentration of paracetamol, i.e. 10-20 microg ml(-1). High doses of paracetamol and a combination of diclofenac and paracetamol cause platelet inhibition and thus may increase risk of surgical bleeding.

Effects of acetaminophen on morphine side-effects and consumption after major surgery: meta-analysis of randomized controlled trials † †Presented in part at the Annual Meeting of the Société Française d’Anesthésie-Réanimation, Paris, April 2004

BACKGROUND

Acetaminophen is commonly used for the management of perioperative pain. However, there is a marked discrepancy between the extent to which acetaminophen is used and the available evidence for an analgesic effect after major surgery. The aim of this systematic review is to determine the morphine-sparing effect of acetaminophen combined with patient-controlled analgesia (PCA) with morphine and to evaluate its effects on opioid-related adverse effects.

METHODS

MEDLINE and the Cochrane Library were searched to select randomized controlled trials which compared PCA morphine alone with PCA morphine plus acetaminophen administered orally or intravenously. Studies were evaluated for their quality based on the Oxford Quality Scale. Outcome measures were morphine consumption over the first 24 h after surgery, patient satisfaction and the incidence of morphine side-effects, including nausea and vomiting, sedation, urinary retention, pruritus and/or respiratory depression.

RESULTS

Seven prospective randomized controlled trials, including 265 patients in the group with PCA morphine plus acetaminophen and 226 patients in the group with PCA morphine alone, were selected. Acetaminophen administration was not associated with a decrease in the incidence of morphine-related adverse effects or an increase in patient satisfaction. Adding acetaminophen to PCA was associated with a morphine-sparing effect of 20% (mean, -9 mg; CI -15 to -3 mg; P=0.003) over the first postoperative 24 h.

CONCLUSION

Acetaminophen combined with PCA morphine induced a significant morphine-sparing effect but did not change the incidence of morphine-related adverse effects in the postoperative period.

Multimodal Analgesia Techniques and Postoperative Rehabilitation

The concept of multimodal analgesia involves the use of different classes of analgesics and different sites of analgesic administration to provide superior dynamic pain relief with reduced analgesic-related side effects. Although multimodal analgesia techniques have assumed increasing importance in the management of perioperative pain, it has become increasingly apparent that postoperative outcome may not be improved. Nevertheless, the integration of multimodal analgesia techniques with a multimodal and multidisciplinary rehabilitation program may enhance recovery, reduce hospital stay, and facilitate early convalescence.

Pharmacokinetics of intravenous paracetamol in children and adolescents under major surgery

BACKGROUND

The aim of this study was to describe the pharmacokinetics of paracetamol (acetaminophen) and to get primary information on its metabolism after first indicated intravenous administration of paracetamol in children and adolescents undergoing major surgery.

METHODS

About 4 weeks after the last chemotherapy, seven children and adolescents (five osteosarcoma, two Ewing tumors) received paracetamol infusion (median: 15.0 mg/kg) for analgesia. Sparse serum (37 samples; 4-7 per patient) and urine samples (27 samples; 0-15 per patient) were analyzed for paracetamol, paracetamol-glucuronide, paracetamol-sulfate, paracetamol-mercapturate and paracetamol-cysteine using capillary electrophoresis. Nonlinear mixed-effect models were used to describe the pharmacokinetics of paracetamol in plasma.

RESULTS

Pharmacokinetics of paracetamol after intravenous administration was best described by a two-compartment model with clearance of 13.2 l/h per 70 kg (between-subject variability: 30%), intercompartmental clearance of 45.7 l/h per 70 kg (both parameters standardized to a 70-kg person using allometric "1/4 power models"), central volume of distribution of 13.2 l per 70 kg (between-subject variability: 71%) and peripheral volume of distribution of 33.0 l per 70 kg. Paracetamol, the glucuronide- and sulfate conjugates as well as cysteine and mercapturic acid conjugates, both products of oxidative pathways of paracetamol, were excreted in urine.

CONCLUSIONS

Surgery, with all its potential influencing factors, together with chemotherapy given about 4 weeks previously do not seem to have a major impact on the pharmacokinetic behavior and the between-subject variability of paracetamol after intravenous administration.

Single High-Dose Rectal Acetaminophen in Children

OBJECTIVE

To determine whether there is sufficient evidence to support the use of one-time high-dose (>30 mg/kg) rectally administered acetaminophen to control postoperative pain in children.

DATA SOURCES

Literature was accessed through MEDLINE (1966–May 2004) and bibliographic searches.

STUDY SELECTION AND DATA EXTRACTION

All articles identified from the data sources were evaluated and all studies regarding the use of greater than 30 mg/kg of acetaminophen in children were included for this review.

DATA SYNTHESIS

A single high dose of rectally administered acetaminophen has been used in children to control postoperative pain. Ten randomized controlled trials and pharmacokinetic studies evaluating the use of greater than 30 mg/kg of rectally administered acetaminophen in children were identified and reviewed. Each study had a unique objective. The studies also differed substantially in regard to design, study population, dosing, rectal formulation used, and monitoring.

CONCLUSIONS

Due to limited study data, wide study variability, and lack of standardization in terms of design, objectives, study population, dosing, rectal formulation, and monitoring, compounded by the fact that children often require additional doses of acetaminophen to control postoperative pain, the practice of using one-time, high-dose, rectally administered acetaminophen in children cannot be recommended at this time.

[Non-opioid analgesics for perioperative pain therapy. Risks and rational basis for use]

Non-opioid analgesics play a central role in the management of postoperative pain. In this review, the pharmacology, the analgesic efficacy and the side-effects of non-opioid analgesics are summarized. First, the pharmacology of diclofenac, acetyl salicylic acid, dipyrone, acetaminophen and the COX-2 inhibitors is described. Second, the analgesic efficacy of non-opioid analgesics is analyzed for moderate pain (e.g. ambulatory surgery) and for moderate to severe pain (e.g. abdominal surgery-in combination with opioids). There is limited evidence for an additive analgesic effect of two non-opioid analgesics. Third, the major side-effects of non-opioid analgesics are discussed in relation to the pathophysiology, the frequency and the clinical relevance of these effects. In particular, side-effects on the gastrointestinal tract (ulcus formation), on coagulation (bleeding and thrombosis), on the renal (renal insufficiency), the pulmonary (bronchospasm) and the hematopoetic systems (agranulocytosis) are described. Recommendations for the clinical use of non-opioid analgesics for perioperative pain therapy are given.