Effects of acetaminophen on constitutive and inducible prostanoid biosynthesis in human blood cells

Paracetamol (acetaminophen): A familiar drug with an unexplained mechanism of action

Paracetamol (acetaminophen) is undoubtedly one of the most widely used drugs worldwide. As an over-the-counter medication, paracetamol is the standard and first-line treatment for fever and acute pain and is believed to remain so for many years to come. Despite being in clinical use for over a century, the precise mechanism of action of this familiar drug remains a mystery. The oldest and most prevailing theory on the mechanism of analgesic and antipyretic actions of paracetamol relates to the inhibition of CNS cyclooxygenase (COX) enzyme activities, with conflicting views on the COX isoenzyme/variant targeted by paracetamol and on the nature of the molecular interactions with these enzymes. Paracetamol has been proposed to selectively inhibit COX-2 by working as a reducing agent, despite the fact that in vitro screens demonstrate low potency on the inhibition of COX-1 and COX-2. In vivo data from COX-1 transgenic mice suggest that paracetamol works through inhibition of a COX-1 variant enzyme to mediate its analgesic and particularly thermoregulatory actions (antipyresis and hypothermia). A separate line of research provides evidence on potentiation of the descending inhibitory serotonergic pathway to mediate the analgesic action of paracetamol, but with no evidence of binding to serotonergic molecules. AM404 as a metabolite for paracetamol has been proposed to activate the endocannabinoid and the transient receptor potential vanilloid-1 (TRPV1) systems. The current review gives an update and in some cases challenges the different theories on the pharmacology of paracetamol and raises questions on some of the inadequately explored actions of paracetamol. List of Abbreviations: AM404, N-(4-hydroxyphenyl)-arachidonamide; CB1R, Cannabinoid receptor-1; Cmax, Maximum concentration; CNS, Central nervous system; COX, Cyclooxygenase; CSF, Cerebrospinal fluid; ED50, 50% of maximal effective dose; FAAH, Fatty acid amidohydrolase; IC50, 50% of the maximal inhibitor concentration; LPS, Lipopolysaccharide; NSAIDs, Non-steroidal anti-inflammatory drugs; PGE2, Prostaglandin E2; TRPV1, Transient receptor potential vanilloid-1.

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.

Variability in the Analgesic Response to Ibuprofen Is Associated With Cyclooxygenase Activation in Inflammatory Pain

The mechanisms underlying interindividual variability in analgesic efficacy of nonsteroidal anti‐inflammatory drugs (NSAIDs) are not well understood. Therefore, we performed pain phenotyping, functional neuroimaging, pharmacokinetic/pharmacodynamic assessments, inflammation biomarkers, and gene expression profiling in healthy subjects who underwent surgical extraction of bony impacted third molars and were treated with ibuprofen (400 mg; N = 19) or placebo (N = 10). Analgesic efficacy was not associated with demographic or clinical characteristics, ibuprofen pharmacokinetics, or the degree of cyclooxygenase inhibition by ibuprofen. Compared with partial responders to ibuprofen (N = 9, required rescue medication within the dosing interval), complete responders (N = 10, no rescue medication) exhibited greater induction of urinary prostaglandin metabolites and serum tumor necrosis factor‐α and interleukin 8. Differentially expressed genes in peripheral blood mononuclear cells were enriched for inflammation‐related pathways. These findings suggest that a less pronounced activation of the inflammatory prostanoid system is associated with insufficient pain relief on ibuprofen alone and the need for additional therapeutic intervention.

Analgesic Use and Ovarian Cancer Risk: An Analysis in the Ovarian Cancer Cohort Consortium

BACKGROUND

Aspirin use is associated with reduced risk of several cancers. A pooled analysis of 12 case-control studies showed a 10% decrease in ovarian cancer risk with regular aspirin use, which was stronger for daily and low-dose users. To prospectively investigate associations of analgesic use with ovarian cancer, we analyzed data from 13 studies in the Ovarian Cancer Cohort Consortium (OC3).

METHODS

The current study included 758 829 women who at study enrollment self-reported analgesic use, among whom 3514 developed ovarian cancer. Using Cox regression, we assessed associations between frequent medication use and risk of ovarian cancer. Dose and duration were also evaluated. All statistical tests were two-sided.

RESULTS

Women who used aspirin almost daily (≥6 days/wk) vs infrequent/nonuse experienced a 10% reduction in ovarian cancer risk (rate ratio [RR] = 0.90, 95% confidence interval [CI] = 0.82 to 1.00, P = .05). Frequent use (≥4 days/wk) of aspirin (RR = 0.95, 95% CI = 0.88 to 1.03), nonaspirin nonsteroidal anti-inflammatory drugs (NSAIDs; RR = 1.00, 95% CI = 0.90 to 1.11), or acetaminophen (RR = 1.05, 95% CI = 0.88 to 1.24) was not associated with risk. Daily acetaminophen use (RR = 1.28, 95% CI = 1.00 to 1.65, P = .05) was associated with elevated ovarian cancer risk. Risk estimates for frequent, long-term (10+ years) use of aspirin (RR = 1.15, 95% CI = 0.98 to 1.34) or nonaspirin NSAIDs (RR = 1.19, 95% CI = 0.84 to 1.68) were modestly elevated, although not statistically significantly so.

CONCLUSIONS

This large, prospective analysis suggests that women who use aspirin daily have a slightly lower risk of developing ovarian cancer (∼10% lower than infrequent/nonuse)-similar to the risk reduction observed in case-control analyses. The observed potential elevated risks for 10+ years of frequent aspirin and NSAID use require further study but could be due to confounding by medical indications for use or variation in drug dosing.

The effects of nonsteroidal anti-inflammatory drugs in the incident and recurrent risk of hepatocellular carcinoma: a meta-analysis

Background

Recent studies have showed that nonsteroidal anti-inflammatory drugs (NSAIDs) could reduce the risk of several types of cancer. However, epidemiological evidence of the association between NSAIDs intake and the risk of hepatocellular carcinoma (HCC) remains controversial.

Methods

To assess the preventive benefit of NSAIDs in HCC, we simultaneously searched the databases of PubMed, EmBase, Web of Science, and Scopus and screened eligible publications.

Results

A total of twelve articles (published from 2000 to 2017) from five countries were identified by retrieval. We observed a significantly lower risk of HCC incidence among users of NSAIDs than among those who did not use NSAIDs (pooled hazard ratio [HR] value =0.81, 95% confidence interval [CI]: 0.69–0.94). No evidence of publication bias was observed (Begg’s test, P=0.755; Egger’s test, P=0.564). However, when stratified according to the categories of NSAIDs, users of non-aspirin NSAIDs (HR =0.81, 95% CI: 0.70–0.94), but not aspirin (HR =0.77, 95% CI: 0.58–1.02), showed a statistically significant reduced HCC incidence. We also found that NSAIDs use significantly reduced the recurrent risk of HCC, with a HR value of 0.79 (95% CI: 0.75–0.84), whereas there was no statistically significant association between NSAIDs use and HCC mortality, with a HR value 0.65 (95% CI: 0.40–1.06).

Conclusion

Taken together, our meta-analysis demonstrates that NSAIDs significantly reduce the incident and recurrent risk of HCC.

Inhibition of prostacyclin and thromboxane biosynthesis in healthy volunteers by single and multiple doses of acetaminophen and indomethacin

This double-blind, randomized crossover study assessed the effect of acetaminophen (1000 mg every 8 hours) versus indomethacin (50 mg every 8 hours) versus placebo on cyclooxygenase enzymes (COX-1 and COX-2). Urinary excretion of 2,3-dinor-6-keto-PGF1α, (prostacyclin metabolite, PGI-M; COX-2 inhibition) and 11-dehydro thromboxane B2 (thromboxane metabolite, Tx-M; COX-1 inhibition) were measured after 1 dose and 5 days of dosing. Peak inhibition of urinary metabolite excretion across 8 hours following dosing was the primary end point. Mean PGI-M excretion was 33.7%, 55.9%, and 64.6% on day 1 and 49.4%, 65.1%, and 80.3% on day 5 (placebo, acetaminophen, and indomethacin, respectively). Acetaminophen and indomethacin inhibited PGI-M excretion following single and multiple doses (P = .004 vs placebo). PGI-M excretion inhibition after 1 dose was similar for indomethacin and acetaminophen, but significantly greater with indomethacin after multiple doses (P = .006). Mean Tx-M excretion was 16.2%, 45.2%, and 86.6% on day 1 and 46.2%, 58.4%, and 92.6% on day 5 (placebo, acetaminophen, and indomethacin, respectively). Tx-M excretion inhibition following 1 dose was reduced by acetaminophen (P ≤ .003). Indomethacin reduced Tx-M excretion significantly more than acetaminophen and placebo after single and multiple doses (P ≤ .001). Acetaminophen and indomethacin inhibited COX-1 and COX-2 following a single dose, but acetaminophen was a less potent COX-1 inhibitor than indomethacin.

New insights into the use of currently available non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs (NSAIDs), which act via inhibition of the cyclooxygenase (COX) isozymes, were discovered more than 100 years ago. They remain a key component of the pharmacological management of acute and chronic pain. The COX-1 and COX-2 isozymes have different biological functions; analgesic activity is primarily (although not exclusively) associated with inhibition of COX-2, while different side effects result from the inhibition of COX-1 and COX-2. All available NSAIDs, including acetaminophen and aspirin, are associated with potential side effects, particularly gastrointestinal and cardiovascular effects, related to their relative selectivity for COX-1 and COX-2. Since all NSAIDs exert their therapeutic activity through inhibition of the COX isozymes, strategies are needed to reduce the risks associated with NSAIDs while achieving sufficient pain relief. A better understanding of the inhibitory activity and COX-1/COX-2 selectivity of an NSAID at therapeutic doses, based on pharmacokinetic and pharmacodynamic properties (eg, inhibitory dose, absorption, plasma versus tissue distribution, and elimination), and the impact on drug tolerability and safety can guide the selection of appropriate NSAIDs for pain management. For example, many NSAIDs with moderate to high selectivity for COX-2 versus COX-1 can be administered at doses that maximize efficacy (~80% inhibition of COX-2) while minimizing COX-1 inhibition and associated side effects, such as gastrointestinal toxicity. Acidic NSAIDs with favorable tissue distribution and short plasma half-lives can additionally be dosed to provide near-constant analgesia while minimizing plasma concentrations to permit recovery of COX-mediated prostaglandin production in the vascular wall and other organs. Each patient’s clinical background, including gastrointestinal and cardiovascular risk factors, should be taken into account when selecting appropriate NSAIDs. New methods are emerging to assist clinicians in the selection of appropriate NSAIDs and their doses/schedules, such as biomarkers that may predict the response to NSAID treatment in individual patients.

Aspirin, nonaspirin nonsteroidal anti-inflammatory drug, and acetaminophen use and risk of invasive epithelial ovarian cancer: a pooled analysis in the Ovarian Cancer Association Consortium

BACKGROUND

Regular aspirin use is associated with reduced risk of several malignancies. Epidemiologic studies analyzing aspirin, nonaspirin nonsteroidal anti-inflammatory drug (NSAID), and acetaminophen use and ovarian cancer risk have been inconclusive.

METHODS

We analyzed pooled data from 12 population-based case-control studies of ovarian cancer, including 7776 case patients and 11843 control subjects accrued between 1992 and 2007. Odds ratios (ORs) for associations of medication use with invasive epithelial ovarian cancer were estimated in individual studies using logistic regression and combined using random effects meta-analysis. Associations between frequency, dose, and duration of analgesic use and risk of ovarian cancer were also assessed. All statistical tests were two-sided.

RESULTS

Aspirin use was associated with a reduced risk of ovarian cancer (OR = 0.91; 95% confidence interval [CI] = 0.84 to 0.99). Results were similar but not statistically significant for nonaspirin NSAIDs, and there was no association with acetaminophen. In seven studies with frequency data, the reduced risk was strongest among daily aspirin users (OR = 0.80; 95% CI = 0.67 to 0.96). In three studies with dose information, the reduced risk was strongest among users of low dose (<100 mg) aspirin (OR = 0.66; 95% CI = 0.53 to 0.83), whereas for nonaspirin NSAIDs, the reduced risk was strongest for high dose (≥500 mg) usage (OR = 0.76; 95% CI = 0.64 to 0.91).

CONCLUSIONS

Aspirin use was associated with a reduced risk of ovarian cancer, especially among daily users of low-dose aspirin. These findings suggest that the same aspirin regimen proven to protect against cardiovascular events and several cancers could reduce the risk of ovarian cancer 20% to 34% depending on frequency and dose of use.

Sedation and analgesia in critically ill children

The interplay of pain, discomfort, and fear can cause agitation in critically ill children. Therefore, sedation and analgesia are essential components in the intensive care unit setting and are best managed with a multidisciplinary team approach. No one standard approach exists to assess and manage pain and anxiety. Many tools are available for the assessment of pain and sedation, but each tool has its advantages and disadvantages. Clinicians should consider adopting a validated tool for routine continuous assessment. Multiple pharmacological therapies are available to manage pain, anxiety, fear, and agitation. Dosing of these agents can be influenced by age-related pharmacokinetic and pharmacodynamic changes. Agents should be selected on the basis of the child's disease state, desired level of sedation, and cardiac and respiratory status.

Variability in the response to non-steroidal anti-inflammatory drugs: mechanisms and perspectives

Non-steroidal anti-inflammatory drugs (NSAIDs) are a chemically heterogeneous group of compounds that provide unmistakable and significant health benefits in the treatment of pain and inflammation. They include traditional NSAIDs (tNSAIDs), which act by inhibiting both cyclooxygenase (COX)-1 and COX-2 and selective COX-2 inhibitors (coxibs). The development of biomarkers predictive of the impact of NSAIDs on COX-1 and COX-2 activities in vitro, ex vivo and in vivo has been essential to read out the clinical consequences of selective and non-selective inhibition of COX isozymes in human beings. The analgesic and anti-inflammatory effects of NSAIDs are COX-2-dependent effects, unrelated to COX-2 selectivity. The intensity and duration of these effects are influenced by dose and half-life of the NSAID. However, the inhibition of COX-1 in cells of the gastrointestinal (GI) system and COX-2 in vascular cells translates into increased risk of serious GI adverse events and atherothrombosis and hypertension, respectively. The COX-2 selectivity of NSAIDs can predict, at least in part, the GI toxicity. In contrast, the CV effects are largely COX-2-dependent effects, unrelated to COX-2 selectivity but are dose dependent. The reduction in the dose is recommended and presumably will limit the number of patients exposed to a CV or a GI hazard by NSAIDs and coxibs. It will not, however, eliminate the risk on an individual level because there is a marked variability in how different people react to these drugs, based on their genetic background. The challenge of the next future will be to develop biomarkers useful to identify the individuals who react abnormally to COX inhibition.

Coxibs: pharmacology, toxicity and efficacy in cancer clinical trials

This chapter briefly summarizes the current knowledge about the role of nonsteroidal anti-inflammatory drugs (NSAIDs), specially focusing on those selective for cyclooxygenase (COX)-2 (coxibs), on colorectal cancer (CRC) onset, and progression. Both epidemiological and experimental studies have reported that these drugs reduce the risk of developing colonic tumors. However, the promising use of coxibs in chemoprevention was halted abruptly due to the detection on enhanced cardiovascular (CV) risks. Thus, we discuss the clinical data and plausible mechanisms of CV hazards associated with traditional NSAIDs and coxibs. The extent of inhibition of COX-2-dependent prostacyclin, an important vasoprotective and anti-thrombotic pathway, in the absence of a complete suppression of COX-1-dependent platelet function, at common doses of NSAIDs, might play a role in CV toxicity. Coxibs might still be reserved for younger patients with familial adenomatous polyposis (FAP). However, it should be taken into consideration that recent findings of enhanced thromboxane (TX)A(2) biosynthesis in colon tumorigenesis, detected in humans. In this context, the use of low-dose aspirin (which mainly acts by inhibiting platelet COX-1-dependent TXA(2)) may have a place for chemoprevention of CRCs (see also Chap. 3 ). The possible use of coxibs to prevent CRC will depend mainly on research progresses in biomarkers able to identify the patients uniquely susceptible to developing thrombotic events by inhibition of COX-2.

Evaluative comparison of systemic aspirin therapy effects on gingival bleeding in post non-surgical periodontal therapy individuals

BACKGROUND

Gingival bleeding is considered as an important clinical sign for diagnosis of periodontal disease pathogenesis. Immune inflammatory reactions caused by local factors are considered as essential reasons for gingival bleeding, as also for the systemic bleeding disorders. In disease-free conditions of gingiva, the bleeding disorders are considered to be the main contender for bleeding. Other than these variables, many systemic drugs including systemic aspirin could also cause gingival bleeding. The main aim of the study was to evaluate the effect of buffered aspirin therapy on gingival bleeding.

MATERIALS AND METHODS

Totally, 36 systemically healthy individuals were included in the 15-day randomized, double-blinded, placebo-controlled clinical trial. The 15 days were divided as: control period for the first 7 days and study period for the following 7 days. On the 1(st) day, all individuals were given oral prophylaxis after recording gingival parameters such as Plaque Index, probing depth, and Bleeding Index, and then blood samples were collected for hematological investigations. Then, all individuals were administered placebo capsules for 1 week as once daily dose. On the 8(th) day, all procedures were repeated and the individuals were prescribed with 325 coated aspirin capsules for 1 week. On the 15(th) day, all parameters were repeated and the results were statistically analyzed.

RESULTS

In the study period, the parameters such as Bleeding Index, bleeding time, and prothrombin time were increased significantly, compared to the control period.

CONCLUSION

The variables such as systemic drug therapy should be considered for the examination of gingiva while the diagnosis is considered mainly based on gingival bleeding.

Identification and development of mPGES-1 inhibitors: where we are at?

Microsomal prostaglandin E synthase-1 (mPGES-1) is the terminal synthase responsible for the synthesis of the pro-tumorigenic prostaglandin E(2) (PGE(2)). mPGES-1 is overexpressed in a wide variety of cancers. Since its discovery in 1997 by Bengt Samuelsson and collaborators, the enzyme has been the object of over 200 peer-reviewed articles. Although today mPGES-1 is considered a validated and promising therapeutic target for anticancer drug discovery, challenges in inhibitor design and selectivity are such that up to this date there are only a few published records of small-molecule inhibitors targeting the enzyme and exhibiting some in vivo anticancer activity. This review summarizes the structures, and the in vitro and in vivo activities of these novel mPGES-1 inhibitors. Challenges that have been encountered are also discussed.

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.

The inducible prostaglandin E synthase mPGES-1 regulates growth of endometrial tissues and angiogenesis in a mouse implantation model

Endometriosis is one of the most common gynecological diseases in women of reproductive age. Although cyclooxygenase (COX)-2 inhibitors are effective in the treatment of endometriosis, the adverse cardiovascular effects associated with these inhibitors have limited their use. Microsomal prostaglandin E synthase-1 (mPGES-1) is an inducible enzyme downstream of COX-2 in prostaglandin E(2) biosynthesis. Previously, we developed mPGES-1 knockout mice (mPGES-1(-/-)) and have identified for the first time the roles of ectopic lesion- and host-associated mPGES-1 in angiogenesis and the growth of endometrial tissues. When mPGES-1(-/-) endometrial fragments were implanted into wild type (WT) mice (mPGES-1(-/-)→WT), or WT fragments implanted into mPGES-1(-/-) mice (WT→mPGES-1(-/-)), the growth of the implants was suppressed at days 14 and 28 after implantation, compared toWT→WT transplantation. An even greater degree of suppression was observed in mPGES-1(-/-) endometrial fragments implanted into mPGES-1(-/-) mice (mPGES-1(-/-)→mPGES-1(-/-)). After WT-WT implantation, mPGES-1 expression was localized at the border of the implanted endometrial tissues. Microvessel density, determined by CD31 immunostaining, was markedly suppressed in the mPGES-1(-/-) endometrial fragments implanted into mPGES-1(-/-) mice, with some suppression also observed in the mPGES-1(-/-)→WT and WT→mPGES-1(-/-) groups. The expression of vascular endothelial growth factor (VEGF-A) was significantly reduced in mPGES-1(-/-) endometrial tissues implanted into mPGES-1(-/-) mice at days 14 and 28, in comparison to the WT→WT group. These results suggested that mPGES-1 enhanced angiogenesis and growth of the endometrial implant, and indicate that mPGES-1 may be a good therapeutic target for endometriosis.

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.

Clinical efficacy and differential inhibition of menstrual fluid prostaglandin F2alpha in a randomized, double-blind, crossover treatment with placebo, acetaminophen, and ibuprofen in primary dysmenorrhea

OBJECTIVE

The purpose of this study was to compare acetaminophen with ibuprofen for pain relief and menstrual fluid prostaglandin F2alpha (PGF2alpha) suppression in primary dysmenorrhea.

STUDY DESIGN

Twelve subjects were randomized to placebo, acetaminophen (1000 mg orally, 4 x daily for 3 days) or ibuprofen (400 mg orally, 4 x daily for 3 days), once during each cycle in a prospective, double-blinded, crossover study. Using preweighed super absorbent tampons, menstrual fluid was collected, extracted, and PGF2alpha radioimmunoassayed.

RESULTS

Ten patients completed the study. Ibuprofen (P = .002) and acetaminophen (P = .022) were rated significantly better than placebo. Total menstrual fluid PGF2alpha with placebo was 36.2 + 6.1 microg but were 14.8 + 3.0 microg with ibuprofen (P = .001) and 21.4 + 3.4 microg with acetaminophen (P = .008). PGF2alpha concentrations with placebo were 0.34 + 0.054 microg/mL, with ibuprofen 0.16 + 0.026 microg/mL (P = .001), and with acetaminophen 0.23 + 0.029 microg/mL (P = .016).

CONCLUSION

Both ibuprofen and acetaminophen were superior to placebo for pain relief and menstrual fluid PGF2alpha suppression, with ibuprofen being more potent.

Anesthesia and analgesia during and after surgery in neonates

BACKGROUND

Historically, the use of anesthetics and analgesics in neonates and infants has been based on extrapolations from studies performed in adults and older children. Over the past 20 years, there has been a growing body of research on the clinical pharmacology and clinical outcomes of these agents in neonates and infants.

OBJECTIVE

This article summarizes clinical pharmacology and clinical outcomes studies of opioids, opioid antagonists, sedative-hypnotics, nonsteroidal anti-inflammatory drugs and acetaminophen, and local anesthetics in neonates and infants to highlight gaps in the available knowledge, review some concerns about study design, and identify drugs that should receive high priority for future study.

METHODS

Relevant studies were identified through a search of MEDLINE and a review of textbooks, conference proceedings, and abstracts. The available literature was subjected to expert committee-based review.

CONCLUSIONS

There is a growing body of information on analgesic and anesthetic pharmacokinetics, pharmacodynamics, and clinical outcomes in neonates and infants, permitting safe and effective use in some clinical settings. Major gaps in knowledge persist, however. Future research may involve a combination of clinical trials and preclinical studies in suitable infant animal surrogate models.

Pain management for the hospitalized pediatric patient

Pediatric hospitalists should make pain assessment and treatment a high priority and a central part of their daily practice. Efforts at improving pain treatment in pediatric hospitals should be multidisciplinary and should involve combined use of pharmacologic and nonpharmacologic approaches. Although available information can permit effective treatment of pain for most children in hospitals, there is a need for more research on pediatric analgesic pharmacology, various nonpharmacologic treatments, and different models of delivery of care.

Drug bioactivation, covalent binding to target proteins and toxicity relevance

A number of therapeutic drugs with different structures and mechanisms of action have been reported to undergo metabolic activation by Phase I or Phase II drug-metabolizing enzymes. The bioactivation gives rise to reactive metabolites/intermediates, which readily confer covalent binding to various target proteins by nucleophilic substitution and/or Schiff's base mechanism. These drugs include analgesics (e.g., acetaminophen), antibacterial agents (e.g., sulfonamides and macrolide antibiotics), anticancer drugs (e.g., irinotecan), antiepileptic drugs (e.g., carbamazepine), anti-HIV agents (e.g., ritonavir), antipsychotics (e.g., clozapine), cardiovascular drugs (e.g., procainamide and hydralazine), immunosupressants (e.g., cyclosporine A), inhalational anesthetics (e.g., halothane), nonsteroidal anti-inflammatory drugs (NSAIDSs) (e.g., diclofenac), and steroids and their receptor modulators (e.g., estrogens and tamoxifen). Some herbal and dietary constituents are also bioactivated to reactive metabolites capable of binding covalently and inactivating cytochrome P450s (CYPs). A number of important target proteins of drugs have been identified by mass spectrometric techniques and proteomic approaches. The covalent binding and formation of drug-protein adducts are generally considered to be related to drug toxicity, and selective protein covalent binding by drug metabolites may lead to selective organ toxicity. However, the mechanisms involved in the protein adduct-induced toxicity are largely undefined, although it has been suggested that drug-protein adducts may cause toxicity either through impairing physiological functions of the modified proteins or through immune-mediated mechanisms. In addition, mechanism-based inhibition of CYPs may result in toxic drug-drug interactions. The clinical consequences of drug bioactivation and covalent binding to proteins are unpredictable, depending on many factors that are associated with the administered drugs and patients. Further studies using proteomic and genomic approaches with high throughput capacity are needed to identify the protein targets of reactive drug metabolites, and to elucidate the structure-activity relationships of drug's covalent binding to proteins and their clinical outcomes.

Nonsteroidal anti-inflammatory drugs and risk of prostate cancer in the Baltimore Longitudinal Study of Aging

BACKGROUND

Laboratory and epidemiologic studies suggest that aspirin and nonaspirin nonsteroidal anti-inflammatory drugs (NSAID) reduce the risk of cancer, possibly via inhibition of the cyclooxygenase enzymes. We evaluated the association of aspirin and nonaspirin NSAIDs with subsequent prostate cancer in a prospective study. We also assessed whether use of these drugs influences serum prostate-specific antigen (PSA) concentration.

METHODS

Participants were 1,244 male members of the Baltimore Longitudinal Study of Aging. Use of prescription and over-the-counter drugs was collected by questionnaire and interview at multiple study visits. One hundred forty-one prostate cancer cases diagnosed between 1980 and May 2004 were confirmed by medical record review. We used Cox proportional hazards regression to estimate the rate ratio (RR) of prostate cancer updating drug use over time and taking into account age and year. We used generalized estimating equations to calculate age-adjusted geometric mean PSA concentration by aspirin or nonaspirin NSAIDs use among 933 of the men without prostate cancer, for whom 3,749 PSA measurements in archived sera had been done previously.

RESULTS

On 46.0% and 21.5% of the visits, current use of aspirin or nonaspirin NSAIDs (mostly ibuprofen) was reported, respectively. The RRs of prostate cancer comparing ever to never use were 0.76 [95% confidence interval (95% CI), 0.54-1.07] for aspirin, 0.79 (95% CI, 0.54-1.16) for nonaspirin NSAIDs, and 0.71 (95% CI, 0.49-1.02) for either medication. The association for ever use of either aspirin or nonaspirin NSAIDs was suggestively more pronounced in men <70 years (RR, 0.54; 95% CI, 0.27-1.03) than in men >/=70 years (RR, 0.78; 95% CI, 0.50-1.22; P(interaction) = 0.73). The RR for current use of either drug was attenuated relative to ever use. Mean PSA concentration did not differ between users and nonusers of either aspirin or nonaspirin NSAIDs (1.01 versus 0.98 ng/mL, P = 0.56).

CONCLUSION

In this prospective study, men, in particular younger men, who had ever used aspirin or nonaspirin NSAIDs had a modest nonstatistically significant lower risk of prostate cancer. The modest inverse association was unlikely due to detection bias that might have resulted if anti-inflammatory drugs had influenced serum PSA concentration.

Mechanism of action of paracetamol

Paracetamol (acetaminophen) is generally considered to be a weak inhibitor of the synthesis of prostaglandins (PGs). However, the in vivo effects of paracetamol are similar to those of the selective cyclooxygenase-2 (COX-2) inhibitors. Paracetamol also decreases PG concentrations in vivo, but, unlike the selective COX-2 inhibitors, paracetamol does not suppress the inflammation of rheumatoid arthritis. It does, however, decrease swelling after oral surgery in humans and suppresses inflammation in rats and mice. Paracetamol is a weak inhibitor of PG synthesis of COX-1 and COX-2 in broken cell systems, but, by contrast, therapeutic concentrations of paracetamol inhibit PG synthesis in intact cells in vitro when the levels of the substrate arachidonic acid are low (less than about 5 mumol/L). When the levels of arachidonic acid are low, PGs are synthesized largely by COX-2 in cells that contain both COX-1 and COX-2. Thus, the apparent selectivity of paracetamol may be due to inhibition of COX-2-dependent pathways that are proceeding at low rates. This hypothesis is consistent with the similar pharmacological effects of paracetamol and the selective COX-2 inhibitors. COX-3, a splice variant of COX-1, has been suggested to be the site of action of paracetamol, but genomic and kinetic analysis indicates that this selective interaction is unlikely to be clinically relevant. There is considerable evidence that the analgesic effect of paracetamol is central and is due to activation of descending serotonergic pathways, but its primary site of action may still be inhibition of PG synthesis. The action of paracetamol at a molecular level is unclear but could be related to the production of reactive metabolites by the peroxidase function of COX-2, which could deplete glutathione, a cofactor of enzymes such as PGE synthase.

Acetaminophen-sensitive prostaglandin production in rat cerebral endothelial cells

Acetaminophen is a widely used antipyretic and analgesic drug whose mechanism of action has recently been suggested to involve inhibitory effects on prostaglandin synthesis via a newly discovered cyclooxygenase variant (COX-3). Because COX-3 expression is high in cerebral endothelium, we investigated the effect of acetaminophen on the prostaglandin production of cultured rat cerebral endothelial cells (CECs). Acetaminophen dose-dependently inhibited both basal and LPS-induced PGE2 production in CECs with IC50 values of 15.5 and 6.9 μM, respectively. Acetaminophen also similarly inhibited the synthesis of 6-keto-PGF1α and thromboxane B2. LPS stimulation increased the expression of COX-2 but not COX-1 or COX-3. In addition, the selective COX-2 inhibitor NS398 (1 μM) was equally as effective as acetaminophen in blocking LPS-induced PGE2 production. Acetaminophen did not influence the expression of the three COX isoforms and the inducible nitric oxide synthase. In LPS-stimulated isolated cerebral microvessels, acetaminophen also significantly inhibited PGE2 production. Our results show that prostaglandin production in CECs during basal and stimulated conditions is very sensitive to inhibition by acetaminophen and suggest that acetaminophen acts against COX-2 and not COX-1 or COX-3. Furthermore, our findings support a critical role for cerebral endothelium in the therapeutic actions of acetaminophen in the central nervous system.

Cyclooxygenase Isozymes: The Biology of Prostaglandin Synthesis and Inhibition

Nonsteroidal anti-inflammatory drugs (NSAIDs) represent one of the most highly utilized classes of pharmaceutical agents in medicine. All NSAIDs act through inhibiting prostaglandin synthesis, a catalytic activity possessed by two distinct cyclooxygenase (COX) isozymes encoded by separate genes. The discovery of COX-2 launched a new era in NSAID pharmacology, resulting in the synthesis, marketing, and widespread use of COX-2 selective drugs. These pharmaceutical agents have quickly become established as important therapeutic medications with potentially fewer side effects than traditional NSAIDs. Additionally, characterization of the two COX isozymes is allowing the discrimination of the roles each play in physiological processes such as homeostatic maintenance of the gastrointestinal tract, renal function, blood clotting, embryonic implantation, parturition, pain, and fever. Of particular importance has been the investigation of COX-1 and -2 isozymic functions in cancer, dysregulation of inflammation, and Alzheimer's disease. More recently, additional heterogeneity in COX-related proteins has been described, with the finding of variants of COX-1 and COX-2 enzymes. These variants may function in tissue-specific physiological and pathophysiological processes and may represent important new targets for drug therapy.

Cyclooxygenases 1, 2, and 3 and the Production of Prostaglandin I2: Investigating the Activities of Acetaminophen and Cyclooxygenase-2-Selective Inhibitors in Rat Tissues

It has been suggested recently that cyclooxygenase-3, formed as a splice variant of cyclooxygenase-1, is the enzymatic target for acetaminophen. To investigate the relative roles of the putative three cyclooxygenase isoforms in different target tissues, we compared the inhibitory effects of acetaminophen, a cyclooxygenase-2-selective inhibitor; rofecoxib, a nonsteroid anti-inflammatory drug; naproxen; and a cyclooxygenase-1-selective inhibitor, SC560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole]. Prostanoid production by aorta, heart, lung, and whole blood was inhibited by all drugs tested with the order of potency SC560 > naproxen > acetaminophen >/= rofecoxib. In brain and cerebellum, no differences among drug potencies were found. Reverse transcription-polymerase chain reaction analysis of aorta, brain, cerebellum, heart, and lung showed general expression of cyclooxygenase-1 and cyclooxygenase-3 mRNA and particular expression of cyclooxygenase-2 mRNA in brain and cerebellum. Western blotting demonstrated general expression of cyclooxygenase-1 in test tissues and cyclooxygenase-2 within the brain and cerebellum. Western blotting using a commercially available antibody raised against canine cyclooxygenase-3 failed to detect any immunoreactive proteins. In conclusion, our studies indicate that cyclooxygenase-1 and cyclooxygenase-2 are the functional forms of the enzyme present in the rat tissues tested and that acetaminophen is not a selective inhibitor of "cyclooxygenase" activities in the central nervous system. This is consistent with the apparent impossibility for the expression of cyclooxygenase active protein from cyclooxygenase-3 mRNA in the rat. Also, our experiments show that the ability of rofecoxib to depress the circulating levels of prostaglandin I(2) is more readily associated with its ability to reduce production from the lung, heart, or brain than from arterial vessels.

The cyclooxygenase isozyme inhibitors parecoxib and paracetamol reduce central hyperalgesia in humans

Non-steroidal antiinflammatory drugs (NSAIDs) are known to induce analgesia mainly via inhibition of cyclooxygenase (COX). Although the inhibition of COX in the periphery is commonly accepted as the primary mechanism, experimental and clinical data suggest a potential role for spinal COX-inhibition to produce antinociception and reduce hypersensitivity. We used an experimental model of electrically evoked pain and hyperalgesia in human skin to determine the time course of central analgesic and antihyperalgesic effects of intravenous parecoxib and paracetamol (acetaminophen). Fourteen subjects were enrolled in this randomized, double blind, and placebo controlled cross-over study. In three sessions, separated by 2-week wash-out periods, the subjects received intravenous infusions of 40 mg parecoxib, 1000 mg paracetamol, or placebo. The magnitude of pain and areas of pinprick-hyperalgesia and touch evoked allodynia were repeatedly assessed before, and for 150 min after the infusion. While pain ratings were not affected, parecoxib as well as paracetamol significantly reduced the areas of secondary hyperalgesia to pinprick and touch. In conclusion, our results provide clear experimental evidence for the existence of central antihyperalgesia induced by intravenous infusion of two COX inhibitors, parecoxib and paracetamol. Since the electrical current directly stimulated the axons, peripheral effects of the COX inhibitors on nociceptive nerve endings cannot account for the reduction of hyperalgesia. Thus, besides its well-known effects on inflamed peripheral tissues, inhibition of central COX provides an important mechanism of NSAID-mediated antihyperalgesia in humans.

Mechanisms of action of paracetamol and related analgesics

Paracetamol and salicylate are weak inhibitors of both isolated cyclooxygenase-1 (COX-1) and COX-2 but are potent inhibitors of prostaglandin (PG) synthesis in intact cells if low concentrations of arachidonic acid are available. The effects of both drugs are overcome by increased levels of hydroperoxides. At low concentrations of arachidonic acid, COX-2 is the major isoenzyme involved in PG synthesis when both COX-1 and COX-2 are present in cells. Therefore, paracetamol and salicylate may selectively inhibit PG synthesis involving COX-2 because the lower flux through this pathway produces lesser levels of the hydroperoxide, PGG(2), than the pathway involving COX-1. Apart from the lack of anti-inflammatory effect of paracetamol in rheumatoid arthritis, the clinical effects of paracetamol and salicylate are very similar and resemble those of the selective COX-2 inhibitors. A splice variant of COX-1, termed COX-3, may be a site of action of these drugs but, further work, particularly at low concentrations of arachidonic acid is required. We suggest that paracetamol, salicylate and, possibly, the pyrazolone drugs, such as dipyrone, may represent a distinct class of atypical NSAIDs which could be termed peroxide sensitive analgesic and antipyretic drugs (PSAADs).

Variants of cyclooxygenase-1 and their roles in medicine

Acetaminophen (paracetamol) and other analgesic/antipyretic drugs such as dipyrone have been postulated to act centrally through inhibition of cyclooxygenases (COXs). COX activity in lipopolysaccharide-stimulated mammalian leukocytes, microglial cells, and platelets is inhibited by these drugs at physiological concentrations. Yet purified COX enzymes are poorly inhibited by acetaminophen, particularly under conditions of high oxidant tone and elevated substrate levels. This suggests the presence of cell-specific differences that govern COX inhibition by these drugs. COX-3, a variant of COX-1, has been found in canine brain and is inhibited by acetaminophen and dipyrone at physiological concentrations. Additionally, other new COX-1-derived proteins called PCOX have been identified that do not make prostaglandins but apparently bind heme and may have other enzymatic properties. Antibodies specific for these variants detect analogous proteins in human tissues. Expression of COX variants is postulated to be an integral part of the mechanism of action of analgesic/antipyretic drugs.