Pharmacokinetic-pharmacodynamic correlations and biomarkers in the development of COX-2 inhibitors

Managing the adverse effects of nonsteroidal anti-inflammatory drugs

Conventional medical treatment for rheumatoid arthritis and osteoarthritis includes the use of NSAIDs (traditional and selective inhibitors of cyclooxygenase [COX]-2), because they provide unmistakable and significant health benefits in the treatment of pain and inflammation. However, they are associated with an increased risk of serious gastrointestinal (GI) and cardiovascular (CV) adverse events. Both beneficial and adverse effects are due to the same mechanism of action, which is inhibition of COX-dependent prostanoids. Since CV and GI risk are related to drug exposure, a reduction in the administered dose is recommended. However, this strategy will not eliminate the hazard owing to a possible contribution of individual genetic background. Further studies will be necessary to develop genetic and/or biochemical markers predictive of the CV and GI risk of NSAIDs.

Role of intravenous acetaminophen in postoperative pain management

SUMMARY The need to safely treat the postoperative pain of patients is apparent. Opioids, although effective, have multiple morbidities associated with their use. A multimodal approach to postoperative pain management can serve to minimize the undesirable effects of opioids. Intravenous acetaminophen (paracetamol) has recently become available in the USA where many practitioners are not familiar with this drug. This article reviews the history, pharmacology and clinical uses of intravenous acetaminophen in the treatment of perioperative pain.

Translation of drug effects from experimental models of neuropathic pain and analgesia to humans

Neuropathic pain research remains a challenging undertaking owing to: (i) the lack of understanding about the underlying disease processes; and (ii) poor predictive validity of the current models of evoked pain used for the screening of novel compounds. Common consensus is that experimental models replicate symptoms (i.e. have face validity but no construct validity). Another issue that requires attention is the sensitivity of endpoints to discriminate drug effects that are relevant to the disease in humans. In this paper we provide an overview of the pre-clinical models that can be used in conjunction with a model-based approach to facilitate the prediction of drug effects in humans. Our review strongly suggests that evidence of the concentration-effect relationship is necessary for translational purposes.

Paracetamol and cyclooxygenase inhibition: is there a cause for concern?

Paracetamol is recommended as first-line therapy for pain associated with osteoarthrosis and is one of the most widely used over-the-counter analgesic drugs worldwide. Despite its extensive use, its mode of action is still unclear. Although it is commonly stated that paracetamol acts centrally, recent data imply an inhibitory effect on the activity of peripheral prostaglandin-synthesising cyclooxygenase enzymes. In this context paracetamol has been suggested to inhibit both isoforms in tissues with low levels of peroxide by reducing the higher oxidation state of cyclooxygenase enzymes. Two recent studies have also demonstrated a preferential cyclooxygenase 2 (COX-2) inhibition by paracetamol under different clinically relevant conditions. This review attempts to relate data on paracetamol's inhibitory action on peripheral cyclooxygenase enzymes to the published literature on its anti-inflammatory action and its hitherto underestimated side-effects elicited by cyclooxygenase inhibition. As a result, a pronounced COX-2 inhibition by paracetamol is expected to occur in the endothelium, possibly explaining its cardiovascular risk in epidemiological studies. A careful analysis of paracetamol's cardiovascular side-effects in randomised studies is therefore strongly advised. On the basis of epidemiological data showing an increased gastrointestinal risk of paracetamol at high doses or when co-administered with classic cyclooxygenase inhibitors, paracetamol's long-term gastrointestinal impact should be investigated in randomised trials. Finally, paracetamol's fast elimination and consequently short-lived COX-2 inhibition, which requires repetitive dosing, should be definitely considered to avoid overdosage leading to hepatotoxicity.

Risk management profile of etoricoxib: an example of personalized medicine

The development of nonsteroidal anti-inflammatory drugs (NSAIDs) selective for cyclooxygenase (COX)-2 (named coxibs) has been driven by the aim of reducing the incidence of serious gastrointestinal (GI) adverse events associated with the administration of traditional (t) NSAIDs – mainly dependent on the inhibition of COX-1 in GI tract and platelets. However, their use has unravelled the important protective role of COX-2 for the cardiovascular (CV) system, mainly through the generation of prostacyclin. In a recent nested-case control study, we found that patients taking NSAIDs (both coxibs and tNSAIDs) had a 35% increase risk of myocardial infarction. The increased incidence of thrombotic events associated with profound inhibition of COX-2-dependent prostacyclin by coxibs and tNSAIDs can be mitigated, even if not obliterated, by a complete suppression of platelet COX-1 activity. However, most tNSAIDs and coxibs are functional COX-2 selective for the platelet (ie, they cause a profound suppression of COX-2 associated with insufficient inhibition of platelet COX-1 to translate into inhibition of platelet function), which explains their shared CV toxicity. The development of genetic and biochemical markers will help to identify the responders to NSAIDs or who are uniquely susceptible at developing thrombotic or GI events by COX inhibition. We will describe possible strategies to reduce the side effects of etoricoxib by using biochemical markers of COX inhibition, such as whole blood COX-2 and the assessment of prostacyclin biosynthesis in vivo.

Pharmacokinetic-pharmacodynamic modeling of the inhibitory effects of naproxen on the time-courses of inflammatory pain, fever, and the ex vivo synthesis of TXB2 and PGE2 in rats

PURPOSE

To quantify and compare the time-course and potency of the analgesic and antipyretic effects of naproxen in conjunction with the inhibition of PGE(2) and TXB(2).

METHODS

Analgesia was investigated in a rat model with carrageenan-induced arthritis using a gait analysis method. Antipyretics were studied in a yeast-induced fever model using telemetrically recorded body temperature. Inhibition of TXB(2) and PGE(2) synthesis was determined ex vivo. Pharmacokinetic profiles were obtained in satellite animals. Population PKPD modeling was used to analyze the data.

RESULTS

The IC(50) values (95% CI) of naproxen for analgesia (27 (0-130) μM), antipyretics (40 (30-65) μM) and inhibition of PGE(2) (13 (6-45) μM) were in similar range, whereas inhibition of TXB(2) (5 (4-8) μM) was observed at lower concentrations. Variability in the behavioral measurement of analgesia was larger than for the other endpoints. The inhibition of fever by naproxen was followed by an increased rebound body temperature.

CONCLUSION

Due to better sensitivity and similar drug-induced inhibition, the biomarker PGE(2) and the antipyretic effect would be suitable alternative endpoints to the analgesic effects for characterization and comparisons of potency and time-courses of drug candidates affecting the COX-2 pathway and to support human dose projections.

Modelling and simulation as research tools in paediatric drug development

Purpose

Although practical and ethical constraints impose special requirements for the evaluation of treatment safety and efficacy in children, the main issue remains the empirical basis for patient stratification and dose selection at the early stage of the development of new chemical and biological entities. The aim of this review is to highlight the advantages and limitations of modelling and simulation (M&S) in supporting decision making during paediatric drug development.

Methods

A literature search on Pubmed’s database Medical Subject Headings (MeSH) has been performed to retrieve relevant publications on the use of model-based approaches in paediatric drug development and therapeutics.

Results

M&S enable the assessment of the impact of different regimens as well as of different populations on a drug’s safety and efficacy profile. It has been widely used in the last two decades to support pre-clinical and early clinical drug development. In fact, M&S have been applied to drug development as decision tools, as study optimization tools and as data analysis tools. In particular, this approach can be used to support dose adjustment in specific subgroups of a population. M&S may therefore allow the individualisation of drug therapy in children, improving the risk–benefit ratio in this population.

Conclusions

The lack of consensus on how to assess the impact of developmental factors on pharmacokinetics, pharmacodynamics, efficacy and safety has so far prevented a broader use of M&S. This problem is compounded by the limited collaboration between stakeholders, which prevents data sharing in this field. In this article, we emphasise the need for a concerted effort to promote the effective use of this technology in paediatric drug development and avoid unnecessary exposure of children to clinical trials.

Tumor necrosis factor-α induces sensitization of meningeal nociceptors mediated via local COX and p38 MAP kinase actions

The proinflammatory cytokine TNF-α has been shown to promote activation and sensitization of primary afferent nociceptors. The downstream signaling processes that play a role in promoting this neuronal response remain however controversial. Increased TNF-α plasma levels during migraine attacks suggest that local interaction between this cytokine and intracranial meningeal nociceptors plays a role in promoting the headache. Here, using in vivo single unit recording in the trigeminal ganglia of anesthetized rats, we show that meningeal TNF-α action promotes a delayed mechanical sensitization of meningeal nociceptors. Using immunohistochemistry, we provide evidence for non-neuronal localization of the TNF receptors TNFR1 to dural endothelial vascular cells and TNFR2 to dural resident macrophages as well as to some CGRP-expressing dural nerve fibers. We also demonstrate that meningeal vascular TNFR1 is co-localized with COX-1 while the perivascular TNFR2 is co-expressed with COX-2. We further report here for the first time that TNF-α evoked sensitization of meningeal nociceptors is dependent upon local action of cyclooxygenase (COX). Finally, we show that local application of TNF-α to the meninges evokes activation of the p38 MAP kinase in dural blood vessels that also express TNFR1 and that pharmacological blockade of p38 activation inhibits TNF-α evoked sensitization of meningeal nociceptors. Our study suggests that meningeal action of TNF-α could play an important role in the genesis of intracranial throbbing headaches such as migraine through a mechanism that involves at least part activation of non-neuronal TNFR1 and TNFR2 and downstream activation of meningeal non-neuronal COX and the p38 MAP kinase.

[Cardiovascular complications with cyclooxygenase inhibitors : Myths and facts]

During the last decade there have been nearly 10,000 publications dealing with the cardiovascular risk of cyclooxygenase inhibitors and it can be concluded that the use of both selective and non-selective inhibitors is accompanied by a substantial cardiovascular risk (e.g. infarction, thromboembolic events, cardiac insufficiency and possibly stroke). As these pharmaceuticals, including paracetamol and acetylsalicylic acid, belong to the most used medications and safer alternatives are still lacking it will be the aim in the future to keep the risk connected with the therapy with these drugs limited despite the fact that the aging population will demand an increased consumption of analgesics. Choosing the right substance (e.g. selective versus non-selective, fast elimination versus slow elimination) and the correct dosage, i.e. the lowest possible dosing range, will help to keep the risk within tolerable limits. In addition biomarkers have emerged which will allow the identification of patients with a high risk of cardiovascular hepatic and gastrointestinal side effects.

Using pharmacokinetic principles to optimize pain therapy

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

Nonsteroidal anti-inflammatory drugs increase TNF production in rheumatoid synovial membrane cultures and whole blood

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase activity and hence PG production. However, the ability of NSAIDs to ameliorate pain and tenderness does not prevent disease progression in rheumatoid arthritis, a disease whose pathogenesis is linked to the presence of proinflammatory cytokines, such as TNF-alpha. To understand this observation, we have examined the effect of NSAIDs on the production of clinically validated proinflammatory cytokines. We show that a variety of NSAIDs superinduce production of TNF from human peripheral blood monocytes and rheumatoid synovial membrane cultures. A randomized, double-blinded, crossover, placebo-controlled trial in healthy human volunteers also revealed that the NSAID drug celecoxib increased LPS-induced TNF production in whole blood. NSAID-mediated increases in TNF are reversed by either the addition of exogenous PGE(2) or by a PGE(2) EP2 receptor agonist, revealing that PGE(2) signaling via its EP2 receptor provides a valuable mechanism for controlling excess TNF production. Thus, by reducing the level of PGE(2), NSAIDs can increase TNF production and may exacerbate the proinflammatory environment both within the rheumatoid arthritis joint and the systemic environment.

Measurement of cyclooxygenase inhibition using liquid chromatography-tandem mass spectrometry

Because cyclooxygenases (COX) convert arachidonic acid into pro-inflammatory cyclic endoperoxides, inhibition of these enzymes and especially the inducible COX-2 form is an important therapeutic approach to manage inflammatory diseases and possibly prevent cancer. Due to side effects of existing non-selective and COX-2 selective non-steroidal anti-inflammatory agents, the discovery of new COX inhibitors continues to be an area of active investigation. Since existing assays are slow or lack specificity, a liquid chromatography-tandem mass spectrometry (LC-MS-MS) based COX inhibition assay was developed and validated for the rapid and accurate quantitative analysis of the COX product prostaglandin E(2). The assay was validated using four COX inhibitors, celecoxib, indomethacin, resveratrol, and diclofenac that exhibit different selectivities towards COX-1 and COX-2. The IC(50) values of celecoxib and resveratrol for ovine and human COX-2 were compared, and the K(m) values were determined. Since considerable inter-species variation was observed, human COX-2 should be used for the discovery of COX inhibitors intended for human use. This sensitive and accurate LC-MS-MS based assay is suitable for the rapid screening of ligands for COX-1 and COX-2 inhibition and for IC(50) determinations.

In Silico Screening of Nonsteroidal Anti-Inflammatory Drugs and Their Combined Action on Prostaglandin H Synthase-1

The detailed kinetic model of Prostaglandin H Synthase-1 (PGHS-1) was applied to in silico screening of dose-dependencies for the different types of nonsteroidal anti-inflammatory drugs (NSAIDs), such as: reversible/irreversible, nonselective/selective to PGHS-1/PGHS-2 and time dependent/independent inhibitors (aspirin, ibuprofen, celecoxib, etc.) The computational screening has shown a significant variability in the IC50s of the same drug, depending on different in vitro and in vivo experimental conditions. To study this high heterogeneity in the inhibitory effects of NSAIDs, we have developed an in silico approach to evaluate NSAID action on targets under different PGHS-1 microenvironmental conditions, such as arachidonic acid, reducing cofactor, and peroxide concentrations. The designed technique permits translating the drug IC₅₀, obtained in one experimental setting to another, and predicts in vivo inhibitory effects based on the relevant in vitro data. For the aspirin case, we elucidated the mechanism underlying the enhancement and reduction (aspirin resistance) of its efficacy, depending on PGHS-1 microenvironment in in vitro/in vivo experimental settings. We also present the results of the in silico screening of the combined action of sets of two NSAIDs (aspirin with ibuprofen, aspirin with celecoxib), and study the mechanism of the experimentally observed effect of the suppression of aspirin-mediated PGHS-1 inhibition by selective and nonselective NSAIDs. Furthermore, we discuss the applications of the obtained results to the problems of standardization of NSAID test assay, dependence of the NSAID efficacy on cellular environment of PGHS-1, drug resistance, and NSAID combination therapy.

Variability among nonsteroidal antiinflammatory drugs in risk of upper gastrointestinal bleeding

OBJECTIVE

Traditional nonsteroidal antiinflammatory drugs (NSAIDs) increase the risk of upper gastrointestinal (GI) bleeding/perforation, but the magnitude of this effect for coxibs in the general population and the degree of variability between individual NSAIDs is still under debate. This study was undertaken to assess the risk of upper GI bleeding/perforation among users of individual NSAIDs and to analyze the correlation between this risk and the degree of inhibition of whole blood cyclooxygenase 1 (COX-1) and COX-2 in vitro.

METHODS

We conducted a systematic review of observational studies on NSAIDs and upper GI bleeding/perforation published between 2000 and 2008. We calculated pooled relative risk (RR) estimates of upper GI bleeding/perforation for individual NSAIDs. Additionally, we verified whether the degree of inhibition of whole blood COX-1 and COX-2 in vitro by average circulating concentrations predicted the RR of upper GI bleeding/perforation.

RESULTS

The RR of upper GI bleeding/perforation was 4.50 (95% confidence interval [95% CI] 3.82-5.31) for traditional NSAIDs and 1.88 (95% CI 0.96-3.71) for coxibs. RRs lower than that for NSAIDs overall were observed for ibuprofen (2.69 [95% CI 2.17-3.33]), rofecoxib (2.12 [95% CI 1.59-2.84]), aceclofenac (1.44 [95% CI 0.65-3.2]), and celecoxib (1.42 [95% CI 0.85-2.37]), while higher RRs were observed for ketorolac (14.54 [95% CI 5.87-36.04]) and piroxicam (9.94 [95% CI 5.99-16.50). Estimated RRs were 5.63 (95% CI 3.83-8.28) for naproxen, 5.57 (95% CI 3.94-7.87) for ketoprofen, 5.40 (95% CI 4.16-7.00) for indomethacin, 4.15 (95% CI 2.59-6.64) for meloxicam, and 3.98 (95% CI 3.36-4.72) for diclofenac. The degree of inhibition of whole blood COX-1 did not significantly correlate with RR of upper GI bleeding/perforation associated with individual NSAIDs (r(2) = 0.34, P = 0.058), but a profound and coincident inhibition (>80%) of both COX isozymes was associated with higher risk. NSAIDs with a long plasma half-life and with a slow-release formulation were associated with a greater risk than NSAIDs with a short half-life.

CONCLUSION

The results of our analysis demonstrate that risk of upper GI bleeding/perforation varies between individual NSAIDs at the doses commonly used in the general population. Drugs that have a long half-life or slow-release formulation and/or are associated with profound and coincident inhibition of both COX isozymes are associated with a greater risk of upper GI bleeding/perforation.

Pharmacokinetic-pharmacodynamic modelling of the analgesic effects of lumiracoxib, a selective inhibitor of cyclooxygenase-2, in rats

BACKGROUND AND PURPOSE

This study establishes a pharmacokinetic/pharmacodynamic (PK/PD) model to describe the time course and in vivo mechanisms of action of the antinociceptive effects of lumiracoxib, evaluated by the thermal hyperalgesia test in rats.

EXPERIMENTAL APPROACH

Female Wistar fasted rats were injected s.c. with saline or carrageenan in the right hind paw, followed by either 0, 1, 3, 10 or 30 mg*kg(-1) of oral lumiracoxib at the time of carrageenan injection (experiment I), or 0, 10 or 30 mg*kg(-1) oral lumiracoxib at 4 h after carrageenan injection (experiment II). Antihyperalgesic responses were measured as latency time (LT) to a thermal stimulus. PK/PD modelling of the antinociceptive response was performed using the population approach with NONMEM VI.

RESULTS

A two-compartment model described the plasma disposition. A first-order model, including lag time and decreased relative bioavailability as a function of the dose, described the absorption process. The response model was: LT=LT(0)/(1 +MED). LT(0) is the baseline response, and MED represents the level of inflammatory mediators. The time course of MED was assumed to be equivalent to the predicted profile of COX-2 activity and was modelled according to an indirect response model with a time variant synthesis rate. Drug effects were described as a reversible inhibition of the COX-2 activity. The in vivo estimate of the dissociation equilibrium constant of the COX-2-lumiracoxib complex was 0.24 microg*mL(-1).

CONCLUSIONS

The model developed appropriately described the time course of pharmacological responses to lumiracoxib, in terms of its mechanism of action and pharmacokinetics.

A randomized double blind comparison of short-term duodenally administrated whale and seal blubber oils in patients with inflammatory bowel disease and joint pain

Compared with soy oil, 10 days treatment with seal oil (SO), 10mLx3 daily, self-administrated through a nasoduodenal feeding tube, relieves joint pain in patients with inflammatory bowel disease (IBD). This randomized, controlled, double blind pilot trial compares SO and whale oil (WO) administered similarly by duodenal tube, for 10 days in 18 patients with IBD-related joint pain (n=9 per group). Other long chain n-3 polyunsaturated fatty acids were prohibited 7-days prior to and during study. Significant changes from baseline to study end were observed in both groups: reduced plasma arachidonic acid to eicosapentaenoic acid ratio and prostaglandin E(2) (PGE(2)) levels (tendency in WO group), decreased IBD-related joint pain and IBD-disease activity, and improved quality of life. These changes were not significantly different between SO and WO groups. Inhibition of cyclooxygenase is consistent with amelioration of IBD-related joint pain, but, as active control was used, effects need confirmation.

The search for new COX-2 inhibitors: a review of 2002 - 2008 patents

BACKGROUND

Two COX isoenzymes are known, COX-1 and COX-2, for which the main inhibitors are the NSAIDs. The common anti-inflammatory drugs (such as aspirin, ibuprofen and naproxen) all act by blocking the action of both the COX-1 and COX-2 enzymes. The COX-2 inhibitors represent a new class of drugs that do not affect COX-1 but selectively block COX-2. This selective action provides the benefits of reducing inflammation without irritating the stomach and cardiovascular effects.

OBJECTIVE

This review focuses on patents published in the field during 2002 - 2008, paying particular attention to promising COX-2 inhibitors.

CONCLUSION

Structural analogues of the COX-2 inhibitors celecoxib and valdecoxib, and novel potential pyridazine, triazole, indole and thione derivatives emerge as promising leads for the treatment of inflammation, pain and other diseases.

Systemic bioavailability of topical diclofenac sodium gel 1% versus oral diclofenac sodium in healthy volunteers

Systemic bioavailability and pharmacodynamics of topical diclofenac sodium gel 1% were compared with those of oral diclofenac sodium 50-mg tablets. In a randomized, 3-way crossover study, healthy volunteers (n = 40) received three 7-day diclofenac regimens: (A) 16 g gel applied as 4 g to 1 knee 4 times daily (4 g on surface area 400 cm(2)), (B) 48 g gel applied as 4 g per knee 4 times daily to 2 knees plus 2 g gel per hand applied 4 times daily to 2 hands (12 g on 1200 cm(2)), and (C) 150 mg oral diclofenac applied as 50-mg tablets 3 times daily. Thirty-nine participants completed all 3 regimens. Systemic exposure was greater with oral diclofenac (AUC(0-24), 3890 +/- 1710 ng x h/mL) than with topical treatments A (AUC(0-24), 233 +/- 128 ng x h/mL) and B (AUC(0-24), 807 +/- 478 ng x h/mL). Oral diclofenac inhibited platelet aggregation, cyclooxygenase-1 (COX-1), and COX-2. Topical diclofenac did not inhibit platelet aggregation and inhibited COX-1 and COX-2 less than oral diclofenac. Treatment-related adverse events were mild and limited to application site reactions with diclofenac sodium gel 1% (n = 4) and gastrointestinal reactions with oral diclofenac (n = 3). Systemic exposure with diclofenac sodium gel 1% was 5- to 17-fold lower than with oral diclofenac. Systemic effects with topical diclofenac were less pronounced.

Impact of chronic inflammation on the pharmacokinetic-pharmacodynamic relationship of naproxen

OBJECTIVES

The use of biomarkers for predicting the clinical doses of analgesic drugs relies on the understanding of the relationship between drug exposure and response under disease conditions. In this study, we demonstrate the relevance of such a relationship for COX-inhibitors by modelling the effect of naproxen on prostaglandin E2 (PGE(2)) and thromboxane B2 (TXB(2)) in a chronic inflammation model in rats.

METHODS

Rats were treated with Freund's complete adjuvant (FCA) by intraplantar injection. On post-inoculation days (PID) 7-21, animals received single or chronic (qd until day 21) doses of naproxen (10mg/kg). Blood samples were collected at various intervals after dosing to characterise naproxen pharmacokinetics and its effects on PGE(2) and TXB(2) production. PK-PD modelling was performed using nonlinear mixed effects in NONMEM.

RESULTS

The inhibition of PGE(2) and TXB(2) could be described by a sigmoid E(max) model. A decrease in the potency estimates of both biomarkers was observed under chronic inflammation, as compared to healthy animals. IC(50) values for PGE(2) inhibition showed a shift from 2840+/-510 to 4000+/-677ng/ml(mean+/-SD), whilst IC(50) values for TXB(2) inhibition increased from 1180+/-323 to 3360+/-453ng/ml in healthy and FCA-inoculated animals, respectively.

CONCLUSIONS

Our results show that chronic inflammation causes a significant change in the potency estimates for COX-inhibition. These findings illustrate the implications of pathophysiological processes on pharmacodynamics and consequently on the required exposure levels for achieving response during chronic treatment.

Parecoxib and indomethacin delay early fracture healing: a study in rats

Nonsteroidal antiinflammatory drugs (NSAIDs) are used to reduce inflammatory response and pain. These drugs have been reported to impair bone metabolism. Parecoxib, a specific COX-2 inhibitor, exerts an inhibitory effect on the mineralization of fracture callus after a tibial fracture in rats. Decreased bone mineral density (BMD) at a fracture site may indicate impairment of early healing, casting doubt on the safety of using COX-2 inhibitors during the early treatment of diaphyseal fractures. Forty-two female Wistar rats were randomly allocated to three groups. They were given parecoxib, indomethacin, or saline intraperitoneally for 7 days after being subjected to a closed tibial fracture stabilized with an intramedullary nail. Two and 3 weeks after surgery, the bone density at the fracture site was measured using dual energy xray absorptiometry (DEXA). Three weeks after the operation the rats were euthanized and the healing fractures were mechanically tested in three-point cantilever bending. Parecoxib decreased BMD at the fracture site for 3 weeks after fracture, indomethacin for 2 weeks. Both parecoxib and indomethacin reduced the ultimate bending moment and the bending stiffness of the healing fractures after 3 weeks. These results suggest COX inhibitors should be avoided in the early phase after fractures.

Role of dose potency in the prediction of risk of myocardial infarction associated with nonsteroidal anti-inflammatory drugs in the general population

OBJECTIVES

We studied the association between the frequency, dose, and duration of different nonsteroidal anti-inflammatory drugs (NSAIDs) and the risk of myocardial infarction (MI) in the general population. We verified whether the degree of inhibition of whole blood cyclooxygenase (COX)-2 by average circulating drug levels can be a surrogate biochemical predictor of the risk of MI by NSAIDs.

BACKGROUND

There is evidence that both traditional NSAIDs and selective inhibitors of COX-2 may increase the risk of MI.

METHODS

From the THIN (The Health Improvement Network) database, we identified 8,852 cases of nonfatal MI in patients 50 to 84 years old between 2000 and 2005 and conducted a nested case-control analysis. We correlated the risk of MI with the degree of inhibition of platelet COX-1 and monocyte COX-2 in vitro by average therapeutic concentrations of individual NSAIDs.

RESULTS

The risk of MI was increased with current use of NSAIDs (relative risk [RR]: 1.35; 95% confidence interval [CI]: 1.23 to 1.48). The risk increased with treatment duration and daily dose. We found a significant correlation between the degree of inhibition in vitro of whole blood COX-2 (r(2) = 0.7458, p = 0.0027), but not whole blood COX-1 (r(2) = 0.0007, p = 0.947), and the risk of MI associated with individual NSAIDs that lacked complete suppression (> or =95%) of platelet COX-1 activity. Individual NSAIDs with a degree of COX-2 inhibition <90% at therapeutic concentrations presented an RR of 1.18 (95% CI: 1.02 to 1.38), whereas those with a greater COX-2 inhibition had an RR of 1.60 (95% CI: 1.41 to 1.81).

CONCLUSIONS

Our findings suggest that the variable risk of MI among NSAIDs that do not inhibit platelet COX-1 completely and persistently is largely related to their extent of COX-2 inhibition.

Comparison of pharmacokinetic and pharmacodynamic profiles of aspirin following oral gavage and diet dosing in rats

Aspirin is one of the oldest drugs and has been purported to have multiple beneficial effects, including prevention of cardiovascular disease and cancer, in addition to its original indication for treatment of inflammation, fever and pain. In cancer chemoprevention studies using animal models, two methods of aspirin administration have been employed: oral gavage and diet. The untested assumption was that exposure and the resultant pharmacological effects are similar for these two administration methods when dosing is normalized on the basis of mg/kg body weight/day. This study examined and compared time-dependent plasma and colon mucosal concentrations of aspirin metabolite salicylate (aspirin concentrations were below level of quantification), plasma thromboxane B(2) concentrations, and colon mucosal prostaglandin E(2) concentration following these two different dosing paradigms in rats. Diet dosing yielded relatively constant plasma and colon salicylate concentration vs. time profiles. On the other hand, oral gavage dosing led to a rapid peak followed by a fast decline in salicylate concentration in both plasma and colon. Nevertheless, the exposure as measured by the area under plasma or colon concentration-time curve of salicylate was linearly related to dose irrespective of the dosing method. Linear relationships were also observed between colon and plasma salicylate areas under the curve and between colon prostaglandin E(2) and plasma thromboxane B(2) areas under the curve. Therefore, more easily accessible plasma salicylate and thromboxane B(2) concentrations were representative of the salicylate exposure and prostaglandin E(2) pharmacodynamic biomarker in the target colon, respectively.

Sensitization of meningeal nociceptors: inhibition by naproxen

Migraine attacks associated with throbbing (manifestation of peripheral sensitization) and cutaneous allodynia (manifestation of central sensitization) are readily terminated by intravenous administration of a non-selective cyclooxygenase (COX) inhibitor. Evidence that sensitization of rat central trigeminovascular neurons was also terminated in vivo by non-selective COX inhibition has led us to propose that COX inhibitors may act centrally in the dorsal horn. In the present study, we examined whether COX inhibition can also suppress peripheral sensitization in meningeal nociceptors. Using single-unit recording in the trigeminal ganglion in vivo, we found that intravenous infusion of naproxen, a non-selective COX inhibitor, reversed measures of sensitization induced in meningeal nociceptors by prior exposure of the dura to inflammatory soup (IS): ongoing activity of Adelta- and C-units and their response magnitude to mechanical stimulation of the dura, which were enhanced after IS, returned to baseline after naproxen infusion. Topical application of naproxen or the selective COX-2 inhibitor N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide (NS-398) onto the dural receptive field of Adelta- and C-unit nociceptors also reversed the neuronal hyper-responsiveness to mechanical stimulation of the dura. The findings suggest that local COX activity in the dura could mediate the peripheral sensitization that underlies migraine headache.

Can drug removals involving cyclooxygenase-2 inhibitors be avoided? A plea for human pharmacology

Within the past 20 years many cyclooxygenase (COX) inhibitors were removed for unwanted drug effects shortly after entering the drug market (e.g. benoxaprofen and isoxicam), whereas others (e.g. diclofenac and ibuprofen) were not. This has continued with the suspension of the sale of the COX-2 inhibitors rofecoxib, valdecoxib and lumiracoxib, whereas others (e.g. celecoxib and etoricoxib) are still available. All these compounds share the same molecular mode of action but differ considerably in their pharmacokinetics. Determination of pharmacokinetic-pharmacodynamic relationships should help to pinpoint deficits, answer pending questions and lead to a safer drug use. Here, we provide evidence that applying the ex vivo human whole-blood assay could provide a valuable tool for defining the lowest effective dose and the adequate dosing interval of COX inhibitors. In our opinion, such an approach could reduce unwanted drug effects and obviate drug removals.

Negative effect of parecoxib on bone mineral during fracture healing in rats

BACKGROUND AND PURPOSE

Non-steroidal anti-inflammatory drugs (NSAIDs) are conventional cyclooxygen-ase (cox) inhibitors commonly used in musculoskeletal trauma to reduce the inflammatory response and pain, but they also seem to affect bone metabolism. Parecoxib is a cox inhibitor that selectively inhibits cox-2. Through their selective mechanism of action, these newer drugs are supposed to reduce the gastrointestinal side effects of conventional cox inhibitors. The effects on bone metabolism and healing have, however, not been fully elucidated. Thus, there are reasons for concern regarding the potential negative effects of these drugs on bone metabolism and bone repair. We investigated the effects of short-term administration of parecoxib on bone mineral formation and bone healing in rats.

ANIMALS AND METHODS

26 female Wistar rats were given parecoxib intraperitoneally for 7 days after a closed tibial fracture that was stabilized with an intra-medullary nail, and 26 animals were given saline. At 2, 3, and 6 weeks after surgery bone mineral density (BMD) at the fracture site was measured using dualenergy X-ray absorptiometry (DEXA). 6 weeks after the fracture, 14 rats from the parecoxib group and 16 rats from the placebo group were killed for mechanical testing, and the rest of the animals were killed for tissue analysis. The healing fractures and the intact contralateral tibias were mechanically tested by three-point cantilever bending.

RESULTS

The BMD at the fracture site was calculated as the average of the results after 2,3, and 6 weeks. Mean BMD was lower in the parecoxib group, 0.23 (SD 0.06) g/ cm2, than in the control group, 0.27 (SD 0.05) g/cm2 (p = 0.01). There were no statistically significant differences in mechanical properties of the healing fractures after 6 weeks. However, the study may have lacked sufficient statistical power to determine whether a negative effect on healing had occurred.

INTERPRETATION

No mechanical differences were detected between the control and treatment groups after 6 weeks, but they may have been present earlier in the fracture healing process. Our findings do, however, indicate that parecoxib given postoperatively for a week has a negative effect on mineralization during the early phase of fracture healing.

Integrated pharmacokinetics and pharmacodynamics in drug development

Drug development is a complex, lengthy and expensive process. Pharmaceutical companies and regulatory authorities have recognised that the drug development process needs optimisation for efficiency in view of the return on investments. Pharmacokinetics and pharmacodynamics are the two main principles determining the relationship between dose and response. This article provides an update on integrated approaches towards drug development by linking pharmacokinetics, pharmacodynamics and disease aspects into mathematical models. Gradually, a transition is taking place from a rather empirical approach towards a modelling- and simulation-based approach to drug development. The main learning phases should be phases 0, I and II, whereas phase III studies should merely have a confirmatory purpose. In model-based drug development, mechanism-based mathematical models, which are iteratively refined along the path of development, incorporate the accumulating knowledge of the investigational drug, the disease and their mutual interference in different subsets of the target population. These models facilitate the design of the next study and improve the probability of achieving the projected efficacy and safety endpoints. In this article, several theoretical and practical aspects of an integrated approach towards drug development are discussed, together with some case studies from different therapeutic areas illustrating the application of pharmacokinetic/pharmacodynamic disease models at different stages of drug development.

Assessment of celecoxib pharmacodynamics in pancreatic cancer

Cyclooxygenase-2 (COX-2) inhibitors are being developed as chemopreventive and anticancer agents. This study aimed to determine the biological effect of the COX-2 inhibitor celecoxib in pancreatic cancer as an early step to the further development of the agent in this disease. Eight patients scheduled for resection of an infiltrating adenocarcinoma of the pancreas were randomized to receive celecoxib at a dose of 400 mg twice daily or placebo for 5 to 15 days before the surgery. In addition, carcinomas from nine additional patients were xenografted in nude mice, expanded, and treated with vehicle or celecoxib for 28 days. Celecoxib markedly decreased the intra-tumor levels of prostaglandin E2 in patient carcinomas and in the heterotransplanted xenografts. However, this effect did not result in inhibition of cell proliferation or microvessel density (as assessed by Ki67 and CD31 staining). In addition, a panel of markers, including bcl-2, COX-1, COX-2, and VEGF, did not change with treatment in a significant manner. Furthermore, there was no evidence of antitumor effects in the xenografted carcinomas. In summary, celecoxib efficiently inhibited the synthesis of prostaglandin E2 both in pancreatic cancer surgical specimens and in xenografted carcinomas but did not exert evident antitumor, antiproliferative, or antiangiogenic effect as a single agent. The direct pancreatic cancer xenograft model proved to be a valuable tool for drug evaluation and biological studies and showed similar results to those observed in resected pancreatic cancer specimens.

Human pharmacology of naproxen sodium

We compared the variability in degree and recovery from steady-state inhibition of cyclooxygenase (COX)-1 and COX-2 ex vivo and in vivo and platelet aggregation by naproxen sodium at 220 versus 440 mg b.i.d. and low-dose aspirin in healthy subjects. Six healthy subjects received consecutively naproxen sodium (220 and 440 mg b.i.d.) and aspirin (100 mg daily) for 6 days, separated by washout periods of 2 weeks. COX-1 and COX-2 inhibition was determined using ex vivo and in vivo indices of enzymatic activity: 1) the measurement of serum thromboxane (TX)B(2) levels and whole-blood lipopolysaccharide-stimulated prostaglandin (PG)E(2) levels, markers of COX-1 in platelets and COX-2 in monocytes, respectively; 2) the measurement of urinary 11-dehydro-TXB(2) and 2,3-dinor-6-keto-PGF(1alpha) levels, markers of systemic TXA(2) biosynthesis (mostly COX-1-derived) and prostacyclin biosynthesis (mostly COX-2-derived), respectively. Arachidonic acid (AA)-induced platelet aggregation was also studied. The maximal inhibition of platelet COX-1 (95.9 +/- 5.1 and 99.2 +/- 0.4%) and AA-induced platelet aggregation (92 +/- 3.5 and 93.7 +/- 1.5%) obtained at 2 h after dosing with naproxen sodium at 220 and 440 mg b.i.d., respectively, was indistinguishable from aspirin, but at 12 and 24 h after dosing, we detected marked variability, which was higher with naproxen sodium at 220 mg than at 440 mg b.i.d. Assessment of the ratio of inhibition of urinary 11-dehydro-TXB(2) versus 2,3-dinor-6-keto-PGF(1alpha) showed that the treatments caused a more profound inhibition of TXA(2) than prostacyclin biosynthesis in vivo throughout dosing interval. In conclusion, neither of the two naproxen doses mimed the persistent and complete inhibition of platelet COX-1 activity obtained by aspirin, but marked heterogeneity was mitigated by the higher dose of the drug.

1,5-Biaryl pyrrole derivatives as EP1 receptor antagonists. Structure–activity relationships of 6-substituted and 5,6-disubstituted benzoic acid derivatives

Herein we describe the SAR of 1,5-biaryl pyrrole derivatives, with substituents in the 6-position of the benzoic acid moiety, as EP(1) receptor antagonists. Substitution at this position was well tolerated and led to the identification of several analogues with high affinity for the EP(1) receptor that displayed good efficacy in the established FCA model of inflammatory pain. Furthermore, several analogues were prepared which combined substitution at the 5- and 6-positions as well as derivatives with an aromatic ring fused to the 5- and 6-positions.

Pharmacological characterization of a selective COX-2 inhibitor MF-tricyclic, [3-(3,4-difluorophenyl)-4-(4-(methylsulfonyl)phenyl)-2-(5H)-furanone], in multiple preclinical species

Selective type 2 cyclooxygenase (COX-2) inhibitors are often used in preclinical studies without potency and selectivity data in the experimental species. To address this issue, we assessed a selective COX-2 inhibitor MF-tricyclic in four commonly used species, namely mice, rats, guinea pigs and rabbits, in the present study. In both the guinea pig and rabbit whole blood assay, the compound inhibited lipopolysaccharide (LPS)-induced PGE(2) production with an IC(50) (COX-2) of 0.6 and 2.8 microM, respectively. By comparison, the compound displayed a much weaker activity on clot-induced formation of thromboxane with an IC(50) (COX-1) of >10 microM (guinea pigs) and 23 microM (rabbits). In keeping with the in vitro potency data, the compound significantly inhibited interleukin-1 beta (IL-1beta) -induced PGE(2) formation in the rabbit synovium at plasma concentrations near the whole blood assay IC(50) for COX-2 but much lower than that for COX-1. MF-tricyclic was also potent and selective toward COX-2 in mice, inhibiting carrageenan-induced PGE(2) accumulation in the air pouch dose-dependently (ED(50)=0.5 mg/kg) without affecting stomach PGE(2) levels. In rats, MF-tricyclic was found to be effective in three standard in vivo assays utilized for assessing COX-2 inhibitors, namely, LPS-induced pyresis, carrageenan-induced paw edema and adjuvant-induced arthritis at the doses that did not inhibit stomach PGE(2) levels. Similar to that in rats, the compound displayed pharmacological efficacy in mice, guinea pigs and rabbits when tested in the LPS pyresis model. Our data reveal that MF-tricyclic has the desired biochemical and pharmacological properties for selective COX-2 inhibition in all four test species.

Immunomodulatory effect of nonsteroidal anti-inflammatory drugs (NSAIDs) at the clinically available doses

Non-steroidal anti-inflammatory drugs (NSAIDs) with cyclooxygenase (COX) inhibitory activity are commonly used in various inflammatory diseases. In this study, to examine the immunomodulatory effects of well known NSAIDs at clinically available doses, macrophage- and T cell-mediated immune responses such as tumor necrosis factor (TNF)-alpha release and nitric oxide (NO) production, cell-cell adhesion, phagocytic uptake and lymphocyte proliferation were investigated. NSAIDs tested significantly enhanced TNF-alpha release from lipopolysaccharide (LPS)-activated RAW264.7 cells at certain concentrations (fenoprofen, indomethacin, piroxicam, aceclofenac, diclofenac and sulindac) or in a dose-dependent manner (aspirin and phenylbutazone). Of NSAIDs, phenylbutazone and aspirin most potently attenuated NO production, although sulindac was the only compound with cytoprotective activity against LPS-induced cytotoxicity. Most NSAIDs used displayed weak or no modulatory effects on phagocytic uptake and CD29- or CD43-mediated cell-cell adhesion. Interestingly, however, phenylbutazone itself triggered cell-cell clustering under normal culture conditions and enhanced the phagocytic activity. Aspirin and phenylbutazone also dose-dependently attenuated CD4+ T cell proliferation stimulated by concanavalin A (Con A) and CD8+ CTLL-2 cell proliferation induced by interleukin (IL)-2. Sulindac only blocked CTLL-2 cell proliferation. These results suggest that NSAIDs may differentially exert immunomodulatory effects on activated macrophages and lymphocytes, and some of the effects may enforce NSAID's therapeutic effect against inflammatory symptoms.

Selective and nonselective cyclooxygenase-2 inhibitors and experimental fracture-healing. Reversibility of effects after short-term treatment

BACKGROUND

Cyclooxygenase-2-specific anti-inflammatory drugs (coxibs) and nonspecific nonsteroidal anti-inflammatory drugs have been shown to inhibit experimental fracture-healing. The present study tested the hypothesis that these effects are reversible after short-term treatment.

METHODS

With use of a standard model of fracture-healing, identical ED50 dosages of either a nonsteroidal anti-inflammatory drug (ketorolac), a coxib (valdecoxib), or vehicle (control) were orally administered to rats for either seven or twenty-one days and fracture-healing was assessed with biomechanical, histological, and biochemical analyses.

RESULTS

When healing was assessed at twenty-one days, the seven-day treatment produced only a trend for a higher rate of nonunion in valdecoxib and ketorolac-treated animals as compared with controls. No differences were observed at thirty-five days. The twenty-one-day treatment produced significantly more nonunions in valdecoxib-treated animals as compared with either ketorolac-treated or control animals (p < 0.05), but these differences disappeared by thirty-five days. The dose-specific inhibition of these drugs on prostaglandin E2 levels and the reversibility of the effects after drug withdrawal were assessed in fracture calluses and showed that ketorolac treatment led to twofold to threefold lower levels of prostaglandin E2 than did valdecoxib. Withdrawal of either drug after six days led to a twofold rebound in these levels by fourteen days. Histological analysis showed delayed remodeling of calcified cartilage and reduced bone formation in association with valdecoxib treatment.

CONCLUSIONS

Cyclooxygenase-2-specific drugs inhibit fracture-healing more than nonspecific nonsteroidal anti-inflammatory drugs, and the magnitude of the effect is related to the duration of treatment. However, after the discontinuation of treatment, prostaglandin E2 levels are gradually restored and the regain of strength returns to levels similar to control.

Pharmacological and histopathological characterization of a hyperalgesia model induced by freeze lesion

Induction of a freeze lesion in human skin is an experimental model of hyperalgesia that allows assessing the antihyperalgesic effects of traditional non-steroidal anti-inflammatory drugs (NSAIDs). We have investigated whether this model is also sensitive to selective cyclooxygenase (COX)-2 inhibitors and have characterized morphological substrates of the generated hyperalgesia in the skin. In eight healthy subjects, a freeze lesion was induced and mechanical pain thresholds (MPT) were tested for 5h following administration of the non-selective COX inhibitor diclofenac (75mg), the COX-2-selective inhibitor parecoxib (40mg) or placebo in a randomized, double-blind cross-over study. In five additional healthy subjects, biopsies were taken from normal skin and the area of freezing injury. Induction of the freeze lesion resulted in hyperalgesia expressed by a decrease of MPT after 24h. Diclofenac and parecoxib, but not placebo, statistically significantly elevated MPT. Histochemical and Western blot analyses of skin biopsies revealed a strong upregulation of COX-2, a slight decrease of COX-1 and activation of nuclear factor kappa B (NF-kappaB) in the area of the freezing injury. These findings indicate that the freeze lesion model is sensitive to NSAIDs including selective COX-2 inhibitors, and that NF-kappaB-dependent COX-2 upregulation contributes to the hyperalgesia in this model.

Pharmacodynamic of cyclooxygenase inhibitors in humans

We provide comprehensive knowledge on the differential regulation of expression and catalysis of cyclooxygenase (COX)-1 and COX-2 in health and disease which represents an essential requirement to read out the clinical consequences of selective and nonselective inhibition of COX-isozymes in humans. Furthermore, we describe the pharmacodynamic and pharmacokinetic characteristics of major traditional nonsteroidal anti-inflammatory drugs (tNSAIDs) and coxibs (selective COX-2 inhibitors) which play a prime role in their efficacy and toxicity. Important information derived from our pharmacological studies has clarified that nonselective COX inhibitors should be considered the tNSAIDs with a balanced inhibitory effect on both COX-isozymes (exemplified by ibuprofen and naproxen). In contrast, the tNSAIDs meloxicam, nimesulide and diclofenac (which are from 18- to 29-fold more potent towards COX-2 in vitro) and coxibs (i.e. celecoxib, valdecoxib, rofecoxib, etoricoxib and lumiracoxib, which are from 30- to 433-fold more potent towards COX-2 in vitro) should be comprised into the cluster of COX-2 inhibitors. However, the dose and frequency of administration together with individual responses will drive the degree of COX-2 inhibition and selectivity achieved in vivo. The results of clinical pharmacology of COX inhibitors support the concept that the inhibition of platelet COX-1 may translate into an increased incidence of serious upper gastrointestinal bleeding but this effect on platelet COX-1 may mitigate the cardiovascular hazard associated with the profound inhibition of COX-2-dependent prostacyclin (PGI2).

Translating genomic biomarkers into clinically useful diagnostics

The landmark sequencing of the human genome has ushered in a new field of large-scale research. Advances in understanding the molecular basis of disease have opened up new opportunities to develop genomics-based tools to diagnose, predict disease onset or recurrence, tailor treatment options, and assess treatment response. Although still in the early stages of research and development, genomic biomarker research has the capability of providing a comprehensive insight into pathophysiological processes as well as more precise predictors of outcome not previously attainable with traditional biomarkers. Before genomic biomarkers are incorporated into clinical practice, several issues will need to be addressed in order to generate the necessary levels of evidence to demonstrate analytical and clinical validity and utility. In addition, efforts will be needed to educate health professionals and the public about genomics-based tools, revise regulatory oversight mechanisms, and ensure privacy safeguards of the information generated from these new tests.

Correlation between in vitro and in vivo concentration-effect relationships of naproxen in rats and healthy volunteers

Understanding the mechanisms underlying the analgesic effect of new cyclooxygenase inhibitors is essential to identify dosing requirements in early stages of drug development. Accurate extrapolation to humans of in vitro and in vivo findings in preclinical species is needed to optimise dosing regimen in inflammatory conditions. The current investigation characterises the inhibition of prostaglandin E2 (PGE(2)) and thromboxane B2 (TXB(2)) by naproxen in vitro and in vivo in rat and human blood. The inhibition of PGE(2) in the absence or presence of increasing concentrations of naproxen (10(-8)-10(-1) M) was measured by ex vivo whole blood stimulation with LPS, whereas inhibition of TXB(2) was measured in serum following blood clotting. In further experiments, inhibition of PGE(2) and TXB(2) levels was also assessed ex vivo in animals treated with naproxen (2.5, 10, 25 mg kg(-1)). Subsequently, pharmacokinetic (PK)/pharmacodynamics (PD) modelling of in vitro and in vivo data was performed using nonlinear mixed effects in NONMEM (V). Inhibition of PGE(2) and TXB(2) was characterised by a sigmoid E(max) model. The exposure-response relationships in vitro and in vivo were of the same order of magnitude in both species. IC(80) estimates obtained in vitro were similar for PGE(2) inhibition (130.8 +/- 11 and 131.9 +/- 19 10(-6) M, mean +/- s.d. for humans and rats, respectively), but slightly different for TXB(2) inhibition (103.9+/-15 and 151.4 +/- 40 10(-6) M, mean +/- s.d. for humans and rats, respectively, P < 0.05). These differences, however, may not be biologically relevant. The results confirm the value of exposure-effect relationships determined in vitro as a means to predict the pharmacological activity in vivo. This analysis also highlights the need to parameterise concentration-effect relationships in early drug development, as indicated by the estimates of IC(80) for PGE(2) and TXB(2) inhibition.

Mechanism-Based Pharmacokinetic–Pharmacodynamic Modeling—A New Classification of Biomarkers

In recent years, pharmacokinetic/pharmacodynamic (PK/PD) modeling has developed from an empirical descriptive discipline into a mechanistic science that can be applied at all stages of drug development. Mechanism-based PK/PD models differ from empirical descriptive models in that they contain specific expressions to characterize processes on the causal path between drug administration and effect. Mechanism-based PK/PD models have much improved properties for extrapolation and prediction. As such, they constitute a scientific basis for rational drug discovery and development. In this report, a novel classification of biomarkers is proposed. Within the context of mechanism-based PK/PD modeling, a biomarker is defined as a measure that characterizes, in a strictly quantitative manner, a process, which is on the causal path between drug administration and effect. The new classification system distinguishes seven types of biomarkers: type 0, genotype/phenotype determining drug response; type 1, concentration of drug or drug metabolite; type 2, molecular target occupancy; type 3, molecular target activation; type 4, physiological measures; type 5, pathophysiological measures; and type 6, clinical ratings. In this paper, the use of the new biomarker classification is discussed in the context of the application of mechanism-based PK/PD analysis in drug discovery and development.