Reduction of cisplatin-induced emesis by a selective neurokinin-1-receptor antagonist. L-754,030 Antiemetic Trials Group

Spirocyclic NK(1) antagonists I: [4.5] and [5.5]-spiroketals

A series of novel spiroketal-based NK(1) antagonists is described. The effect of modifications to the spiroether ring and aromatic substituents are discussed, leading to the identification of compounds with high affinity and excellent CNS penetration.

Identification of metabolites of a substance P (neurokinin 1 receptor) antagonist in rat hepatocytes and rat plasma

[3R,5R,6S]-3-(2-cyclopropyloxy-5-trifluoromethoxyphenyl)-6-phenyl-1-oxa-7-azaspiro[4.5]decane is a substance P (Neurokinin 1 receptor) antagonist. Substance P antagonists are proven in concept to have excellent potential for the treatment of major depression, and they allow superior and sustained protection from acute and delayed chemotherapy-induced emesis. The metabolism of this compound was investigated in rat hepatocytes, and circulating rat plasma metabolites were identified following oral and intravenous dosing. The turnover in rat hepatocytes within 4 h was about 30%, and the major metabolites were identified as two nitrones and a lactam associated with the piperidine ring. Although these metabolites were also observed in rat plasma, the major circulating metabolite was a keto acid following oxidative de-amination of the piperidine ring. Liquid chromatography/tandem mass spectrometry and nuclear magnetic resonance were used to confirm the structure of the latter metabolite. A mechanism leading to the formation of the keto acid metabolite has been suggested, and most intermediates were observed in rat plasma.

Control of nausea and vomiting after chemotherapy: what is the evidence?

The control of nausea and vomiting is an important problem for patients undergoing chemotherapy. With the introduction of newer agents, including 5-HT3 antagonists, nausea and vomiting control after chemotherapy has much improved but is not always optimal. While there is an intrinsic limitation to the efficacy of anti-emetic drugs, their efficacy can be further reduced if the drugs are not used appropriately. In some circumstances newer anti-emetics may be unnecessary and better nausea and vomiting control may be established by use of older agents. This paper summarizes current evidence regarding the optimal approach to management of nausea and vomiting in patients undergoing chemotherapy.

Conflicts of interest in drug development: the practices of Merck & Co., Inc

Conflicts of interest are common and exist in academia, government, and many industries, including pharmaceutical development. Medical journal editors and others have recently criticized "the pharmaceutical industry," citing concerns over investigator access to data, approaches to analysis of clinical trial data, and publication practices. Merck & Co., Inc. is a global, research-driven pharmaceutical company that discovers, develops, manufactures, and markets a broad range of human and animal health products, directly and through its joint ventures. Although part of its mission is to provide a superior rate of return to its investors, Merck does not believe this creates an irreconcilable conflict of interest, particularly in activities concerning clinical drug development. We employ rigorous scientific methods to design, conduct, analyze, and report results of clinical trials in the development of innovative drugs and vaccines, with a focus on meeting unmet medical needs and with an ethic that puts the interests of the patient first. This article describes Merck's approaches to potential conflicts of interest in drug development, particularly with regard to clinical trials. We believe that proprietary interests of the Company can be respected while observing objectivity and transparency in communicating clinical research results. The standards for the review of manuscripts reporting such trials for peer-reviewed publication should be the same, whether they are from Merck or elsewhere.

Anti-emetics in development

Despite important advances in pharmacotherapeutic options for the prevention and treatment of nausea and vomiting during the 1990s, a significant proportion of patients still suffer debilitating nausea and vomiting symptoms. The most problematic areas are chemotherapy-induced nausea and vomiting particularly delayed emesis, postoperative nausea and vomiting, opioid-induced nausea and vomiting and motion sickness. The most vigorous research into new anti-emetics has focused on the neurokinin-1 (substance P) antagonists. Clinical trials conducted to date indicate that these agents have similar efficacy to 5-HT(3) antagonists in acute chemotherapy-induced nausea and vomiting, superior efficacy to available agents in delayed emesis, possibly superior efficacy against emesis in postoperative nausea and vomiting and no evidence of efficacy versus opioid or motion-induced nausea and vomiting. Other pharmacological strategies in development include agonising CB1 (cannabinoid) receptors, "broad spectrum" receptor antagonists and 5-HT(1A) receptor agonists, although clinical trials of these types of agents are not yet available. The neurokinin-1 antagonists appear to be promising agents for some nausea and vomiting states, although further clarification of their role is required.

Prevention of cisplatin-induced acute and delayed emesis by the selective neurokinin-1 antagonists, L-758,298 and MK-869

BACKGROUND

Recent studies have suggested that antiemetic therapy with a triple combination of the neurokinin-1 receptor antagonist MK-869, a serotonin (5-HT(3)) antagonist, and dexamethasone provides enhanced control of cisplatin-induced emesis compared with standard therapy regimens. The authors compared the antiemetic activity of a dual combination of MK-869 and dexamethasone with that of a standard dual combination of ondansetron and dexamethasone to characterize further the efficacy and tolerability profile of MK-869.

METHODS

This was a multicenter, double-blind, randomized, active agent-controlled study of 177 cisplatin-naïve patients with malignant disease. On Day 1, MK-869 was given intravenously as its water-soluble prodrug, L-758,298. Patients were randomized to one of three groups as follows. Group I received L-758,298 100 mg intravenously (i.v.), then dexamethasone 20 mg i.v., and cisplatin >or= 70 mg/m(2) on Day 1 followed by 300 mg MK-869 (tablet) orally on Days 2-5; Group II received L-758,298 100 mg i.v., then dexamethasone 20 mg i.v., and cisplatin >or= 70 mg/m(2) on Day 1 followed by placebo on Days 2-5; and Group III received ondansetron 32 mg i.v., then dexamethasone 20 mg i.v., and cisplatin >or= 70 mg/m(2) on Day 1 followed by placebo on Days 2-5. Emesis was recorded over Days 1-5 in a diary. Nausea was assessed every 24 hours by visual analog scale. Additional medication was available for emesis or nausea at any time. The primary efficacy parameters of interest were the proportion of patients without emesis and the proportion without emesis or rescue therapy on Day 1 (acute phase) and on Days 2-5 (delayed phase).

RESULTS

No serious adverse events were attributed to L-758,298 or MK-869. On Day 1, the proportions of patients with no emesis and no use of rescue medication were 44% of patients in Group I, 36% of patients in Group II, 40% of patients in Groups I and II combined, and 83% of patients in Group III (P < 0.001 for Group III vs. the combined Groups I and II). The proportions of patients with no emesis and no use of rescue medication on Days 2-5 were 59% of patients in Group I, 46% of patients in Group II, and 38% of patients in Group III (P < 0.05 for Group I vs. Group III). The proportions of patients who were without emesis on Day 1 were 49% of patients in Group I, 47% of patients in Group II, and 84% of patients in Group III (P < 0.01 for Group I or II vs. Group III). On Days 2-5, however, the proportions of patients who were without emesis on Days 2-5 were 65% of patients in Group I, 61% of patients in Group II, and 41% of patients in Group III (P < 0.05 for Group I or II vs. Group III). Nausea scores in the acute phase were lower for Group III than for Group I, Group II, or Groups I and II combined (P < 0.05), although there was no significant difference among groups either for the delayed phase or overall for Days 1-5.

CONCLUSIONS

Although the L-758,298 and dexamethasone combination reduced acute (Day 1) emesis compared with historic rates, dual therapy with ondansetron and dexamethasone was superior in controlling acute emesis. Continued dosing with MK-869 may enhance control of other measures of delayed emesis, such as the use of rescue medication, although confirmation is required before a definitive conclusion may be drawn. MK-869 given as dual therapy with dexamethasone was superior to ondansetron with dexamethasone for the control of delayed emesis (Days 2-5) and control of the need for rescue medication on Days 2-5.

Substance P and affective disorders: new treatment opportunities by neurokinin 1 receptor antagonists?

Substance P (SP) is a neuropeptide which is abundant in the periphery and the central nervous system, where it is colocalized with other neurotransmitters such as serotonin or dopamine. SP has been proposed to play a role in the regulation of pain including migraine and fibromyalgia, asthma, inflammatory bowel disease, emesis, psoriasis as well as in central nervous system disorders. This review summarizes our current knowledge of the role of SP in the pathogenesis of neuropsychiatric disorders with special emphasis on affective disorders including bipolar disorders. It also reviews current treatment approaches with neurokinin 1 receptor antagonists which appear to be promising drugs for the future treatment of affective disorders.

A new class of antiemetic agents on the horizon

This article reviews a new class of antiemetic agents, the neurokinin-1 (NK-1) receptor antagonists (RAs). Clinical trials of an NK-1 RA, aprepitant, are ongoing.

Anti-emetics for cancer chemotherapy-induced emesis: Potential of alternative delivery systems

Currently, the most commonly used routes of administration of antiemetics in chemotherapeutic regimens are oral and intravenous. Patient compliance and thus efficacy of conventional drug schedules and formulations are often impaired by difficulties associated with oral or intravenous uptake of the administered chemotherapy. Alternative or new drug delivery systems should overcome these problems by improving patient compliance. Several new drug delivery systems are available and development of these new systems is ongoing, in particular to meet delivery requirements of modern biological therapeutics and the application of gene therapy. However, at the present time, the implementation of new techniques of alternative antiemetic drug administration for chemotherapy-induced emesis is very limited. The challenge for clinical investigations to further develop new delivery systems, in particular for antiemetic therapies, remains.

Management of Chemotherapy-Induced Nausea and Vomiting

Nausea and vomiting are among the most distressing adverse effects of cancer chemotherapy. They can lead to both physical and psychological complications if uncontrolled. The exact mechanism for chemotherapy-induced nausea and vomiting is not known; it is thought to occur through numerous neuronal pathways acting on different sites. Chemotherapy-induced nausea and vomiting are broken down into 3 phases: acute, delayed, and anticipatory. The incidence of each phase depends largely on the chemotherapy agent used and is primarily treated with different antiemetic agents. Pharmacists can assist in optimizing antiemetic use by selecting appropriate antiemetics based on the emetogenicity of the cancer treatment and helping to individualize therapy to each patient’s specific needs.

New agents, new treatment, and antiemetic therapy

With the introduction of newer antineoplastic agents, the challenge for supportive care is enlarging. For the most part, these targeted therapies are given in addition to more classic anticancer drugs, either in combination or in sequence, underscoring the need for prevention of emesis and attention to all treatment toxicities. Strategies for preventing these side effects need to be investigated while appropriately addressing more familiar problems such as emesis. Two directions for improving emetic control are clear. First is the development of newer antiemetics that enhance current control rates, and second is the proper use of existing agents in all emetic settings. This report outlines the rationale behind the development of neurokinin type 1 antagonists, and reviews consensus recommendations in the prevention of acute and delayed emesis.

Central neurocircuitry associated with emesis

Ingestion of toxin, traumatic events, adverse drug reactions, and motion can all result in nausea and emesis. In addition, cyclic vomiting syndrome is quite prevalent in the pediatric population. Coordination of the various autonomic changes associated with emesis occurs at the level of the medulla oblongata of the hindbrain. Chemosensitive receptors detect emetic agents in the blood and relay this information by means of neurons in the area postrema to the adjacent nucleus tractus solitarius (NTS). Abdominal vagal afferents that detect intestinal luminal contents and gastric tone also terminate in the NTS (gelatinosus, commissural, and medial subnuclei). The NTS is viscerotopically organized into subnuclei that subserve diverse functions related to swallowing (subnucleus centralis), gastric sensation (subnucleus gelatinosus), laryngeal and pharyngeal sensation (intermediate and interstitial NTS), baroreceptor function (medial NTS), and respiration (ventrolateral NTS). Neurons from the NTS project to a central pattern generator (CPG), which coordinates the sequence of behaviors during emesis, as well as directly to diverse populations of neurons in the ventral medulla and hypothalamus. Thus, it is critical to realize that there is not an isolated "vomiting center," but rather groups of loosely organized neurons throughout the medulla that may be activated in sequence by a CPG. The newer antiemetic agents appear to block receptors in the peripheral endings of vagal afferents to reduce "perception" of emetic stimuli and/or act in the dorsal vagal complex. A primary site of action of 5-HT(3)-receptor antagonists is by means of the vagal afferents. Neurokinin-1 receptor (NK(1)R) antagonists are antiemetics, because they act at a site in the dorsal vagal complex. Part of their effectiveness may be the result of inhibition of the NK(1)R on vagal motor neurons to prevent fundic relaxation, which is a prodromal event essential for emesis. Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the major psychoactive component of marijuana, can be therapeutically useful as an antiemetic. The site of action of Delta(9)-THC is on cannabinoid CB1 receptors in the dorsal vagal complex. However, it decreases fundic tone and antral motility. It is not easy to predict the potential antiemetic effects of drugs that alter motility. Although antiemetic drugs are available for management of acute chemotherapeutic-induced emesis, few treatments are effective for delayed emesis or cyclic vomiting syndrome.

Prospective evaluation of antiemetic outcome following high-dose chemotherapy with hematopoietic stem cell support

Considerable progress has been made in improving the control of chemotherapy-induced emesis. The impact of available antiemetic options for patients receiving stem cell transplants is unclear, as few prospective data have been collected. We prospectively evaluated antiemetic outcome in patients receiving stem cell transplantation over a 7-day period following the initiation of chemotherapy. The primary endpoints were the number of emetic episodes and the extent of nausea measured on a four-point scale. Eighty-two patients were evaluated. Ninety-five percent of patients had nausea during the first week of treatment; 80% had at least one emetic episode. The percentage of patients with emesis was as follows: day 1: 13%, day 2: 21%, day 3: 30%, day 4: 38%, day 5: 44%, day 6: 39%, day 7: 18%. In multivariate analysis, gender, emesis with prior chemotherapy, history of morning or motion sickness, type of transplant (auto vs allo), use of total body irradiation, or use of dexamethasone did not effect emesis control. Most patients receiving high-dose chemotherapy experience incompletely controlled emesis. Control of nausea and emesis progressively worsened with each subsequent day following initiation of chemotherapy, reaching a nadir on day 5. New treatment approaches are needed to improve emesis control in this patient population.

Localization of phosphodiesterase-4 isoforms in the medulla and nodose ganglion of the squirrel monkey

Pre-clinical and clinical studies are currently underway to evaluate the potential of phosphodiesterase-4 (PDE4) inhibitors for the treatment of chronic obstructive pulmonary disease and other inflammatory conditions of the airways. The most common side effect associated with this class of compounds is emesis. The squirrel monkey provides a model for evaluating the efficacy of PDE4 inhibitors and their emetic potential. The distribution of three PDE4 isoforms (A, C and D) has been investigated in the squirrel monkey medulla and nodose ganglion to determine which isoform(s) could be responsible for the emetic adverse effects. The distribution of PDE4 isoforms was delineated using immunohistochemistry with antibodies specific for PDE4A, PDE4C and PDE4D and by in situ hybridization with isoform-selective riboprobes. PDE4A was present in the medulla where expression was mostly restricted to glial cells and the vasculature. PDE4C was not detected in either the medulla or nodose ganglion. Finally, the PDE4D isoform was localized to neurons in the nodose ganglion and found through many structures of medulla including the area postrema, neurons of the nucleus tractus solitarius and locus coeruleus. These data are consistent with a role for PDE4D in the emetic response.

Effects of CP-99, 994, a tachykinin NK(1) receptor antagonist, on abdominal afferent vagal activity in ferrets: evidence for involvement of NK(1) and 5-HT(3) receptors

The effect of CP-99, 994, a tachykinin NK(1) receptor antagonist, on abdominal vagal afferent nerve activity in the ferret was investigated. Substance P (1 microg/kg, i.v.) increased vagal afferent activity by 449.0+/-51.9% and this was reduced to 145.9+/-5.7% (p<0.01) by pre-treatment with CP-99, 994 (1 mg/kg, i.v.), and to 149.5+/-1.5% (p<0.001) by granisetron (1 mg/kg, i.v.), a 5-HT(3) receptor antagonist. In addition, the increase in vagal nerve activity induced by 5-HT (25 microg/kg, i.v., 552.0+/-57.0% increase from pre-injection level) was significantly reduced (401.3+/-10.6% increase from pre-injection level, p<0.05) by CP-99, 994 (100 microg/kg, i.v.). These results provide evidence for an involvement of peripheral NK(1) and 5-HT(3) receptors in substance P-induced vagal afferent activation. While the functional consequences (if any) of such peripheral effects were not investigated, they could contribute either directly (e.g. by blockade of receptors on vagal afferents) or indirectly (e.g. modulation of 5-HT release or reduction of local inflammatory response) to the antiemetic effects of CP-99, 994 against cisplatin and other emetic agents acting primarily via the vagus.

Substance P: a new era, a new role

Substance P has been extensively studied and is considered the prototypic neuropeptide of the more than 50 known neuroactive molecules. The understanding of substance P has evolved beyond the original concept as the pain transmitter of the dorsal horn. Animal and genetic research, recent developments of nonpeptide substance P antagonists, and important changes in the understanding of neurotransmission have each contributed to the current understanding of substance P After 7 decades, the physiologic role of substance P is known as a modulator of nociception, involved in signaling the intensity of noxious or aversive stimuli. Genetic studies in mice and development of substance P antagonists provide more recent results that support the redefinition of the central role of substance P Evidence suggests that this neuropeptide is an integral part of central nervous system pathways involved in psychologic stress.

The broad-spectrum anti-emetic activity of AS-8112, a novel dopamine D2, D3 and 5-HT3 receptors antagonist

The anti-emetic and pharmacological profile of AS-8112 ((R)-5-bromo-N-(1-ethyl-4-methylhexahydro-1H-1,4-diazepin-6-yl)-2-methoxy-6-methylamino-3-pyridinecarboxamide.2 fumarate), a novel and potent dopamine D2, D3 and 5-hydroxytryptamine-3 (5-HT3) receptors ligand, was investigated in the present study. In guinea-pig isolated colon, AS-8112 produced a rightward shift of the concentration-response curves of 2-methyl-5HT, a 5-HT3 receptor agonist (pA2 value of 7.04). Other 5-HT3 receptor antagonists also produced such a shift in the following antagonistic-potency order: granisetron> ondansetron=AS-8112>>metoclopramide. In mice, AS-8112 (1.0 - 3.0 mg kg(-1) s.c.) potently inhibited hypothermia induced by the dopamine D3 receptor agonist; R(+)-7-OH-DPAT (R(+)-7-hydroxy-2-(N,N-di-n-propylamino)tetraline) (0.3 mg kg(-1) s.c.). Domperidone and haloperidol, which have affinity for dopamine D3 receptor, also inhibited R(+)-7-OH-DPAT-induced hypothermia. In ferrets or dogs, AS-8112 dose-dependently inhibited emesis induced by R(+)-7-OH-DPAT, apomorphine, morphine or cisplatin with ID50 values of 2.22 microg kg(-1) s.c., 10.5 microg kg(-1) s.c., 14.2 microg kg(-1) i.v. and 17.6 microg kg(-1) i.v., respectively. Moreover, oral administration of AS-8112 significantly inhibited emesis induced by these emetogens. AS-8112 (0.3 mg kg(-1) i.v.) significantly inhibited emesis induced by cyclophosphamide and doxorubicin. In conclusion, AS-8112 is a potent dopamine D2, D3 and 5-HT3 receptors antagonist, and a novel anti-emetic agent with a broad-spectrum of anti-emetic activity. These results suggest that this compound is worthy of clinical investigation.

Conditioned food aversion in Suncus murinus (house musk shrew) - a new model for the study of nausea in a species with an emetic reflex

The lack of a small animal model with an emetic reflex in which the relationship between conditioned food aversion and emesis could be investigated prompted a study of the insectivore, Suncus murinus (the house musk shrew). A novel food (either tuna or chicken cat food) was paired (C+) with a single exposure to either nicotine (4 mg/kg sc), motion (1 Hz, 4 cm, 10 min) or lithium chloride (100 mg/kg ip) or was paired (C-) with either saline or sham exposure to motion. Nicotine and motion both induced emesis (retching/vomiting) but lithium chloride did not. All three treatments produced a conditioned food aversion after a single pairing with consumption of C+ food. When given a choice between the two foods, S. murinus given lithium chloride, motion exposure and nicotine consumed, respectively, only 25%, 23% and 1% of their total intake from the C+ food. This study shows that a conditioned food aversion can be readily induced in S. murinus and that the induction of emesis can be uncoupled from food aversion. S. murinus provides a promising new model in which the relationship between emesis, nausea and conditioned food aversion can be investigated.

Quantitative analysis of dimethyl titanocene by iodometric titration, gas chromatography and NMR

In this study we report the use of an automated iodometric titration method and a novel gas chromatography (GC) method for the quantitative analysis of dimethyl titanocene (DMT), a key raw material in drug synthesis. Both approaches are based on the reaction of DMT in toluene or tetrahydrofuran solutions with iodine. In the case of iodometric titration, excess iodine is titrated with a standardized aqueous sodium thiosulfate solution to a potentiometric end-point for the determination of DMT concentration. Alternatively, GC is employed to measure the concentration of iodomethane, a product of the reaction between DMT and iodine, in order to determine the concentration of DMT in the solution. Excellent agreement between iodometric titration, GC and NMR results using several DMT samples confirms the accuracy of the two methods and strongly supports the use of either method as a replacement to the expensive NMR for quantitative DMT analysis. The relatively few sources of error associated with the two methods, their ubiquitous nature and ease of application in routine analysis make them the analytical methods of choice, among all. Both methods have been validated according to ICH requirements. The use of iodometric titration method for DMT analysis is demonstrated with a couple of applications.

Comparison of L-758,298, a prodrug for the selective neurokinin-1 antagonist, L-754,030, with ondansetron for the prevention of cisplatin-induced emesis

Substance P is localised in brainstem regions associated with emesis. Based on studies in the ferret, it was postulated that a neurokinin-1 (NK1) receptor antagonist would have antiemetic activity as monotherapy in humans receiving chemotherapy. L-758,298 is a water-soluble, intravenous (i.v.) prodrug for L-754,030, a potent and selective NK1 receptor antagonist. This double-blind, randomised, active-agent (ondansetron)-controlled study enrolled 53 cisplatin-naïve patients and evaluated the prevention of both acute (0-24 h) and delayed (days 2-7) emesis after cisplatin treatment (50-100 mg/m(2)). All patients received i.v. L-758,298 (60 or 100 mg) (n=30) or ondansetron (32 mg) (n=23) before cisplatin and efficacy was evaluated up to day 7 post-cisplatin. Nausea was assessed by means of a four-point ordinal scale at intervals over the 7 day period. In the acute period, the proportion of patients without emesis in the L-758,298 and ondansetron groups was 37 and 52%, respectively (no significant difference between the groups). Comparing the distribution of average nausea scores over the entire first 24 h revealed no significant difference between the groups. In the delayed period, the proportion of patients without emesis in the L-758,298 and ondansetron treatment groups was 72 and 30%, respectively (P=0.005). The distribution of average nausea scores in the delayed period was lower in the L-758,298 group compared with the ondansetron group (P=0.15 for the entire delayed period and P=0.043 for day 2 only). No serious adverse events were attributed to L-758,298. A single dose of L-758,298 substantially suppressed the delayed nausea and vomiting characteristic of high dose cisplatin and also appeared to reduce acute emesis post-cisplatin. The data also support the proposition that the underlying mechanism(s) of acute and delayed emesis are different.

Localization of NK1 and NK3 receptors in guinea-pig brain

In this study the localizations of tachykinin neurokinin-1 (NK1) and neurokinin-3 (NK3) receptors in the guinea-pig brain are described. In agreement with studies in rat and human brain, the neurons that exhibited the most marked NK1 receptor immunoreactivity were found in the dorsomedial caudate putamen. NK1 receptors were also widely distributed in diencephalic structures and in the mid and hind brain. NK3 receptors were distributed in both superficial and deep layers of the cortex and many appeared to be located on cells with astrocyte-like morphology in the glia limitans. In several regions including the thalamus, hypothalamus, amygdala, periaqueductal gray, substantia nigra and area postrema, both NK1 and NK3 immunoreactivity were found. The present study revealed that tachykinin receptors are widely distributed in the guinea-pig central nervous system.

Prevention of cisplatin-induced emesis by the oral neurokinin-1 antagonist, MK-869, in combination with granisetron and dexamethasone or with dexamethasone alone

PURPOSE

The NK1-receptor antagonist MK-869 (L-754,030) has demonstrated antiemetic activity in humans receiving chemotherapy. Objectives of the present trial included the first assessment of oral MK-869 plus dexamethasone compared with a 5HT(3) antagonist plus dexamethasone for prevention of acute and delayed emesis after high-dose cisplatin. Furthermore, the study sought to confirm that addition of MK-869 to a 5HT(3) antagonist plus dexamethasone was more effective than just the 5HT(3) antagonist plus dexamethasone for prevention of acute and delayed emesis.

METHODS

This multicenter, double-blind, parallel-group trial in 351 cisplatin-naïve patients evaluated prevention of acute (0 to 24 hours) and delayed emesis (primary efficacy parameter; days 2 to 5) after cisplatin (> or =70 mg/m(2)). Patients were randomized to four groups (I to IV) (n = number randomized; number evaluable): granisetron (10 microg/kg intravenously) pre-cisplatin followed by placebo on days 2 to 5 (group I) (n = 90; 90); granisetron and MK-869 (400 mg PO [by mouth]) pre-cisplatin, followed by MK-869 (300 mg PO) on days 2 to 5 (group II) (n = 86; 84); MK-869 (400 mg PO) the evening before and pre-cisplatin, followed by MK-869 (300 mg PO) on days 2 to 5 (group III) (n = 89; 88); or MK-869 (400 mg PO) pre-cisplatin, followed by MK-869 (300 mg PO) on days 2 to 5 (group IV) (n = 86; 84). All patients also received dexamethasone (20 mg PO) before cisplatin. Additional medication was available to treat emesis or nausea at any time.

RESULTS

In the acute period, 57%, 80%, 46%, and 43% of patients were without emesis in groups I, II, III, and IV, respectively (P <.01 for group II v group I). In the delayed period, the proportion of patients without emesis in groups I, II, III, and IV was 29%, 63%, 51%, and 57%, respectively (P <.01 for groups II, III, and IV v group I). The distribution of nausea scores in the delayed period was lower when comparing group II with group I (P <.05 for days 1 to 5 and days 2 to 5). One serious adverse event (dizziness) was rated as possibly related to MK-869.

CONCLUSION

Once daily oral administration of MK-869 was effective in reducing delayed emesis and nausea after high-dose cisplatin. However, the combination of the 5HT3 antagonist plus dexamethasone was numerically superior to MK-869 plus dexamethasone in reducing acute emesis. Confirming and extending previous findings, the triple combination of a 5HT(3) antagonist, MK-869, and dexamethasone provided the best control of acute emesis.

A multinational study to measure the value that patients with cancer place on improved emesis control following cisplatin chemotherapy

BACKGROUND

The neurokinin-1 (NK1) receptor antagonists are a new class of agents designed to reduce the risk of emesis following chemotherapy, particularly with cisplatin. Early data from double-blind randomised trials suggest that an orally administered NK1 antagonist can reduce the absolute risk of acute and delayed emesis following cisplatin by 20 and 30%, respectively.

OBJECTIVE

To measure the value that patients with cancer place on improved emesis control and quality of life.

DESIGN

Willingness-to-pay analysis.

SETTING

Five study sites in Canada, Italy, Spain and Greece.

PATIENTS AND PARTICIPANTS

245 patients with cancer either receiving chemotherapy with cisplatin or who had received cisplatin-based chemotherapy within the previous 6 months.

METHODS

After background information had been presented, patients were asked to define the maximum that they would pay per day for a drug that reduced their risk of acute and delayed (days 2 to 5) emesis by 20 and 30%, respectively. Costs were converted to US dollars ($US) using year 2000 exchange rates.

RESULTS

For a 20% improvement in acute emesis, Canadian, Italian and Spanish patients with cancer were willing to pay $US46, $US34 and $US63 per day, respectively, compared with $US8 for patients from Greece (p < 0.001). For a 30% improvement in delayed emesis, Canadian, Italian and Spanish patients with cancer were also willing to pay more than their Greek counterparts (SUS41, $US31, $US50 and $US9 daily for 4 days, respectively; p < 0.001). These significant differences in patient value between countries remained, even after adjusting for socioeconomic variables and previous history of emesis.

CONCLUSIONS

There are substantial cultural differences in how patients with cancer value benefit and improved quality of life. Since the majority of the world's population resides outside North America and Western Europe, there may be a need to re-evaluate perceived levels of patient benefit and measures of quality of life.

Response of the cricothyroid and thyroarytenoid muscles to stereotactic injection of substance P into the region of the nucleus tractus solitarius in developing dogs

Substance P (SP), a putative sensory neurotransmitter, mediates reflex laryngeal adductor activity in developing dogs. Such reflex activity includes life-threatening laryngospasm induced by stimulation of distal esophageal afferent nerves. The site of SP's activity is unknown. This research was undertaken to determine whether injection of SP into the nucleus tractus solitarius (NTS) of developing beagles alters laryngeal adductor motor activity. Six animals, 57 to 78 days of age, underwent stereotactic injection of 5 to 10 microL of SP into the region of the NTS, identified by electrical stimulation of the ipsilateral superior laryngeal nerve. In 8 additional studies, SP was injected into the cerebellum (2) or brain stem (6) distant from the NTS. Cardiovascular and electromyographic (EMG) responses of the diaphragm and the cricothyroid (CT) and/or thyroarytenoid (TA) muscles were recorded in all 6 animals. Injection of SP into the region of the NTS induced a decrease in blood pressure in all animals and an increase in either ipsilateral CT or TA activity. Three of these animals experienced mixed apnea characterized by sustained EMG activity (spasm) of the ipsilateral CT or TA muscles and an absence of diaphragm EMG activity. The apnea event was fatal in 1 of these animals. In the 6 animals who underwent injections in the brain stem but outside the region of the NTS, diaphragm and laryngeal EMG activity generally did not change after injection of SP, with the exception of 1 animal who experienced a mild, short-lived increase in ipsilateral CT activity. A brief phasic increase in ipsilateral CT activity was seen in both animals who underwent injection of SP into the cerebellum. A putative sensory neurotransmitter, SP evokes ipsilateral CT and/or TA EMG activity when injected into the region of the NTS in developing beagle dogs. This research suggests that SP in the NTS may play a role in mediating life-threatening laryngeal adductor reflexes in developing mammals and may provide important information regarding therapeutic intervention.

Localization of tachykinin receptors and Fos-like immunoreactivity induced by substance P in guinea-pig brain

1. In the present study, a comparison was made between the distribution of tachykinin NK1 and NK3 receptor immunoreactivity and the distribution of Fos-like immunoreactivity induced by the tachykinin agonist substance P (SP) in the guinea-pig brain. 2. In agreement with results from previous studies in rat brain, NK1 receptor-immunoreactive neurons were found to be widely distributed throughout the brain in the striatum and in diencephalic and mesencephalic structures, while NK3 receptor-immunoreactive neurons were mainly in telencephalic structures. Considerable overlap was observed between NK1 and NK3 receptor distributions. 3. Substance P induced Fos-like immunoreactivity (Fos-LI) in extensive areas of the guinea-pig brain. The induction of Fos-LI was markedly inhibited in many areas by pretreatment with the NK1 receptor antagonist SR 140333. The NK3 receptor antagonist SR 142801 reduced Fos-LI staining in fewer areas, although a reduction was observed in the cortex, striatum and hypothalamus. 4. In general, tachykinin receptors were located at sites corresponding to areas of functional activation by SP, as shown by Fos-LI. These results extend previous studies by adding a functional dimension to tachykinin receptor localization studies.

Tachykinin NK1 and NK3 receptors in the prefrontal cortex of the human brain

1. The tachykinins are neuropeptides found in both the central and peripheral nervous systems that play a role in inflammation and pain mechanisms and some autonomic reflexes and behaviours. 2. Although the distribution of the tachykinin receptors has been described in the brains of various animal species, little is known about the distribution of the NK1 and NK3 receptors in the human brain. 3. The present paper examines the distribution of the NK1 and NK3 receptors in the prefrontal cortex of formalin-fixed postmortem human brain tissue by immunohistochemical techniques. 4. The majority of NK1 receptor immunoreactivity appeared as a thin band of punctate staining at the pial surface, with dark brown dots of NK1 receptor immunoreactivity predominantly scattered across the mid to upper cortical layers. 5. The NK3 receptor immunoreactivity was found in the glia limitans at the pial surface, where astrocytes and beaded fibres were intensely stained. Dots of NK3 receptor immunoreactivity were scattered across all cortical layers. In the white matter, astrocytes and beaded fibres displayed NK3 receptor immunoreactivity, particularly in areas surrounding blood vessels.

Potential of substance P antagonists as antiemetics

The introduction of serotonin 5-HT3 receptor antagonists into clinical practice allowed for a dramatic improvement in the management of nausea and vomiting. Despite this, postoperative and chemotherapy-induced emesis remains a significant, unresolved issue in many patients even when a combination of antiemetic drugs is used. Numerous neurotransmitters have been implicated in triggering emesis; however, the tachykinin substance P, by virtue of its localisation within both the gastrointestinal vagal afferent nerve fibres and brainstem emetic circuitry, and its ability to induce vomiting when administered intravenously, is thought to play a key role in emetic responses. Because substance P is the most likely endogenous ligand for the neurokinin-1 (NK1) receptor, the development of nonpeptide NK1 receptor antagonists led scientists to evaluate these compounds as antiemetics. The five NK1 receptor inhibitors that have been studied initially in humans are: vofopitant (GR-205171), CP-122721, ezlopitant (CJ-11974), MK-869 (L-754030) and its prodrug L-758298. Except for monotherapy in acute cisplatin-induced emesis, this new class of drugs has proven to be highly effective in the control of both chemotherapy-induced nausea and vomiting, and postoperative nausea and vomiting. No major adverse event was reported in the preliminary trials. Further investigation is mandatory in order to assess the optimal treatment regimen and to make sure the wide spectrum activity of the NK1 receptor inhibitors does not cause significant adverse effects in the context of the treatment of nausea and vomiting.

Substance P antagonists: novel agents in the treatment of depression

The field of neuropeptides has been expanding very rapidly in recent years. Apart from understanding their physiology and elucidating their functional role as putative neurotransmitters, research has focused on producing drugs that may treat a variety of illnesses in a novel way. Substance P antagonists occupy a central role in this area of intensive scientific activity. Substance P (SP), an undecapeptide, is abundant both in the periphery and in the CNS, where it is usually co-localised with one of the classical neurotransmitters, most commonly serotonin (5-HT). A role for SP is proposed in the regulation of pain, asthma, psoriasis, inflammatory bowel disease and, in the CNS, emesis, migraine, schizophrenia, depression and anxiety. A recently published positive study of MK 869, in depression, a novel SP antagonist has generated excitement amongst psychopharmacologists. It is the first time that a drug, not directly related to monoamine transmitters, has showed efficacy in depression. Although MK 869 has been suspended from further development, a host of other compounds, with similar action and better pharmacological profile, are currently under development. In this review, the pharmacology of central SP and its receptors are discussed, together with the exploration of the prospects and implications for future treatments of depression.

Comparison of the neurokinin-1 antagonist GR205171, alone and in combination with the 5-HT3 antagonist ondansetron, hyoscine and placebo in the prevention of motion-induced nausea in man

AIMS

In man a neurokinin-1 (NK1) receptor antagonist has previously been shown to be ineffective in the prevention of motion-induced nausea. The antiemetic efficacy of NK1 receptor antagonists against chemotherapy-induced emesis is, however, enhanced when combined with a 5-HT3 receptor antagonist. Hence the efficacy of the NK1 antagonist GR205171 in combination with the 5-HT3 antagonist ondansetron (Zofrantrade mark) was assessed in motion-induced nausea.

METHODS

GR205171 25 mg i.v., with and without concomitant administration of ondansetron 8 mg i.v., and hyoscine hydrobromide 0. 6 mg orally (positive control) were compared with placebo in a model of motion-induced nausea. The study was performed to a four-period, randomized, balanced, double-blind, crossover design in 16 healthy subjects. The end-point was the exposure to the motion stimulus required to produce moderate nausea in the subjects.

RESULTS

The motion stimulus required to produce moderate nausea was significantly greater for the positive control than placebo (P < 0. 001). There was no significant difference between either GR205171 or GR205171 plus ondansetron and placebo (P = 0.648 and 0.342, respectively).

CONCLUSIONS

The enhancement of NK1 receptor antagonist antiemetic activity through combination with a 5-HT3 receptor antagonist is not replicated in motion-induced nausea.

A new class of antiemetics: the NK-1 receptor antagonists

Emesis is one of the most unpleasant and debilitating side effects of anticancer chemotherapy. In acute emesis (vomiting occurring 0-24 hours after chemotherapy administration), the 5-HT3 receptor antagonists and corticosteroids are highly effective, with few significant side effects, and can safely be combined. Delayed emesis (vomiting occurring >24 hours after chemotherapy administration), however, is both not well understood and less well controlled. Studies have yielded conflicting results concerning the use of 5-HT3 receptor antagonists alone in delayed emesis. The data of NK-1 receptor antagonists in the control of acute emesis, although promising, need confirmation in a properly designed study.

Neuropeptides--an overview

The present article provides a brief overview of various aspects on neuropeptides, emphasizing their multitude and their wide distribution in both the peripheral and central nervous system. Interestingly, neuropeptides are also expressed in various types of glial cells under normal and experimental conditions. The recent identification of, often multiple, receptor subtypes for each peptide, as well as the development of peptide antagonists, have provided an experimental framework to explore functional roles of neuropeptides. A characteristic of neuropeptides is the plasticity in their expression, reflecting the fact that release has to be compensated by de novo synthesis at the cell body level. In several systems peptides can be expressed at very low levels normally but are upregulated in response to, for example, nerve injury. The fact that neuropeptides virtually always coexist with one or more classic transmitters suggests that they are involved in modulatory processes and probably in many other types of functions, for example exerting trophic effects. Recent studies employing transgene technology have provided some information on their functional role, although compensatory mechanisms in all probability could disguise even a well defined action. It has been recognized that both 'old' and newly discovered peptides may be involved in the regulation of food intake. Recently the first disease-related mutation in a peptidergic system has been identified, and clinical efficacy of a substance P antagonist for treatment of depression has been reported. Taken together it seems that peptides may play a role particularly when the nervous system is stressed, challenged or afflicted by disease, and that peptidergic systems may, therefore, be targets for novel therapeutic strategies.

Localisation of tachykinin NK1 and NK3 receptors in the human prefrontal and visual cortex

The distribution of tachykinin NK(1) and NK(3) receptors in the prefrontal (Brodmann area 9) and visual cortex (Brodmann area 17) of formalin-fixed postmortem human brain tissue was studied by immunohistochemistry. NK(1)-like immunoreactivity (NK(1)-LI) was observed as a thin band at the cortical surface and dots of NK(1)-LI localised on small non-pyramidal cells and in the neuropil (layers I-III). NK(3)-LI was found in beaded fibres and cells with astrocyte-like morphology in the superficial cortical layers and white matter. Dots of NK(3)-LI were prominent in the neuropil and on pyramidal (layers III/V) and non-pyramidal (layers V/VI) cells. The NK(3)-LI was more abundant and widespread than the NK(1)-LI. This is the first report of the distribution of the NK(1) receptor in the prefrontal and visual cortex of the human brain by immunohistochemistry.

Neurokinin receptor antagonists

Studies on tachykinin peptides and the corresponding neurokinin receptors (NKr) have increased dramatically recently due to the discovery of selective, orally-active, metabolically stable and sometimes CNS penetrating NKr antagonists. After demonstrating the potential use for NKr antagonists in animal models, some compounds have recently progressed into clinical trials and a few results have been published. NKr antagonists have demonstrated efficacy for the treatment of emesis and depression, while results in other areas have been disappointing. Nonetheless, this area is coming to the exciting time of proof of concept in humans. Demonstration of the involvement of tachykinin peptides in biological functions continues to grow, as do the potential indications for NKr antagonists. More drug candidates are undergoing clinical trials for various conditions and these results could widen the potential use for NKr antagonists.

Phosphorylated morpholine acetal human neurokinin-1 receptor antagonists as water-soluble prodrugs

The regioselective dibenzylphosphorylation of 2 followed by catalytic reduction in the presence of N-methyl-D-glucamine afforded 2-(S)-(1-(R)-(3, 5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluoro)phenyl-4-(5-(2- phosphoryl-3-oxo-4H,-1,2,4-triazolo)methylmorpholine, bis(N-methyl-D-glucamine) salt, 11. Incubation of 11 in rat, dog, and human plasma and in human hepatic subcellular fractions in vitro indicated that conversion to 2 would be expected to occur in vivo most readily in humans during hepatic circulation. Conversion of 11 to 2 occurred rapidly in vivo in the rat and dog with the levels of 11 being undetectable within 5 min after 1 and 8 mg/kg doses iv in the rat and within 15 min after 0.5, 2, and 32 mg/kg doses iv in the dog. Compound 11 has a 10-fold lower affinity for the human NK-1 receptor as compared to 2, but it is functionally equivalent to 2 in preclinical models of NK-1-mediated inflammation in the guinea pig and cisplatin-induced emesis in the ferret, indicating that 11 acts as a prodrug of 2. Based in part on these data, 11 was identified as a novel, water-soluble prodrug of the clinical candidate 2 suitable for intravenous administration in humans.

Novel approaches to the treatment of nausea and vomiting

Nausea and vomiting are debilitating symptoms complicating many clinical conditions. Conventional antiemetic agents act as muscarinic, histamine, and dopamine receptor antagonists in the central nervous system. In a retrospective analysis, tricyclic antidepressant drugs demonstrated efficacy in long-term treatment of functional nausea. Some cases of vomiting result from impaired gastrointestinal motor activity. Agents which act on gastric serotonin (5-HT4), dopamine, and motilin receptors accelerate gastric emptying and relieve symptoms in gastroparesis. Recent investigations suggest that some patients with refractory gastroparesis may benefit from gastric electrical pacing. The treatment of acute chemotherapy-induced emesis was revolutionized by 5-HT3 receptor antagonists; however, these agents are less efficacious in delayed vomiting. Neurokinin (NK-1) receptor antagonists show promise in treating delayed chemotherapy-evoked emesis. Furthermore, animal studies indicate a broad spectrum of action for NK-1 antagonists in treating diverse causes of nausea and vomiting. The cyclic vomiting syndrome is characterized by discrete episodes of relentless vomiting separated by asymptomatic intervals and is associated with migraine headaches. Antimigraine therapies including the 5-HT1D receptor agonists sumatriptan reduce the severity of cyclic vomiting attacks. Investigations into these and other novel treatments may provide important advances in the care of difficult cases of nausea and vomiting resulting from disparate illnesses.

History of the development of antiemetic guidelines at Mayo Clinic Rochester

This article describes the historic experience of the development of antiemetic guidelines for patients taking chemotherapy drugs at Mayo Clinic Rochester. The initial guidelines for the use of serotonin (5-hydroxytryptamine3) receptor antagonists for the prevention of chemotherapy-induced nausea and vomiting were developed in early 1995 and implemented in September 1995. In February 1997, the guidelines were reviewed and modified. In the spring of 1998, major changes were made based on new data from the literature and discussions with antiemetic authorities in the United States. These guidelines were implemented in July 1998. The guidelines were again reviewed and modified in December 1998. In addition, we compared costs associated with the 1997 guidelines and the December 1998 guidelines. The developed guidelines, utilizing clinically available agents, seem to provide high-quality patient care at a reasonable cost.

The novel NK1 receptor antagonist MK-0869 (L-754,030) and its water soluble phosphoryl prodrug, L-758,298, inhibit acute and delayed cisplatin-induced emesis in ferrets

The anti-emetic profile of the novel brain penetrant tachykinin NK1 receptor antagonist MK-0869 (L-754,030) 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)phenylethoxy)-3-(S)-(4-fluor o)phenyl-4-(3-oxo-1,2,4-triazol-5-yl)methylmorpholine and its water soluble prodrug, L-758,298, has been examined against emesis induced by cisplatin in ferrets. In a 4 h observation period, MK-0869 and L-758,298 (3 mg/kg i.v. or p.o.) inhibited the emetic response to cisplatin (10 mg/kg i.v.). The anti-emetic protection afforded by MK-0869 (0.1 mg/kg i.v.) was enhanced by combined treatment with either dexamethasone (20 mg/kg i.v.) or the 5-HT3 receptor antagonist ondansetron (0.1 mg/kg i.v.). In a model of acute and delayed emesis, ferrets were dosed with cisplatin (5 mg/kg i.p.) and the retching and vomiting response recorded for 72 h. Pretreatment with MK-0869 (4-16 mg/kg p.o.) dose-dependently inhibited the emetic response to cisplatin. Once daily treatment with MK-0869 (2 and 4 mg/kg p.o.) completely prevented retching and vomiting in all ferrets tested. Further when daily dosing began at 24 h after cisplatin injection, when the acute phase of emesis had already become established, MK-0869 (4 mg/kg p.o. at 24 and 48 h after cisplatin) prevented retching and vomiting in three out of four ferrets. These data show that MK-0869 and its prodrug, L-758,298, have good activity against cisplatin-induced emesis in ferrets and provided a basis for the clinical testing of these agents for the treatment of emesis associated with cancer chemotherapy.

Discovery of the antidepressant and anti-emetic efficacy of substance P receptor (NK1) antagonists

The development of small-molecule antagonists of the substance P (SP)-preferring tachykinin NK1 receptor during the past decade represents an important opportunity to exploit these molecules as novel therapeutic agents. On the basis of its anatomical localization and function, SP has been implicated in diverse pathophysiologies; of these, diseases of the CNS have been examined in the greatest detail. Although SP is best known as a pain neurotransmitter, it also controls vomiting and various behavioural, neurochemical and cardiovascular responses to stress. Recent clinical trials have confirmed the efficacy of NK1 receptor antagonists to alleviate depression and emesis but, surprisingly, not pain. Thus, multiple clinical trials, targeted to appropriate patient populations, are necessary to define the therapeutic potential of novel neurotransmitter ligands.

Substance P-induced vasodilatation is mediated by the neurokinin type 1 receptor but does not contribute to basal vascular tone in man

AIMS

Following intravenous administration of its prodrug, L-758,298, we assessed the pharmacodynamics of L-754,030, a novel and highly selective NK1 receptor antagonist, by examining systemic haemodynamics and the blood flow responses to intra-arterial substance P infusion.

METHODS

Sixteen healthy male volunteers participated in a double-blind, randomised, placebo controlled crossover trial of L-758 298. Forearm blood flow was measured using venous occlusion plethysmography during intrabrachial substance P infusion (0.125-128 pmol min-1 ). In part 1, eight subjects received substance P infusions before and during placebo, 0.25 mg, 1 mg or 5 mg of L-758 298. In part 2, eight subjects received substance P infusions 24 h after placebo or 1.43 mg of L-758 298.

RESULTS

L-758 298 caused dose dependent inhibition of substance P induced vasodilatation (P<0.001). Placebo adjusted differences (95% CI) in baseline forearm blood flow, mean arterial pressure and heart rate showed no relevant changes with 5 mg of L-758 298 (>1400-fold shift in substance P response): 0.00 (-0.49 to +0.49) ml 100 ml-1 min-1, 1. 0 (-3.2 to +5.2) mmHg and 1.9 (-5.9 to +9.7) beats min-1, respectively. Twenty-four hours after 1.43 mg of L-758,298, there was approximately 34-fold shift in response to substance P induced vasodilatation (P<0.008) at plasma L-754 030 concentrations of 2-3 ng ml-1. L-758 298 was generally well tolerated without serious adverse events.

CONCLUSIONS

Substance P induced forearm vasodilatation is mediated by the endothelial cell NK1 receptor in man but endogenous substance P does not appear to contribute to the maintenance of peripheral vascular tone or systemic blood pressure.

The tachykinin NK1 receptor in the brain: pharmacology and putative functions

After its discovery in 1931, substance P (SP) remained the only mammalian member of the family of tachykinin peptides for several decades. Tachykinins thus refer to peptides sharing the common C-terminal amino acid sequence Phe-X-Gly-Leu-Met x NH2. In recent years the family of mammalian tachykinins has grown with the isolation of two novel peptides from bovine and porcine central nervous system (CNS), neurokinin A and neurokinin B. In parallel with the identification of multiple endogenous tachykinins several classes of tachykinin receptors were discovered. The receptors described so far are named tachykinin NK1 receptor, tachykinin NK2 receptor and tachykinin NK1 receptor, respectively. The present review focuses on the pharmacology and putative function of tachykinin NK1 receptors in brain. The natural ligand with the highest affinity for the tachykinin NK1 receptor is SP itself. The C-terminal sequence is essential for activity, the minimum length of a fragment with reasonable affinity for the tachykinin NK1 receptor is the C-terminal hexapeptide. A rapid advance of knowledge was caused by development of non-peptidic tachykinin NK1 receptor antagonists. This area is under rapid development and a variety of different chemical classes of compounds are involved. Species-dependent affinities of tachykinin NK1 receptor antagonists reveal two clusters of compounds, targeting the tachykinin NK1 receptor subtype found in guinea pig, human or ferret or the one in rat or mouse, respectively. The most recently developed compounds are highly selective, enter the brain and are orally bioavailable. Distinct behavioural effects in experimental animals suggest the involvement of tachykinin NK1 receptors in nociceptive transmission, basal ganglia function or anxiety and depression. Recent clinical trials in man showed that tachykinin NK1 receptor antagonists are effective in treating depression and chemotherapy-induced emesis. Therefore, it is well possible that tachykinin NK1 receptor antagonists will be clinically used for treatment of specific CNS disorders within a short period of time.

Methotrexate produces delayed emesis in dogs: a potential model of delayed emesis induced by chemotherapy

We investigated the emetic effects of cisplatin and methotrexate in dogs, the effects of ondansetron on cisplatin-induced vomiting, and the effects of ondansetron, dexamethasone and a combination of the two on the vomiting induced by methotrexate. Ondansetron was administered 30 min before cisplatin administration. Ondansetron, dexamethasone or a combination of the two was administered 8, 24 and 48 h after methotrexate administration. Cisplatin (3 mg/kg, i.v.) induced acute vomiting but failed to induce delayed vomiting. The acute vomiting was markedly inhibited by ondansetron (3 mg/kg, p.o.; 1 mg/kg, i.v.). Methotrexate (2.5 mg/kg, i.v.) caused delayed vomiting, which was partly inhibited by ondansetron (1 mg/kg, i.v.) or dexamethasone (2.5 mg/kg, i.v.). The combination of the two agents was more effective. These results suggest that methotrexate-induced emesis in dogs would be useful for studying delayed emesis.