Evidence that 5-hydroxytryptamine3 receptors mediate cytotoxic drug and radiation-evoked emesis

Chemotherapy-induced gastrointestinal toxicity: Pathogenesis and current management

Chemotherapy is the most common treatment for malignant tumors. However, chemotherapy-induced gastrointestinal toxicity (CIGT) has been a major concern for cancer patients, which reduces their quality of life and leads to treatment intolerance and even cessation. Nevertheless, prevention and treatment for CIGT are challenging, due to the prevalence and complexity of the condition. Chemotherapeutic drugs directly damage gastrointestinal mucosa to induce CIGT, including nausea, vomiting, anorexia, gastrointestinal mucositis, and diarrhea, etc. The pathogenesis of CIGT involves multiple factors, such as gut microbiota disorders, inflammatory responses and abnormal neurotransmitter levels, that synergistically contribute to its occurrence and development. In particular, the dysbiosis of gut microbiota is usually linked to abnormal immune responses that increases inflammatory cytokines' expression, which is a common characteristic of many types of CIGT. Chemotherapy-induced intestinal neurotoxicity is also a vital concern in CIGT. Currently, modern medicine is the dominant treatment of CIGT, however, traditional Chinese medicine (TCM) has attracted interest as a complementary and alternative therapy that can greatly alleviate CIGT. Accordingly, this review aimed to comprehensively summarize the pathogenesis and current management of CIGT using PubMed and Google Scholar databases, and proposed that future research for CIGT should focus on the gut microbiota, intestinal neurotoxicity, and promising TCM therapies, which may help to develop more effective interventions and optimize managements of CIGT.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Therapeutic potential of serotonin 4 receptor for chronic depression and its associated comorbidity in the gut

The latest estimates from world health organization suggest that more than 450 million people are suffering from depression and other psychiatric conditions. Of these, 50-60% have been reported to have progression of gut diseases. In the last two decades, researchers introduced incipient physiological roles for serotonin (5-HT) receptors (5-HTRs), suggesting their importance as a potential pharmacological target in various psychiatric and gut diseases. A growing body of evidence suggests that 5-HT systems affect the brain-gut axis in depressive patients, which leads to gut comorbidity. Recently, preclinical trials of 5-HT4R agonists and antagonists were promising as antipsychotic and prokinetic agents. In the current review, we address the possible pharmacological role and contribution of 5-HT4R in the pathophysiology of chronic depression and associated gut abnormalities. Physiologically, during depression episodes, centers of the sympathetic and parasympathetic nervous system couple together with neuroendocrine systems to alter the function of hypothalamic-pituitary-adrenal (HPA) axis and enteric nervous system (ENS), which in turn leads to onset of gastrointestinal tract (GIT) disorders. Consecutively, the ENS governs a broad spectrum of physiological activities of gut, such as visceral pain and motility. During the stages of emotional stress, hyperactivity of the HPA axis alters the ENS response to physiological and noxious stimuli. Consecutively, stress-induced flare, swelling, hyperalgesia and altered reflexes in gut eventually lead to GIT disorders. In summary, the current review provides prospective information about the role and mechanism of 5-HT4R-based therapeutics for the treatment of depressive disorder and possible consequences for the gut via brain-gut axis interactions. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

A History of Drug Discovery for Treatment of Nausea and Vomiting and the Implications for Future Research

The origins of the major classes of current anti-emetics are examined. Serendipity is a recurrent theme in discovery of their anti-emetic properties and repurposing from one indication to another is a continuing trend. Notably, the discoveries have occurred against a background of company mergers and changing anti-emetic requirements. Major drug classes include: (i) Muscarinic receptor antagonists-originated from historical accounts of plant extracts containing atropine and hyoscine with development stimulated by the need to prevent sea-sickness among soldiers during beach landings; (ii) Histamine receptor antagonists-searching for replacements for the anti-malaria drug quinine, in short supply because of wartime shipping blockade, facilitated the discovery of histamine (H1) antagonists (e.g., dimenhydrinate), followed by serendipitous discovery of anti-emetic activity against motion sickness in a patient undergoing treatment for urticaria; (iii) Phenothiazines and dopamine receptor antagonists-investigations of their pharmacology as "sedatives" (e.g., chlorpromazine) implicated dopamine receptors in emesis, leading to development of selective dopamine (D2) receptor antagonists (e.g., domperidone with poor ability to penetrate the blood-brain barrier) as anti-emetics in chemotherapy and surgery; (iv) Metoclopramide and selective 5-hydroxytryptamine3(5-HT3) receptor antagonists-metoclopramide was initially assumed to act only via D2 receptor antagonism but subsequently its gastric motility stimulant effect (proposed to contribute to the anti-emetic action) was shown to be due to 5-hydroxytryptamine4 receptor agonism. Pre-clinical studies showed that anti-emetic efficacy against the newly-introduced, highly emetic, chemotherapeutic agent cisplatin was due to antagonism at 5-HT3 receptors. The latter led to identification of selective 5-HT3 receptor antagonists (e.g., granisetron), a major breakthrough in treatment of chemotherapy-induced emesis; (v) Neurokinin1receptor antagonists-antagonists of the actions of substance P were developed as analgesics but pre-clinical studies identified broad-spectrum anti-emetic effects; clinical studies showed particular efficacy in the delayed phase of chemotherapy-induced emesis. Finally, the repurposing of different drugs for treatment of nausea and vomiting is examined, particularly during palliative care, and also the challenges in identifying novel anti-emetic drugs, particularly for treatment of nausea as compared to vomiting. We consider the lessons from the past for the future and ask why there has not been a major breakthrough in the last 20 years.

A systematic review of methodologies, endpoints, and outcome measures in randomized trials of radiation therapy-induced nausea and vomiting

PURPOSE

Clinical trials in radiation therapy-induced nausea and vomiting (RINV) appear to have varied methodologies, endpoints, and outcome measures. This complicates trial comparisons, weakens practice guideline recommendations, and contributes to variability in supportive care patterns of practice. We systematically reviewed RINV trials to describe and compare their pertinent design features.

MATERIALS AND METHODS

Ovid versions of the Cochrane Central Register of Controlled Trials, the Cochrane Database of Systematic Reviews, EMBASE, and MEDLINE to January/February 2017 were searched for adult phase III trials of RINV management strategies. Key abstracted data included trial interventions and eligibility criteria, standard radiation therapy (RT) metrics, symptom assessment procedures, symptom definitions and grading systems, pre-specified and reported endpoints, and other outcome measures.

RESULTS

From 1166 references identified in the initial database search, we selected 34 trials for analysis that collectively randomized 4529 patients (median 61, range 11-1492). Twenty-eight trials (82%) were published prior to the year 2000. Twenty-seven trials (79%) involved multiple fraction RT and 7 (21%) single fraction RT. Twenty-four trials (71%) evaluated prophylactic interventions, 9 (26%) rescue interventions, and 1 trial did not specify. Thirty-three trials (97%) evaluated pharmacologic interventions. Twenty trials (59%) had patient report symptoms, 5 (15%) healthcare professionals or researchers, and 10 (29%) did not specify. Nausea was not defined in any trial but was reported as a stand-alone symptom in 26 trials (76%) and was graded in 20 (59%), with categorical qualitative scales being the most common method. Vomiting was defined in 3 trials (9%), was reported as a stand-alone symptom in 17 (47%), and was graded in 7 (21%), with continuous numerical scales being the most common method. Retching was defined in 3 trials, was not reported as a stand-alone symptom in any trial, and was graded in 1 (3%). Twenty-one trials (62%) created compound symptom measures that combined individual symptoms. Fifteen trials (44%) reported "emetic episode/event" measures but only 9 defined them. Seventeen trials (50%) reported complicated endpoints (e.g., "response," "control," "success") that combined multiple symptom or compound symptom measures, but 7 did not define them comprehensively. Ten trials (29%) defined a primary endpoint a priori.

CONCLUSIONS

Methodologies, endpoints, and outcome measures varied considerably among 34 randomized trials in RINV.

The involvement of TRPV1 in emesis and anti-emesis

Diverse transmitter systems (e.g. acetylcholine, dopamine, endocannabinoids, endorphins, glutamate, histamine, 5-hydroxytryptamine, substance P) have been implicated in the pathways by which nausea and vomiting are induced and are targets for anti-emetic drugs (e.g. 5-hydroxytryptamine₃ and tachykinin NK₁ antagonists). The involvement of TRPV1 in emesis was discovered in the early 1990s and may have been overlooked previously as TRPV1 pharmacology was studied in rodents (mice, rats) lacking an emetic reflex. Acute subcutaneous administration of resiniferatoxin in the ferret, dog and Suncus murinus revealed that it had “broad–spectrum” anti-emetic effects against stimuli acting via both central (vestibular system, area postrema) and peripheral (abdominal vagal afferents) inputs. One of several hypotheses discussed here is that the anti-emetic effect is due to acute depletion of substance P (or another peptide) at a critical site (e.g. nucleus tractus solitarius) in the central emetic pathway. Studies in Suncus murinus revealed a potential for a long lasting (one month) effect against the chemotherapeutic agent cisplatin. Subsequent studies using telemetry in the conscious ferret compared the anti-emetic, hypothermic and hypertensive effects of resiniferatoxin (pungent) and olvanil (non-pungent) and showed that the anti-emetic effect was present (but reduced) with olvanil which although inducing hypothermia it did not have the marked hypertensive effects of resiniferatoxin. The review concludes by discussing general insights into emetic pathways and their pharmacology revealed by these relatively overlooked studies with TRPV1 activators (pungent an non-pungent; high and low lipophilicity) and antagonists and the potential clinical utility of agents targeted at the TRPV1 system.

Mechanism of gastrointestinal abnormal motor activity induced by cisplatin in conscious dogs

AIM: To investigate whether 5-hydroxytryptamine (serotonin; 5-HT) is involved in mediating abnormal motor activity in dogs after cisplatin administration.

METHODS: After the dogs had been given a 2-wk recovery period, all of them were administered cisplatin, and the motor activity was recorded using strain gauge force transducers. Blood and intestinal fluid samples were collected to measure 5-HT for 24 h. To determine whether 5-HT in plasma or that in intestinal fluids is more closely related to abnormal motor activity we injected 5-HT into the bloodstream and the intestinal tract of the dogs.

RESULTS: Cisplatin given intravenously produced abnormal motor activity that lasted up to 5 h. From 3 to 4 h after cisplatin administration, normal intact dogs exhibited retropropagation of motor activity accompanied by emesis. The concentration of 5-HT in plasma reached the peak at 4 h, and that in intestinal fluids reached the peak at 3 h. In normal intact dogs with resection of the vagus nerve that were administered kytril, cisplatin given intravenously did not produce abnormal motor activity. Intestinal serotonin administration did not produce abnormal motor activity, but intravenous serotonin administration did.

CONCLUSION: After the intravenous administration of cisplatin, abnormal motor activity was produced in the involved vagus nerve and in the involved serotonergic neurons via another pathway. This study was the first to determine the relationship between 5-HT and emesis-induced motor activity.

Suppression of lithium chloride-induced conditioned gaping (a model of nausea-induced behaviour) in rats (using the taste reactivity test) with metoclopramide is enhanced by cannabidiolic acid

We aimed to determine the potential of various doses of metoclopramide (MCP, a dopamine antagonist) to reduce lithium chloride (LiCl)-induced conditioned gaping (a nausea-induced behaviour) in rats, using the taste reactivity test. We then evaluated whether an ineffective low dose of cannabidiolic acid (CBDA, 0.1 μg/kg, Rock and Parker, 2013), the potent acidic precursor of cannabidiol (CBD, a non-psychoactive component of cannabis) could enhance the anti-nausea effects of an ineffective low dose of MCP. MCP (3.0 mg/kg) reduced conditioned gaping responses. Coadministration of ineffective doses of MCP (0.3 mg/kg) and CBDA (0.1 μg/kg) enhanced the suppression of conditioned gaping, over that of either drug alone, without interfering with conditioned taste avoidance. MCP dose-dependently reduced nausea-induced conditioned gaping in rats. As well, the suppression of conditioned gaping was enhanced when ineffective doses of MCP and CBDA were coadministered. These data suggest that CBDA could be a powerful adjunct treatment to anti-emetic regimens for chemotherapy-induced nausea.

Chemotherapy-induced nausea and vomiting: optimizing prevention and management

BACKGROUND

Nausea and vomiting are serious side effects of cancer chemotherapy that can cause significant negative impacts on patients' quality of life and on their ability to tolerate and comply with therapy. Despite advances in the prevention and management of chemotherapy-induced nausea and vomiting (CINV), these side effects remain among the most distressing for patients.

OBJECTIVE

To discuss CINV and the current pharmacologic approaches to its management.

DISCUSSION

This article outlines the mechanism of CINV followed by a review of current approaches to pharmacologic therapy and current practice guidelines from national cancer organizations. This information will help providers and payers understand the optimal management of patients with CINV including practical considerations and value-based decision-making that considers cost issues.

CONCLUSION

Numerous preventive and treatment options are available to manage CINV Addressing antiemetic regimens requires ongoing patient evaluation to determine the best approach for each individual patient.

Cisplatin-induced emesis: systematic review and meta-analysis of the ferret model and the effects of 5-HT₃ receptor antagonists

Purpose

The ferret cisplatin emesis model has been used for ~30 years and enabled identification of clinically used anti-emetics. We provide an objective assessment of this model including efficacy of 5-HT₃ receptor antagonists to assess its translational validity.

Methods

A systematic review identified available evidence and was used to perform meta-analyses.

Results

Of 182 potentially relevant publications, 115 reported cisplatin-induced emesis in ferrets and 68 were included in the analysis. The majority (n = 53) used a 10 mg kg⁻¹ dose to induce acute emesis, which peaked after 2 h. More recent studies (n = 11) also used 5 mg kg⁻¹, which induced a biphasic response peaking at 12 h and 48 h. Overall, 5-HT₃ receptor antagonists reduced cisplatin (5 mg kg⁻¹) emesis by 68% (45–91%) during the acute phase (day 1) and by 67% (48–86%) and 53% (38–68%, all P < 0.001), during the delayed phase (days 2, 3). In an analysis focused on the acute phase, the efficacy of ondansetron was dependent on the dosage and observation period but not on the dose of cisplatin.

Conclusion

Our analysis enabled novel findings to be extracted from the literature including factors which may impact on the applicability of preclinical results to humans. It reveals that the efficacy of ondansetron is similar against low and high doses of cisplatin. Additionally, we showed that 5-HT₃ receptor antagonists have a similar efficacy during acute and delayed emesis, which provides a novel insight into the pharmacology of delayed emesis in the ferret.

A randomized, double-blind, parallel, comparative study to evaluate the efficacy and safety of ramosetron plus dexamethasone injection for the prevention of acute chemotherapy-induced nausea and vomiting

OBJECTIVE

To evaluate the efficacy of intravenous ramosetron plus dexamethasone for the prevention of acute chemotherapy-induced nausea and vomiting.

METHODS

Cancer patients scheduled to receive chemotherapy containing either of the four drugs (cisplatin, doxorubicin, epirubicin or oxaliplatin) were enrolled. They were randomized to receive intravenous ramosetron 0.3 mg plus dexamethasone 20 mg or granisetron 3 mg plus dexamethasone 20 mg 30 min before chemotherapy on day 1. The primary efficacy parameter is complete response rate, which was defined by the proportion of patients without vomiting and no requirement for rescue drugs within 24 h after chemotherapy.

RESULTS

A total of 285 patients were enrolled. The primary efficacy analysis included 274 patients. The complete response rate was 77.37% in the ramosetron 0.3 mg plus dexamethasone 20 mg group (137 patients) and 81.75% in the granisetron 3 mg plus dexamethasone 20 mg group (137 patients) with a difference of -4.38% (95% confidence interval: -14.64, 5.89). Therefore, non-inferiority of ramosetron 0.3 mg plus dexamethasone 20 mg to granisetron 3 mg plus dexamethasone 20 mg was demonstrated with non-inferiority margin -15%. For patients treated with cisplatin, non-inferiority of ramosetron 0.3 mg plus dexamethasone 20 mg to granisetron 3 mg plus dexamethasone 20 mg could not be demonstrated. Only a few patients required rescue medications, 7.3% in the ramosetron 0.3 mg plus dexamethasone 20 mg group and 5.1% in the granisetron 3 mg plus dexamethasone 20 mg group (P = 0.44). All 285 patients were included for safety analysis; 36.11% (52/144) and 23.40% (33/141) experienced at least one adverse event within 24 h in the ramosetron 0.3 mg plus dexamethasone 20 mg and granisetron 3 mg plus dexamethasone 20 mg groups, respectively. Four ramosetron-related adverse events among 144 patients were observed including two moderate elevation of liver enzymes and one each of mild hiccup and moderate skin rash.

CONCLUSIONS

The combination of ramosetron plus dexamethasone was an effective treatment to prevent acute chemotherapy-induced nausea and vomiting.

Casopitant: a novel NK(1)-receptor antagonist in the prevention of chemotherapy-induced nausea and vomiting

Chemotherapy-induced nausea and vomiting (CINV) are among the most feared and distressing symptoms experienced by patients with cancer. The knowledge of the pathogenesis and neuropharmacology of CINV has expanded enormously over the last decades, the most significant discoveries being the role of 5-hydroxytryptamine (5-HT)(3)- and neurokinin (NK)(1) receptors in the emetic reflex arch. This has led to the development of two new classes of antiemetics acting as highly selective antagonists at one of these receptors. These drugs have had a huge impact in the protection from chemotherapy-induced vomiting, whereas the effect on nausea seems to be limited. The first NK(1) receptor antagonist, aprepitant, became clinically available in 2003, and casopitant, the second in this class of antiemetics, has now completed phase III trials. This review delineates the properties and clinical use of casopitant in the prevention of CINV.

Gastrointestinal toxicity of chemotherapeutic agents

Chemotherapy-induced toxicities commonly occur in sites within the gastrointestinal (GI) tract and account for dose-limiting effects. These toxicities are major contributing factors to dose reduction, delays, and cessation of cancer treatment. Through intensive therapies including surgery, combination chemotherapy, hormonal therapy, and targeted therapy, an increasing number of patients with cancer are experiencing improved survival and long-term disease-free survival, as well as palliation of disease-related symptoms. Thus, GI toxicities should be predicted and appropriate interventions initiated to prevent them when possible and provide effective supportive measures and comprehensive follow-up care. This review will discuss the etiology, incidence, prevention, and treatment of GI toxicities of cancer chemotherapy.

Differential action of domperidone to modify emesis and behaviour induced by apomorphine in the ferret

The action of domperidone (1 mg/kg, i.p.) on spontaneous behaviour and the emesis and behavioural change induced by apomorphine (0.25 mg/kg, s.c.) were studied in the ferret. Domperidone was inactive to modify spontaneous behaviour but apomorphine-induced emesis and increased locomotor activity (distance travelled and velocity of movement; P<0.05); the emesis, but not the modification of locomotor activity was antagonized significantly (P<0.01) by domperidone. However, apomorphine did not modify significantly other behavioural measures (i.e. lip licking, rearing, burrowing, backward walking, curling-up activity, or defecatory frequency; P>0.05). The action of apomorphine to modify behaviour and its interaction with domperidone in this species is discussed in relation to animal models of nausea.

The antiemetic effect of a novel tropisetron patch in anticancer agents-induced kaolin pica model using rats

The efficacy of a novel transdermal patch containing tropisetron, a 5-hydroxytryptamine 3 (5-HT(3)) receptor antagonist, against emesis induced by anticancer agents were evaluated, in comparison with the effect of traditional tropisetron injection, in rats. The antiemetic effects were assessed via the inhibitory activity on the anticancer agent-induced kaolin-consuming behavior, a pica model representing vomiting in emesis-resistant rodents. The tropisetron patch (10mg/patch, 3.5cm(2)) was attached on the shaved back area of rats. Eight h later, each anticancer agent, cisplatin (10mg/kg, i.v.), cyclophosphamide (200mg/kg, i.p.) or doxorubicin (8mg/kg, i.v.), was administered, and thereafter, daily kaolin consumption was measured for 3 days. In comparison, the effect of daily injection of tropisetron (2mg/kg, i.v.), given 10min, 24 and 48h after the anticancer agent administration, was also evaluated. Kaolin intake greatly increased to 21, 17 and 10 folds of control ingestion on the first day after administration with the anticancer agents, cisplatin, cyclophosphamide and doxorubicin, respectively, and then gradually decreased to near control level on day 3. Such anticancer agent-induced increases in the kaolin consumption were remarkably attenuated by the attachment of tropisetron patch, resulting in the reduction to half levels, which is comparable to the efficacy of daily tropisetron injection. In particular, the blood concentration of tropisetron following patch attachment reached a maximum level of 30-40ng/ml in 12h and exhibited a plateau until detachment of the patch, in contrast to a rapid elimination with a half-life of 2.21h after injection of the drug. Taken together, it is suggested that the novel tropisetron patch could be a promising regimen for the relief of emesis, based on the long-term antiemetic effects on the diverse anticancer agents and the convenience to use the transdermal delivery system for the cancer patients who have difficulty in taking drugs due to surgical operation or gastrointestinal dysfunction.

Effect of granisetron on radiation-induced alterations of colonic motility and fluid absorption in rats

BACKGROUND

Radiation-induced diarrhoea is attributed to both mucosal injury and alterations of intestinal motility. Previous reports have indicated that 5-hydroxytryptamine is released following irradiation, which may contribute to these changes.

AIMS

To investigate the effects of granisetron (5-hydroxytryptamine type-3 receptor antagonist) on colonic motility, fluid absorption and 5-hydroxytryptamine colonic content following abdominal irradiation (10 Gy) in rats.

METHODS

In vivo measurements of motility and fluid absorption in the proximal and distal colon, respectively, diarrhoea score and 5-hydroxytryptamine tissue levels were performed 3 and 7 days after abdominal irradiation. The effects of post-irradiation granisetron (0.3 mg/kg subcutaneously) were also evaluated.

RESULTS

Colonic motility and fluid/Na(+) absorption were reduced 3 and 7 days after irradiation. All rats developed diarrhoea (3 days) concomitant with increased colonic mucosal 5-hydroxytryptamine levels. Granisetron prevented diarrhoea, attenuated decreased colonic motility and reduced 5-hydroxytryptamine levels on day 3, although fluid absorption was only slightly improved. On day 7, colonic motility and fluid/Na(+) absorption were restored in granisetron-dosed animals.

CONCLUSIONS

These results indicate that radiation-induced diarrhoea involves alterations of both colonic motility and fluid/Na(+) absorption. 5-Hydroxytryptamine could be one of the mediators implicated in these alterations, as post-irradiation dosage with a 5-hydroxytryptamine type-3 receptor antagonist improved colonic motility and prevented diarrhoea on day 3.

The effects of propofol in the area postrema of rats

Propofol has an antiemetic effect that may be mediated by gamma-aminobutyric acid (GABA) influences on the serotonin system, the mechanism of which is not known. We used three techniques, immunohistochemistry, High Performance Liquid Chromatography, and electrophysiology, to define propofol's effects on the rat's brainstem. Paired male Wistar rats received propofol, 20 mg/kg/hr, or Intralipid for 6 h. The brains were then subjected to immunohistochemical analysis of serotonin. In a separate experiment after a propofol or Intralipid infusion, cerebrospinal fluid (CSF) was extracted from the fourth ventricle and analyzed for the amount of serotonin and 5-hydroxyindoleacetic acid. Electrophysiological neuronal recordings were made in the area postrema (AP) in response to propofol with and without a GABA or serotonin antagonist. Results showed that immunohistochemical staining for serotonin in the propofol rats was significantly increased (28 +/- 12%) in the dorsal raphe and decreased in the AP (17 +/- 6%) compared with control. There were no significant changes in the isoflurane-anesthetized animals. Both serotonin and 5-hydroxyindoleacetic acid in the CSF of the fourth ventricle at the level of the AP were significantly reduced by 63% and 36%, respectively. Both propofol and pentobarbital injections reduce AP neuronal activity, but only the propofol response was blocked by bicuculline, a GABA antagonist. We conclude that the reduced levels of serotonin in the AP and the CSF may explain the antiemetic property of propofol. Propofol may also directly act on AP neurons via a GABA(A) receptor to reduce their activity.

IMPLICATIONS

Propofol may produce its antiemetic effect by depleting the area postrema of serotonin as well as by a direct gamma-aminobutyric acid-mediated inhibition.

Double-blind, randomized, parallel-group study on the efficacy and safety of oral granisetron and oral ondansetron in the prophylaxis of nausea and vomiting in patients receiving hyperfractionated total body irradiation

The efficacy and safety of granisetron and ondansetron for the prophylaxis of nausea and vomiting resulting from hyperfractionated total body irradiation (TBI) were assessed. Thirty-four patients randomly received double-blind, oral granisetron (2 mg, 1 h before first daily fraction of radiation) or ondansetron (8 mg, 1.5 h prior to each fraction of TBI). Ninety patients who received the same TBI regimen prior to bone marrow transplantation (BMT), but no 5-HT3-receptor antagonist, were identified and comprised the historical control group. By design, this study was only powered to show a difference between each of the active treatment groups and the historical control group. Significantly more patients given granisetron (33.3%) or ondansetron (26.7%) had zero emetic episodes over 4 days, the primary efficacy end point, than those in the historical control group (0%) (P < 0.01; intent-to-treat). Secondary efficacy end points were also evaluated. During the first 24 h, significantly more patients taking granisetron (61.1%) or ondansetron (46.7%) had zero emetic episodes than patients in the historical control group (6.7%) (P < 0.01). Complete emetic control (no emesis or rescue antiemetic) over 4 days was more frequent in patients taking granisetron (27.8%) or ondansetron (26.7%) compared with the historical control group (0%) (P < 0.01). Significantly fewer patients taking granisetron (18/18), but not those taking ondansetron (12/15), experienced more than five emetic episodes during the 4 days of the study compared with the historical control group (40/90; P < 0.01). Oral granisetron and ondansetron are safe and effective for the prevention of nausea and vomiting resulting from TBI.

Intravenous itasetron: establishing the effective dose range for the prophylactic control of acute emesis in cancer patients undergoing high-dose cisplatin chemotherapy

Nausea and vomiting induced by chemotherapy are a major cause of distress to patients and reduce compliance with potentially beneficial treatment. Itasetron hydrochloride is a new 5-hydroxytryptamine3 (5-HT3) antagonist with potent antiemetic properties. It is more potent than ondansetron in animal models and in early clinical studies it demonstrates a long half-life and does not undergo hepatic biotransformation before elimination. The aim of this open, uncontrolled study was to establish the effective dose range of itasetron hydrochloride given intravenously (i.v.) to patients due to receive high-dose cisplatin chemotherapy (50-120 mg/m2) for the first time. Thirty-nine patients were enrolled in the trial and received a single i.v. infusion of itasetron hydrochloride at a dose of 17-280 microg/kg body weight before commencing the cisplatin infusion (median dose 90-110 mg/m2). Antiemetic protection was demonstrated by doses in the range of 35-280 microg/kg. The 17 microg/kg dose was not effective. Treatment failure (>5 emetic episodes/24 hours) was reported in only six (16%) of the 38 evaluable patients over all treatment groups. Adverse events were generally mild or moderate and of a similar type and incidence to those of current 5-HT3 antagonists. Physicians' and patients' assessments of efficacy and tolerability of itasetron hydrochloride were similar, the majority rating the treatment as 'good' or 'very good'. In conclusion, itasetron hydrochloride is effective in the dose range 35-280 microg/kg in preventing cisplatin-induced emesis. Taken together with results from a larger dose-finding study, a dose corresponding to 35 microg/kg (equivalent to 2.5 mg itasetron, calculated as free base) has been pursued in Phase III studies with the i.v. formulation.

Randomized double-blind comparison of single high-dose ondansetron and multiple standard-dose ondansetron in chemotherapy-naive pediatric oncology patients

This prospective, double-blind, randomized study compares the antiemetic efficacy of an equivalent dose of ondansetron administered as a single high dose or as multiple standard doses in pediatric oncology patients. Thirty-one chemotherapy-naive patients were randomized at diagnosis to receive either single high-dose ondansetron (0.6 mg/kg, maximum dose 32 mg) or multiple standard-dose ondansetron (0.15 mg/kg, maximum dose 8 mg, every 4 hr for four doses). Antiemetic efficacy was assessed by an emesis scale described as follows: 1, no nausea or emesis; 2, nauseous but able to eat; 3, nauseous and unable to eat; and 4, emesis. Sixteen patients received high-dose and 15 received standard-dose ondansetron. Patients receiving moderately or severely emetogenic chemotherapy were evenly distributed between the two treatment groups. Eighty-one percent of patients receiving high-dose and 80% receiving standard-dose ondansetron rated 1 or 2 on the emesis scale (p = 0.93). No patient experienced any clinical or laboratory toxicity. Our study suggests that single high-dose ondansetron is as efficacious as the multiple standard-dose regimen and is well tolerated. Its use will facilitate the administration of ondansetron in pediatric patients receiving chemotherapy.

Pharmacokinetics of granisetron in rat blood and brain by microdialysis

To characterize the pharmacokinetics of protein-free granisetron in blood and brain we implanted microdialysis probes into the jugular vein and cerebral frontal cortex of the rat. Granisetron (3 or 6 mg/kg, i.v., n=6) was then administered, and microdialysates from blood and brain were collected from both sites and assayed by a validated high-performance liquid chromatographic method. Pharmacokinetics parameters were calculated from the corrected dialysate concentrations of granisetron versus time data. The elimination half-lives of granisetron in blood and brain were 51.3+/-5.5 and 69.7+/-6.3 min for 6 mg/kg, and 50.7+/-4.3 and 74.3+/-12.5 min for 3 mg/kg, respectively. Granisetron rapidly entered the extracellular fluid of cerebral frontal cortex at Tmax of 24 min. The results suggest that simultaneous microdialysis in blood and brain can be usefully applied to study the pharmacokinetics of granisetron in the periphery and the central nervous system.

Selective 5-hydroxytryptamine3 (5-HT3) receptor blocking activity of KB-R6933, a novel benzimidazole derivative

5-Hydroxytryptamine3 (5-HT3)-receptor blocking activities of KB-R6933 (6-amino-5-chloro-1-isopropyl-2-(4-methyl-1-piperazinyl)-benzimidazole dimaleate) were assessed in vivo and in vitro. Intravenous administration of KB-R6933, granisetron, ondansetron and azasetron inhibited 5-HT-induced bradycardia (von Bezold-Jarisch reflex) in anesthetized rats, with ED50 values of 0.071, 0.71, 4.0 and 0.82 microg/kg, respectively. The inhibitory effect of KB-R6933 at a dose of 0.3 microg/kg lasted for at least 8 hr, whereas those of granisetron at 30 microg/kg, ondansetron at 100 microg/kg and azasetron at 30 microg/kg nearly disappeared within 2-4 hr. Oral administration of KB-R6933 and granisetron also inhibited the bradycardia, with ED50 values of 0.41 and 76.3 microg/kg, respectively. In guinea pig ileum, KB-R6933 concentration-dependently antagonized 5-HT-evoked contraction and reduced the maximal contraction (pK(B)=8.75). Granisetron, ondansetron and azasetron shifted the dose-response curve for 5-HT to higher concentrations with no reduction of maximal contraction, and their pK(B)s were 7.65, 7.00 and 6.29, respectively. In a radioligand receptor binding study, KB-R6933, granisetron, ondansetron and azasetron displaced [3H]GR65630 binding to rat entorhinal cortex membrane, with Ki values of 0.066, 0.99, 2.70 and 2.5 nM, respectively. On the other hand, KB-R6933 exhibited negligible affinities for other receptors or binding sites tested, except for a weak affinity for the cholinergic M1-receptor, even at concentrations up to 10 microM. These results suggest that KB-R6933 is a potent and selective 5-HT3-receptor antagonist with a longer duration of action than those of existing 5-HT3-receptor antagonists.

Supplementation of general anaesthesia with tramadol or fentanyl in parturients undergoing elective caesarean section

PURPOSE

Tramadol has been recommended for analgesia in parturients undergoing vaginal delivery. The present report investigated the effect of tramadol versus fentanyl on umbilical vein (UV) blood gases and Apgar scores of neonates delivered via elective Caesarean section under general anaesthesia.

METHODS

Forty ASA I or II parturients undergoing elective Caesarean section were included in a randomized double-blinded study. The patients were divided into a tramadol (n = 20) and fentanyl groups (n = 20). During preoxygenation, one group received 100 mg tramadol i.v., while the second received 100 micrograms fentanyl. Anaesthesia was induced in both groups by 3 mg.kg-1 thiopentone and 1.5 mg.kg-1 succinylcholine was given to facilitate tracheal intubation. Anaesthesia was maintained during the induction-delivery period with nitrous oxide 50% in oxygen.

RESULTS

The umbilical vein PO2 was higher in the fentanyl (34 +/- 5 mmHg) than in the tramadol group (24 +/- 6 mmHg) (P < 0.01), while the UV PCO2 was higher in the tramadol group (50 +/- 5 vs 45 +/- 4 mmHg) (P < 0.01). The Apgar scores at one and five minutes were not different between the two groups. Post operatively, two patients in the tramadol group recalled the crying of their newborn at delivery.

CONCLUSION

Tramadol is associated with a high incidence of intraoperative maternal recall and can result in lower umbilical vein PO2 and higher PCO2 than in the fentanyl group.

A risk-benefit assessment of serotonin 5-HT3 receptor antagonists in antineoplastic therapy-induced emesis

Insight into the pathophysiology of antineoplastic therapy-induced nausea and vomiting led to the development of the serotonin 5-HT3 receptor antagonists as the most potent class of antiemetic agents. Among those which have been investigated are ondansetron, granisetron, tropisetron and dolasetron. A risk-benefit analysis of these drugs must not only account for the modest clinical differences in efficacy and tolerability, but also should include such issues as ease of use, route of administration, dosage considerations and patient preference. Pharmacokinetic and preclinical studies reveal distinctions among these antiemetics, but, overall, these distinctions do not translate in to clinically significant differences. In clinical trials, the most widely studied members of the 5-HT3 receptor antagonists are granisetron and ondansetron, which have been found to possess equivalent antiemetic efficacy. Dolasetron and tropisetron are also available, and some randomised trials have also documented their similar antiemetic activity, depending on the doses and schedules used. The equivalent efficacy of oral granisetron 2 mg versus intravenous ondansetron 32 mg has recently been demonstrated in prospective randomised clinical trials in patients receiving either highly emetogenic or moderately emetogenic antineoplastic therapy. The utilisation and efficacy of oral ondansetron and dolasetron in patients receiving moderately emetogenic antineoplastic therapy has also been documented. This review offers a brief overview of the pharmacokinetic and preclinical research on the 5-HT3 antagonists, a review of the comparative clinical trials of the major members of this class and a summary risk-benefit assessment that considers clinical applicability and cost, as well as efficacy and safety.

Physiology of chemotherapy-induced emesis and antiemetic therapy. Predictive models for evaluation of new compounds

The physiology of emesis has been studied for several hundred years, focusing on the different centres involved and the mechanics of expulsion. The vomiting centre receives inputs from various emetic detectors such as the gut, the vestibular labyrinths and the chemoreceptor trigger zone. Emesis is a common disabling effect in motion sickness, postoperative conditions and in radio- and chemotherapy. Our current understanding of the mechanisms has been provided mainly by the recent introduction of serotonin 5-HT3 receptor antagonists into therapeutic use. Nevertheless, despite the considerable advances made in the understanding of the different pathways involved in emesis, there are number of areas that still require experimental investigation. Different animal and human models are available to study the physiology of emesis and to evaluate the antiemetic activity of new compounds, but they need to be predictors of clinical situations.

VB20B7, a novel 5-HT-ergic agent with gastrokinetic activity. I. Interaction with 5-HT3 and 5-HT4 receptors

This study describes the in-vitro interaction of the gastrokinetic agent 2[1-(4-piperonyl)piperazinyl]benzothiazole (VB20B7) with the 5-hydroxytryptamine 5-HT3 and 5-HT4 receptor subtypes, using functional as well as radioligand binding studies. The benzamide derivative cisapride was used as a comparison. In radioligand binding assays VB20B7 showed, like cisapride, a weak affinity at 5-HT3 receptors from rat cerebral cortex. The new compound lacked any affinity at other 5-HT receptors or at dopaminergic D2 receptors, whereas cisapride showed high affinity for the 5-HT4 receptors from guinea-pig hippocampus and moderate affinity at dopaminergic D2 receptors. In the non-stimulated guinea-pig ileum, the concentration-response curves to the specific 5-HT3 agonist 2-Me-5-HT and to 5-HT were shifted to the right by VB20B7. In the rat oesophagus tunica muscularis mucosae preparation (TMM), VB20B7 was evaluated for its activity at 5-HT4 receptors. VB20B7 behaved as a 5-HT4 receptor agonist, inducing a concentration-dependent relaxation of the preparation precontracted with carbachol. In this preparation, VB20B7 and cisapride were able to stimulate adenylate cyclase activity, an effect probably mediated through activation of 5-HT4 receptors, as can be inferred from the blockade by the 5-HT4 antagonist, tropisetron, of the enhanced cAMP formation. However, consistent with the lack of affinity at central 5-HT4 receptors, VB20B7 did not stimulate cAMP formation in guinea-pig hippocampal slices. VB20B7 also caused an increase in the twitch response of the transmurally stimulated guinea-pig ileum, although at a concentration higher than cisapride. This effect was blocked by desensitization of the 5-HT4 receptor with 5-MeOT and also by the 5-HT4 receptor antagonist tropisetron. Both VB20B7 and cisapride increased the K(+)-evoked acetylcholine release in this preparation. The results show that VB20B7 possesses affinity for 5-HT4 receptors located in the rat TMM and guinea-pig ileum preparations, but is devoid of affinity at central 5-HT4 receptors. In addition, VB20B7 shows low to moderate affinity at both central and peripheral (enteric) 5-HT3 receptors. The interaction of VB20B7 with the peripheral 5-HT4 and 5-HT3 receptors may be relevant for the gastrokinetic effects of the new compound.

New perspectives in antiemetic treatment

Though antiemetic therapy has improved markedly in the past 15 years, patients still regard nausea and vomiting as two of the most distressing adverse events during chemotherapy. A major progress was the development of the serotonin3 (5-HT3) receptor antagonists. A possible antiemetic effect, achieved by interference with the "serotonergic system", is not restricted to antagonism at 5-HT3 receptors, however, but also includes agonism at 5-HT1A and 5-HT2 receptors, and serotonin synthesis inhibitors. The number of receptors thought to be involved in the emetic reflex has been augmented by neurokinin1 receptors with substance P as the preferred ligand. Animal studies have demonstrated a broad antiemetic profile of substance P antagonists. The somatostatin analogue octreotide has an antiemetic effect in patients with gastrointestinal obstruction, but has not been investigated against chemotherapy-induced emesis. The next few years will disclose, whether the efficacy and safety profiles of one or more of these drugs will make it clinically useful in the treatment of chemotherapy-induced nausea and vomiting.

5-Hydroxyindoleacetic acid (5-HIAA) and cortisol excretion as predictors of chemotherapy-induced emesis

This study evaluated the relationship between prechemotherapy cortisol and 5-hydroxyindoleacetic acid (5-HIAA) excretion and chemotherapy-induced emesis. The urinary excretion of cortisol and the serotonin metabolite 5-HIAA in the night before chemotherapy administration were measured in 28 and 49 female patients receiving > 300 mg m-2 carboplatin. Vomiting and nausea were documented over a 3 day observation period. Lower basal cortisol excretion was significantly correlated with vomiting with or without nausea occurring within the observation period. 5-HIAA showed only a weak correlation with emesis on days 1-3, but low 5-HIAA excretion was correlated with a higher proportion of patients vomiting on days 2-3 following chemotherapy. Low basal cortisol excretion might be useful as a predictor for chemotherapy-induced emesis and therefore should be evaluated prospectively in future studies.

5-Hydroxyindoleacetic acid excretion following combination chemotherapy with cyclophosphamide, epirubicin and 5-fluorouracil plus ondansetron compared to ondansetron alone

The aim of the work was to evaluate the impact of cyclophosphamide and ondansetron on serotonin metabolism measured by urinary 5-hydroxyindoleacetic acid (5-HIAA) excretion. The pattern of urinary 5-HIAA excretion was analysed within 24 h following cyclophosphamide, epirubicin and 5-fluorouracil (FEC) chemotherapy (n = 14), ondansetron as single agent (n = 31), and in a control group (n = 62). 5-HIAA was measured by a fluorescence/polarisation immunoassay. Both FEC and ondansetron alone induced a significantly higher 5-HIAA increase following the first 12 h after drug administration when compared to the control group. The comparison of quantitative variables of 5-HIAA excretion between FEC and ondansetron failed to reveal any statistical differences. Cyclophosphamide-based chemotherapy is associated with only minor increases of 5-HIAA excretion. Analysis of 5-HIAA excretion does not help in the description of the pathophysiology of cyclophosphamide-induced emesis. In contrast to experimental data, serotonin 3 receptor antagonism with ondansetron induces an increase of 5-HIAA excretion in humans.

Biotransformation of the antiemetic 5-HT3 antagonist tropisetron in liver and kidney slices of human, rat and dog with a comparison to in vivo

Species differences in the biotransformation of the antiemetic tropisetron, a potent 5-hydroxytryptamine type 3 (5-HT3) receptor antagonist, were evident in liver slice incubates of human, rat and dog, and reflected the species differences observed in vivo with respect to the relative importance of individual pathways. The dominant biotransformation pathway of tropisetron (10 microM) in human liver slices was formation of 6-hydroxy-tropisetron, whereas in rat liver slices it was 5-hydroxy-tropisetron, and in dog liver slices N-oxide formation. Initial rates of tropisetron metabolite formation in the liver slices (8 mm in diameter, 200 +/- 25 microns thickness) of human (83 +/- 61 pmol/h/mg slice protein), rat (413 +/- 98 pmol/h/mg slice protein) and dog (426 +/- 38 pmol/h/mg slice protein) would predict less of a first-pass effect in humans compared to the rat or the dog. For human and rat, the prediction matched well with the species ranking of tropisetron bioavailability; however, for dog the in vitro data overestimated the apparent first-pass effect. The jejunum is not expected to contribute to the first-pass effect in humans, since human jejunum microsomes did not metabolize tropisetron. The major organ of excretion for tropisetron and its metabolites is the kidney, but the contribution of the kidney to the overall metabolism of tropisetron would be small. Species independent N-oxide formation (2-12 pmol/h/mg slice protein) was the major pathway in human, rat and dog kidney slices, and was comparable to N-oxide formation in the rat and human liver slices but was 1/10 the rate in dog liver slices. This study has demonstrated that the liver is the primary site of tropisetron biotransformation, and the usefulness of organ slices to characterize cross species differences in the dominant biotransformation pathways.

Granisetron: the second serotonin-receptor antagonist

OBJECTIVE

To review the pharmacology, pharmacokinetics, clinical efficacy, and adverse effects of granisetron, focusing on critical analysis of published clinical trials and comparison with other antiemetic agents, including ondansetron.

DATA SOURCES

MEDLINE (1966-1995) and CANCERLIT (1991-1995) searches of English-language literature using the terms "granisetron" and "granisetron (rn)" were performed.

STUDY SELECTION AND DATA EXTRACTION

All articles were considered for possible inclusion in this review. Abstracts of clinical trials were included only when they were judged to add critical information not otherwise available in the medical literature. For studies published more than once, the most recent publication was cited.

DATA SYNTHESIS

Nausea and vomiting are rated by patients as the most distressing chemotherapy-related adverse effects and may produce potentially life-threatening complications. The discovery of the role of serotonin in nausea and vomiting and the development of selective serotonin3-receptor (5-HT3) antagonists has significantly diminished the incidence and consequences of chemotherapy-related nausea and vomiting. Granisetron is the second 5-HT3-receptor antagonist to be marketed in the US. Granisetron has been compared with other antiemetic agents, including ondansetron, against highly and moderately emetogenic chemotherapy. The results of these trials have shown granisetron to be superior to conventional antiemetics and as effective as ondansetron in the prevention of chemotherapy-induced nausea and vomiting. The optimal dose of granisetron has yet to be determined. Formulary decisions should be based on a cost comparison among the 5-HT3-receptor antagonists at individual institutions.

CONCLUSIONS

Granisetron is a safe, effective antiemetic agent for the management of nausea and vomiting caused by cancer chemotherapy.

Comparison of the antiemetic effects of a 5-HT1A agonist, LY228729, and 5-HT3 antagonists in the pigeon

Vomiting may be induced by a variety of agents such as drugs, oncolytics, and provocative motion, as well as being conditioned to occur to environmental stimuli. Such emesis has recently been shown to be blocked by agonists at the 5-HT1A subtype of serotonin receptor. The antiemetic effects of LY228729 [(-)-4-(dipropylamine)-1,3,4,5-tetrahydrobenz-(c,d)indole-6- carboxamide], a 5-HT1A receptor agonist, were tested and compared to the antiemetic effects of the 5-HT3 receptor antagonists ondansetron, tropisetron, and MDL 72222 (3-tropanyl-3,5-dichlorobenzoate). The emetic stimuli tested are known to be blocked by 5-HT3 antagonists in species other than the pigeon. In the pigeon, LY228729 totally abolished vomiting induced by fully emetic doses of cisplatin (10 mg/kg), ipecac (3 ml/kg), emetine (10 mg/kg), and a 5-HT3 agonist, m-(chlorophenyl)-biguanide (1.25 mg/kg). MDL 72222 blocked ipecac-induced vomiting in a dose-related manner and was partially effective in attenuating cisplatin-induced emesis. Ondansetron and tropisetron were partially effective in blocking emetine- and mCPBG-induced vomiting. Ondansetron exhibited an intrinsic emetic response that could not be blocked by MDL 7222, but which was eliminated by LY228729. It was concluded that 5-HT1A agonists are more effective in the pigeon than are 5-HT3 antagonists against these types of emetic stimuli. These results broaden the range of emetic stimuli that are blocked by 5-HT1A agonists in the pigeon.

Serotonin metabolism following platinum-based chemotherapy combined with the serotonin type-3 antagonist tropisetron

The administration of platinum-based chemotherapy induces serotonin release from the enterochromaffin cells, causing nausea and vomiting. This study was conducted to evaluate parameters of serotonin metabolism following platinum-based chemotherapy given in combination with the serotonin type-3 antagonist tropisetron as an antiemetic agent. In nine chemotherapy-naive patients with disseminated germ-cell tumors, parameters of serotonin metabolism in both blood and urine were evaluated during two consecutive courses of platinum-based chemotherapy. Serotonin concentrations in platelet-rich plasma and platelet-poor plasma as well as urinary 5-hydroxyindoleacetic acid (5-HIAA) and serotonin levels were measured during the full length of the courses. By means of comparison with the antiemetic agent chlorpromazine, used on day 1 of the first course only, the effect of the serotonin type-3 antagonist tropisetron, the antiemetic agent used during the rest of the courses, on these parameters was studied. Clinical effects were also recorded. No change in the parameters of serotonin metabolism could be demonstrated during either course by the serotonin type-3 antagonist tropisetron. Also in vitro, no effect of tropisetron on the active serotonin uptake by platelets was found. Serotonin levels in platelets showed no correlation with emetic response. However, the platelet serotonin content decreased significantly between the first and the second course (P < 0.01). The significant reduction in platelet serotonin content observed between the first and the second course indicates a depletion of total body serotonin. The role of a serotonin type-3 antagonist might be affected by the altered serotonin equilibrium during later courses of chemotherapy.

The role of serotonin as a mediator of emesis induced by different stimuli

The aim of this work was to evaluate the impact of changes in serotonin metabolism on the pathophysiology of different types of emesis: pregnancy-induced emesis, emesis associated with inner-ear dysfunction, and cisplatin-induced emesis. The urinary excretion of 5-hydroxyindoleacetic acid (5-HIAA), the main metabolite of serotonin, was measured in 13 women with pregnancy-induced emesis, 12 patients who had nausea and vomiting following inner-ear dysfunctions, 27 patients with cisplatin-induced emesis and a control group of 21 women. 5-HIAA was measured with a fluorescence polarization immunoassay (Abbott) and corrected for varying urine concentrations. Both patients with emesis associated with inner-ear dysfunction and patients with pregnancy-associated emesis showed a similar 5-HIAA excretion pattern compared with the control group. No correlation between intensity of nausea or vomiting and changes in 5-HIAA excretion could be detected. In patients receiving cisplatin, the 5-HIAA excretion increased rapidly within the 12 h following cisplatin administration and returned to baseline levels after 24 h. There was a parallel increase of 5-HIAA excretion and numbers of emetic episodes in the first 12 h, but delayed emesis was not associated with elevated 5-HIAA excretion. Our results provide evidence that serotonin is involved in the pathophysiology of cisplatin-induced acute emesis. Cisplatin-induced delayed emesis, pregnancy-associated emesis, and emesis due to inner-ear dysfunction are not associated with elevated levels of 5-HIAA excretion. The serotonin pathway probably represents only one of many different afferent mechanisms capable of initiating the emesis cascade.

5-HT3 receptors: pharmacologic and therapeutic aspects

The serotonin 5-HT3 receptor is unique among the seven serotonin receptor "families" that have been recognized so far. It functions not as a G-protein coupled but as a direct ion channel gated receptor. Because of the varied neural functions linked to this receptor, intensive research interest has developed in recent years about its basic and clinical pharmacology, which are summarized in this review. Some new agonists and many new antagonists have been developed. These agents have a useful role as selective pharmacologic research probes, and some of them can be used therapeutically as potent and selective anti-nausea and antiemetic drugs, particularly in patients undergoing cancer chemotherapy treatment or general anesthesia procedures. Potential applications of these agents include the treatment of some behavioral disorders in mental disease, drug addiction, and certain types of pain syndromes.

In vitro characterization of cytochrome P450 catalysed metabolism of the antiemetic tropisetron

The new 5-hydroxytryptamine type 3 (5HT3) receptor antagonist tropisetron is used in the treatment of chemotherapy-related nausea. The drug is extensively metabolized in man, with the enzymes involved in tropisetron biotransformation being unknown. Identification of these enzymes would make it possible to predict both interindividual variability in plasma concentrations and metabolic interaction potential. The present in vitro study was therefore aimed at identifying and characterizing the cytochrome P450 enzymes catalysing tropisetron metabolism. Enzyme kinetics for formation of 5-hydroxy (5-OH-ICS), 6-hydroxy (6-OH-ICS) and N-demethyl tropisetron (N-De-ICS) were studied in the microsomal fraction of eight human livers (seven livers from extensive metabolizer (EM), one liver from a poor metabolizer (PM) for CYP2D6). Formation of 5-OH-ICS and 6-OH-ICS was biphasic with a high (5-OH: Km 3.9 +/- 2.1 microM; Vmax 1.88 +/- 0.73 pmol/mg/min; 6-OH: Km 4.66 +/- 1.84 microM; Vmax 4.00 +/- 1.77 pmol/mg/min) and low (5-OH: Km 172 +/- 51 microM; Vmax 17.0 +/- 9.4 pmol/mg/min; 6-OH: Km 266.0 +/- 76.0 microM; Vmax 81.4 +/- 27.9 pmol/mg/min) affinity component. The high-affinity component was identified as CYP2D6 which exhibits a genetic polymorphism in man. This component was absent in the PM liver. The low-affinity component was present in EM and PM livers and was identified as CYP3A4. LKM1 antibodies directed against CYP2D6 completely inhibited the high affinity component. Quinidine (0.5 microM) inhibited 5- and 6-hydroxylation at 10-80 microM tropisetron concentrations competitively by 70% with Ki values of 10 and 18 nM, respectively. Stably-expressed CYP2D6 catalysed the formation of both 5-OH-ICS and 6-OH-ICS. Both inhibition experiments and use of stably-expressed enzymes revealed formation of N-De-ICS to be mediated by CYP3A4. Based on in vitro intrinsic clearances CYP2D6-catalysed 5-OH-ICS and 6-OH-ICS is the predominant route of tropisetron elimination. Large phenotype-related differences in total clearance are to be expected after administration of tropisetron. However, in view of the wide therapeutic index of tropisetrone and the rather high Ki for inhibition of the metabolism of other drugs by tropisetron, both the interindividual variability and the interaction potential appear to be of no clinical relevance.

Development of antiemetic therapy in cancer patients

Patients still consider nausea and vomiting to be severe adverse consequences of cancer chemotherapy. The physiology of chemotherapy-induced nausea is generally unknown, but the finding that high doses of metoclopramide induce the antiemetic effect by antagonizing 5-HT3 receptors, has evoked increased interest in serotonin as a possible neurotransmitter. This has led to development of more selective 5-HT3 antagonists, such as ondansetron, granisetron and tropisetron, with improvement of antiemetic therapy, especially in patients receiving cisplatin-based chemotherapy. The efficacy of serotonin antagonists is further optimized by the addition of steroids and the dopamine D2 antagonist metopimazine. Many questions in antiemetic treatment are still unanswered and future trials should focus on patients receiving multiple-day chemotherapy or multiple cycles of chemotherapy and on patients resistant to initial antiemetic therapy.

A randomized cross-over study of high-dose metoclopramide plus dexamethasone versus granisetron plus dexamethasone in patients receiving chemotherapy with high-dose cisplatin

We carried out a randomized, single-blind, cross-over trial to compare the antiemetic effect, for both acute and delayed emesis, of granisetron plus dexamethasone (GRN+Dx) with that of high-dose metoclopramide plus dexamethasone (HDMP+Dx). Fifty-four patients with primary or metastatic lung cancer, given single-dose cisplatin (> 80 mg/m2) chemotherapy more than twice, were enrolled in this study. They were treated with both HDMP+Dx and GRN+Dx in two consecutive chemotherapy courses. On day 1, patients experienced a mean of 2.5 (SD = 4.3) and 0.1 (SD = 0.4) episodes of vomiting in the HDMP+Dx and the GRN+Dx groups, respectively (P = 0.0008). Complete response rate on day 1 was 45 and 90% in the HDMP+Dx and the GRN+Dx groups, respectively (P = 0.0001). Patients treated with GRN+Dx had a tendency to suffer more episodes of vomiting than the HDMP+Dx group on days 2-5, but it was not statistically significant. Twenty-four patients (57%) preferred the GRN+Dx treatment and 14 patients (33%), HDMP+Dx. In the HDMP+Dx group, nine patients (21%) had an extrapyramidal reaction, and 5 patients (12%) had constipation that lasted for at least two days. In contrast, no patients had extrapyramidal reactions, and 18 patients (43%) had constipation in the GRN+Dx group (P < 0.01). GRN+Dx was more effective than HDMP+Dx only in preventing the acute emesis induced by cisplatin. An effective treatment for delayed emesis is still needed.

Emesis induced in domestic pigs: a new experimental tool for detection of antiemetic drugs and for evaluation of emetogenic potential of new anticancer agents

The domestic pig was used to develop a new model for evaluating the emetogenic potential of anticancer drugs and determining the antiemetic activity of drugs. Emesis was characterized by expulsion of solid or liquid material. In each animal, the number of vomits after infusion of the emetogenic drug (infusion in ketamine and xylazine anesthesia) was recorded in 1-hr periods during the first 4 hr and then in a 4- and a 16-hr period. Intravenous infusion of cisplatin caused a concentration-dependent emetic response. Anti-cancer drugs other than cisplatin such as carboplatin, dactinomycin, cyclophosphamide, and ifosfamide, also induced emesis, indicating that the domestic pig is suitable to detect the emetogenic potential of chemotherapeutic agents. A cisplatin dose of 2 mg/kg i.v. proved to be most suitable for studying the effect of potential antiemetic drugs (applied as i.v. injection), because this cisplatin dose caused consistent emetic responses without other toxic signs in the 24 hr following its infusion. Emesis induced by cisplatin was reduced by high doses of metoclopramide (25 mg/pig; approximately 0.8 mg/kg). The more selective dopamine D2 receptor antagonists, alizapride and domperidone, even at high doses (25-50 mg/pig; approximately 0.8-1.6 mg/kg), did not inhibit cisplatin-induced emesis, nor did haloperidol up to 20 mg/pig (approximately 0.6 mg/kg). Sulpride (50 mg/pig; approximately 1.6 mg/kg) halved the occurrence of vomits in the first 4 hr after cisplatin, but this effect was followed by an increase in the frequency of vomits; thus, no change in the total number of vomits was observed in the 24-hr observation period.(ABSTRACT TRUNCATED AT 250 WORDS)

Antiemetic effects of 5-HT1A agonists in the pigeon

Ditolyguanidine (DTG) induced a dose-dependent emetic response in pigeons, with 100% of the birds vomiting after 5.6 mg/kg. Retching and vomiting originally induced by DTG could be conditioned to the test situation. Both the unconditioned and conditioned emetic responses were dose-dependently blocked by 8-hydroxy-(di-n-propylamino)tetralin (8-OH-DPAT) and LY228729, agonists at the 5-HT1A subtype of serotonin receptor, but not by the 5-HT3, antagonist tropisetron. Higher doses (0.25-0.5 mg/kg) of tropisetron exhibited intrinsic emetic activity which could also be prevented by 8-OH-DPAT. NAN-190, a putative 5-HT1A partial agonist, produced both an antiemetic response when administered before DTG and also attenuated the antiemetic effects of 8-OH-DPAT. Pentobarbital blocked the conditioned, but not the unconditioned DTG-induced emesis. These results support the possibility that 5-HT1A agonists exhibit antiemetic activity against a broad range of emetic stimuli, including conditioned vomiting which is usually resistant to pharmacological attenuation.

Mechanisms of cisplatin- and m-chlorophenylbiguanide-induced emesis in ferrets

We investigated the involvement of peripheral and central serotonin (5-HT)3 receptors in cisplatin- and 5-HT3 receptor agonist-induced emesis in ferrets. Cisplatin (10 mg/kg i.v.)-induced emesis was inhibited by intravenous YM060 (0.003-0.1 microgram/kg). A highly selective and potent 5-HT3 receptor agonist, m-chlorophenylbiguanide (1-10 mg/kg i.p.), dose dependently elicited emesis an effect which was inhibited by YM060 (0.003-0.3 microgram/kg i.v.). Vagotomy markedly reduced this emesis, and the combination of abdominal vagotomy and greater splanchnicectomy abolished emesis. Lesion of greater splanchnic nerves alone did not markedly inhibit emesis. Intracerebroventricularly (4th ventricle) administered YM060 inhibited cisplatin- and m-chlorophenylbiguanide-induced emesis only at higher doses (0.01-0.1 and 0.01-0.03 microgram, respectively). Intracerebroventricularly (4th ventricle) administered m-chlorophenylbiguanide (30-100 micrograms) produced only a weak retching response. These results indicate that stimulation of abdominal vagal afferent nerves via peripheral 5-HT3 receptors is important for triggering cisplatin- and m-chlorophenylbiguanide-induced emesis in ferrets.

The antiemetic efficacy and safety of granisetron compared with metoclopramide plus dexamethasone in patients receiving fractionated chemotherapy over 5 days. The Granisetron Study Group

The antiemetic efficacy and safety of granisetron (40 micrograms/kg), a selective and potent 5-hydroxytryptamine (serotonin) antagonist, was compared with that of metoclopramide (7 mg/kg) plus dexamethasone (12 mg) in patients receiving fractionated chemotherapy. Patients receiving cisplatin at doses of at least 15 mg/m2 or etoposide at least 120 mg/m2 or ifosfamide at least 1.2 g/m2 on each of 5 consecutive days were eligible. A total of 143 patients received granisetron and 141 received the comparator regimen. The 5-day complete response rate (no vomiting, no worse than mild nausea) for granisetron (46.8%) was equivalent to that for metoclopramide plus dexamethasone (43.9%). The overall 5-day response profile was superior for granisetron (P = 0.013) because of fewer failures in this group. The overall incidence of adverse experiences was significantly lower in the granisetron group (60.8% versus 77.3%, P = 0.003). Headache and constipation, more prevalent in the granisetron group, are recognized side-effects of serotonin antagonists. Extrapyramidal syndrome, not seen in any granisetron patients, occurred in 20.6% of comparator patients (P < 0.0001). The majority of granisetron patients only required a single prophylactic dose of the drug on each treatment day (at least 82%). In conclusion, granisetron showed at least equivalent efficacy to metoclopramide plus dexamethasone in patients receiving 5-day fractionated chemotherapy. In addition it offered a simple and convenient dosing regimen and a safer side-effect profile.

Effects of detergents on binding of 5-hydroxytryptamine3 receptor antagonist [3H]GR65630 to rat cortical membranes

In the absence of detergent, specific binding of [3H]GR65630, a 5-hydroxytryptamine3 (5-HT3) antagonist, determined in the presence of 5-HT3 receptor antagonist ICS205-930, was at most 30% of the total binding. To decrease the level of nonspecific binding, the effects of detergents on [3H]GR65630 binding to rat cortical membranes were investigated. The use of a detergent (0.1% Lubrol PX or Triton X-100) decreased nonspecific binding, increasing the proportion of specific binding to 70% of total binding. In the presence of 0.1% Triton X-100, binding of [3H]GR65630 was rapid, reversible and saturable at 25 degrees C. The rank order of 5-HT3 receptor active drugs in inhibiting [3H]GR65630 binding was quipazine > ICS205-930 > 2-methyl-5-HT = 5-HT > metoclopramide, which confirmed that [3H]GR65630 efficiently labeled 5-HT3 receptors in the presence of Triton X-100. Triton X-100 improved 5-HT3 receptor binding with rat brain membranes.