5-HT3-receptor antagonists and the cytochrome P450 system: clinical implications

The safety of lanreotide for neuroendocrine tumor

INTRODUCTION

Lanreotide autogel is a synthetic somatostatin analogue which has been FDA and EMA approved for unresectable, well to moderately differentiated, locally advanced or metastatic gastroenteropancreatic neuroendocrine tumor. Its action is mediated by its affinity to somatostatin receptors, especially sst2 and sst5 receptors. Its longer half-life offers the convenience of 4-week dosing over the need for frequent injections of short-acting somatostatin analogues. Areas covered: Lanreotide ATG offers progression-free survival benefit in locally advanced or metastatic neuroendocrine tumor (NET) compared to placebo, reflecting a strong antiproliferative signal. As lanreotide is commonly used for management of NET, it is imperative to recognize and appropriately manage any drug-related toxicities. In this review, we will provide an overview of the toxicity with lanreotide and its management. Expert opinion: Lanreotide is highly effective in managing carcinoid symptoms and has a robust anti-tumor effect in NET. Overall, it is well tolerated with low rates of treatment discontinuation due to toxicity. It's toxicity profile is mostly predictable, and patients should be informed of the transient nature of some of the upfront toxicities.

Comparative Pharmacology and Guide to the Use of the Serotonin 5-HT3 Receptor Antagonists for Postoperative Nausea and Vomiting

Since the introduction of the serotonin 5-hydroxy tryptamine 3 (5-HT₃) receptor antagonists in the early 1990s, the incidence of postoperative nausea and vomiting (PONV) and post-discharge nausea and vomiting (PDNV) has decreased, yet continues to be a problem for the surgical patient. The clinical application of the 5-HT₃ receptor antagonists has helped define the approach and role of these antiemetics in the prevention and treatment of PONV and PDNV. Pharmacological and clinical differences exist among these medications resulting in corresponding differences in effectiveness, safety, optimal dosage, time of administration, and use as combination and rescue antiemetic therapy. The clinical application of the 5-HT₃ receptor antagonist antiemetics has improved the prevention and treatment of PONV and PDNV. The most recent consensus guidelines for PONV published in 2014 outline the use of these antiemetics. The 5-HT₃ receptor antagonists play an important role to help prevent PONV and PDNV in perioperative care pathways such as Enhanced Recovery After Surgery (ERAS). Comparisons and guidelines for use of the 5-HT₃ receptor antagonists in relation to the risk for PONV and PDNV are reviewed.

Cancer Drug Delivery

Advancements in cancer drug delivery have led to the development of personalized oncology care through molecularly-driven targeted therapies. Understanding molecular and cellular mechanisms which drive tumor progression and resistance is critical in managing new treatment strategies which have shifted from empiric to biomarker-directed therapy selection. Biomarker-directed therapies have improved clinical outcomes in multiple malignancies as monotherapy and in combination with other treatment modalities, however the changing scope of treatment options presents new opportunities and challenges for research. Furthermore, pharmacogenetics may provide a rationale method of personalizing anticancer drug dosing and supportive care management for oncology patients. This chapter reviews biomarker classifications and pharmacogenetics in anticancer therapy and supportive care. Examples of biomarker-directed therapies and clinical assays, in addition to future directions of molecular profiling in oncology therapy management are discussed.

The Human Serotonin Type 3 Receptor Gene (HTR3A-E) Allelic Variant Database

Serotonin type 3 (5-HT₃ ) receptors are ligand-gated ion channels formed by five subunits (5-HT3A-E), which are encoded by the HTR3A, HTR3B, HTR3C, HTR3D, and HTR3E genes. Functional receptors are pentameric complexes of diverse composition. Different receptor subtypes confer a predisposition to nausea and vomiting during chemotherapy, pregnancy, and following surgery. In addition, different subtypes contribute to neurogastroenterologic disorders such irritable bowel syndrome (IBS) and eating disorders as well as comorbid psychiatric conditions. 5-HT₃ receptor antagonists are established treatments for emesis and IBS and are beneficial in the treatment of psychiatric diseases. Several case-control and pharmacogenetic studies have demonstrated an association between HTR3 variants and psychiatric and neurogastroenterologic phenotypes. Recently, their potential as predictors of nausea and vomiting and treatment of psychiatric disorders became evident. This information is now available in the serotonin receptor 3 HTR3 gene allelic variant database (www.htr3.uni-hd.de), which contains five sub-databases, one for each of the five different serotonin receptor genes HTR3A-E. Information on HTR3 variants, their functional relevance, associated phenotypes, and pharmacogenetic data such as drug response and side effects are available. This central information pool should help clinicians as well as scientists to evaluate their findings and to use the relevant information for subsequent genotype-phenotype correlation studies and pharmacogenetic approaches.

Does pharmacogenomics account for variability in control of acute chemotherapy-induced nausea and vomiting with 5-hydroxytryptamine type 3 receptor antagonists?

Chemotherapy-induced nausea and vomiting is one of the most concerning adverse drug effects from cytotoxic chemotherapy. Despite appropriate use of antiemetic guidelines, 20-30 % of patients experience breakthrough nausea and vomiting secondary to chemotherapy. To assess the variability of 5-hydroxytryptamine type 3 receptor antagonist efficacy caused by genetic variation, a review of the available literature was conducted. From the literature, three sources of pharmacogenomic variability were identified: polymorphisms associated with 5-hydroxytryptamine type 3 receptor subunits, drug metabolism via cytochromes P450, and drug transport in the body. Testing for receptor subunit polymorphisms is not applicable to a clinical setting at this time; however, cytochrome P450 2D6 testing is FDA-approved and widely accessible. Cytochrome P450 2D6 ultrarapid metabolizers and poor metabolizers displayed altered antiemetic efficacy when compared with intermediate metabolizers and extensive metabolizers. We postulate that testing for cytochrome P450 2D6 phenotypes may be the most accessible way to provide individualized antiemetic therapy in the future.

WITHDRAWN: Serotonin receptor antagonists for highly emetogenic chemotherapy in adults

This review is now out of date although it is correct as of the date of publication. The latest version of this review (available in ‘Other versions’ tab on The Cochrane Library) may still be useful to readers.

The editorial group responsible for this previously published document have withdrawn it from publication.

Ondansetron does not Modify Emergence Agitation in Children

In this prospective, placebo-controlled study, we evaluated the effect of prophylactic ondansetron therapy on emergence agitation of children who underwent minor surgery below the umbilicus. Seventy children aged one to six years and American Society of Anesthesiologists physical status I were studied. Children were premedicated with midazolam rectally and were randomly assigned to receive either ondansetron (Group O) or placebo (Group P) in combination with caudal anaesthesia. Children in Group O received intravenous ondansetron (0.1 mg/kg for children weighing <40 kg, 4 mg for children weighing >40 kg) and Group P (n=35) received normal saline 2 ml following anaesthesia induction with sevoflurane. Airway management was provided with LMA-Proseal without muscle relaxation and anaesthesia maintenance was provided with a 60:40 N2O:O2 mixture and sevoflurane. Emergence agitation was evaluated with a ten point scale and pain level was assessed every 10 minutes for the first 30 minutes after admission to the recovery room.

There were no significant differences between the placebo and ondansetron groups with respect to demographic, anaesthetic and surgical details. Incidences of emergence agitation in ondansetron and placebo groups were similar (32.4% and 30.3% at 10 minutes respectively). Mean modified Children's Hospital of Eastern Ontario pain scale scores and mean ten-point scale scores and emergence agitation incidences decreased similarly after 10 minutes in both groups. Ready time for discharge was similar between the groups. Agitated patients had significantly increased ready time for discharge compared to non-agitated patients (P=0.001).

Prophylactic intravenous ondansetron administration does not reduce emergence agitation comparing to placebo after sevoflurane anaesthesia.

Tropisetron and paracetamol association in post-operative patients

Studies in animals and in healthy volunteers have demonstrated the central serotonergic analgesic mechanism of action of paracetamol involving the inhibition of this analgesia by tropisetron, a 5-HT3 antagonist. This randomized, double-blind, controlled study aims at studying this interaction in post-operative patients after ear surgery. Thirty-six patients are included in two parallel groups with intravenous paracetamol (1 g) and either tropisetron (T, 5 mg/mL) or placebo (c, NaCl 0.9%) administered at the end of surgery. Numerical pain evaluations are performed every 30 min, six times after awakening. The difference between the sums of numerical scales of both groups [9 ± 10 (T) vs. 6 ± 7 (c)] is not significant, but the tropisetron group displays higher pain scores despite additional rescue analgesia. The limits of this trial call for a much larger study to investigate further this pharmacodynamic interaction.

Anti-emetic drugs in oncology: pharmacology and individualization by pharmacogenetics

OBJECTIVE

Nausea and vomiting are the most distressful side effects of cytotoxic drugs in cancer patients. Antiemetics are commonly used to reduce these side effects. However, the current antiemetic efficacy is about 70-80% in patients treated with highly-emetogenic cytotoxic drugs. One of the potential factors explaining this suboptimal response is variability in genes encoding enzymes and proteins which play a role in metabolism, transport and receptors related to antiemetic drugs. Aim of this review was to describe the pharmacology and pharmacogenetic concepts of of antiemetics in oncology.

METHOD

Pharmacogenetic and pharmacology studies of antiemetics in oncology published between January 1997 and February 2010 were searched in PubMed. Furthermore, related textbooks were also used for exploring the pharmacology of antiemetic drugs. The antiemetic drugs which were searched were the 5-hydroxytryptamine 3 receptor antagonists (5-HT3RAs), dopamine antagonists, corticosteroids, benzodiazepines, cannabinoids, antihistamines and neurokinin-1 antagonists.

RESULT

The 5-HT3RAs are widely used in highly emetogenic chemotherapy in combination with dexamethasone and a neurokinin-1 antagonist, especially in acute phase. However, the dopamine antagonists and benzodiazepines were found more appropriate for use in breakthrough and anticipatory symptoms or in preventing the delayed phase of chemotherapy induced nausea and vomiting. The use of cannabinoids and antihistamines need further investigation. Only six articles on pharmacogenetics of the 5-HT3RAs in highly emetogenic chemotherapy are published. Specifically, these studies investigated the association of the efficacy of 5-HT3RAs and variants in the multi drug resistance 1 (MDR1) gene, 5-HT3A,B and C receptor genes and CYP2D6 gene. The pharmacogenetic studies of the other antiemetics were not found in this review.

CONCLUSION

It is concluded that pharmacogenetic studies with antiemetics are sparse. It is too early to implement results of pharmacogenetic association studies of antiemetic drugs in clinical practice: confirmation of early findings is required.

5-HT(3) receptors: role in disease and target of drugs

Serotonin type 3 (5-HT(3)) receptors are pentameric ion channels belonging to the superfamily of Cys-loop receptors. Receptor activation either leads to fast excitatory responses or modulation of neurotransmitter release depending on their neuronal localisation. 5-HT(3) receptors are known to be expressed in the central nervous system in regions involved in the vomiting reflex, processing of pain, the reward system, cognition and anxiety control. In the periphery they are present on a variety of neurons and immune cells. 5-HT(3) receptors are known to be involved in emesis, pain disorders, drug addiction, psychiatric and GI disorders. Progress in molecular genetics gives direction to personalised medical strategies for treating complex diseases such as psychiatric and functional GI disorders and unravelling individual drug responses in pharmacogenetic approaches. Here we discuss the molecular basis of 5-HT(3) receptor diversity at the DNA and protein level, of which our knowledge has greatly extended in the last decade. We also evaluate their role in health and disease and describe specific case-control studies addressing the involvement of polymorphisms of 5-HT3 subunit genes in complex disorders and responses to drugs. Furthermore, we focus on the actual state of the pharmacological knowledge concerning not only classical 5-HT(3) antagonists--the setrons--but also compounds of various substance classes targeting 5-HT(3) receptors such as anaesthetics, opioids, cannabinoids, steroids, antidepressants and antipsychotics as well as natural compounds derived from plants. This shall point to alternative treatment options modulating the 5-HT(3) receptor system and open new possibilities for drug development in the future.

Serotonin receptor antagonists for highly emetogenic chemotherapy in adults

BACKGROUND

Serotonin receptor antagonists (5-HT(3) RAs) are used to control chemotherapy-induced emesis. Although they have the same general mechanism of action (blockade of serotonin receptors), they have different chemical structures and may have different effects.

OBJECTIVES

To compare efficacy of different serotonin receptor antagonists (5-HT(3) RAs) in the control of acute and delayed emesis induced by highly emetogenic chemotherapy.

SEARCH STRATEGY

We searched CENTRAL, the Specialised Register of the Cochrane PaPaS Group, PubMed, EMBASE, and LILACS databases. Our most recent search was in March 2009.

SELECTION CRITERIA

Randomised trials comparing 5-HT(3) RAs in an adult cancer population.

DATA COLLECTION AND ANALYSIS

We extracted information from the included studies on the control of acute and delayed nausea and vomiting, either as a single or a combined outcome. Where appropriate, we combined the results of similar trials. We carried out sensitivity and subgroup analyses to test the robustness of our findings.

MAIN RESULTS

We included 16 randomised trials (7808 participants). Nine of the trials compared granisetron versus ondansetron. No other drug comparison was studied in more than one trial. The meta-analyses of the granisetron versus ondansetron trials found similar results for the two drugs on acute vomiting (eight trials, 4256 participants, odds ratio (OR) 0.89; 95% CI 0.78 to 1.02), acute nausea (seven trials, 4160 participants, OR 0.97; 95% CI 0.85 to 1.10), delayed vomiting (three trials, 1119 participants, OR 1.00; 95% CI 0.74 to 1.34) and delayed nausea (two trials, 1024 participants, OR 0.96; 95% CI 0.75 to 1.24). Granisetron and ondansetron showed similar effects on headache and diarrhoea, with the possible exception of less constipation associated with ondansetron.One study of 1114 participants comparing palonosetron plus dexamethasone versus granisetron plus dexamethasone showed superiority of palonosetron in controlling delayed vomiting (OR 1.45; 95% CI 1.14 to 1.85) and delayed nausea (OR 1.63; 95% CI 1.27 to 2.10). Complete response for delayed nausea and vomiting was also in favour of the combination palonosetron and dexamethasone (OR 1.63; 95% CI 1.29 to 2.07).

AUTHORS' CONCLUSIONS

Ondansetron and granisetron appear to be equivalent drugs for the prevention of acute and delayed emesis following the use of highly emetogenic chemotherapy.According to one single trial the combination of palonosetron and dexamethasone was superior to granisetron and dexamethasone in controlling delayed emesis. However, more evidence is needed before palonosetron could become the candidate 5-HT(3) RA for the control of delayed emesis induced by highly emetogenic chemotherapy.

The impact of CYP2D6 genetic polymorphisms on postoperative morphine consumption

BACKGROUND

Endogenous morphine-like compounds have been identified in humans and are released in response to stress. Human monocytes and granulocytes express the micro opiate receptor, micro3, which is morphine selective but opiate peptide insensitive. Recent studies have shown that CYP2D6 acts at critical steps for endogenous morphine biosynthesis. We theorized that ultrarapid (UM) CYP2D6 metabolizers may have an enhancement of their endogenous pain modulating mechanisms.

METHODS

After institutional review board approval, a previously developed surgical patient database was evaluated for information concerning CYP2D6 genotypes and morphine consumption. One hundred forty-two patients were found to have adequate information to be included in this current analysis. The study group was divided, based on morphine consumption, into two subgroups: low morphine consumers (LMC) (< or =10 mg/4 h, N = 80) and high morphine consumers (HMC) (>10 mg/4 h, N = 62). DNA was extracted from blood in all patients and was genotyped by the Amplichip (Roche, Pleasanton, CA) to determine the specific CYP2D6 genotypes.

RESULTS

CYP2D6 UM were found to occur more frequently in the LMC group than in the HMC group (8/80 vs 0/62, P = 0.0091). No significant differences were noted for the poor, intermediate, or extensive metabolizers.

CONCLUSIONS

Our current results suggest that CYP2D6 UM appear to require less morphine in the acute postoperative period compared with other CYP2D6 metabolizer groups. One possible mechanism for this observation is that CYP2D6 UM may have higher efficiency in synthesizing endogenous morphine compared with other metabolizers, thus increasing endogenous pain modulation and reducing the need for exogenous morphine.

Tropisetron, Ondansetron, and Granisetron for Control of Chemotherapy-Induced Emesis in Turkish Cancer Patients: A Comparison of Efficacy, Side-Effect Profile, and Cost

BACKGROUND

Tropisetron, ondansetron, and granisetron are considered equally efficacious, supported by several international studies. However, there are interindividual variations in their metabolism that could affect efficacy. The clustering of such variations may change from one to another nation. Therefore, their equality must be validated in Turkish patients. The aim of this study was to compare their efficacies, side-effect profiles, and costs in the prophylaxis of emesis induced by moderate to high emetogenic chemotherapies.

METHODS

A total of 158 patients with a median age of 48 years, 115 (72.8 percent) female and 43 (27.2 percent) male, were included, respectively. Fifty-one, 61, and 46 patients were allocated to tropisetron (5 mg), ondansetron (8 mg), and granisetron (3 mg IV) in combination with 8 mg dexamethasone, which were continued 5 mg once a day, 8 mg b.i.d. and 1 mg b.i.d. PO for 5 days, respectively.

RESULTS

The complete response (CR) rates in the control of acute emesis were 80.4 percent with tropisetron, 72.1 percent with ondansetron, and 71.7 percent granisetron (p = 0.877). CR rates in delayed emesis (Days 2-5) were 68.6 percent, 68.9 percent, and 76.1 percent, respectively (p = 0.527). Rates of freedom from nausea in the same period were 37.3 percent, 35.9 percent, and 33.9 percent (p = 0.949). Nausea control rates, side-effect profile did not differ. However, headache seemed to be encountered higher (45.6 percent) in Turkish patients than others (3.9-9 percent). Tropisetron is the least expensive one ($95.3 per cycle) according to current prices in Turkey.

CONCLUSIONS

There were no differences among the 3 serotonin antagonists with respect to efficacy and frequency of side-effects in our patients. Tropisetron is the least expensive at current prices. The choice may be based on other parameters, such as ease of administration and patient preference.

The metabolism of the 5HT3antagonists ondansetron, alosetron and GR87442 I: A comparison ofin vitroandin vivometabolism andin vitroenzyme kinetics in rat, dog and human hepatocytes, microsomes and recombinant human enzymes

The metabolism of the structurally related 5HT3 antagonists ondansetron, alosetron and GR87442 in the rat, dog and human was determined in hepatocytes, liver microsomes and human recombinant microsomes. The profiles of phase I metabolites were similar in human hepatocytes and microsomes. The metabolites of all three compounds produced in rat, dog and human microsomes and hepatocytes were similar to those seen in vivo, with the major routes of metabolism being N-dealkylation and/or hydroxylation. There was more extensive metabolic processing in hepatocytes than in microsomes; however, sequential metabolism was less extensive in vitro compared with in vivo. The pharmacokinetics of the three 5HT3 antagonists investigated were dominated by CYP3A4 (and/or 2C9) compared with CYP1A2 in man, possibly determined by enzyme capacity rather than relative enzyme affinity. These data support the use of rat, dog and human hepatocytes for the prediction of in vivo metabolites of ondansetron, alosetron and GR87442.

Antiemetic care for patients with breast cancer: focus on drug interactions and safety concerns

PURPOSE

The drug interactions and adverse events that should be considered when individualizing antiemetic therapy for patients undergoing treatment for breast cancer are reviewed.

SUMMARY

A variety of antiemetic agents are available, including antihistamines, dopamine-receptor antagonists, serotonin-receptor antagonists, and neurokinin-receptor antagonists. To ensure optimal symptom control for each patient without unnecessarily prolonging treatment, patient- and treatment-specific risk factors must be considered. Neurokinin-receptor antagonists, the newest class of antiemetics, are effective in preventing acute and delayed chemotherapy-induced nausea and vomiting but must be used in combination with a serotonin-receptor antagonist and a corticosteroid. The serotonin-receptor antagonists have become the mainstay of antiemetic therapy, but current guidelines do not distinguish among the different agents in this class. However, there are distinct pharmacologic differences that may affect the potential for drug interactions and, ultimately, patient outcomes and the occurrence of adverse events. Therefore, the potential for drug interactions must be considered when selecting an antiemetic, particularly for patients who are taking multiple concomitant medications. Further, because a number of breast cancer therapies and some antiemetic agents carry cardiovascular warnings or precautions and since breast cancer patients may already be suffering from cardiovascular complications, the possible cardiotoxic effects of the antiemetic or chemotherapy agents or the combinations of these agents should be considered.

CONCLUSION

Antiemetic treatment is essential for patients with breast cancer who are undergoing moderately to highly emetogenic cytotoxic treatment. When selecting an antiemetic, clinicians must select an agent that provides optimal protection against nausea and vomiting while avoiding drug-drug interactions and additional adverse events.

Rational prescription of drugs within similar therapeutic or structural class for gastrointestinal disease treatment: Drug metabolism and its related interactions

AIM: To review and summarize drug metabolism and its related interactions in prescribing drugs within the similar therapeutic or structural class for gastrointestinal disease treatment so as to promote rational use of medicines in clinical practice.

METHODS: Relevant literature was identified by performing MEDLINE/Pubmed searches covering the period from 1988 to 2006.

RESULTS: Seven classes of drugs were chosen, including gastric proton pump inhibitors, histamine H₂-receptor antagonists, benzamide-type gastroprokinetic agents, selective 5-HT₃ receptor antagonists, fluoroquinolones, macrolide antibiotics and azole antifungals. They showed significant differences in metabolic profile (i.e., the fraction of drug metabolized by cytochrome P450 (CYP), CYP reaction phenotype, impact of CYP genotype on interindividual pharmacokinetics variability and CYP-mediated drug-drug interaction potential). Many events of severe adverse drug reactions and treatment failures were closely related to the ignorance of the above issues.

CONCLUSION: Clinicians should acquaint themselves with what kind of drug has less interpatient variability in clearance and whether to perform CYP genotyping prior to initiation of therapy. The relevant CYP knowledge helps clinicians to enhance the management of patients with gastrointestinal disease who may require treatment with polytherapeutic regimens.

Comparative activity of antiemetic drugs

Nausea and vomiting continues to be an important problem for cancer patients receiving chemotherapy. Chemotherapy-induced nausea and vomiting (CINV) are classified as acute, occurring within the first 24h, or delayed, occurring after the first 24h. A number of antiemetic agents are available for the management of nausea and vomiting, including 5-HT3-receptor-antagonists, corticosteroids, NK-1-receptor-antagonists, dopamine-receptor antagonists, benzodiazepines, neuroleptics and cannabinoids. With modern antiemetic therapy, vomiting can be prevented in 70-80% of patients, whereas the control of nausea remains suboptimal. The development of acute emesis is known to depend on serotonin. The pathophysiology of delayed emesis is less well understood, and multiple mechanisms may contribute, including substance P. Here, the most recent developments in the antiemetic therapy, including new antiemetic drugs and the latest guidelines for antiemetic prophylaxis, are reviewed.

Gastrointestinal medications

Medications to address gastrointestinal disorders are among the most commonly dispensed somatic medications. The authors examine proton pump inhibitors, H(2) blockers, 5-HT(3) receptor-antagonists, and a few other drugs that are used to address this domain of medical concerns. The metabolic pathways, interactions with the P-glycoprotein transporter, and capabilities of inhibiting or inducing metabolic enzymes are elucidated for each drug. Specific drug-drug interactions with each agent are also detailed, including both psychotropic and non-psychotropic agents. Also, the article explores how different genotypic variants for specific cytochrome P450 enzymes have an impact on the effectiveness and likelihood of drug-drug interactions relating to specific gastro-intestinal medications.

Prophylaxis of postoperative nausea and vomiting: controversies in the use of serotonin 5-hydroxytryptamine subtype 3 receptor antagonists

Postoperative nausea and vomiting (PONV) continues to be a "big little problem" despite recent advances in anesthesia. Because of an increased interest in, and the abundant publications on this topic, guidelines for the management of PONV were published in 2003. Several key but controversial issues regarding PONV prophylaxis were left unaddressed, however. These included whether clinical differences exist between the 5-hydroxytryptamine subtype 3 (5-HT3) receptor antagonists, concern over optimal dosage and timing of administration, optimal 5-HT3 receptor antagonist combination therapy, and whether rescue therapy is effective after prior administration of the same or a different 5-HT3 receptor antagonist. The application of these antiemetics in clinical practice has raised questions regarding the role of the 5-HT3 receptor antagonists in the treatment of postdischarge nausea and vomiting and opioid-induced nausea and vomiting. A brief overview of the incidence, risk factors and current management recommendations for PONV and current controversies with special emphasis on the 5-HT3 receptor antagonists, is discussed.

Effects of serotonin-3 receptor antagonists on cytochrome P450 activities in human liver microsomes

The effects of three serotonin-3 (5-HT(3)) receptor antagonists, azasetron, ondansetron, and ramosetron, on cytochrome P450 (CYP) 1A2-mediated 7-ethoxyresorufin O-deethylation, CYP2C9-mediated tolbutamide hydroxylation, CYP2C19-mediated S-mephenytoin 4'-hydroxylation, CYP2D6-mediated debrisoquine 4-hydroxylation, CYP2E1-mediated chlorzoxazone 6-hydroxylation, CYP3A4-mediated nifedipine oxidation, and CYP3A4-mediated testosterone 6beta-hydroxylation activities in human liver microsomes were compared. Azasetron and ramosetron at a concentration of 1 or 10 muM neither inhibited nor stimulated any of the metabolic activities. On the other hand, ondansetron competitively inhibited CYP1A2 and CYP2D6 activities, and the inhibition constants (K(i)) were 3.2 and 21.0 muM, respectively, which are much higher than the reported plasma concentrations after clinical intravenous or oral dosing. The free fractions of the three 5-HT(3) receptor antagonists in the incubation mixture estimated by ultracentrifugation were more than 68.6%. These results suggest that azasetron, ondansetron, and ramosetron do not cause clinically significant interactions with other drugs that are metabolized by CYPs via the inhibition of metabolism.

Prevention of Postoperative Nausea and Vomiting with Granisetron and Dolasetron in Relation to CYP2D6 Genotype

We investigated the efficacy of granisetron and dolasetron in preventing postoperative nausea and vomiting. Because the metabolism of the various antiemetic 5-hydroxytryptamine type 3 (5-HT3) antagonists involves different isoforms of the hepatic cytochrome P450 system, we examined the relationship between the clinical efficacy of these drugs and polymorphic cytochrome P450 2D6 (CYP2D6) genotype. This prospective, randomized, double-blind study involved 150 adult patients with a moderate to high risk for postoperative nausea and vomiting. All subjects received dexamethasone at induction of anesthesia followed by either 12.5 mg of dolasetron or 1 mg of granisetron. We analyzed the number of complete responders (no vomiting or rescue medication) during the first 24 hours after surgery. CYP2D6 genotyping was performed using a TaqMan real-time polymerase chain reaction. A complete response was more frequent in the granisetron group (54.7%) compared with the dolasetron group (38.7%, P < 0.05). In subjects receiving dolasetron, carriers of the duplication of the CYP2D6 allele predicting ultrarapid metabolizer status had more frequent vomiting episodes (P < 0.05) than patients in the granisetron group. It is postulated that the difference in the antiemetic efficacy between two investigated 5-HT3 receptor antagonists may be associated with differences in the carrier status for the duplication of the CYP2D6 allele.

Chemotherapy-induced emesis in elderly cancer patients: the role of 5-HT3-receptor antagonists in the first 24 hours

OBJECTIVE

This review highlights the need to optimize 5-HT3-receptor-antagonist-based antiemetic therapy for elderly cancer patients, particularly during the first 24 h after receiving chemotherapy, based on knowledge of the chemotherapeutic regimen, comorbidity, polypharmacy, dosing convenience and age-related health.

BACKGROUND

The proportion of elderly people (over 65 years of age) in the general population is increasing. Compared with the general population, elderly people have a greater risk of serious diseases, such as cancer and cardiovascular disease. Their chemotherapy can be compromised by factors including comorbidity, declining organ function, polypharmacy, drug-drug interactions and cognitive impairments. The use of aprepitant in this elderly population with many concomitant medications is not discussed. Many chemotherapeutic regimens are highly emetogenic, and nausea and vomiting are rated among the most distressing side effects of chemotherapy. The emetogenic potential of various chemotherapy regimens is reviewed, demonstrating clear differences in severity and time of symptom onset. Such differences are particularly important during the first 24 h after administration, when control of emetic symptoms can help to prevent the occurrence of subsequent episodes. The matter is further complicated by inter-patient differences in susceptibility to nausea and vomiting resulting from multiple factors including gender, age and alcohol intake. Individual patient evaluation is essential to identify those patients most at risk. Elderly patients may also be particularly sensitive to the serious physiological and physical effects of nausea and vomiting. Education about symptom management needs to recognize specific learning barriers in the elderly, such as declining sensory perception or cognitive impairment. 5-HT3-receptor antagonists have long been the gold standard for treating chemotherapy-induced nausea and vomiting. Pharmacological differences between 5-HT3-receptor antagonists suggest the need for careful consideration of individual patient characteristics. Selection of the most appropriate agent will optimize antiemetic therapy for elderly cancer patients.

CONCLUSION

Chemotherapy-induced emesis in elderly cancer patients needs optimal control by a 5-HT3-receptor antagonist with uncomplicated 24-hour efficacy and good tolerability. Choosing a 5-HT3-receptor antagonist with a long duration of action, low risk of drug-drug interactions and once-daily dosing is important to ensure effective prophylaxis against nausea and vomiting in the elderly and simplify management for patients with cognitive impairment, declining organ function and comorbidity.

Antiemetic therapy in cancer: an update

Although nausea and vomiting are widely recognised as two of the most distressing symptoms of cytotoxic therapy, there is still concern over the adequate control of these symptoms in the cancer population. Recently updated Antiemetic Consensus Guidelines recommend the prophylactic treatment of all patients at moderate-to-high risk of experiencing nausea and vomiting following chemotherapy and radiotherapy. It is important that these guidelines are fully adhered to; however, when considering which antiemetic regimen is most appropriate in an individual patient, it is also important to consider individual patient-related factors. In addition, certain patient groups, such as the young or the elderly, may be in need of specific consideration due to age-related factors that may influence treatment decisions.

5-HT(3)-receptor antagonists in the management of nausea and vomiting in cancer and cancer treatment

The 5-HT(3)-receptor antagonists, considered as 'gold standard' therapy for cancer patients, are generally perceived to have similar efficacy and safety profiles, andmost antiemetic guidelines do not distinguish between agents. However, important pharmacological differences exist between agents, which may translate into potential benefits for some patients. In particular, 5-HT(3)-receptor antagonists vary in the nature of their receptor antagonism and plasma half-lives, possibly leading to differences in duration of action. Agents with a longer duration of action provide antiemetic protection throughout the acute emetic period (24 h) with a single daily dose, whereas shorter-acting agents, e.g. ondansetron, may require multiple dosing for full efficacy. Differences also exist between agents in their hepatic metabolism and cardiovascular safety, which may present particular problems for elderly patients who often receive additional medications for comorbid conditions, increasing the risk of drug-drug interaction. Recent antiemetic guidelines from the National Comprehensive Cancer Network recommend preferential use of palonosetron for moderately emetogenic chemotherapy; however, this agent is newly approved and key clinical questions remain unanswered by clinical trial data. Selection of an appropriate 5-HT(3)-receptor antagonist should be based on proven efficacy and safety, as well as on the individual characteristics of the patient.

5-hydroxytryptamine type-3 receptor antagonists for chemotherapy-induced and radiotherapy-induced nausea and emesis: can we safely reduce the dose of administered agents?

BACKGROUND

Nausea and emesis as a consequence of chemotherapy or radiotherapy can have an adverse effect on patients' quality of life during cancer treatment and may last for > 5 days after administration. Guidelines suggest that, used at appropriate doses, the 5-hydroxytryptamine type-3 (5-HT3) receptor antagonists--which are considered the antiemetic "gold standard" when they are administered in combination with corticosteroids--demonstrate equivalent efficacy and safety. However, due to financial considerations, these agents often are used at lower doses than recommended.

METHODS

A literature review of relevant publications pertaining to the control of chemotherapy-induced nausea and emesis and dosing issues of the 5-HT3 receptor antagonists was undertaken to provide a comprehensive review of dosing issues relevant to the 5-HT3 receptor antagonists.

RESULTS

The issue of "down dosing" was particularly pertinent because of the nature of the 5-HT3 receptor antagonist dose-response curve: A steep dose-response profile within a narrow dose range suggests that antiemetic control will be lost suddenly after dose deescalation. However, the array of predisposing and confounding patient factors indicates that it is unlikely that a loss of antiemetic control will be apparent across a population; rather, individuals will experience loss of control as the dose is reduced below threshold. Of the 4 5-HT3 receptor antagonists currently licensed in the United States (granisetron, ondansetron, dolasetron, and palonosetron), ondansetron is used sometimes at lower than optimal doses, and there is evidence to suggest that even the approved oral dose of dolasetron may be suboptimal.

CONCLUSIONS

Suboptimal dosing not only will be detrimental to patients' quality of life but, ultimately, will prove counterproductive in terms of hospital resources, and it will add to the already significant socioeconomic burden associated with cancer therapy. Therefore, the dose of antiemetic agent administered should be sufficiently high to ensure good emesis control across the whole patient population.

Drug–drug interactions in oncology: Why are they important and can they be minimized?

Adverse drug-drug interactions are a major cause of morbidity and mortality. Cancer patients are at particularly high risk of such interactions because they commonly receive multiple medications, including cytotoxic chemotherapy, hormonal agents and supportive care drugs. In addition, the majority of cancer patients are elderly, and so require medications for co-morbid conditions such as cardiovascular, gastrointestinal, and rheumatological diseases. Furthermore, the age-related decline in hepatic and renal function reduces their ability to metabolize and clear drugs and so increases the potential for toxicity. Not all drug-drug interactions can be predicted, and those that are predictable are not always avoidable. However, increased awareness of the potential for these interactions will allow healthcare providers to minimize the risk by choosing appropriate drugs and also by monitoring for signs of interaction. This review considers the basic principles of drug-drug interactions, and presents specific examples that are relevant to oncology.

Influence of the Cyto-Protective Agent Amifostine on the Pharmacokinetics of Low-Dose Paclitaxel

BACKGROUND

Pharmacokinetic parameters (PHK) of low-dose weekly paclitaxel (PAC) are not well known, particularly when administered with the cytoprotective agent amifostine (AMI).

METHODS

Patients with non-small cell lung cancer (NSCLC) received PAC alone or PAC + AMI. Blood samples were drawn at the end of the infusion at 0, 0.25, 0.5, 1, 2 and 4 h for the measurement of plasma PAC using HPLC. Area under the concentration-time curve (AUC), the peak plasma concentrations (Cmax) and the residence time of paclitaxel in plasma at concentrations >0.1 microM (TPP >or=0.1) and >0.05 microM (TPP >or=0.05) were calculated using a two-compartmental model. ANOVA was used for statistical analysis.

RESULTS

Pharmacokinetic studies were completed for 43 doses among 11 patients receiving PAC alone and for 26 doses among 8 patients receiving the combination AMI + PAC (from the first to the fifth week). Statistically significant differences in all parameters except AUC were observed between the 2 treatment groups. A significantly higher Cmax was observed for patients receiving PAC + AMI versus PAC alone. Both TPP >or=0.1 and TPP >or=0.05 were also more prolonged in AMI + PAC cycles.

CONCLUSION

AMI produces a prolongation in PAC plasma circulation time. Further specifically designed studies are needed to quantify the resultant effects on PAC's efficacy and toxicity.

Granisetron in the control of radiotherapy-induced nausea and vomiting: a comparison with other antiemetic therapies

Radiotherapy-induced nausea and vomiting (RINV) can be one of the most distressing symptoms of radiotherapy treatment, which if incompletely controlled may last for several weeks with fractionated radiotherapy and prevent completion of the planned treatment course. Current treatment guidelines recommend the use of 5-HT(3) receptor antagonists with or without corticosteroids for highly and moderately emetogenic radiotherapy, though only granisetron and ondansetron are currently indicated for RINV in most countries. Granisetron is a potent and highly selective 5-HT(3) receptor antagonist, with demonstrated efficacy in RINV in both placebo-controlled and comparative studies. In this paper the clinical experience with granisetron in RINV is reviewed, and its efficacy and safety compared with other antiemetic therapies.

Optimising antiemetic therapy: what are the problems and how can they be overcome?

BACKGROUND

Management of chemotherapy- or radiotherapy-induced emesis has improved significantly following the introduction of the 5-HT3-receptor antagonists. Prophylactic use of these agents is recommended for the prevention of both chemotherapy- and radiotherapy-induced nausea and vomiting, given with a corticosteroid. Despite these advances, nausea and vomiting remain among the most feared and debilitating adverse effects of cytotoxic therapy. The shift towards a more elderly population of patients with cancer presents additional considerations for supportive care, with an emphasis on achieving control of nausea and vomiting, whilst minimising toxicity and avoiding drug-drug interactions. This review presents some of the key issues for consideration in optimising antiemetic therapy. The PubMed search engine was used to search for relevant literature (up to December 2004) and relevant international congress materials collected during 2003 and 2004.

SCOPE

While the early stages of nausea and vomiting are 5-HT-mediated, identification of a role for substance P in late emesis has led to the development of the NK1-receptor antagonist, aprepitant. As a new agent, the clinical profile of aprepitant is still being explored, including its interaction with concomitant medications. Patients who achieve good control of acute and late-acute nausea and vomiting have a reduced risk of experiencing delayed onset symptoms, emphasising the importance of prophylactic management with effective agents. Although the 5-HT3-receptor antagonists are widely considered to have equivalent efficacy, they vary in half-life and the nature of antagonism at receptors. Their metabolic profiles also differ, with cytochrome P450 (CYP) metabolism affecting their propensity for drug-drug interactions. Several sets of guidelines are available that outline recommendations for selection and use of antiemetic therapy. However, under-use of 5-HT3 receptor antagonists has been reported in both the radiotherapy and chemotherapy settings, and some commonly used doses may be suboptimal.

CONCLUSION

In optimising antiemetic therapy, wider implementation of guidelines is desirable, as is consideration of each patient's individual needs. Safety and tolerability of supportive care medications should be a key consideration, and cardiovascular warnings and the possibility of drug-drug interactions should be given sufficient consideration, particularly in view of the older age of the population with cancer.

Selective serotonin 5-HT3 receptor antagonists for postoperative nausea and vomiting: are they all the same?

Selective serotonin 5-HT(3) receptor antagonists have proven safe and effective for the management of postoperative nausea and vomiting. Dolasetron, granisetron, ondansetron and tropisetron selectively and competitively bind to 5-HT(3) receptors, blocking serotonin binding at vagal afferents in the gut and in the regions of the CNS involved in emesis, including the chemoreceptor trigger zone and the nucleus tractus solitarii. Despite their shared mechanism of action, 5-HT(3) receptor antagonists have different chemical structures and exhibit differences in receptor binding affinity, dose response and duration of effect. Furthermore, although dolasetron, granisetron, ondansetron and tropisetron are all extensively metabolised by the cytochrome P450 (CYP) system, different components of this system predominate in the metabolism of each of these agents. Hence, although these agents are considered equally effective in the overall population, their pharmacokinetic and pharmacodynamic differences may explain the variability in individual responses to these drugs. This review discusses the pharmacological profiles of dolasetron, granisetron, ondansetron and tropisetron, and the clinical implications of differences in their profiles.

Is there a pharmacological basis for differences in 5-HT3-receptor antagonist efficacy in refractory patients?

5-HT3-receptor antagonists are the current antiemetic 'gold standard' for chemotherapy- and radiotherapy-induced nausea and vomiting. Interestingly, studies have shown that patients experiencing poor control of acute chemotherapy-induced nausea and vomiting with one antiemetic therapy may respond well to another agent, including a drug of the same class. This review examines pharmacological differences between the 5-HT3-receptor antagonists in order to determine potential reasons for their differing efficacy, particularly in relation to refractory emesis. Differences in drug metabolism by the cytochrome P450 system, inadequate dosing of the respective agents, differences in onset and duration of action, and effects on serotonin release and reuptake are discussed.

Pharmacokinetics of palonosetron in combination with aprepitant in healthy volunteers

BACKGROUND

Palonosetron is a second-generation 5-HT(3) receptor antagonist with a prolonged duration of action and higher receptor binding affinity than first-generation agents (ondansetron, granisetron, and dolasetron). Aprepitant is a selective antagonist of substance P/neurokinin 1 that augments the benefit of 5-HT(3) receptor antagonists in the prevention of chemotherapy-induced nausea and vomiting.

METHODS

This randomized, open-label, two-way, crossover trial was designed to evaluate the effect of oral aprepitant on the pharmacokinetics and safety of a single intravenous (IV) dose of palonosetron in 12 healthy subjects. Treatment A consisted of a single IV bolus dose of palonosetron 0.25mg on day 1. Treatment B added oral aprepitant 125 mg on day 1 (30 minutes prior to palonosetron) and 80 mg on days 2 and 3. Blood for pharmacokinetic evaluations was collected through 168 hours after palonosetron administration on days 1 and 15; safety was monitored through day 22.

RESULTS

Mean plasma concentration-time plots for palonosetron were virtually identical for palonosetron administered alone or with concomitant aprepitant. The ratio of geometric least-square mean values (with:without aprepitant) for C(max) was 98.6% (90% confidence interval [CI]: 61.8-157%), and for AUC(0-infinity) the ratio was 101% (90% CI: 85.6-119%). With and without aprepitant coadministration, respectively, mean plasma elimination half-life was 40 hours and 43 hours (difference: -3.0 hours; p = 0.348), mean total body clearance was 130 mL/min and 136 mL/min (difference: -5.6 mL/min; p = 0.735), and mean volume of distribution at steady-state was 410.9 L and 442.3 L (difference: -31.4 L; p = 0.463). Palonosetron alone and the palonosetron/aprepitant regimen were well tolerated.

CONCLUSION

These results indicate no significant differences in pharmacokinetic parameters for palonosetron between the two treatments, and suggest that palonosetron can be safely coadministered with aprepitant with no alterations in the expected safety profile and no dosage adjustment necessary.

The effect of granisetron on in vitro metabolism of doxorubicin, irinotecan and etoposide

OBJECTIVE

Doxorubicin, irinotecan and etoposide are all associated with the debilitating side-effects of nausea and vomiting, thereby necessitating concomitant antiemetic therapy. However, this may increase the potential for drug-drug interactions by inhibition or induction of the cytochrome P450 enzymes. A study was undertaken to investigate the effects of the 5-HT(3) -receptor antagonist granisetron on the metabolism of doxorubicin, irinotecan and etoposide in vitro in human liver microsomal preparations.

RESEARCH DESIGN AND METHODS

Doxorubicin, 20 microM, irinotecan, 10 microM, and etoposide, 50 microM, were incubated in the presence of granisetron, 0 nM, 20 nM, 200 nM and 2000 nM, in human liver microsomal preparations (250 microg). The levels of unchanged doxorubicin, irinotecan and etoposide in the incubation mixture were determined by high-performance liquid chromatography. Positive controls were ketoconazole, 20 microM, a potent inhibitor of CYP3A metabolism, for irinotecan and etoposide and quercitrin, 2 mM, a potent inhibitor of aldo-keto reductase, for doxorubicin.

RESULTS

In the absence of granisetron, unchanged doxorubicin, irinotecan and etoposide levels decreased by 34.2 +/- 5.5%, 21.3 +/- 2.9% and 13.4 +/- 1.6% of control, respectively. Ketoconazole prevented the breakdown of both irinotecan and etoposide, while quercitrin inhibited the breakdown of doxorubicin. Granisetron had no effect on the rate of reduction of doxorubicin, irinotecan or etoposide.

CONCLUSIONS

The results from this study suggest that granisetron neither inhibits nor induces the enzymes involved in the metabolism of doxorubicin, irinotecan or etoposide. Thus, granisetron can be used safely to treat nausea and vomiting induced by these agents with minimal risk of drug-drug interactions.

Nausea: the neglected symptom?

Advances in antiemetic therapy over the past decade have undoubtedly eased the burden of radiotherapy- and chemotherapy-induced nausea and vomiting. Despite this, these distressing side-effects of cancer therapy are still experienced by some patients. Moreover, nausea has both a higher incidence and a greater effect on patient quality of life than vomiting. The impact of nausea may therefore warrant more attention than perhaps it has received previously, and there is undoubtedly room for improvement regarding its treatment. Recognizing and treating nausea is complicated by the fact that it can only be measured subjectively by the patient rather than objectively by clinical staff. However, various patient-centred strategies may be employed by nurses to ensure self-reporting of the occurrence and impact of nausea. Nurses may also be best placed to identify patient-related prognostic factors in order to determine the risk of nausea. Antiemetic guidelines recommend the use of a 5-HT3-receptor antagonist for the control of emesis with moderate and highly emetogenic cancer therapy. Although guidelines do not distinguish between the available agents, pharmacological differences do exist, and it is necessary to consider this when tailoring regimens to individual patients. As with any therapy, less complicated dosing regimens are likely to improve compliance, an issue that may be particularly pertinent in nauseated patients who are unable to ingest multiple doses. Furthermore, the focus of antiemetic therapy should be on prevention, as the presence and severity of acute symptoms have been linked to occurrence of symptoms in the delayed phase and the likelihood of anticipatory nausea and vomiting with further treatment cycles. This review aims to assess the potentially neglected symptom of nausea and focuses on recognizing and controlling this side-effect of cancer therapy.

Granisetron versus tropisetron for prophylaxis of acute chemotherapy-induced emesis: a pooled analysis

This analysis compares the antiemetic efficacy of the 5-HT3-receptor antagonists granisetron and tropisetron in acute chemotherapy-induced nausea and vomiting (CINV). All published randomized studies comparing granisetron with tropisetron in conventionally-dosed, emetogenic chemotherapy are included in this pooled analysis. The target criterion for antiemetic success was 'acute complete response' (complete absence of vomiting in the 24 h after the start of chemotherapy) and the rate of successful treatment reported as 'response rate' (acute complete response rate per patient). Twelve studies were used comprising 810 patients. Comparison between granisetron and tropisetron in patients receiving cisplatin-based therapy showed superiority of granisetron (odds ratio above 1.0) in six out of seven studies. However, this difference did not reach statistical significance. In patients receiving noncisplatin-based therapies, four out of five studies showed an advantage of granisetron over tropisetron with one study showing a significant advantage. Pooled analysis of all studies demonstrated a significant overall advantage for granisetron over tropisetron (p=0.042). This is supported by the individual studies: overall, ten out of the 12 studies analyzed showed an advantage for granisetron, with a 6.4% difference in response rate. This advantage was more pronounced in noncisplatin-based therapy (7.3%), whereas in cisplatin-based therapy, the difference was 5.4%. The overall results of this pooled analysis of cisplatin and noncisplatin-based studies suggest that granisetron has a marginal but clinically potentially relevant statistically significant advantage in efficacy over tropisetron for the control of acute CINV.

Granisetron: An Update on its Clinical Use in the Management of Nausea and Vomiting

Nausea and vomiting are typical side effects of cytotoxic therapy and some surgical procedures. These symptoms can represent a major therapeutic challenge and, if inadequately controlled by antiemetic treatment, will result in increased mortality, morbidity, and health care costs. However, the management of nausea and vomiting has improved greatly in recent years following the introduction of the 5-HT3-receptor antagonists, known as 'setrons.' In light of recent developments in antiemetic care, including the approval of the first neurokinin-1-receptor antagonist aprepitant (Emend; Merck and Company, Inc.; West Point, PA) and a new 5-HT3 receptor antagonist palonosetron (Aloxi; MGI Pharma; Minneapolis, MN), this article provides an update on the clinical experience gained with the 5-HT3-receptor antagonist granisetron (Kytril; Roche Laboratories, Inc.; Nutley, NJ) for the management of chemotherapy-induced, radiation-induced, and postoperative nausea and vomiting, and also reviews its use in special patient populations. Granisetron is a potent and highly selective 5-HT3-receptor antagonist that has little or no affinity for other receptors, a characteristic that is thought to underlie the favorable side-effect and safety profiles of this agent. Extensive clinical trial data have shown granisetron to be an effective and well-tolerated agent for the treatment of nausea and vomiting in the oncology and surgical settings. Granisetron has also been shown to be effective and well tolerated in special populations, such as patients refractory to antiemetic treatment, patients with hepatic or renal impairment, and children. Data also suggest that its safety profile and minimal potential for drug-drug interactions would make it an antiemetic agent of choice for elderly cancer patients.

Treatment implications for radiation-induced nausea and vomiting in specific patient groups

Radiation-induced nausea and vomiting (RINV) affect the management and quality of life of cancer patients. Current guidelines for RINV prevention recommend prophylaxis with a 5-hydroxytryptamine (5-HT(3))-receptor antagonist for patients receiving moderately or highly emetogenic radiotherapy regimens. Randomised trials have compared such antagonists with conventional antiemetics, and have demonstrated their efficacy and safety. Special consideration is needed for antiemetic treatment in certain patient groups, particularly the elderly and those with renal or hepatic impairment. Radiation oncologists should be aware of the effect on antiemetic treatment of factors such as comorbid conditions (particularly cardiovascular disease), polypharmacy and drug-drug interactions, and choose the agent with the lowest potential for additional complications. The most appropriate antiemetic treatment to improve patient compliance and quality of life should ideally combine proven efficacy with uncomplicated administration and convenient dosing regimens.

Same Old Story? Do We Need to Modify Our Supportive Care Treatment of Elderly Cancer Patients? Focus on Antiemetics

The incidence of cancer is highest among individuals > or =65 years of age. Physiological changes associated with aging, such as cognitive decline, renal and hepatic dysfunction, can often complicate treatment options, and the elderly represent a particular challenge to the oncologist because of the high incidence of comorbidity and polypharmacy. Effective supportive care is of particular importance in elderly cancer patients as they may recover less satisfactorily if adverse events are poorly controlled. Nevertheless, evidence suggests that supportive care agents, for example, antiemetics, are underutilised in this patient population. Chemotherapy and radiotherapy regimens are frequently associated with nausea and vomiting--symptoms that can have deleterious effects on vulnerable patients if not adequately managed. The serotonin 5-HT3-receptor antagonists represent a class of antiemetics that are currently regarded as the gold standard treatment for chemotherapy- and radiotherapy-induced nausea and vomiting. They are recommended as first-line treatment for patients at moderate-to-high risk of emesis. However, antiemetic guidelines do not differentiate between these agents and, more importantly, do not contain specific recommendations for the elderly. Pharmacological differences exist between the commonly available 5-HT3-receptor antagonists (dolasetron, granisetron, ondansetron, tropisetron and palonosetron), namely receptor sensitivity, duration of action, metabolism and tolerability profile. Of particular concern with prescriptions to elderly cancer patients is the convenience of once-daily administration, the low potential for drug-drug interactions and cardiovascular adverse effect profile. Moreover, the addition of the newly approved neurokinin NK1-receptor antagonist aprepitant to the choice of antiemetic regimen may complicate therapy and exacerbate the drug-drug interaction risk in elderly patients. Therefore, the use of antiemetics that are well tolerated and with the lowest risk of drug-drug interactions is imperative in this patient population and will enable even those patients with several comorbidities and a high level of polypharmacy to receive effective antiemetic therapy.

The effect of granisetron on in vitro metabolism of paclitaxel and docetaxel

PURPOSE

Paclitaxel and docetaxel are effective anticancer agents; however, these agents can be associated with the debilitating side effects of nausea and vomiting, thereby necessitatingthe administration of concomitant antiemetic agents. This increases the potential fordrug-drug interactionsthrough inhibition or induction of the cytochrome P450 (CYP) enzymes. The 5-HT3-receptor antagonists are currently regarded as the antiemetic 'gold standard' and this study was undertaken to investigate the effects of granisetron on the metabolism of paclitaxel and docetaxel in human liver microsomal preparations in vitro.

METHODS

Paclitaxel, 5 nM, and docetaxel, 1.25 nM, were incubated in the presence of granisetron, 0, 10, 100, and 1000 pM, in human liver microsomal preparations (500 microg). The levels of unchanged paclitaxel and docetaxel in the incubation mixture were determined by high-performance liquid chromatography. Ketoconazole, 10 nM, a potent inhibitor of CYP3A metabolism, served as a positive control.

RESULTS

In the absence of granisetron, unchanged paclitaxel and docetaxel levels measured were 27.2 +/- 2.8% and 44.3 +/- 4.0% of control, respectively. Ketoconazole prevented the breakdown of both paclitaxel and docetaxel, to the degree that no unchanged paclitaxel or docetaxel was detected in the incubation mixture. Granisetron had no effect on the rate of reduction of either paclitaxel or docetaxel; unchanged paclitaxel and docetaxel decreased to 25.0 +/- 1.5%, 26.4 +/- 1.0%, and 27.6 +/- 6.4%, and 44.2 +/- 1.5%, 41.2 +/- 4.1%, and 43.1 +/- 0.5%, respectively.

DISCUSSION

The results from this study suggest that granisetron neither inhibits nor induces the enzymes involved in the metabolism of paclitaxel or docetaxel. Thus, granisetron can be used safely as a supportive care agent to treat paclitaxel or docetaxel chemotherapy-induced nausea and vomiting with minimal risk of drug-drug interactions.