Characterisation of the cytochrome P450 enzymes involved in the in vitro metabolism of granisetron

Mechanism Underlying Conflicting Drug-Drug Interaction Between Aprepitant and Voriconazole via Cytochrome P450 3A4-Mediated Metabolism

Background

Voriconazole is an antifungal drug for which therapeutic monitoring is recommended to prevent side effects. Temporary administration of the antiemetic drug fosaprepitant remarkably decreases the plasma concentration of voriconazole from the therapeutic range. The ratio of the major metabolite voriconazole N-oxide to voriconazole exceeded that at any other time for a patient who started chemotherapy during voriconazole therapy. We attributed this unpredictable result to cytochrome P450 3A4 induced by aprepitant that was converted from fosaprepitant in vivo.

Methods

Concentrations of voriconazole and voriconazole N-oxide were measured using liquid chromatography-mass spectrometry/mass spectrometry in primary human hepatocytes after incubation with aprepitant. Aprepitant suppressed voriconazole N-oxide formation within 24 h, followed by a continuous increase. Levels of drug-metabolizing cytochrome P450 mRNA were measured using real-time PCR in primary human hepatocytes incubated with aprepitant.

Results

Cytochrome P450 3A4 and 2C9 mRNA levels increased ~4- and 2-fold, respectively, over time. Cytochrome P450 3A4 induction was confirmed using reporter assays. We also assessed L-755446, a major metabolite of aprepitant that lacks a triazole ring. Both compounds dose-dependently increased reporter activity; however, induction by L-755446 was stronger than that by aprepitant.

Conclusion

These results indicate that aprepitant initially inhibited voriconazole metabolism via its triazole ring and increased cytochrome P450 3A4 induction following L-755446 formation. The decrease in plasma voriconazole concentration 7 days after fosaprepitant administration was mainly attributed to cytochrome P450 3A4 induction by L-755446.

Simulation of drug-drug interactions between breast cancer chemotherapeutic agents and antiemetic drugs

BACKGROUND

Chemotherapy-induced nausea and vomiting are commonly experienced side effects in breast cancer (BCa) patients. Antiemetic drugs used in BCa treatment are either inhibitors or inducers of cytochrome P450 (CYP) enzymes, while anticancer drugs are metabolized by CYPs.

OBJECTIVES

The purpose of the present work was to evaluate in silico drug-drug interaction (DDI) potential between BCa chemotherapeutic drugs and antiemetic agents.

METHODS

The Drug-Drug Interaction™ module of GastroPlus™ was employed to assess CYP-related interactions between antiemetic and anticancer therapy combinations. The CYP inhibitory or inducing parameters (IC50, Ki, EC50) used in simulations were obtained from the literature.

RESULTS

Analyses of twenty-three BCa drugs indicated that 22% of the chemotherapeutic drugs do not need an antiemetic agent due to their low emetogenicity, whereas 30% of the anticancer drugs are not metabolized by CYPs. The remaining eleven anticancer drugs metabolized by CYPs generated ninety-nine combinations with nine antiemetics. Simulation of DDIs suggest that about half of the pairs did not demonstrate any potential for DDI, whereas 30%, 10%, and 9% of the pairs showed weak, moderate, and strong interaction potential, respectively. In the present study, netupitant was the only antiemetic that showed strong inhibitory interactions (predicted AUC ratio > 5) with CYP3A4-metabolzied anticancer therapies (e.g., docetaxel, ribociclib, olaparib). Moderate to no interactions were observed with ondansetron, aprepitant, rolapitant, and dexamethasone in combination with anticancer agents.

CONCLUSION

It is critical to recognize that these interactions can get amplified in cancer patients because of the severity of the disease and chemotherapy toxicities. Clinicians need to be aware of the DDI likelihood of the drug combinations used in BCa treatment.

Rapid structure identification of nineteen metabolites of ondansetron in human urine using LC/MSn

Ondansetron, a 5-hydroxytryptamine type 3 (5-HT₃ ) receptor antagonist, is regarded as an excellent candidate to treat chemotherapy- and radiotherapy-induced nausea and vomiting. To better understand the metabolic profiles of ondansetron in human urine, the metabolites were analyzed using liquid chromatography/mass spectrometry (LC/MSⁿ ). Urine samples were collected after oral administration of 8 mg ondansetron to healthy volunteers. Then samples were treated by solid-phase extraction and detected with LC/MSⁿ . Besides ondansetron, in human urine, a total of 19 metabolites including 13 new metabolites were detected and identified via comparing the retention time and product ion spectra with those of reference standards isolated and characterized. The results showed that ondansetron was metabolized via hydroxylation, glucuronidation, sulfation and minor N-demethylation in human. LC/MSⁿ was demonstrated to be useful and sensitive in the metabolic study of ondansetron.

Intestinal Microbiota Mediates the Susceptibility to Polymicrobial Sepsis-Induced Liver Injury by Granisetron Generation in Mice

Sepsis-induced liver injury is recognized as a key problem in intensive care units. The gut microbiota has been touted as an important mediator of liver disease development; however, the precise roles of gut microbiota in regulating sepsis-induced liver injury are unknown. Here, we aimed to investigate the role of the gut microbiota in sepsis-induced liver injury and the underlying mechanism. Cecal ligation and puncture (CLP) was used to induce polymicrobial sepsis and related liver injury. Fecal microbiota transplantation (FMT) was used to validate the roles of gut microbiota in these pathologies. Metabolomics analysis was performed to characterize the metabolic profile differences between sepsis-resistant (Res; survived to 7 days after CLP) and sepsis-sensitive (Sen; moribund before or approximately 24 hours after CLP) mice. Mice gavaged with feces from Sen mice displayed more-severe liver damage than did mice gavaged with feces from Res mice. The gut microbial metabolic profile between Sen and Res mice was different. In particular, the microbiota from Res mice generated more granisetron, a 5-hydroxytryptamine 3 (5-HT₃ ) receptor antagonist, than the microbiota from Sen mice. Granisetron protected mice against CLP-induced death and liver injury. Moreover, proinflammatory cytokine expression by macrophages after lipopolysaccharide (LPS) challenge was markedly reduced in the presence of granisetron. Both treatment with granisetron and genetic knockdown of the 5-HT_3A receptor in cells suppressed nuclear factor kappa B (NF-кB) transactivation and phosphorylated p38 (p-p38) accumulation in macrophages. Gut microbial granisetron levels showed a significantly negative correlation with plasma alanine aminotransferase (ALT)/aspartate aminotransferase (AST) levels in septic patients. Conclusion: Our study indicated that gut microbiota plays a key role in the sensitization of sepsis-induced liver injury and associates granisetron as a hepatoprotective compound during sepsis development.

Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for CYP2D6 genotype and use of ondansetron and tropisetron

5-hydroxytryptamine type 3 (5-HT3) receptor antagonists are used in the prevention of chemotherapy- induced, radiation-induced and postoperative nausea and vomiting. CYP2D6 polymorphisms can influence the metabolism of some of these drugs (i.e. ondansetron and tropisetron) thereby affecting drug efficacy. We summarize evidence from the published literature supporting these associations and provide therapeutic recommendations for ondansetron and tropisetron based on CYP2D6 genotype (updates at www.pharmgkb.org ).

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.

Clinical practice guidelines on antiemetics in oncology

The tolerability of chemotherapy has been significantly improved by the advent of effective drugs and protocols for the amelioration of chemotherapy-induced nausea and vomiting. Variables such as the timing of nausea and vomiting (acute, delayed or anticipatory) and the emetogenicity of the chemotherapy must be taken into account in developing guidelines for antiemetic prophylaxis and treatment. Although there are a number of 5-hydroxytryptamine antagonists available, the clinical differences between them are small. The use of drugs with a different mechanism of action, such as the recently introduced neurokinin-1 receptor antagonist aprepitant, may be a useful adjunct to 5-hydroxytryptamine-3 receptor antagonists or steroid prophylaxis. The addition of aprepitant to standard antiemetic regimens increases the proportion of complete responses to antiemetic therapy. For the use of highly emetogenic chemotherapy in oncology a combination of 5-hydroxytryptamine-3 receptor antagonist, dexamethasone and aprepitant is recommended in the acute phase, and dexamethasone plus aprepitant during the subsequent days (many patients do not have their symptoms controlled by 5-hydroxytryptamine-3 receptor antagonist and steroid alone). In either case, lorazepam can be added as required. For moderately emetogenic chemotherapy, a regimen of 5-hydroxytryptamine, dexamethasone and aprepitant is recommended in the acute phase, followed by aprepitant alone in the delayed phase. Alternatively, a 5-hydroxytryptamine-3 receptor antagonist and dexamethasone can be used in the acute phase, followed by dexamethasone for prophylaxis in the delayed phase. For chemotherapy with a low emetogenicity, either dexamethasone, metoclopramide, prochlorperazine or triethyperazine alone is recommended. No prophylaxis is generally required during the delayed phase and indeed may not be necessary during the acute phase either.

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.

Granisetron as an add-on to risperidone for treatment of negative symptoms in patients with stable schizophrenia: randomized double-blind placebo-controlled study

Some 5-HT3 antagonists such as ondansetron have shown beneficial effects on negative symptoms of patients with schizophrenia. We aimed to evaluate the efficacy of granisetron (another 5-HT3 antagonist) add-on therapy in the treatment of negative symptoms of patients with stable schizophrenia. In a randomized, double-blind, and placebo-controlled study, forty stable patients with schizophrenia (DSM-IV-TR), were randomized to either granisetron (1 mg twice daily) or placebo (twice daily) in addition to risperidone up to 6 mg/day for eight weeks. The patients were assessed using positive and negative syndrome scale (PANSS) and extrapyramidal symptom rating scale (ESRS) at baseline, week 4 and 8. Hamilton depression rating scale (HDRS) was used to assess depression at baseline and week 8. Thirty-eight patients completed the trial. Granisetron group showed a significantly greater improvement on negative subscale than the placebo group at endpoint [t(38) = 6.046, mean difference (±95% CI) = 3.2(1.8-3.7), P < 0.001]. The same effect was observed for total score [t(38) = 4.168, mean difference (95% CI) = 3.2(1.6-4.7), P < 0.001]. However the placebo and granisetron groups did not differ in their reduction of positive and general psychopathology symptoms scores. HDRS scores and its changes did not differ between the two groups. The ESRS score at week 4 was significantly lower in the granisetron than the placebo group while the two groups showed similar ESRS score at week 8. Frequency of other side effects was similar between the two groups. In summary, granisetron add-on can safely and effectively reduce the primary negative symptoms of patients with schizophrenia.

Granisetron adjunct to fluvoxamine for moderate to severe obsessive-compulsive disorder: a randomized, double-blind, placebo-controlled trial

BACKGROUND

Several small studies have shown beneficial effects of ondansetron, a serotonin 5-HT(3) receptor antagonist, in the treatment of obsessive-compulsive disorder (OCD). The efficacy of other 5-HT(3) receptor antagonists in patients with OCD is still unclear. Granisetron does not alter cytochrome P450 activity and might have a lower risk of drug interactions, a longer duration of action and a better tolerability profile than other 5-HT(3) receptor antagonists.

OBJECTIVE

The objective of this study was to assess the efficacy and tolerability of granisetron augmentation of fluvoxamine in patients with OCD.

STUDY DESIGN

This was a two-centre, randomized, double-blind, placebo-controlled, parallel-group study conducted from November 2011 to March 2012.

STUDY SETTING

The study setting was outpatient clinics of two large referral centres.

PATIENTS

Study participants were men and women, aged 18-60 years, who met the diagnostic criteria of OCD based on the DSM-IV-TR and who had a Yale-Brown Obsessive Compulsive Scale (Y-BOCS) score of at least 21.

INTERVENTIONS

Participants were randomly assigned to granisetron (Kytril(®); SmithKline Beecham, Philadelphia, PA, USA) 1 mg every 12 hours or placebo every 12 hours in addition to fluvoxamine for 8 weeks.

MAIN OUTCOME MEASURE

Patients were assessed using the Y-BOCS at baseline, second, fourth, sixth and eighth weeks. The primary outcome measure was the difference in the score change of Y-BOCS total score from baseline to week 8 between the two groups. We also compared changes in the obsession and compulsion subscales of the Y-BOCS, and frequencies of partial response (≥25% reduction in Y-BOCS score), complete response (≥35% reduction in Y-BOCS score) and remission (Y-BOCS score ≤16) between the two groups.

RESULTS

Of the 42 included patients, 39 (20 in the placebo group, 19 in the granisetron group) completed the study. Significant time X treatment interaction was observed for total Y-BOCS (F [2.097, 79.678] = 4.941, p = 0.009), obsession (F [2.337, 88.799] = 4.938, p = 0.006) and compulsion (F [2.050, 77.899] = 4.674, p = 0.012) subscales. By week 8, complete response and remission were achieved by 20 (100%) and 18 (90%) patients in the granisetron group and by 7 (35%) patients in the placebo group (p-value of Fisher's exact test <0.001, risk ratio (RR) [95% CI] = 3.857 [2.039, 7.297]). There was no significant difference in the tolerability between the two regimens.

CONCLUSION

Granisetron is an efficacious adjunct for the short-term treatment of patients with moderate to severe OCD and is well tolerated.

CLINICAL TRIAL REGISTRATION NUMBER

IRCT201202041556N32.

Chemical inhibitors of cytochrome P450 isoforms in human liver microsomes: a re-evaluation of P450 isoform selectivity

The majority of marketed small-molecule drugs undergo metabolism by hepatic Cytochrome P450 (CYP) enzymes (Rendic 2002). Since these enzymes metabolize a structurally diverse number of drugs, metabolism-based drug-drug interactions (DDIs) can potentially occur when multiple drugs are coadministered to patients. Thus, a careful in vitro assessment of the contribution of various CYP isoforms to the total metabolism is important for predicting whether such DDIs might take place. One method of CYP phenotyping involves the use of potent and selective chemical inhibitors in human liver microsomal incubations in the presence of a test compound. The selectivity of such inhibitors plays a critical role in deciphering the involvement of specific CYP isoforms. Here, we review published data on the potency and selectivity of chemical inhibitors of the major human hepatic CYP isoforms. The most selective inhibitors available are furafylline (in co-incubation and pre-incubation conditions) for CYP1A2, 2-phenyl-2-(1-piperidinyl)propane (PPP) for CYP2B6, montelukast for CYP2C8, sulfaphenazole for CYP2C9, (-)-N-3-benzyl-phenobarbital for CYP2C19 and quinidine for CYP2D6. As for CYP2A6, tranylcypromine is the most widely used inhibitor, but on the basis of initial studies, either 3-(pyridin-3-yl)-1H-pyrazol-5-yl)methanamine (PPM) and 3-(2-methyl-1H-imidazol-1-yl)pyridine (MIP) can replace tranylcypromine as the most selective CYP2A6 inhibitor. For CYP3A4, ketoconazole is widely used in phenotyping studies, although azamulin is a far more selective CYP3A inhibitor. Most of the phenotyping studies do not include CYP2E1, mostly because of the limited number of new drug candidates that are metabolized by this enzyme. Among the inhibitors for this enzyme, 4-methylpyrazole appears to be selective.

Aprepitant: drug-drug interactions in perspective

The implications of chemotherapeutic drug-drug interactions can be serious and thus need to be addressed. This review concerns the potential interactions of the antiemetic aprepitant, a neurokinin-1 receptor antagonist indicated for use (in Europe) in highly emetogenic chemotherapy and moderately emetogenic chemotherapy (MEC) in combination with a 5-hydroxytryptamine-3 (5-HT3) receptor antagonist and corticosteroids and (in the United States) in combination with other antiemetic agents, for the prevention of acute and delayed nausea and vomiting associated with initial and repeat courses of highly emetogenic cancer chemotherapy including high-dose cisplatin. When considering use of aprepitant for prevention of chemotherapy-induced nausea and vomiting, its potential drug-drug interaction profile as a moderate inhibitor of cytochrome P-450 isoenzyme 3A4 (CYP3A4) has been a source of concern for some physicians and other health care professionals. We explore in this paper how real those concerns are. Our conclusion is that either no interaction or no clinically relevant interaction exists with chemotherapeutic agents (intravenous cyclophosphamide, docetaxel, intravenous vinorelbine) or 5-HT3 antagonists (granisetron, ondansetron, palonosetron). For relevant interactions, appropriate measures, such as corticosteroid dose modifications and extended International Normalized Ratio monitoring of patients on warfarin therapy, can be taken to effectively manage them. Therefore, the concern of negative interactions remains largely theoretical but needs to be verified with new agents extensively metabolized through the 3A4 pathway.

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.

Effect of casopitant, a novel NK-1 antagonist, on the pharmacokinetics of dolasetron and granisetron

OBJECTIVE

The objective of this study was to characterize the impact of casopitant, a novel neurokinin-1 receptor antagonist under investigation for the prevention of postoperative and chemotherapy-induced nausea and vomiting, on the pharmacokinetics of the commonly prescribed 5-hydroxytryptamine receptor 3 receptor antagonists, dolasetron or granisetron.

MATERIALS AND METHODS

In a phase I, open-label, two-part, two-period, single-sequence study, two cohorts of healthy subjects received either oral dolasetron (100 mg once daily for 3 days) or oral granisetron (2 mg once daily for 3 days) alone (period 1) and combined with oral casopitant, 150 mg day 1, 50 mg days 2 and 3 (period 2). Pharmacokinetics of hydrodolasetron and granisetron were assessed on days 1 and 3 of each period. Log-transformed area under the curve (AUC) and Cmax were statistically analyzed by performing an analysis of variance. Eighteen subjects were enrolled in the dolasetron cohort; nine subjects were CYP2D6 extensive metabolizers (EMs) and nine subjects were CYP2D6 poor metabolizers. Nineteen subjects were enrolled in the granisetron cohort.

RESULTS

The largest changes in hydrodolasetron exposure after coadministration with casopitant were seen in CYP2D6 EMs, with a 24% increase in hydrodolasetron AUC on day 1 and 30% increase in Cmax on days 1 and 3. All other changes in hydrodolasetron exposure were <20%, and granisetron exposure was not altered to any relevant extent (<11%).

CONCLUSION

None of the changes observed are considered clinically meaningful, and coadministration of casopitant with dolasetron or granisetron was well tolerated.

Ketobemidone is a substrate for cytochrome P4502C9 and 3A4, but not for P-glycoprotein

The role of the major drug-metabolizing cytochrome P450 (CYP) enzymes as well as P-glycoprotein (PGP) was investigated in the disposition of ketobemidone in vitro. Formation of norketobemidone from ketobemidone was studied and compared with the activities of 11 major CYP enzymes in human liver microsomes. The formation of norketobemidone from ketobemidone (1 microM) correlated best with CYP2C9 activity, measured as losartan oxidation (rs = 0.82, n = 19, p < 0.001), but there was also a strong correlation with CYP3A4 activity. Additionally, a good correlation was observed with CYP2C19, CYP2C8 and CYP2B6 at a ketobemidone concentration of 50 microM. Inhibition studies confirmed the involvement of CYP2C9 and CTP3A4 in the formation of norketobemidone. The formation rate of norketobemidone was three times higher in the CYP2C9*1*1 genotype group compared with the CYP2C9*1*2, CYP2C9*1*3 and CYP2C9*3*3 genotypes (p < 0.01). Treatment with verapamil as a PGP inhibitor did not affect the transport of ketobemidone in Caco-2 cells, indicating that PGP is not involved. The data suggest that CYP2C9 and CYP3A4 play a major role in the formation of norketobemidone at clinically relevant concentrations.

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.

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.

Interethnic differences in genetic polymorphisms of CYP2D6 in the U.S. population: clinical implications

DNA polymorphisms have been identified in the genes encoding a number of the cytochrome P450 (CYP) enzymes, leading to wide interindividual variation in drug clearance. CYP2D6 metabolizes a significant number of clinically used medications, and genetic variants of the CYP2D6 isozyme that result in varying levels of metabolic activity are of clinical importance in some settings. The exact nature of the clinical effect caused by polymorphisms of the gene depends on the drug in question and the specific variant alleles expressed, as individual variants result in differing phenotypes with a range of levels of enzymatic activity. Compromised drug efficacy due to CYP2D6 variation has been documented with a variety of agents, and this review considers a number of examples, including the 5-HT(3)-receptor antagonists, which are used in oncology supportive care for the prophylaxis of nausea and vomiting. CYP2D6 is involved in the metabolism of all of the most commonly available agents, except granisetron, and their efficacy and side effects may therefore be affected by the CYP2D6 polymorphism. Significant interethnic differences in CYP2D6 allele frequencies have been demonstrated from studies across many countries. However, incidences of polymorphisms in the U.S. population have been challenging to characterize because of the country's wide ethnic diversity. The CYP2D6 polymorphism may become more important as robust clinical tests become widely available and as the use of multiple medications and the attendant risk for drug-drug interactions increases.

Quantification of granisetron in human plasma by liquid chromatography coupled to electrospray tandem mass spectrometry

A simple, sensitive and rapid high-performance liquid chromatography/electrospray ionization tandem mass spectrometry method was developed and validated for the assay of granisetron in human plasma. Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase C18 column and analyzed by MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 313/138 for granisetron and m/z 409/228 for the IS. The assay exhibited a linear dynamic range of 0.1-20 ng/mL for granisetron in human plasma. The lower limit of quantification was 100 pg/mL with a relative standard deviation of less than 5%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.

Genetic determinants of cancer drug efficacy and toxicity: practical considerations and perspectives

Drug-metabolizing enzymes are responsible for the activation or detoxification of cytotoxic drugs. Allelic variants are present with a variable frequency in different populations around the world and have an important role in the therapeutic index of such drugs. It is known that polymorphisms in thiopurine methyltransferase and dihydropyrimidine dehydrogenase have been associated with altered drug metabolism and increased risk of severe toxicity from 6-mercaptopurine and 5-fluorouracil, respectively. Additionally, a variant number of dinucleotide-repeat sequences in the promotor for uridine 5'-diphosphate glucuronosyltransferase 1A1 influences the glucuronidation of SN-38, the active metabolite of irinotecan, which is associated with severe toxicity, including diarrhea and neutropenia. In the same way, polymorphisms in thymidylate synthase have been associated with pyrimidine-associated toxicity and also with response to chemotherapy. The examples shown in this review demonstrate the usefulness of pre-screening patients for well-characterized polymorphism to identify the best-tolerated and most-effective treatment.

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.

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.

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.

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: 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.

5-HT3 receptor antagonists for prevention of late acute-onset emesis

OBJECTIVE

To review the currently available literature on the efficacy of the 5-HT(3) receptor antagonists in the prevention of late acute-onset chemotherapy-induced nausea and vomiting (12-24 h after cytotoxic treatment).

DATA SOURCES

Primary articles were identified by PubMed search (performed in March 2004) and through secondary sources. Search terms included granisetron, ondansetron, tropisetron, dolasetron, acute, chemotherapy, nausea, and vomiting (a further search was performed for palonosetron in March 2004).

STUDY SELECTION AND DATA EXTRACTION

All studies that performed regular assessments (every 2-6 h) of antiemetic control over the first 24 hours with 5-HT(3) receptor antagonists were evaluated.

DATA SYNTHESIS

Current guidelines recommend the use of 5-HT(3) receptor antagonists for the control of chemotherapy-induced nausea and vomiting but do not differentiate between the available agents. However, there is variability in the pharmacokinetic and pharmacodynamic profiles of these agents, and this has implications for dosing regimen, safety, efficacy, and potential drug-drug interactions. Cytotoxic agents vary in the time profile of their emetic effect; this must be considered when choosing an appropriate 5-HT(3) receptor antagonist. The optimal agent should be simple to administer and provide safe and effective antiemetic protection over the whole 24-hour period.

CONCLUSIONS

The differences between the 5-HT(3) receptor antagonists have important consequences for their dosing and efficacy in the control of late acute-onset chemotherapy-induced nausea and vomiting.

CYTOCHROME P450 3A4 IS THE MAJOR ENZYME INVOLVED IN THE METABOLISM OF THE SUBSTANCE P RECEPTOR ANTAGONIST APREPITANT

The contribution of human cytochrome P450 (P450) isoforms to the metabolism of aprepitant in humans was investigated using recombinant P450s and inhibition studies. In addition, aprepitant was evaluated as an inhibitor of human P450s. Metabolism of aprepitant by microsomes prepared from baculovirus-expressed human P450s was observed only when CYP1A2, CYP2C19, or CYP3A4 was present in the expression system. Incubation with CYP1A2 and CYP2C19 yielded only products of O-dealkylation, whereas CYP3A4 catalyzed both N- and O-dealkylation reactions. The metabolism of aprepitant by human liver microsomes was inhibited completely by ketoconazole or troleandomycin. No inhibition was observed with other P450 isoform-selective inhibitors. Aprepitant was evaluated also as a P450 inhibitor in human liver microsomes. No significant inhibition of CYP1A2, CYP2B6, CYP2C8, CYP2D6, and CYP2E1 was observed in experiments with isoform-specific substrates (IC50 > 70 microM). Aprepitant was a moderate inhibitor of CYP3A4, with Ki values of approximately 10 microM for the 1'- and 4-hydroxylation of midazolam, and the N-demethylation of diltiazem, respectively. Aprepitant was a very weak inhibitor of CYP2C9 and CYP2C19, with Ki values of 108 and 66 microM for the 7-hydroxylation of warfarin and the 4'-hydroxylation of S-mephenytoin, respectively. Collectively, these results indicated that aprepitant is both a substrate and a moderate inhibitor of CYP3A4.

The effect of repeat dosing with cimetidine on the pharmacokinetics of intravenous granisetron in healthy volunteers

The primary route of elimination of granisetron is by oxidative hepatic metabolism, thus its pharmacokinetic profile may be altered by co-administration of other drugs that inhibit or induce hepatic drug metabolizing enzymes. This open-label study investigated the effect of inhibition of cimetidine, a potent inhibitor of CYP1A2, CYP2D6 and CYP3A4, on the pharmacokinetic profile of intravenous granisetron in healthy male volunteers. Subjects (n = 12; 18-60 years) received granisetron (40 microg kg(-1)) infused over 3 min, six days before and on the eighth day of dosing with cimetidine (200 mg, four times a day). Blood samples were taken for pharmacokinetic analysis at intervals over 48 h following the administration of each dose of granisetron. Clinical chemistry, haematology and urinalysis were performed before, and 24 h after, each infusion. Electrocardiogram (ECG), resting blood pressure (BP) and pulse were monitored. There were no significant changes in the ECG, lead II trace or ECG time intervals, pulse or blood pressure on each study day. Minor falls in pulse rate and BP (likely to be related to recumbent posture) were seen during both granisetron dosing days, lasting 2 h after each infusion. No significant changes were apparent in the clinical chemistry, haematology or urinalysis measurements following granisetron dosing. No pharmacokinetic parameters measured after cimetidine administration were significantly different from those taken before. Adverse events were mild-to-moderate in severity and were similar to those reported in other studies with granisetron. The pharmacokinetics of granisetron, when administered as a single dose, appeared to be unaltered by cimetidine, an inhibitor of multiple hepatic enzymes (CYP1A2, CYP2D6 and CYP3A4). Granisetron was equally well tolerated before and after repeated dosing with cimetidine.

Granisetron: new insights into its use for the treatment of chemotherapy-induced nausea and vomiting

Granisetron (Kytril, Roche) is a 5-hydroxytryptamine 3 (5-HT(3))-receptor antagonist indicated for the prevention of nausea and/or vomiting associated with initial and repeat courses of emetogenic chemotherapy, including high-dose cisplatin. Its indication expanded in August 2002, with approval from the FDA for the prevention and treatment of postoperative nausea and vomiting. Granisetron strongly and selectively binds to the 5-HT(3) receptor with a binding constant of 0.26 nM and exhibits a 4000 - 40,000 times greater binding affinity for the 5-HT(3) receptor than other binding sites, including other 5HT subtypes and adrenergic, histaminergic and opioid receptors. Its selectivity to the 5-HT(3) receptor over other receptor types is > 1000:1. Granisetron noncompetitively binds to the 5-HT(3) receptor and is associated with a long duration of action as shown by the inhibition of a 5-HT axonal response flare for up to 24 h. Granisetron is unique among the 5-HT(3)-receptor antagonists because it is not metabolised via the cytochrome P450 (CYP) 2D6 pathway and is, therefore, less susceptible to variation in patient response because of factors such as pharmacogenomic differences. Granisetron and other 5-HT(3)-receptor antagonists are first-line agents for acute chemotherapy-induced nausea and vomiting (CINV), whereas combination therapy with 5-HT(3)-receptor antagonists, dexamethasone and neurokinin (NK)-1 receptor antagonism (i.e., with the recently approved aprepitant) is an effective approach to prevent delayed CINV. Granisetron has been shown to be an effective within-class rescue antiemetic for prophylactic failures, which may be linked to its pharmacological properties including non-competitive, insurmountable binding to the 5-HT(3) receptor. As with other 5-HT(3)-receptor antagonists, granisetron is well-tolerated with adverse events of mild severity including headache, asthenia and constipation. Overall, data demonstrate that granisetron is an efficacious, safe and cost-effective member of the 5HT(3)-receptor antagonist class for the prevention of CINV.

Benefits and risks of newer treatments for chemotherapy-induced and postoperative nausea and vomiting

Nausea and vomiting are common adverse effects of chemotherapy, radiation therapy, anaesthesia and surgery. The incidence of chemotherapy-induced nausea and vomiting (CINV) is estimated to vary from 30 to 90%, depending on the type of chemotherapeutic agent used. Radiation-induced emesis varies with anatomical site radiated but is estimated to have an overall incidence of approximately 40%. The incidence of postoperative nausea and vomiting (PONV) depends on the type of anaesthesia and surgery, but overall is estimated to be 20-30%. Evidence-based medicine and meta-analysis have been used to direct medical therapy to help determine equivalence, optimal dose, timing, safety and efficacy of antiemetic medications. Concepts such as the number needed to treat and number needed to harm are helpful to guide the clinician regarding the benefits and risks of a particular treatment. The serotonin 5-HT(3) receptor antagonists ondansetron, granisetron, tropisetron and dolasetron have been important additions to the antiemetic armamentarium. The 5-HT(3) receptor antagonists are similar in chemical structure, efficacy and adverse effect profile. They appear to have no important differences among themselves in clinical outcomes for CINV and PONV. Headache, dizziness, constipation and diarrhoea are their most common adverse effects, and when they occur they are usually mild and easily managed. Haemodynamic changes and extrapyramidal adverse effects are uncommon. ECG changes such as prolonged corrected QT (QTc) interval are infrequent, dose-related and overall judged to be clinically insignificant. As most studies with the 5-HT(3) antagonists have been conducted on relatively healthy patients, caution should be exercised when these drugs are used in susceptible patients with co-morbidities. The clinician must weigh the benefit of administering an antiemetic for CINV or PONV against the risk of occurrence of an adverse event.

Current position of 5HT3 antagonists and the additional value of NK1 antagonists; a new class of antiemetics

The advent of the 5HT(3) receptor antagonists (5HT(3) antagonists) in the 1990 s and the combination with dexamethasone has resulted in acute emesis protection in 70% of patients receiving highly emetogenic chemotherapy. Despite complete protection in the acute phase, however, 40% of patients as yet have symptoms in the delayed phase. 5HT(3) antagonists and dexamethasone are only modestly effective in this delayed phase. Moreover, the antiemetic protection over repeated cycles is not sustained. Neurokinine 1 receptor antagonists (NK(1) antagonists) belong to a new class of antiemetic agents that specifically target the NK(1) receptor, which is involved in both the acute and, particularly, the delayed phase of emesis. Clinical studies have demonstrated that the addition of NK(1) antagonists to dual therapy with a 5HT(3) antagonist plus dexamethasone improves the acute emesis protection by a further 10-15%. In the delayed phase, the proportion of patients remaining free of emesis increases by even 20-30%. Since the effectiveness of this triplet combination was found to be sustained over six cycles of chemotherapy, the chance for an individual patient to remain completely protected during both the acute and the delayed phase over six chemotherapy cycles is nearly doubled.

Effects of aprepitant on the pharmacokinetics of ondansetron and granisetron in healthy subjects

BACKGROUND

The neurokinin-1-receptor antagonist aprepitant, when given in combination with a corticosteroid and a 5-hydroxytryptamine type 3 (5-HT(3))-receptor antagonist, has been shown to be effective for the prevention of acute and delated chemotherapy-induced nausea and vomiting (CINV).

OBJECTIVE

Two studies were conducted to determine whether concomitant administration of aprepitant altered the pharmacokinetic profiles of ondansetron and granisetron, two 5-HT(3)-receptor antagonists commonly used as antiemetic therapy for CINV.

METHODS

The 2 studies were randomized, open-label, crossover trials conducted in healthy subjects aged between 18 and 46 years. Study 1 involved the following 2 treatment regimens: aprepitant 375 mg PO, dexamethasone 20 mg PO, and ondansetron 32 mg IV on day 1, followed by aprepitant 250 mg PO and dexamethasone 8 mg PO on days 2 through 5; and dexamethasone 20 mg PO and ondansetron 32 mg IV on day 1, followed by dexamethasone 8 mg PO on days 2 through 5. Study 2 involved the following 2 treatment regimens: aprepitant 125 mg PO with granisetron 2 mg PO on day 1, followed by aprepitant 80 mg PO on days 2 and 3; and granisetron 2 mg PO on day 1 only. Individual plasma samples were used to estimate area under the plasma concentration-time curve from time zero to infinity (AUC(0- infinity )), peak plasma concentration, and apparent terminal elimination half-life (t(12)) of both ondansetron and granisetron.

RESULTS

Study 1 included 19 subjects (10 women, 9 men), and study 2 included 18 subjects (11 men, 7 women). Coadministration of aprepitant 375 mg produced a small but statistically significant increase in the AUC(0- infinity ) for intravenous ondansetron (from 1268.3 to 1456.5 ng.h/mL; P = 0.019), with no significant effect on peak concentration at the end of the infusion (360.8 ng/mL with aprepitant vs 408.4 ng/mL without) or t(12) (5.0 vs 4.5 hours, respectively). Coadministration of aprepitant 125 mg/80 mg did not alter the mean pharmacokinetic characteristics of oral granisetron (AUC(0- infinity ), 101.4 ng.h/mL with aprepitant vs 92.2 ng.h/mL without; maximum plasma concentration, 9.0 ng/mL with and without aprepitant; time to maximum plasma concentration, both 3.0 hours; t(12), 6.5 vs 6.9 hours, respectively).

CONCLUSION

Concomitant administration of aprepitant had no clinically significant effect on the mean pharmacokinetic characteristics of either ondansetron or granisetron in these healthy subjects.