Pharmacology of the human metabolites of dolasetron, an antiemetic 5-HT3 receptor antagonist

Preliminary pharmacokinetics of intravenous and subcutaneous dolasetron and pharmacodynamics of subcutaneous dolasetron in healthy cats

Objectives The objectives were to evaluate the pharmacokinetics (PK) of subcutaneous (SC) and intravenous (IV) dolasetron and the pharmacodynamics (PD) of SC dolasetron in healthy cats. Methods Five cats with unremarkable complete blood count, serum biochemistry and urinalyses were utilized. In the PK study, cats received 0.8 mg/kg SC and IV dolasetron in a crossover format. Serum samples were obtained via a jugular catheter at 0, 0.25, 0.5, 1, 2, 4, 8, 12, 24, 36 and 48 h after the administration of dolasetron. Dolasetron and the active metabolite hydrodolasetron were measured using liquid chromatography/tandem mass spectrometry. Non-compartmental PK analysis was performed. In the PD study, SC dolasetron (0.8 mg/kg and 1.0 mg/kg) and saline were administered 30 mins prior to administration of 0.44 mg/kg intramuscular xylazine in a randomized three-way crossover. Number of emetic events, lip licks, time to onset of emesis and visual nausea score were scored by a blinded observer. Results In the PK study, dolasetron was quickly metabolized to the active metabolite hydrodolasetron, limiting assessment of dolasetron PK parameters. Median (range) PK parameters for IV hydrodolasetron were as follows: maximum serum concentration (C_max) 116 ng/ml (69-316 ng/ml), time to maximum concentration (T_max) 0.5 h (0.3-0.5 h), half-life 3.3 h (2.9-7.2 h) and area under the curve until the last measurable concentration (AUC_last) 323 h/ng/ml (138-454 h/ng/ml). Median (range) PK parameters for SC hydrodolasetron were as follows: C_max 67.9 ng/ml (60.4-117 ng/ml), T_max 0.5 h (0.5-1.0 h), half-life 3.8 h (2.9-5.3 h) and AUC_last 437 h/ng/ml (221.5-621.8 h/ng/ml). There was no significant difference in exposure to hydrodolasetron between the routes of administration. With regard to PD, when dolasetron was administered prior to xylazine, there was no significant difference in the mean number of emetic events, lip licks, time to onset of emesis or visual nausea score when compared with saline. Conclusions and relevance Administration of 0.8 mg/kg dolasetron does not maintain serum concentrations of active metabolite for 24 h. Administration of dolasetron at 0.8 mg/kg and 1 mg/kg did not prevent xylazine-induced vomiting. Additional feline dose studies are needed to determine if a higher dose is efficacious.

Lack of Effect of Aprepitant on Hydrodolasetron Pharmacokinetics in CYP2D6 Extensive and Poor Metabolizers

To prevent chemotherapy-induced nausea and vomiting, aprepitant is given with a corticosteroid and a 5-hydroxytryptamine type 3 antagonist, such as dolasetron. Dolasetron is converted to the active metabolite hydrodolasetron, which is cleared largely via CYP2D6. The authors determined whether aprepitant, a moderate CYP3A4 inhibitor, alters hydrodolasetron pharmacokinetics in CYP2D6 poor and extensive metabolizers. Six CYP2D6 poor and 6 extensive metabolizers were randomized in an open-label, crossover fashion to treatment A (dolasetron 100 mg on day 1) and treatment B (dolasetron 100 mg plus aprepitant 125 mg on day 1, aprepitant 80 mg on days 2-3). For hydrodolasetron area under the concentration-versus-time curve (AUC0-infinity) and peak plasma concentration (Cmax), geometric mean ratios (B/A) and 90% confidence intervals (CIs) fell below the predefined limit (2.0) for clinical significance (AUC0-infinity, 1.09 [90% CI, 1.01-1.18], Cmax, 1.08 [90% CI, 0.94-1.24]). Aprepitant did not affect the pharmacokinetics of hydrodolasetron, regardless of CYP2D6 metabolizer type, and was generally well tolerated when coadministered with dolasetron in volunteers.

Optimization of sample pretreatment methods for simultaneous determination of dolasetron and hydrodolasetron in human plasma by HPLC-ESI-MS

A high-performance liquid chromatographic method coupled with electrospray mass spectrometry was developed for the simultaneous determination of dolasetron and its major metabolite, hydrodolasetron, in human plasma. A new sample pretreatment method, i.e., salt induced phase separation extraction (SIPSE), was proposed and compared with four other methods, i.e., albumin precipitation, liquid-liquid extraction, hydrophobic solvent-induced phase separation extraction and subzero-temperature induced phase separation extraction. Among these methods, SIPSE showed the highest extraction efficiency and the lowest matrix interferences. The extraction recoveries obtained from the SIPSE method were all more than 96% for dolasetron, hydrodolasetron and ondansetron (internal standard). The SIPSE method is also very fast and easy because protein precipitation, analyte extraction and sample cleanup are combined into one simple process by mixing acetonitrile with plasma and partitioning with 2 mol/L sodium carbonate aqueous solution. The correlation coefficients of the calibration curves were all more than 0.997, in the range of 7.9-4750.0 ng/mL and 4.8-2855.1 ng/mL for dolasetron and hydrodolasetron, respectively. The limits of quantification were 7.9 and 4.8 ng/mL for dolasetron and hydrodolasetron, respectively. The intra-day and inter-day repeatability were all less than 10%. The method was successfully applied to the pharmacokinetic study of dolasetron.

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.

Comparative review of 5-HT3 receptor antagonists in the treatment of acute chemotherapy-induced nausea and vomiting

Since their introduction, 5-HT3 receptor antagonists have become the agents of choice in the prevention of acute chemotherapy-induced nausea and vomiting and are generally superior to high-dose metoclopramide regimens. The availability of four different agents (ondansetron, granisetron, dolasetron, and tropisetron) within this class has prompted investigations into potential differences between the drugs, which appear to be few. More importantly, the results of recently conducted randomized comparative trials in patients receiving moderately or highly emetogenic chemotherapy have demonstrated similar efficacy. Although study designs and patient populations differed, seven large comparative trials in patients receiving highly emetogenic chemotherapy reported no significant differences in complete or complete plus major response rates among the agents. Similar results were generally reported in trials evaluating patients receiving moderately emetogenic chemotherapy. The safety and tolerability of these agents also appear to be similar. The most common adverse events include headache, gastrointestinal effects, lightheadedness, and sedation. All agents are available in both intravenous and oral dosage forms and may be administered as a single dose.

Pooled analysis of three large clinical trials to determine the optimal dose of dolasetron mesylate needed to prevent postoperative nausea and vomiting. The Dolasetron Prophylaxis Study Group

STUDY OBJECTIVE

To identify the maximally effective dolasetron dose (i.e., maximum efficacy with minimum adverse events) for prevention of postoperative nausea and vomiting (PONV) using the statistical power generated in a pooled patient sample from three large, nearly identical clinical trials.

DESIGN

Three randomized, multicenter, placebo-controlled, double-blinded trials.

SETTING

Trials 1, 2, and 3 enrolled patients at 10, 25, and 17 hospitals and/or surgical centers, respectively.

PATIENTS

A total of 1,946 ASA physical status, I, II, and III patients. Trials 1 and 2 enrolled only female patients (n = 916) undergoing gynecologic surgery. Trial three enrolled 722 females (approximately 70% gynecologic surgeries) and 308 males (approximately 46% orthopedic surgeries) undergoing a variety of surgical procedures.

INTERVENTIONS

All surgical procedures used balanced general anesthesia. Patients received 12.5, 25, 50, or 100 mg of the antiemetic, dolasetron, near the end of anesthesia.

MEASUREMENTS AND MAIN RESULTS

Efficacy endpoints were identical and measured for 24 hours: complete response (no vomiting or rescue medication) and maximum nausea, reported using a 100-mm visual analog scale (VAS). Safety was assessed using adverse event reports, laboratory and electrocardiographic data, and vital signs. All four dolasetron doses produced significant increases in complete response and decreases in maximum VAS nausea compared with placebo (p < 0.01). No increased efficacy was observed with dolasetron doses higher than 12.5 mg. Safety was similar between each dolasetron dose and placebo.

CONCLUSION

Dolasetron 12.5 mg, given near the end of anesthesia, is the maximally effective dose studied for preventing postoperative nausea and vomiting.

Guidelines for anti-emetic therapy: acute emesis

Anti-emetic therapy has become integral to the management of patients with cancer. Goals related to complete emesis control include providing treatment that reduces hospitalisation and time in the ambulatory setting, care that is convenient for the patient and therapy that enhances patients' quality of life. A panel of clinical, health economic and basic scientists with expertise in various oncology disciplines reviewed published literature to develop evidence-based consensus guidelines for the prevention and treatment of chemotherapy-induced emesis. Currently, serotonin receptor antagonists and corticosteroids are the two categories of anti-emetics that are most effective, have the fewest side-effects and are convenient to use. These agents are recommended in combination for highly emetogenic chemotherapy regimens and as single agents or in combination for moderately to highly emetogenic chemotherapy. When possible, these agents may be given orally in single doses; current evidence does not support dose escalation for either category of anti-emetics. In special situations, such as the use of high-dose chemotherapy combination regimens, the most emetogenic component of the regimen should dictate the choice of anti-emetic. Appropriate anti-emetic use described in these guidelines represents both good medical practice and a sensible economic approach to care.

Intravenous pharmacokinetics and absolute oral bioavailability of dolasetron in healthy volunteers: part 1

In this first part of a two-part investigation, the intravenous dose proportionality of dolasetron mesylate, a 5-HT3 receptor antagonist, and the absolute bioavailability of oral dolasetron mesylate were investigated. In an open-label, randomized, four-way crossover design, 24 healthy men between the ages of 19 and 45 years received the following doses: 50, 100, or 200 mg dolasetron mesylate administered by 10-min intravenous infusion or 200 mg dolasetron mesylate solution administered orally. Serial blood and urine samples were collected for 48 h after dosing. Following intravenous administration, dolasetron was rapidly eliminated from plasma, with a mean elimination half-life (t1/2) of less than 10 min. Dolasetron was rarely detected in plasma after oral administration of the 200 mg dose. Hydrodolasetron, the active primary metabolite of dolasetron, appeared rapidly in plasma following both oral and intravenous administration of dolasetron mesylate, with a mean time to maximum concentration (t(max)) of less than 1 h. The mean t1/2 of hydrodolasetron ranged from 6.6-8.8 h. The plasma area under the concentration-time curve (AUC0-infinity)) for both dolasetron and hydrodolasetron increased proportionally with dose over the intravenous dose range of 50-200 mg dolasetron mesylate. Approximately 29-33%) and 22% of the dose was excreted in urine as hydrodolasetron following intravenous and oral administration of dolasetron, respectively. For dolasetron as well as hydrodolasetron, mean systemic clearance (C1), volume of distribution (Vd), and t1/2 were similar at each dolasetron dose. The mean 'apparent' bioavailability of dolasetron calculated using plasma concentrations of hydrodolasetron was 76%. The R(+) enantiomer of hydrodolasetron represented the majority of drug in plasma (> 75%) and urine (> 86%). Dolasetron was well tolerated following both oral and intravenous administration.

Single- and multiple-dose pharmacokinetics of oral dolasetron and its active metabolites in healthy volunteers: part 2

The single- and multiple-dose pharmacokinetics and dose-proportionality of oral dolasetron and its active metabolites over the therapeutic dose range was investigated in 18 healthy men. In an open-label, randomized, complete three-way crossover design, each subject received three separate doses: 50, 100, and 200 mg doses of dolasetron mesylate solution given orally. Each dose was administered on the morning of Days 1 and 3-7 during each of the three treatment periods. Serial blood and urine samples were collected for 48 h after the first and last doses. Blood was analysed for dolasetron and hydrodolasetron concentrations; urine was analysed for dolasetron, the R(+) and S(-)-enantiomers of hydrodolasetron, and the 5'-hydroxy and 6'-hydroxy metabolites of hydrodolasetron. Dolasetron was rarely detected in plasma. Hydrodolasetron was formed rapidly, with a time to maximum concentration (t(max)) of less than 1 h. Steady-state conditions for hydrodolasetron were reached 2-3 days after starting once-daily dosing. Although statistical significance was found for hydrodolasetron AUC(0->infinity) and C(max) between dose groups after both single and multiple doses of dolasetron, the differences were small and unlikely to be of clinical significance. About 17-22% of the dose was excreted in urine as hydrodolasetron, with the majority (> 83%) as the R(+) enantiomer.

Effect of infusion rate on the pharmacokinetics and tolerance of intravenous dolasetron mesylate

OBJECTIVE

To evaluate the safety, tolerance, and pharmacokinetics of dolasetron mesylate and its active metabolite hydrodolasetron when dolasetron mesylate was administered intravenously at increasing infusion rates.

DESIGN

A double-blind, placebo-controlled, parallel-group study.

METHODS

Forty-nine healthy nonsmoking male volunteers were randomly assigned to receive intravenous doses of dolasetron mesylate 100 mg or placebo. Three groups of 16 subjects each (12 dolasetron mesylate, 4 placebo) received escalating infusion rates (50, 100, then 200 mg/min). Physical examinations, vital signs, laboratory tests, and adverse events were recorded before and after administration of the study drug. Serial blood samples and 12-lead electrocardiogram measurements were obtained for 24 hours after the infusion. Plasma samples were analyzed for dolasetron and hydrodolasetron.

RESULTS

Dolasetron mesylate was well tolerated, with no apparent differences in vital signs or adverse event profiles among the different rates of infusion. In general, the pharmacokinetics of dolasetron and hydrodolasetron were superimposable among the three infusion rate groups. Plasma dolasetron concentrations declined rapidly in all three infusion rate groups, with mean elimination half-life (t1/2) of less than 10 minutes. The reduced metabolite hydrodolasetron, which accounts for most pharmacologic activity, formed rapidly, with maximum concentrations occurring between 0.4 and 0.5 hours and disappeared with a mean t1/2 of 8-9 hours. The correlation coefficients of least-squares regression analysis between the pharmacokinetic parameters and the infusion rate of dolasetron were less than 0.083 and the slopes were not significantly different from 0, suggesting that none of the hydrodolasetron pharmacokinetic parameters were affected by rate of infusion.

CONCLUSIONS

The intravenous administration of dolasetron 100 mg over 0.5-2 minutes did not significantly alter the pharmacokinetic profiles of either dolasetron or hydrodolasetron. In addition, the safety profile of dolasetron did not change with increasing rate of infusion. Therefore, the rate of infusion of dolasetron mesylate appears to have no pharmacokinetic or clinical implications when assessed over a 0.5-2-minute time period.

Pharmacokinetics of dolasetron after oral and intravenous administration of dolasetron mesylate in healthy volunteers and patients with hepatic dysfunction

In previous studies, dolasetron was shown to have both renal and hepatic elimination mechanisms. This study was conducted to determine the impact of varying degrees of hepatic dysfunction on the pharmacokinetics and safety of dolasetron and its reduced metabolites. Seventeen adults were studied: six healthy volunteers (group I), seven patients with mild hepatic impairment (Child-Pugh class A; group II), and four patients with moderate to severe hepatic impairment (Child-Pugh class B or C1; group III). Single 150-mg doses of dolasetron mesylate were administered intravenously and orally, with a 7-day washout period separating treatments. After intravenous administration, no differences were observed between healthy volunteers and patients with hepatic impairment in maximum plasma concentration (Cmax), areas under the plasma concentration-time curve (AUC), or elimination half-life (t1/2) of intact dolasetron. No significant differences were found in Cmax, AUC, or apparent clearance (C(lapp)) of hydrodolasetron, the primary metabolite of dolasetron. The mean t1/2 increased from 6.87 hours in group I to 11.69 hours in group III. After oral administration, C(lapp) of hydrodolasetron decreased by 42%, and Cmax increased by 18% in patients with moderate to severe hepatic impairment. There were less changes in patients with mildly hepatic impairment. Total percentage of dose excreted as metabolites was similar for healthy volunteers and patients with hepatic impairment, although urinary metabolite profiles differed slightly. Dolasetron was well tolerated and there were no apparent differences in adverse effects between groups or treatments. Because hepatic impairment did not influence Cl(app) of hydrodolasetron after intravenous administration, and the range of plasma concentrations of hydrodolasetron after oral administration was not different from those observed in healthy volunteers, dosage adjustments are not recommended for patients with hepatic disease and normal renal function.

Intravenous dolasetron and ondansetron in prevention of postoperative nausea and vomiting: a multicenter, double-blind, placebo-controlled study

BACKGROUND

Intravenous dolasetron mesilate has shown efficacy in the prevention of postoperative nausea and vomiting (PONV) when administered as a single dose prior to emergence from anesthesia. This trial compared intravenous dolasetron and ondansetron for the prevention of PONV when administered at induction of anesthesia.

METHODS

This double-blind, placebo-controlled, multicenter trial randomized patients to one of four single IV treatments placebo, 25 or 50 mg dolasetron, or 4 mg ondansetron. Efficacy was measured by complete response (0 emetic episodes and no rescue medication), nausea severity and patient satisfaction as measured on a visual analog scale (VAS), investigator's rating, of nausea severity, and total response (complete response with no nausea [< or = 5 mm VAS]).

RESULTS

514 patients at 24 sites were evaluated for efficacy. The 50 mg dolasetron and 4 mg ondansetron doses were statistically equivalent, and superior to placebo, for all efficacy measures. Complete response rates were 49%, 51%, 71% and 64% for placebo, 25 and 50 mg dolasetron, and ondansetron, respectively. Dolasetron 50 mg was statistically superior to 25 mg dolasetron for complete response, total response, VAS maximum nausea, time to first emetic episode, and patient satisfaction. The majority of adverse events were of mild-to-moderate intensity. Headache was the most frequently reported treatment-related adverse event with a 3%-5% incidence across treatments.

CONCLUSION

When given at induction of anesthesia, 50 mg intravenous dolasetron is equivalent to 4 mg ondansetron and superior to 25 mg dolasetron and placebo for the prevention of PONV. All treatments were safely administered and well tolerated.

Intravenous dolasetron mesilate in the prevention of postoperative nausea and vomiting in females undergoing gynecological surgery

STUDY OBJECTIVE

To evaluate a range of doses of intravenous (i.v.) dolasetron mesilate, in preventing postoperative nausea and vomiting (PONV).

DESIGN

Double-blind, placebo-controlled, randomized, multicenter trial.

SETTING

Ten hospitals and/or surgical centers.

PATIENTS

281 women undergoing gynecologic surgery with general anesthesia.

INTERVENTIONS

Patients received one of four single, i.v. doses of dolasetron mesilate (12.5 mg, 25 mg, 50 mg, and 100 mg) or placebo administered following cessation of anesthesia.

MEASUREMENTS AND MAIN RESULTS

Patients were monitored for 24 hours following study drug administration. The antiemetic efficacy of each dolasetron mesilate dose was evaluated by recording the number and timing of emetic episodes, and the effects on nausea were assessed by use of visual analog scales (VAS). Safety was assessed by adverse event reports, clinical laboratory tests, electrocardiographic (ECG) measurements, and monitoring vital signs. Complete responses (patients with no emetic episodes and no escape antiemetic medication requirements in 24 hours) were achieved by 54% in the 12.5-mg, 67% in the 25-mg, and 59% in both the 50-mg and 100-mg dolasetron mesilate dose groups, and by 43% in the placebo group. Nausea VAS assessments demonstrated that dolasetron-treated patients were significantly (p = 0.048) more likely to report no nausea (VAS score < 5 mm) than those in the placebo group. Adverse events reported generally were mild in intensity, and there were no clinically significant changes in laboratory tests, vital signs, or ECG parameters.

CONCLUSIONS

Dolasetron was effective and well tolerated for the prevention of PONV in female patients undergoing gynecologic surgery with general anesthesia.

Intravenous dolasetron mesilate ameliorates postoperative nausea and vomiting

PURPOSE

To compare the efficacy, safety, and tolerability of dolasetron mesilate with placebo for the treatment of postoperative nausea and vomiting (PONV).

METHODS

In a randomized, multicentre, double-blind, placebo-controlled study 337 adult patients undergoing surgery with general anaesthesia received one of four single, doses of dolasetron mesilate iv (12.5, 25, 50, or 100 mg) or placebo. Study medication was administered postoperatively when the patient reported nausea lasting 10 min or when one emetic episode occurred within two hours of the patient's arrival in the recovery room. Efficacy was assessed by the investigators over the 24-hr study period by recording the number and timing of emetic episodes, the severity of nausea, the timing of administration of escape antiemetic medications, and patients' and investigators' satisfaction with antiemetic therapy.

RESULTS

The study sample was predominately women, and the surgical procedures were primarily gynaecological. All dolasetron mesilate doses produced higher complete response rates than placebo (P < 0.05). Only approximately one-third of dolasetron patients required escape antiemetic medication compared with more than 50% of patients in the placebo group. Both patient and physician satisfaction with dolasetron treatment was high. The most common adverse event was mild or moderate headache for both placebo-treated patients and dolasetron-treated patients. Clinical laboratory results were unremarkable.

CONCLUSION

Single doses of dolasetron mesilate iv, given after the first episode of PONV, were both effective and safe in this adult patient population.

A double-blind, multicentre comparison of intravenous dolasetron mesilate and metoclopramide in the prevention of nausea and vomiting in cancer patients receiving high-dose cisplatin chemotherapy

The potent serotonin receptor (5-HT3) antagonists are new highly selective agents for the prevention and control of chemotherapy-induced nausea and vomiting that have been shown to be comparable to or more effective than traditional metoclopramide regimens. This study was designed to compare the antiemetic efficacy of dolasetron and metoclopramide in chemotherapy-naive and non-naive cancer patients receiving high-dose cisplatin-containing chemotherapy. This multicentre, double-blind, randomized trial compared the efficacy and safety of single i.v. doses of dolasetron mesilate salt (1.2 or 1.8 mg/kg) and metoclopramide (7 mg/kg) in 226 patients for the prevention of acute emesis and nausea associated with the administration of high-dose (> or = 80 mg/m2) cisplatin. Efficacy and safety were evaluated for 24 h. Complete responses were achieved by 57%, 48%, and 35% of patients given dolasetron mesilate 1.8 mg/kg (P = 0.0009 vs metoclopramide), dolasetron mesilate 1.2 mg/kg (P = 0.0058 vs metoclopramide), and metoclopramide, respectively. Overall, dolasetron was significantly more effective than metoclopramide for time to first emetic episode, nausea, patient satisfaction, and investigator global assessment of efficacy. Males, chemotherapy-naive patients, and alcoholics had higher response rates. Dolasetron was well tolerated, with mild-to-moderate headache most commonly reported. Twelve percent of patients receiving metoclopramide reported extrapyramidal symptoms compared with 0% of patients receiving dolasetron. In conclusion, dolasetron mesilate was effective for the prevention of CINV with high-dose cisplatin. Single i.v. doses of dolasetron mesilate were more effective than 7 mg/kg metoclopramide in preventing nausea and vomiting induced by highly emetogenic cisplatin-containing chemotherapy. In addition, 1.8 mg/kg dolasetron mesilate consistently produced the highest response rates and appears to be the most effective dose for further clinical development.

Validation of a reversed-phase HPLC method for directly quantifying the enantiomers of MDL 74,156, the primary metabolite of dolasetron mesylate, in human plasma

A direct chiral HPLC method has been developed and validated to quantitate the enantiomers of MDL 74156, the primary metabolite of dolasetron mesylate, in human plasma over the concentration range 1.70-340 ng ml-1. Dolasetron mesylate is a 5-HT3 receptor antagonist that is currently being developed as an antiemetic. Both enantiomers of MDL 74154 and the internal standard (granisetron) were first extracted from alkanized plasma using methyl t-butyl ether. The analytes were then back-extracted into formic acid, separated on a ovomucoid-bonded HPLC column, and detected by native fluorescence (excitation wavelength of 274 nm and emission wavelength of 345 nm). The complete validation demonstrated the method to be accurate, precise, and specific for the direct quantitation of MDL 74156 enantiomers in human plasma. This procedure has been used on a routine basis to quantify the relative concentrations of each enantiomer of MDL 74 156 in both oral and intravenous pharmacokinetic studies of dolasetron mesylate in normal human volunteers.

Antiemetic efficacy of two different single intravenous doses of dolasetron in patients receiving high-dose cisplatin-containing chemotherapy

This randomized, double-blind, parallel-group, multicenter study compared the antiemetic effectiveness, safety, and tolerability of two different intravenous (i.v.) doses of dolasetron mesylate (0.6 and 1.8 mg/kg) in cancer patients receiving their first course of high-dose cisplatin-containing chemotherapy (> or = 75 mg/m2). Efficacy was assessed by recording the timing, number, and severity of emetic episodes in the 24 h following high-dose cisplatin. Safety was evaluated by monitoring adverse events, vital signs, clinical laboratory parameters, and electrocardiograms. Of the 62 patients enrolled in the study, 29 received 0.6 mg/kg of dolasetron mesylate and 33 received 1.8 mg/kg. Patients who received dolasetron mesylate 1.8 mg/kg consistently experienced a greater degree of antiemetic control than those who received 0.6 mg/kg. Complete responses were achieved by 55% of patients who received 1.8 mg/kg compared with 31% for the 0.6-mg/kg group. The 1.8-mg/kg group achieved a significantly (p = 0.039) higher complete/ major response rate than the 0.6-mg/kg group (77% vs 55%, respectively) and a significantly (p = 0.004) longer time to the first emetic episode (> 24 h vs 13.5 h, respectively). More than 80% of patients were either satisfied or very satisfied with dolasetron treatment. The most common adverse events were mild to moderate in intensity, consistent with other studies, and included headache (24.1% of patients) and diarrhea (4.8%). These results demonstrated that a single 1.8-mg/kg i.v. dose of dolasetron mesylate provided effective antiemetic activity in a majority of patients given high-dose cisplatin for the first time and should be evaluated further in clinical trials.

Pharmacokinetics of single intravenous and oral doses of dolasetron mesylate in healthy elderly volunteers

Dolasetron mesylate (MDL 73,147EF, Anzemet; Hoechst Marion Roussel, Laval, Canada) is a 5-HT3 receptor antagonist undergoing clinical evaluation for use as an antiemetic agent. The pharmacokinetics of dolasetron and its reduced metabolite (MDL 74,156) were studied after administration of single intravenous and oral doses of dolasetron mesylate 2.4 mg/kg in 18 healthy elderly subjects. Expressed as the dolasetron base, this dose was 1.8 mg/kg. Dolasetron was rapidly metabolized to the reduced metabolite, which appeared in plasma within 10 minutes after intravenous or oral administration. The mean half-life (t1/2) of dolasetron was 0.24 hours after intravenous administration and 0.50 hours after oral administration. The pharmacokinetic parameters of the reduced metabolite were similar after intravenous and oral administration. The apparent absolute bioavailability of the reduced metabolite was 89%, and it had an elimination t1/2 of approximately 7 hours and an apparent volume of distribution (Vd beta) of 4.69 L/kg. Dolasetron was not detected in urine. Metabolites were excreted in urine almost completely within 24 hours of administration. The primary metabolite detected in urine was the (+)-enantiomer of the reduced metabolite, which accounted for 25.35% (+/- 7.79%) and 18.88% (+/- 7.65%) of the intravenous and oral doses, respectively. Hydroxylated metabolites accounted for 5% or less of the total dose via either route. The pharmacokinetics of the reduced metabolite after single intravenous or oral doses in elderly volunteers were consistent with pharmacokinetics observed in both young healthy men and cancer patients receiving high-dose cisplatin chemotherapy. Dosage adjustments of dolasetron mesylate on the basis of age do not appear to be necessary.

A double-blind, placebo-controlled trial of i.v. dolasetron mesilate in the prevention of radiotherapy-induced nausea and vomiting in cancer patients

The aim of this work was to measure the safety and efficacy of single i.v. doses of dolasetron mesilate for the control of emesis caused by single high-dose (at least 6 Gy) radiotherapy to the upper abdomen. The double-blind, placebo-controlled, multicenter study stratified patients on the basis of being naive or nonnaive to radiotherapy. Patients with or without a history of previous chemotherapy were enrolled. Patients were randomized to receive placebo or 0.3, 0.6, or 1.2 mg/kg dolasetron mesilate 30 min before radiotherapy, then monitored for 24 h. Antiemetic efficacy was assessed from the time to the first emetic episode or rescue, from whether there was a complete response (0 emetic episodes /no rescue medication) or a complete-plus-major response (0-2 emetic episodes/no rescue medication), from the severity of nausea (rated by patients and the investigator), and from the investigator's assessment of efficacy. Fifty patients completed the study (owing to changing medical practice, enrollment objectives were not met; consequently, no significant linear dose trend was expected). Pooled dolasetron was superior to the placebo in its effect on the time to first emesis or rescue in radiotherapy-nonnaive patients (P = 0.015). Dolasetron was statistically superior to the placebo in the overall population on the basis of a complete plus major response: 54%, 100%, 93%, and 83% for the placebo and 0.3-, 0.6-, and 1.2-mg/kg doses respectively (P = 0.002). The low response in the highest dose group may be due to an imbalance in the number of chemotherapy-nonnaive patients in that group. Dolasetron was superior to the placebo on the basis of nausea assessed by the investigator (P = 0.024) and administration of rescue medication (P = 0.006). Complete response at the 0.3-mg/ kg dose was superior to results with the placebo (P = 0.050). Treatment-related adverse events were rare, mild to moderate in intensity, and evenly distributed across the four groups. Overall, dolasetron mesilate was effective and well-tolerated in the control of single, high-dose radiotherapy-induced emesis.

Therapeutic equivalence of single oral doses of dolasetron mesilate and multiple doses of ondansetron for the prevention of emesis after moderately emetogenic chemotherapy. European Dolasetron Comparative Study Group

This multicentre, randomised, double-blind study was designed to compare the anti-emetic efficacy and safety of single oral doses of dolasetron mesilate with that of the approved oral, multiple-dose regimen of ondansetron in 399 cancer patients receiving moderately emetogenic chemotherapy. Single oral doses of 25, 50, 100 or 200 mg of dolasetron mesilate were administered 1 h prior to the initiation of moderately emetogenic chemotherapy. Multiple doses of ondansetron (8 mg x 3 or 8 mg x 4) capsules, or matching placebo for patients randomised to dolasetron, were given 1.5 h before and 6.5, 14.5 and 22.5 h after the start of chemotherapy (total dose = 32 mg). Efficacy was evaluated for 24 h after the initiation of chemotherapy. The most frequently used moderately emetogenic chemotherapeutic agents included cyclophosphamide, doxorubicin and carboplatin (28.4, 23.1 and 20.6% of patients, respectively). A statistically significant (P < 0.001) linear dose-response relationship was observed over the entire dolasetron dosage range for all efficacy parameters. Complete response rates were 45.0, 49.4, 60.5 and 76.3% for 25, 50, 100 and 200 mg dolasetron mesilate, respectively, and 72.3% of ondansetron patients. A single oral 200 mg dolasetron mesilate dose was therapeutically equivalent to ondansetron for all efficacy parameters and patient satisfaction was high. Overall, there were no significant differences in the incidence of adverse events between any of the dolasetron mesilate doses, or between dolasetron and ondansetron. Headache was most frequently reported (approximately 15% for each drug). No clinically important changes in vital signs or clinical laboratory parameters were observed with either drug. In conclusion, a single oral 200 mg dolasetron mesilate dose was therapeutically equivalent to multiple-dose ondansetron in the prevention of emesis and nausea following moderately emetogenic chemotherapy.

Stereoselectivity of the carbonyl reduction of dolasetron in rats, dogs, and humans

The initial step in the metabolism of dolasetron or MDL 73,147EF [(2 alpha, 6 alpha, 8 alpha, 9a beta)-octahydro-3-oxo-2,6-methano-2H- quinolizin-8-yl 1H-indol-3-carboxylate, monomethanesulfonate] is the reduction of the prochiral carbonyl group to give a chiral secondary alcohol "reduced dolasetron." An HPLC method, using a chiral column to separate reduced dolasetron enantiomers, has been developed and used to measure enantiomers in urine of rats, dogs, and humans after dolasetron administration. In all cases, the reduction was enantioselective for the (+)-(R)-enantiomer, although the dog showed lower stereoselectivity, especially after iv administration. An approximate enantiomeric ratio (+/-) of 90:10 was found in rat and human urine. The contribution of further metabolism to this enantiomeric ratio was considered small as preliminary studies showed that oxidation of the enantiomeric alcohols by human liver microsomes demonstrated only minor stereoselectivity. Further evidence for the role of stereoselective reduction in man was obtained from in vitro studies, where dolasetron was incubated with human whole blood. The enantiomeric composition of reduced dolasetron formed in human whole blood was the same as that found in human urine after administration of dolasetron. Enantioselectivity was not due to differences in the absorption, distribution, metabolism, or excretion of enantiomers, as iv or oral administration of rac-reduced dolasetron to rats and dogs lead to the recovery, in urine, of essentially the same enantiomeric composition as the dose administered. it is fortuitous that the (+)-(R)-enantiomer is predominantly formed by carbonyl reductase, as it is the more active compound.