Effects on Electrocardiogram

QTcF interval was evaluated in a randomized, placebo and active (moxifloxacin 400 mg once-daily) controlled crossover study in 80 healthy adults, with 14 measurements over 24 hours on Day 4. The maximum mean (95% upper confidence bound) differences in QTcF from placebo after baseline-correction were 14.1 (16.1) ms and 36.6 (38.6) ms for 100 mg and supratherapeutic 300 mg ANZEMET, administered intravenously, respectively. ANZEMET 300 mg once daily resulted in approximately 3-fold higher mean Cmax values of dolasetron mesylate and its active metabolite hydrodolasetron on Day 4 compared to those observed with the therapeutic 100 mg ANZEMET dose.

Based on exposure-response analysis in healthy volunteers, QTc interval prolongations appear to be associated with concentrations of hydrodolasetron. Using the established exposure-response relationship, the mean predicted increase (95% upper prediction interval) in QTcF intervals were 16.0 (17.1) ms and 17.9 (19.1) ms for renally impaired and elderly subjects following an oral dose of 100 mg.

In the thorough QT study, exposure dependent prolongation of the PR and QRS interval was also noted in healthy subjects receiving ANZEMET. The maximum mean (95% upper confidence bound) difference in PR from placebo after baseline-correction was 9.8 (11.6) ms and 33.1 (34.9) ms for 100 mg and supratherapeutic 300 mg ANZEMET, respectively. The maximum mean (95% upper confidence bound) difference in QRS from placebo after baseline-correction was 3.5 (4.5) ms and 13 (14.5) ms for 100 mg and supratherapeutic 300 mg ANZEMET, respectively. Over one-fourth of the subjects treated with the 300 mg dose had an absolute PR over 200 ms and absolute QRS of over 110 ms post-treatment. A change from baseline ≥ 25% was noted in several of these subjects (see WARNINGS).

Pharmacokinetics in Humans

Oral dolasetron is well absorbed, although parent drug is rarely detected in plasma due to rapid and complete metabolism to the most clinically relevant species, hydrodolasetron.

The reduction of dolasetron to hydrodolasetron is mediated by a ubiquitous enzyme, carbonyl reductase. Cytochrome P-450 (CYP) 2D6 is primarily responsible for the subsequent hydroxylation of hydrodolasetron and both CYP3A and flavin monooxygenase are responsible for the N-oxidation of hydrodolasetron.

Hydrodolasetron is excreted in the urine unchanged (61.0% of administered oral dose). Other urinary metabolites include hydroxylated glucuronides and N-oxide.

Hydrodolasetron appears rapidly in plasma, with a maximum concentration occurring approximately 1 hour after dosing, and is eliminated with a mean half-life of 8.1 hours (%CV=18%) and an apparent clearance of 13.4 mL/min/kg (%CV=29%) in 30 adults. The apparent absolute bioavailability of oral dolasetron, determined by the major active metabolite hydrodolasetron, is approximately 75%. Orally administered dolasetron intravenous solution and tablets are bioequivalent. Food does not affect the bioavailability of dolasetron taken by mouth.

Hydrodolasetron is eliminated by multiple routes, including renal excretion and, after metabolism, mainly, glucuronidation and hydroxylation. Two thirds of the administered dose is recovered in the urine and one third in the feces. Hydrodolasetron is widely distributed in the body with a mean apparent volume of distribution of 5.8 L/kg (%CV=25%, N=24) in adults.

Sixty-nine to 77% of hydrodolasetron is bound to plasma protein. In a study with 14C labeled dolasetron, the distribution of radioactivity to blood cells was not extensive. Approximately 50% of hydrodolasetron is bound to α1-acid glycoprotein. The pharmacokinetics of hydrodolasetron are linear and similar in men and women.

The pharmacokinetics of hydrodolasetron, in special and targeted patient populations following oral administration of dolasetron, are summarized in Table 1. The pharmacokinetics of hydrodolasetron are similar in adult (young and elderly) healthy volunteers and in adult cancer patients receiving chemotherapeutic agents. The apparent clearance following oral administration of hydrodolasetron is approximately 1.6- to 3.4-fold higher in children and adolescents than in adults. The clearance following oral administration of hydrodolasetron is not affected by age in adult cancer patients. The apparent oral clearance of hydrodolasetron decreases 42% with severe hepatic impairment and 44% with severe renal impairment. No dose adjustment is necessary for renally impaired or elderly patients, however ECG monitoring is recommended (see WARNINGS and PRECAUTIONS, Geriatric Use). No dose adjustment is recommended for patients with hepatic impairment.

The pharmacokinetics of ANZEMET Tablets have not been studied in the pediatric population. However, the following pharmacokinetic data are available on intravenous ANZEMET Injection administered orally to children.

Thirty-two pediatric cancer patients ages 3 to 11 years (N=19) and 12 to 17 years (N=13), received 0.6, 1.2, or 1.8 mg/kg ANZEMET Injection diluted with either apple or apple-grape juice and administered orally. In this study, the mean apparent clearances of hydrodolasetron were 3 times greater in the younger pediatric group and 1.8 times greater in the older pediatric group than those observed in healthy adult volunteers. Across this spectrum of pediatric patients, maximum plasma concentrations were 0.6 to 0.7 times those observed in healthy adults receiving similar doses.

For 12 pediatric patients, ages 2 to 12 years receiving 1.2 mg/kg ANZEMET Injection diluted in apple or apple-grape juice and administered orally, the mean apparent clearance was 34% greater and half-life was 21% shorter than in healthy adults receiving the same dose.

The table below summarizes the pharmacokinetic data from multiple populations. Please note that the doses studied may have exceeded the maximum recommended dose.

Clinical Studies

Oral ANZEMET at a dose of 100 mg prevents nausea and vomiting associated with moderately emetogenic cancer therapy as shown by 24 hour efficacy data from two double-blind studies. Efficacy was based on complete response (i.e., no vomiting, no rescue medication).

The first randomized, double-blind trial compared single oral ANZEMET doses of 25, 50, 100 and 200 mg in 60 men and 259 women cancer patients receiving cyclophosphamide and/or doxorubicin. There was no statistically significant difference in complete response between the 100 mg and 200 mg dose. Results are summarized in Table 2.

Another trial also compared single oral ANZEMET doses of 25, 50, 100, and 200 mg in 307 patients receiving moderately emetogenic chemotherapy. In this study, the 100 mg ANZEMET dose gave a 73% complete response rate.

QT Interval Prolongation

ANZEMET prolongs the QT interval in a dose dependent fashion. Torsade de Pointes has been reported during post-marketing experience. Avoid ANZEMET in patients with congenital long QT syndrome, hypomagnesemia, or hypokalemia. Hypokalemia and hypomagnesemia must be corrected prior to ANZEMET administration. Monitor these electrolytes after administration as clinically indicated. Use ECG monitoring in patients with congestive heart failure, bradycardia, renal impairment, and elderly patients (see CLINICAL PHARMACOLOGY).

PR and QRS Interval Prolongation

ANZEMET has been shown to cause dose dependent prolongation of the PR and QRS interval and reports of second or third degree atrioventricular block, cardiac arrest and serious ventricular arrhythmias including fatalities in both adult and pediatric patients. At particular risk are patients with underlying structural heart disease and preexisting conduction system abnormalities, elderly, patients with sick sinus syndrome, patients with atrial fibrillation with slow ventricular response, patients with myocardial ischemia or patients receiving drugs known to prolong the PR interval (such as verapamil) and QRS interval (e.g., flecainide or quinidine). ANZEMET should be used with caution and with ECG monitoring in these patients. ANZEMET should be avoided in patients with complete heart block or at risk for complete heart block, unless they have an implanted pacemaker (see CLINICAL PHARMACOLOGY).

Serotonin Syndrome

The development of serotonin syndrome has been reported with 5-HT3 receptor antagonists. Most reports have been associated with concomitant use of serotonergic drugs (e.g., selective serotonin re-uptake inhibitors (SSRIs), serotonin and norepinephrine re-uptake inhibitors (SNRIs), monoamine oxidase inhibitors, mirtazapine, fentanyl, lithium, tramadol, and intravenous methylene blue). Some of the reported cases were fatal. Serotonin syndrome occurring with overdose of another 5-HT3 receptor antagonist alone has also been reported. The majority of reports of serotonin syndrome related to 5-HT3 receptor antagonist use occurred in a post-anesthesia care unit or an infusion center.

Symptoms associated with serotonin syndrome may include the following combination of signs and symptoms: mental status changes (e.g., agitation, hallucinations, delirium, and coma), autonomic instability (e.g., tachycardia, labile blood pressure, dizziness, diaphoresis, flushing, hyperthermia), neuromuscular symptoms (e.g., tremor, rigidity, myoclonus, hyperreflexia, incoordination), seizures, with or without gastrointestinal symptoms (e.g., nausea, vomiting, diarrhea). Patients should be monitored for the emergence of serotonin syndrome, especially with concomitant use of Anzemet and other serotonergic drugs. If symptoms of serotonin syndrome occur, discontinue Anzemet and initiate supportive treatment. Patients should be informed of the increased risk of serotonin syndrome, especially if Anzemet is used concomitantly with other serotonergic drugs (see DRUG INTERACTIONS, Patient Counseling Information).

General

Dolasetron should be administered with caution in patients who have or may develop prolongation of cardiac conduction intervals, particularly QTc. These include patients with hypokalemia or hypomagnesemia, patients taking diuretics with potential for inducing electrolyte abnormalities, patients with congenital QT syndrome, patients taking anti-arrhythmic drugs or other drugs which lead to QT prolongation, and cumulative high dose anthracycline therapy.

Cross hypersensitivity reactions have been reported in patients who received other selective 5-HT3 receptor antagonists. These reactions have not been seen with dolasetron mesylate.

Drug Interactions

The potential for clinically significant drug-drug interactions posed by dolasetron and hydrodolasetron appears to be low for drugs commonly used in chemotherapy because hydrodolasetron is eliminated by multiple routes. See PRECAUTIONS, General for information about potential interaction with other drugs that prolong the QTc interval.

When oral dolasetron (200 mg once daily) was co-administered with cimetidine (300 mg four times daily) for 7 days, the systemic exposure (i.e., AUC) of hydrodolasetron increased by 24% and the maximum plasma concentration of hydrodolasetron increased by 15%. When oral dolasetron (200 mg once daily) was co-administered with rifampin (600 mg once daily) for 7 days, the systemic exposure of hydrodolasetron decreased by 28% and the maximum plasma concentration of hydrodolasetron decreased by 17%.

Caution should be exercised when ANZEMET is co-administered with drugs, including those used in chemotherapy, that prolong ECG intervals and/or cause hypokalemia or hypomagnesemia (see WARNINGS).

In patients taking furosemide, nifedipine, diltiazem, ACE inhibitors, verapamil, glyburide, propranolol, and various chemotherapy agents, no effect was shown on the clearance of hydrodolasetron. Clearance of hydrodolasetron decreased by about 27% when dolasetron mesylate was administered intravenously concomitantly with atenolol. Dolasetron mesylate did not inhibit the antitumor activity of four chemotherapeutic agents (cisplatin, 5-fluorouracil, doxorubicin, cyclophosphamide) in four murine models.

Serotonin syndrome (including altered mental status, autonomic instability, and neuromuscular symptoms) has been described following the concomitant use of 5-HT3 receptor antagonists and other serotonergic drugs, including selective serotonin re-uptake inhibitors (SSRIs) and serotonin and noradrenaline re-uptake inhibitors (SNRIs).

Carcinogenesis, Mutagenesis, Impairment of Fertility

In a 24-month carcinogenicity study, there was a statistically significant (P<0.001) increase in the incidence of combined hepatocellular adenomas and carcinomas in male mice treated with 150 mg/kg/day and above. In this study, mice (CD-1) were treated orally with dolasetron mesylate 75, 150, or 300 mg/kg/day (225, 450 or 900 mg/m2/day). For a 50 kg person of average height (1.46 m2 body surface area), these doses represent 3, 6, and 12 times the recommended clinical dose (74 mg/m2) on a body surface area basis. No increase in liver tumors was observed at a dose of 75 mg/kg/day in male mice and at doses up to 300 mg/kg/day in female mice.

In a 24-month rat (Sprague-Dawley) carcinogenicity study, oral dolasetron mesylate was not tumorigenic at doses up to 150 mg/kg/day (900 mg/m2/day, 12 times the recommended human dose based on body surface area) in male rats and 300 mg/kg/day (1800 mg/m2/day, 24 times the recommended human dose based on body surface area) in female rats.

Dolasetron mesylate was not genotoxic in the Ames test, the rat lymphocyte chromosomal aberration test, the Chinese hamster ovary (CHO) cell (HGPRT) forward mutation test, the rat hepatocyte unscheduled DNA synthesis (UDS) test or the mouse micronucleus test.

Dolasetron mesylate was found to have no effect on fertility and reproductive performance at oral doses up to 100 mg/kg/day (600 mg/m2/day, 8 times the recommended human dose based on body surface area) in female rats and up to 400 mg/kg/day (2400 mg/m2/day, 32 times the recommended human dose based on body surface area) in male rats.

Pregnancy: Teratogenic Effects.

Teratology studies have not revealed evidence of impaired fertility or harm to the fetus due to dolasetron mesylate. These studies have been performed in pregnant rats at oral doses up to 100 mg/kg/day (8 times the recommended human dose based on body surface area) and pregnant rabbits at oral doses up to 100 mg/kg/day (16 times the recommended human dose based on body surface area). There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.

Nursing Mothers

It is not known whether dolasetron mesylate is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when ANZEMET Tablets are administered to a nursing woman.

Pediatric Use (see PRECAUTIONS, General)

Safety and effectiveness in pediatric patients (2 years and older) is based on pharmacokinetic studies and efficacy data in adults. Safety and effectiveness in pediatric patients under 2 years of age have not been established.

ANZEMET Tablets are expected to be as safe and effective as when ANZEMET Injection is given orally to pediatric patients. ANZEMET Tablets are recommended for children old enough to swallow tablets (see CLINICAL PHARMACOLOGY, Pharmacokinetics in Humans).

Geriatric Use

Elderly patients are at particular risk for prolongation of the PR, QRS, and QT interval; therefore, caution should be exercised and ECG monitoring should be performed when using ANZEMET in this population (see WARNINGS).

In controlled clinical trials in the prevention of chemotherapy-induced nausea and vomiting, 301 (29%) of 1026 patients were 65 years of age or older. Of the 301 geriatric patients in the trial, 282 received oral ANZEMET Tablets. No overall differences in safety or effectiveness were observed between geriatric and younger patients, and other reported clinical experience has not identified differences in responses between geriatric and younger patients, but greater sensitivity of some older individuals cannot be ruled out.

The pharmacokinetics, including clearance of oral ANZEMET Tablets, in elderly and younger patients are similar (see CLINICAL PHARMACOLOGY, Pharmacokinetics in Humans). Dosage adjustment is not needed in patients over the age of 65.