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.