CLINICAL PHARMACOLOGY
Dolasetron mesylate and its active metabolite,
hydrodolasetron (MDL 74,156), are selective serotonin 5-HT3 receptor
antagonists not shown to have activity at other known serotonin receptors and
with low affinity for dopamine receptors. The serotonin 5-HT3 receptors are
located on the nerve terminals of the vagus in the periphery and centrally in
the chemoreceptor trigger zone of the area postrema. It is thought that
chemotherapeutic agents produce nausea and vomiting by releasing serotonin from
the enterochromaffin cells of the small intestine, and that the released
serotonin then activates 5-HT3 receptors located on vagal efferents to initiate
the vomiting reflex.
In healthy volunteers (N=64), dolasetron mesylate in
single intravenous doses up to 5 mg/kg produced no effect on pupil size or
meaningful changes in EEG tracings. Results from neuropsychiatric tests
revealed that dolasetron mesylate did not alter mood or concentration. Multiple
daily doses of dolasetron have had no effect on colonic transit in humans.
Dolasetron has no effect on plasma prolactin concentrations.
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) 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) 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.
Table 1: Pharmacokinetic Values for Plasma
Hydrodolasetron Following Oral Administration of ANZEMET*
|
Age (years) |
Dose |
CLapp (mL/min/kg) |
t½ (h) |
Cmax (ng/mL) |
Young Healthy Volunteers (N=30) |
19-45 |
200 mg |
13.4 (29%) |
8.1 (18%) |
556 (28%) |
Elderly Healthy Volunteers (N=15) |
65-75 |
2.4 mg/kg |
9.5 (36%) |
7.2 (32%) |
662 (28%) |
Cancer Patients |
Adults (N=61)† |
24-84 |
25-200 mg |
12.9 (49%) |
7.9 (43%) |
--‡ |
Adolescents (N=13) |
12-17 |
0.6-1.8 mg/kg |
26.5 (67%) |
6.4 (30%) |
374§ (32%) |
Children (N=19) |
3-11 |
0.6-1.8 mg/kg |
44.2 (49%) |
5.5 (39%) |
217|| (67%) |
Patients with Severe Renal Impairment (N=12) (Creatinine clearance ≤ 10 mL/min) |
28-74 |
200 mg |
7.2 (48%) |
10.7 (29%) |
701 (21%) |
Patients with Severe Hepatic Impairment (N=3) |
42-52 |
150 mg |
8.8 (57%) |
11.0 (36%) |
410 (12%) |
CLapp: apparent clearance t½: terminal elimination
half-life ( ): coefficient of variation in %
*: mean values
†: analyzed by nonlinear mixed effect modeling with data pooled across dose
strengths
‡: sampling times did not allow calculation
§: results from adolescents (dose=1.8 mg/kg, N=3) the maximum dose exceeded 100
mg. When data from patients who received greater than 47 mg (N=9) are combined
and normalized to the 1.8 mg/kg dose with a cap of 100 mg, the mean Cmax was
229 ng/mL (51%).
| |: results from children (dose=1.8 mg/kg, N=7) |
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.
Table 2: Prevention of Chemotherapy-Induced Nausea and
Vomiting from Moderately Emetogenic Chemotherapy
Response Over 24 Hours |
ANZEMET Tablets |
25 mg
(N=78) |
50 mg
(N=83) |
100 mg†
(N=80) |
200 mg
(N=78) |
p-value for Linear Trend |
Complete Response‡ |
24 (31%) |
34 (41%) |
49 (61%) |
46 (59%) |
P < 0001 |
Nausea Score§ |
49 |
10 |
11 |
7 |
P=0006 |
†: The recommended dose
‡: No emetic episodes and no rescue medication.
§: Median 24-h change from baseline nausea score using visual analog scale
(VAS): Score range 0=“none” to 100=“nausea as bad as it could be.” |
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.