CLINICAL PHARMACOLOGY
Mechanism Of Action
Telotristat, the active metabolite of telotristat ethyl,
is an inhibitor of tryptophan hydroxylase, which mediates the rate limiting
step in serotonin biosynthesis. The in vitro inhibitory potency of telotristat
towards tryptophan hydroxylase is 29 times higher than that of telotristat
ethyl. Serotonin plays a role in mediating secretion, motility, inflammation,
and sensation of the gastrointestinal tract, and is over-produced in patients
with carcinoid syndrome. Through inhibition of tryptophan hydroxylase,
telotristat and telotristat ethyl reduce the production of peripheral
serotonin, and the frequency of carcinoid syndrome diarrhea.
Pharmacodynamics
In healthy subjects, telotristat ethyl 500 mg three times
daily (twice the recommended dosage) for 14 days decreased whole blood
serotonin and 24-hour urinary 5-hydroxyindolacetic acid (u5- HIAA) from
baseline. A decrease in 24-hour u5-HIAA was observed as early as after 5 days
of treatment.
In patients with metastatic neuroendocrine tumors and
carcinoid syndrome diarrhea, 24-hour u5- HIAA decreased from baseline following
6 and 12 weeks of treatment with Xermelo 250 mg three times a day, whereas
placebo did not decrease u5-HIAA.
Cardiac Electrophysiology
At a dose 6 times the recommended dose of 250 mg, Xermelo
does not prolong the QT interval to any clinically relevant extent.
Pharmacokinetics
Absorption
After a single oral dose of telotristat ethyl to healthy
subjects, telotristat ethyl was absorbed and metabolized to its active
metabolite, telotristat. Peak plasma concentrations of telotristat ethyl were
achieved within 0.5 to 2 hours, and those of telotristat within 1 to 3 hours.
Plasma concentrations thereafter declined in a biphasic manner. Following
administration of a single 500 mg dose of telotristat ethyl (twice the
recommended dosage) under fasted conditions in healthy subjects, the mean Cmax and
AUC0-inf were 4.4 ng/mL and 6.23 ng•hr/mL, respectively for telotristat ethyl.
The mean Cmax and AUC0-inf were 610 ng/mL and 2320 ng•hr/mL, respectively for
telotristat. Peak plasma concentrations and AUC of telotristat ethyl and telotristat
appeared to be dose proportional following administration of a single dose of
telotristat ethyl in the range of 100 mg (0.4 times the lowest recommended dose
to 1000 mg [4 times the highest recommended dose]) under fasted conditions.
Following multiple-dose administration of telotristat
ethyl 500 mg three times daily, there was negligible accumulation at steady
state for both telotristat ethyl and telotristat.
In patients with metastatic neuroendocrine tumors and
carcinoid syndrome diarrhea treated with SSA therapy, the median Tmax for
telotristat ethyl and telotristat was approximately 1 and 2 hours,
respectively. Following administration of 500 mg telotristat ethyl three times
daily, with meals in patients, the mean Cmax and AUC0-6hr were approximately 7
ng/mL and 22 ng•hr/mL, respectively, for telotristat ethyl. The mean Cmax and
AUC0-6hr were approximately 900 ng/mL and 3000 ng•hr/mL, respectively for
telotristat. The pharmacokinetic parameters for both telotristat ethyl and
telotristat were highly variable with about 55% coefficient of variation.
Food Effect
Administration of a single 500 mg dose of Xermelo (twice
the recommended dose) with food resulted in higher exposure to both telotristat
ethyl and telotristat. The systemic exposure to telotristat ethyl, was
significantly increased following administration with a high-fat meal, with Cmax,
and AUC0-inf being 112%, and 264% higher, respectively compared to the fasted
state. Following administration of a single 500 mg dose of telotristat ethyl
under the fed conditions in healthy subjects, the mean Cmax and AUC0-inf were
10.5 ng/mL and 21.6 ng•hr/mL, respectively for telotristat ethyl. The Cmax and
AUC0-inf values for telotristat were also increased by 47% and 33%,
respectively, with a high-fat meal compared to the fasted state. The mean Cmax and
AUC0-inf were 908 ng/mL and 2980 ng•hr/mL, respectively for telotristat under
the fed condition. [see DOSAGE AND ADMINISTRATION].
Distribution
Both telotristat ethyl and telotristat are greater than
99% bound to human plasma proteins.
In vitro data suggests that telotristat is a substrate of
P-glycoprotein.
Elimination
Following a single 500 mg oral dose of telotristat ethyl
in healthy subjects, the apparent half-life was approximately 0.6 hours for
telotristat ethyl and 5 hours for telotristat. The apparent total clearance at
steady state (CL/Fss) following oral dosing with telotristat ethyl 500 mg three
times daily for 14 days (twice the recommended dosage) in healthy subjects was
2.7 and 152 L/hr for telotristat ethyl and telotristat, respectively.
Metabolism
After oral administration, telotristat ethyl undergoes
hydrolysis via carboxylesterases to telotristat, its active metabolite.
Telotristat is further metabolized. Among the metabolites of telotristat, the
systemic exposure to an acid metabolite of oxidative deaminated decarboxylated telotristat
was about 35% of that of telotristat. In vitro data suggest that telotristat
ethyl and telotristat are not substrates for CYP enzymes.
Excretion
Following a single 500 mg oral dose of 14C-telotristat
ethyl, 93.2% of the dose was recovered over 240 hours: 92.8% was recovered in
the feces, with less than 0.4% being recovered in the urine.
Specific Populations
Age and Sex
Population pharmacokinetic analysis indicated that age
(18 to 83 years) and sex do not affect the pharmacokinetics of telotristat.
Renal Impairment
Population pharmacokinetic analysis indicated that
creatinine clearance (20 to 89 mL/min) does not affect the pharmacokinetics of
telotristat. Xermelo was not studied in end-stage renal disease (ESRD) patients
who require dialysis.
Hepatic Impairment
Population pharmacokinetic analysis indicated that mild
hepatic impairment (defined as total bilirubin greater than 1 to 1.5 times the
upper limit of normal [ULN] or AST greater than the ULN) does not affect the
pharmacokinetics of telotristat. The effect of moderate or severe hepatic
impairment (defined as total bilirubin greater than 1.5 times the ULN and any
value for AST) is unknown.
Drug Interaction Studies
Effect of Telotristat Ethyl on Other Drugs
In Vitro Studies
The potential for telotristat ethyl and telotristat to
induce CYP enzymes (1A2 and 2B6) or inhibit CYP enzymes (2B6, 2C8, and 2C9) has
not been adequately studied in vitro.
In vitro telotristat ethyl inhibited P-glycoprotein
(P-gp) and breast cancer resistance protein (BCRP), but telotristat did not
inhibit P-gp and BCRP at the clinically relevant concentrations. However, in
vivo drug interaction potential via inhibition of BCRP is low based on in vitro
studies and in vivo findings.
Based on in vitro studies, in vivo drug interaction
potential via inhibition of organic cation transporter 1 (OCT1), OCT2, organic
anion transporter 1 (OAT1), OAT3, organic anion transporting polypeptide 1B1
(OATP1B1), OATP1B3, or bile salt export pump (BSEP) transporters by telotristat
ethyl and telotristat is low at the recommended dosage.
Midazolam (sensitive CYP3A4 substrate)
Following administration of multiple doses of telotristat
ethyl, the systemic exposure to concomitant midazolam was significantly
decreased. When 3 mg midazolam was coadministered orally after 5 day treatment
with telotristat ethyl 500 mg three times daily (twice the recommended dosage),
the mean Cmax, and AUC0-inf for midazolam were decreased by 25%, and 48%,
respectively, compared to administration of midazolam alone. The mean Cmax, and
AUC0-inf for the active metabolite, 1'-hydroxymidazolam, were also decreased by
34%, and 48%, respectively. The reduction in the systemic exposure to both midazolam
and its active metabolite suggests that the glucuronidation of
1'-hydroxymidazolam may have been increased by telotristat ethyl [see DRUG
INTERACTIONS].
Fexofenadine (sensitive P-gp substrate)
The Cmax and AUC of fexofenadine increased by 16% when a
single 180 mg dose of fexofenadine was co-administered orally with the final
dose of telotristat ethyl 500 mg administered three times daily (twice the
recommended dosage) for 5 days. Clinically meaningful interactions with P-gp
substrates are unlikely.
Effect of Other Drugs on Telotristat Ethyl
Short-Acting Octreotide
The mean Cmax and AUC0-last of telotristat ethyl were
decreased by 86% and 81%, respectively, following administration of a single
500 mg dose of Xermelo (twice the recommended dose), coadministered with
short-acting octreotide 200 mcg injected subcutaneously in healthy subjects. The
mean Cmax and AUC0-last of telotristat were decreased by 79% and 68%,
respectively [see Clinical Studies].
Clinical Studies
A 12-week double-blind, placebo-controlled, randomized,
multicenter trial of Xermelo was conducted in adult patients with a
well-differentiated metastatic neuroendocrine tumor and carcinoid syndrome
diarrhea who were having between 4 to 12 daily bowel movements despite the use
of SSA therapy at a stable dose for at least 3 months. Patients were randomized
to placebo or treatment with Xermelo 250 mg three times daily.
Study medication was administered within 15 minutes
before or within 1 hour after a meal or snack [see DOSAGE AND ADMINISTRATION].
All patients were required to stay on their baseline SSA regimen and were
allowed to use rescue medication (short-acting octreotide) and antidiarrheals
(e.g., loperamide) for symptomatic relief. A total of 90 patients were
evaluated for efficacy. The mean age of the population was 63 years of age
(range 37 to 83 years), 50% were male, and 90% were White.
The primary efficacy endpoint was the change from
baseline in the number of daily bowel movements averaged over the 12-week
treatment period. The analysis results can be found in Table 2 below. The
average was based on the number of days with valid, non-missing data. When a
patient had more than 6 weeks of missing data, the change from baseline was
considered equal to zero. A week of missing data was defined as a patient
missing at least 4 days of diary data in that week.
Table 2: Change from Baseline in Bowel Movements/Day
Averaged Over 12 Weeks in Adult Patients with Carcinoid Syndrome Diarrhea
|
Parameter |
Xermelo 250 mg three times daily |
Placebo |
Bowel |
Number of Patients |
45 |
45 |
Movements/Day |
Baseline Mean (SD) |
6.1 (2.1) |
5.2 (1.4) |
At Baselinea |
Median (Min, Max) |
5.5 (3.5, 13.0) |
5.1 (3.5, 9.0) |
Change From Baseline In Bowel Movements/Day |
Change Averaged over 12 |
|
|
Weeks: Mean (SD) |
-1.4 (1.4) |
-0.6 (0.8) |
Median (Min, Max) |
-1.3 (-6.1, 1.6) |
-0.6 (-2.7,0.8) |
Averaged Over 12 Weeks |
Estimate of Treatment Difference (97.5% CL)b |
-0.8c (-1.3, -0.3) |
— |
CL=confidence limit; SD=standard deviation.
a Baseline Bowel Movements/Day was assessed over the 3-4 week
screening/run-in period.
b Statistical tests used a blocked 2-sample Wilcoxon Rank Sum
statistic (van Elteren test) stratified by the u5-HIAA stratification at
randomization. CLs were based on the Hodges- Lehmann estimator of the median
paired difference.
c p < 0.001 |
In the 12-week study, a difference in average weekly
reductions in bowel movement frequency between Xermelo and placebo was observed
as early as 1 to 3 weeks, and persisted for the remaining 9 weeks of the study.
To aid in the interpretation of the bowel movement
reduction results, the proportion of patients reporting any particular level of
reduction in overall average bowel movement frequency is depicted in Figure 1
below. For example, 33% of patients randomized to Xermelo and 4% of patients
randomized to placebo experienced a reduction in overall average bowel
movements from baseline of at least 2 bowel movements per day.
Figure 1: Cumulative Proportion of Patients with
Carcinoid Syndrome Diarrhea Reporting Change in Overall Average Bowel Movement
Frequency
Other symptoms of carcinoid syndrome (abdominal pain or
flushing) did not show improvement in the comparison of Xermelo to placebo.
The average number of daily short-acting octreotide
injections used for rescue therapy over the 12-week double-blind treatment
period was 0.3 and 0.7 in the Xermelo and placebo groups, respectively. In the
subgroup of patients who received short-acting octreotide injections, observed
reductions in the number of bowel movements per day and treatment differences
were generally consistent with the reductions and differences observed in
patients who did not receive rescue therapy, and were similar to the overall
data presented in Table 2 above [see DOSAGE AND ADMINISTRATION, DRUG
INTERACTIONS].
A third randomized treatment arm of Xermelo 500 mg three
times daily did not demonstrate additional treatment benefit on the primary
endpoint and had a greater incidence of adverse reactions than Xermelo 250 mg
three times daily. Therefore, Xermelo 500 mg three times daily is not
recommended [see DOSAGE AND ADMINISTRATION].