CLINICAL PHARMACOLOGY
Mechanism Of Action
Naldemedine is an opioid antagonist with binding
affinities for mu-, delta-, and kappa-opioid receptors. Naldemedine functions
as a peripherally-acting mu-opioid receptor antagonist in tissues such as the
gastrointestinal tract, thereby decreasing the constipating effects of opioids.
Naldemedine is a derivative of naltrexone to which a side
chain has been added that increases the molecular weight and the polar surface
area, thereby reducing its ability to cross the blood-brain barrier (BBB).
Naldemedine is also a substrate of the P-glycoprotein
(P-gp) efflux transporter. Based on these properties, the CNS penetration of
naldemedine is expected to be negligible at the recommended dose levels,
limiting the potential for interference with centrally-mediated opioid
analgesia.
Pharmacodynamics
Use of opioids induces slowing of gastrointestinal
motility and transit. Antagonism of gastrointestinal mu-opioid receptors by
naldemedine inhibits opioid-induced delay of gastrointestinal transit time.
Effect On Cardiac Repolarization
At a dose up to 5-times the recommended dose, SYMPROIC
does not prolong the QT interval to any clinically relevant extent.
Pharmacokinetics
Absorption
Following oral administration, naldemedine is absorbed
with the time to achieve peak concentrations (Tmax) of approximately 0.75 hours
in a fasted state. Across the range of doses evaluated, the maximum plasma
concentration (Cmax) and area under the plasma concentration-time curve (AUC)
increased in a dose-proportional or almost dose-proportional manner.
Accumulation was minimal following multiple daily doses of naldemedine.
Food Effect
A high-fat meal decreased the rate, but not the extent of
naldemedine absorption. The Cmax was decreased by approximately 35% and time to
achieve Cmax was delayed from 0.75 hours in the fasted state to 2.5 hours in
the fed state, whereas there was no meaningful change in the AUC in the fed
state [see DOSAGE AND ADMINISTRATION].
Distribution
Plasma protein binding of naldemedine in humans is 93% to
94%. The mean apparent volume of distribution during the terminal phase (Vz/F)
is 155 L.
Elimination
The terminal elimination half-life of naldemedine is 11
hours.
Metabolism
Naldemedine is primarily metabolized by CYP3A to
nor-naldemedine, with minor contribution from UGT1A3 to form naldemedine 3-G.
Nor-naldemedine and naldemedine 3-G have been shown to have antagonistic
activity for opioid receptors, with less potent effect than naldemedine.
Following oral administration of [14C]-labeled
naldemedine, the primary metabolite in plasma was nornaldemedine, with a
relative exposure compared to naldemedine of approximately 9% to 13%.
Naldemedine 3-G was a minor metabolite in plasma, with a relative exposure to
naldemedine of less than 3%.
Naldemedine also undergoes cleavage in the GI tract to
form benzamidine and naldemedine carboxylic acid.
Excretion
Following oral administration of [14C]-labeled
naldemedine, the total amount of radioactivity excreted in the urine and feces
was 57% and 35% of the administered dose of naldemedine, respectively. The
amount of naldemedine excreted unchanged in the urine was approximately 16% to
18% of the administered dose. Benzamidine was the most predominant metabolite
excreted in the urine and feces, representing approximately 32% and 20% of the
administered dose of naldemedine, respectively. The percentage of unchanged
drug in feces has not been estimated.
Use In Specific Populations
Age: Geriatric Population, Sex, Race/Ethnicity
A population pharmacokinetic analysis from clinical
studies with naldemedine did not identify a clinically meaningful effect of
age, sex, or race on the pharmacokinetics of naldemedine.
Renal Impairment
The pharmacokinetics of naldemedine after administration
of a 0.2 mg single oral dose of SYMPROIC was studied in 8 subjects with mild
(n=8, estimated glomerular filtration rate [eGFR] of 60 to 89 mL/min/1.73 m²),
moderate (n=8, eGFR 30 to 59 mL/min/1.73 m²), and severe (n=6, eGFR less than
30 mL/min/1.73 m²) renal impairment, and subjects with end-stage renal disease
(ESRD) requiring hemodialysis (n=8), and compared to healthy subjects with
normal renal function (n=8, estimated creatinine clearance of at least 90
mL/min). The pharmacokinetics of naldemedine between subjects in all groups
were similar.
Plasma concentrations of naldemedine in subjects with ESRD
requiring hemodialysis were similar when SYMPROIC was administered either
pre-or post-hemodialysis, indicating that naldemedine was not removed from the
blood by hemodialysis.
Hepatic Impairment
The effect of hepatic impairment on the pharmacokinetics
of a 0.2 mg single oral dose of SYMPROIC was studied in subjects with hepatic
impairment classified as mild (n=8, Child-Pugh Class A) or moderate (n=8,
Child-Pugh Class B) and compared with healthy subjects with normal hepatic
function (n=8). The pharmacokinetics of naldemedine between subjects in all
groups were similar.
The effect of severe hepatic impairment (Child-Pugh Class
C) on the pharmacokinetics of naldemedine was not evaluated [see Use In Specific
Populations].
Drug Interaction Studies
Effect Of Naldemedine On Other Drugs
In in vitro studies at clinically relevant
concentrations, naldemedine did not inhibit the major CYP enzymes (including
CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4/5, or
CYP4A11 isozymes) and is not an inhibitor of transporters (including OATP1B1,
OATP1B3, OCT1, OCT2, OAT1, OAT3, BCRP, or P-gp). Naldemedine did not cause
significant induction of CYP1A2, CYP2B6, CYP3A4, UGT1A2, UGT1A6, or UGT2B7
isozymes.
Effect Of Other Drugs On Naldemedine
Naldemedine is primarily metabolized by CYP3A4 enzyme
with minor contribution from UGT1A3. Naldemedine is a substrate of P-gp. The
effects of co-administered drugs on the pharmacokinetics of naldemedine are
summarized in Figure 1.
Figure 1: Effect of Co-Administered Drugs on the
Pharmacokinetics of Naldemedine
Efavirenz (moderate CYP3A inducer)
Simulation using physiologically-based pharmacokinetic
modeling suggested that concomitant use of efavirenz decreases exposure to
naldemedine by 43%. The clinical consequence of this decreased exposure is
unknown.
No drug interaction studies have been conducted for
SYMPROIC with drugs that alter gastric pH (e.g., antacids, proton-pump
inhibitors).
Clinical Studies
SYMPROIC was evaluated in two replicate, 12-week,
randomized, double-blind, placebo-controlled trials (Study 1 and Study 2) in
which SYMPROIC was used without laxatives in patients with OIC and chronic
non-cancer pain.
Patients receiving a stable opioid morphine equivalent
daily dose of at least 30 mg for at least 4 weeks before enrollment and
self-reported OIC were eligible for clinical trial participation.
Patients with evidence of significant structural
abnormalities of the GI tract were not enrolled in these trials.
In Studies 1 and 2, patients had to either be not using
laxatives or willing to discontinue laxative use at the time of screening and
willing to use only the provided rescue laxatives during the screening and
treatment periods.
In Studies 1 and 2, OIC was confirmed through a two-week
run in period and was defined as no more than 4 spontaneous bowel movements
(SBMs) total over 14 consecutive days and less than 3 SBMs in a given week with
at least 25% of the SBMs associated with one or more of the following
conditions: (1) straining; (2) hard or lumpy stools; (3) having a sensation of
incomplete evacuation; and (4) having a sensation of anorectal
obstruction/blockage.
An SBM was defined as a bowel movement (BM) without
rescue laxative taken within the past 24 hours. Patients with no BMs over the 7
consecutive days prior to and during the 2 week screening period or patients
who have never taken laxatives were excluded.
In the screening and treatment periods, bisacodyl was
used as rescue laxative if patients had not had a BM for 72 hours and were
allowed one-time use of an enema, if after 24 hours of taking bisacodyl they
still had not had a BM.
A total of 547 patients in Study 1 and 553 patients in
Study 2 were randomized in a 1:1 ratio to receive SYMPROIC 0.2 mg once daily or
placebo for 12 weeks. Study medication was administered without regard to
meals.
The mean age of subjects in Studies 1 and 2 was 54 years;
59% were women; and 80% were white. The most common types of pain in Studies 1
and 2 were back or neck pain (61%). The mean baseline number of SBMs was 1.3
and 1.2 per week for Studies 1 and 2, respectively.
Prior to enrollment, patients were using their current
opioid for a mean duration of approximately 5 years. A wide range of types of
opioids were used. The mean baseline opioid morphine equivalent daily dosage
was 132 mg and 121 mg per day for Studies 1 and 2, respectively.
The efficacy of SYMPROIC was assessed in Studies 1 and 2
using a responder analysis. A responder was defined as a patient who had at
least 3 SBMs per week and a change from baseline of at least 1 SBM per week for
at least 9 out of the 12 weeks and 3 out of the last 4 weeks in Studies 1 and
2.
The responder rates in Studies 1 and 2 are shown in Table 4.
Table 4: Efficacy Responder Rates in Studies 1 and 2
in Patients with OIC and Chronic Non-Cancer Pain
|
Study 1 |
Study 2 |
SYMPROIC 0.2 mg once daily
(N=273) |
Placebo
(N=272) |
Treatment Difference [95% CI] |
SYMPROIC 0.2 mg once daily
(N=276) |
Placebo
(N=274) |
Treatment Difference [95% Cl] |
Responder# |
130 (48%) |
94 (35%) |
13% [5%, 21%] |
145 (53%) |
92 (34%) |
19% [11%, 27%] |
p value* |
|
|
0.0020 |
|
|
<0.0001 |
#The primary endpoint was defined as a patient who had at
least 3 SBMs per week and a change from baseline of at least 1 SBM per week for
at least 9 out of the 12 study weeks and 3 out of the last 4 weeks.
CI=Confidence Interval
*Cochran-Mantel-Haenszel test adjusted for opioid dose strata (30 to 100 mg;
greater than 100 mg) |
In Studies 1 and 2, the mean increase in frequency of
SBMs per week from baseline to the last 2 weeks of the 12-week treatment period
was 3.1 for SYMPROIC vs. 2.0 for placebo (difference 1.0, 95% CI 0.6, 1.5), and
3.3 for SYMPROIC vs. 2.1 for placebo (difference 1.2, 95% CI 0.8, 1.7),
respectively.
During week 1 of the treatment period, the mean increase
in frequency of SBMs per week from baseline was 3.3 for SYMPROIC vs. 1.3 for
placebo (difference 2.0, 95% CI 1.5, 2.5) in Study 1 and 3.7 for SYMPROIC vs. 1.6
for placebo (difference 2.1, 95% CI 1.5, 2.6) in Study 2.
The mean increase in the frequency of complete SBM (CSBM)
per week from baseline to the last 2 weeks of 12-week treatment period was 2.3
for SYMPROIC vs. 1.5 for placebo (difference 0.8, 95% CI 0.4, 1.2) in Study 1
and 2.6 for SYMPROIC vs. 1.6 for placebo (difference 1.1, 95% CI 0.6, 1.5) in
Study 2. A CSBM was defined as a SBM that was associated with a sense of
complete evacuation.
The change in the frequency of SBMs without straining per
week from baseline to the last 2 weeks of the treatment period was 1.3 for
SYMPROIC vs. 0.7 for placebo (difference 0.6, 95% CI 0.2, 0.9) in Study 1 and 1.8
for SYMPROIC vs. 1.1 for placebo (difference 0.7, 95% CI 0.3, 1.2) in Study 2.