CLINICAL PHARMACOLOGY
Mechanism Of Action
Renvela contains sevelamer
carbonate, a non-absorbed phosphate binding crosslinked polymer, free of metal
and calcium. It contains multiple amines separated by one carbon from the
polymer backbone. These amines exist in a protonated form in the intestine and
interact with phosphate molecules through ionic and hydrogen bonding. By
binding phosphate in the gastrointestinal tract and decreasing absorption,
sevelamer carbonate lowers the phosphate concentration in the serum (serum
phosphorus).
Pharmacodynamics
In addition to effects on serum phosphorus levels,
sevelamer hydrochloride has been shown to bind bile acids in vitro and in vivo in
experimental animal models. Because sevelamer binds bile acids, it may
interfere with normal fat absorption and thus may reduce absorption of fat
soluble vitamins such as A, D and K. In clinical trials of sevelamer
hydrochloride, both the mean total and LDL cholesterol declined by 15-31%; the
clinical significance of this finding, which was observed after 2 weeks, is
unclear. Triglycerides, HDL cholesterol and albumin did not change.
Pharmacokinetics
A mass balance study using 14C-sevelamer
hydrochloride, in 16 healthy male and female volunteers showed that sevelamer
hydrochloride is not systemically absorbed. No absorption studies have been
performed in patients with renal disease.
Drug Interactions
In vivo
Sevelamer carbonate has been studied in human drug-drug
interaction studies (9.6 grams once daily with a meal) with warfarin and digoxin.
Sevelamer hydrochloride, which contains the same active moiety as sevelamer
carbonate, has been studied in human drug-drug interaction studies (2.4-2.8
grams single dose or three times daily with meals or two times daily without
meals) with ciprofloxacin, digoxin, enalapril, iron, metoprolol, mycophenolate
mofetil and warfarin.
Co-administered single dose of 2.8 grams of sevelamer
hydrochloride in fasted state decreased the bioavailability of ciprofloxacin by
approximately 50% in healthy subjects.
Concomitant administration of sevelamer and mycophenolate
mofetil in adult and pediatric patients decreased the mean MPA Cmax and AUC0-12h
by 36% and 26% respectively.
Sevelamer carbonate or sevelamer hydrochloride did not
alter the pharmacokinetics of enalapril, digoxin, iron, metoprolol and warfarin
when co-administered.
During postmarketing experience, cases of increased
thyroid stimulating hormone (TSH) levels have been reported in patients
co-administered sevelamer hydrochloride and levothyroxine. Reduction in
concentrations of cyclosporine and tacrolimus leading to dose increases has
also been reported in transplant patients when co-administered with sevelamer
hydrochloride without any clinical consequences (for example, graft rejection).
The possibility of an interaction cannot be excluded with these drugs.
Clinical Studies
The ability of sevelamer to control serum phosphorus in
CKD patients on dialysis was predominantly determined from the effects of the
hydrochloride salt to bind phosphate. Six clinical trials used sevelamer
hydrochloride and three clinical trials used sevelamer carbonate. The sevelamer
hydrochloride studies include one double-blind, placebo-controlled 2-week study
(sevelamer N=24); two open-label, uncontrolled, 8-week studies (sevelamer
N=220) and three active-controlled open-label studies with treatment durations
of 8 to 52 weeks (sevelamer N=256). The sevelamer carbonate studies include one
double-blind, active-controlled, crossover study with two 8-week treatment
periods using sevelamer carbonate tablets (N=79), one open-label,
active-controlled, cross-over study with two 4-week treatment periods using
sevelamer carbonate powder (N=31) and one randomized, parallel, open-label
study using sevelamer carbonate powder (N=144) dosed once daily or sevelamer
hydrochloride tablets (N=73) dosed three times daily for 24 weeks. Six of the
active-controlled studies are described here (three sevelamer carbonate and
three sevelamer hydrochloride studies).
Cross-Over Study Of Sevelamer Carbonate (Renvela®) 800 mg
Tablets And Sevelamer Hydrochloride (Renagel®) 800 mg Tablets
Stage 5 CKD patients on hemodialysis were entered into a
five-week sevelamer hydrochloride run-in period and 79 patients received, in
random order, sevelamer carbonate 800 mg tablets and sevelamer hydrochloride
800 mg tablets for eight weeks each, with no intervening washout. Study dose
during the cross-over period was determined based on the sevelamer
hydrochloride dose during the run-in period on a gram per gram basis. The
phosphorus levels at the end of each of the two cross-over periods were
similar. Average actual daily dose was 6 g/day divided among meals for both
treatments. Thirty-nine of those completing the cross-over portion of the study
were entered into a two-week washout period during which patients were
instructed not to take any phosphate binders; this confirmed the activity of
sevelamer in this study.
Cross-Over Study Of Sevelamer Carbonate (Renvela®) Powder
And Sevelamer Hydrochloride (Renagel®) Tablets
Stage 5 CKD patients on hemodialysis were entered into a
four-week sevelamer hydrochloride run-in period and 31 patients received, in
random order, sevelamer carbonate powder and sevelamer hydrochloride tablets
for four weeks each with no intervening washout. Study dose during the
cross-over period was determined based on the sevelamer hydrochloride dose
during the run-in period on a gram per gram basis. The phosphorus levels at the
end of each of the two cross-over periods were similar. Average actual daily
dose was 6.0 g/day divided among meals for sevelamer carbonate powder and 6.4
g/day divided among meals for sevelamer hydrochloride tablets.
Clinical Study Of Sevelamer Carbonate (Renvela®) Powder And
Tablets In Pediatric Patients
A clinical study with sevelamer carbonate was conducted
in 101 patients 6 to 18 years of age with chronic kidney disease. This study
included a washout period for patients on a phosphate binder, a 2-week,
double-blind, Fixed Dose Period (FDP) in which patients were randomized to sevelamer
carbonate (n=50) or placebo (n=51), and a 26-week, open-label, sevelamer
carbonate Dose Titration Period (DTP). Most patients were 13 to 18 years of age
(73%) and had a BSA ≥ 1.2 m² (84%). Approximately 78% of patients were CKD
patients on dialysis.
Sevelamer carbonate significantly reduced serum
phosphorus through Week 2 (primary endpoint) by an LS Mean difference of -0.90
(SE 0.27) mg/dL compared to placebo (p=0.001). A similar treatment response was
observed in patients who received sevelamer carbonate during the 6-month
open-label DTP. Approximately 30% of subjects reached their target serum
phosphorus. The median prescribed daily dose was approximately 7.0 g per day
during the titration period.
The results of the primary efficacy endpoint were consistent
by BSA subgroup. In contrast, a treatment effect was not observed in subjects
with a baseline serum phosphorus below 7 mg/dL, many of whom were the subjects
6 to < 13 years of age or the subjects not on dialysis (Figure 2).
Figure 2: Change in serum phosphorus (mg/dL) from
baseline to Week 2 by subgroup
Sevelamer Hydrochloride Versus
Active-Control, Cross-Over Study In Hemodialysis Patients
Eighty-four CKD patients on
hemodialysis who were hyperphosphatemic (serum phosphorus > 6.0 mg/dL)
following a two-week phosphate binder washout period were randomized in a
crossover design to receive in random order sevelamer hydrochloride and
active-control for eight weeks each. Treatment periods were separated by a
two-week phosphate binder washout period. Patients started on treatment three
times per day with meals. Over each eight-week treatment period, at three
separate time points the dose of sevelamer hydrochloride could be titrated up
to control serum phosphorus, the dose of active-control could also be altered
to attain phosphorus control. Both treatments significantly decreased mean
serum phosphorus by about 2 mg/dL (Table 6).
Table 6: Mean Serum Phosphorus (mg/dL) at Baseline and
Endpoint
|
Sevelamer Hydrochloride
(N=81) |
Active Control
(N=83) |
Baseline at End of Washout |
8.4 |
8.0 |
Endpoint |
6.4 |
5.9 |
Change from Baseline at Endpoint (95% Confidence Interval) |
-2.0* (-2.5, -1.5) |
-2.1* (-2.6, -1.7) |
*p < 0.0001, within treatment
group comparison |
The distribution of responses
is shown in Figure 3. The distributions are similar for sevelamer hydrochloride
and active control. The median response is a reduction of about 2 mg/dL in both
groups. About 50% of subjects have reductions between 1 and 3 mg/dL.
Figure 3: Percentage of
patients (Y-axis) attaining a phosphorus reduction from baseline (mg/dL) at
least as great as the value of the X-axis.
Average daily sevelamer
hydrochloride dose at the end of treatment was 4.9 g (range of 0.0 to 12.6 g).
Sevelamer Hydrochloride Versus
Active-Control In Hemodialysis Patients
Two hundred CKD patients on
hemodialysis who were hyperphosphatemic (serum phosphorus > 5.5 mg/dL)
following a two-week phosphate binder washout period were randomized to receive
sevelamer hydrochloride 800 mg tablets (N=99) or an active-control (N=101). At
week 52, using last-observation-carried-forward, sevelamer and active-control
both significantly decreased mean serum phosphorus (Table 7).
Table 7: Mean Serum Phosphorus (mg/dL) and Ion Product
at Baseline and Change from Baseline to End of Treatment
|
Sevelamer HCl
(N=94) |
Active-Control
(N=98) |
Phosphorus |
Baseline |
7.5 |
7.3 |
Change from Baseline at |
Endpoint |
-2.1 |
-1.8 |
Ca x Phosphorus Ion Product |
Baseline |
70.5 |
68.4 |
Change from Baseline at |
Endpoint |
-19.4 |
-14.2 |
Sixty-one percent of sevelamer
hydrochloride patients and 73% of the control patients completed the full 52
weeks of treatment.
Figure 4, a plot of the
phosphorus change from baseline for the completers, illustrates the durability
of response for patients who are able to remain on treatment.
Figure 4: Mean Phosphorus
Change from Baseline for Patients who Completed 52 Weeks of Treatment
Average daily sevelamer
hydrochloride dose at the end of treatment was 6.5 g (range of 0.8 to 13 g).
Sevelamer Hydrochloride Versus
Active-Control In Peritoneal Dialysis Patients
One hundred and forty-three
patients on peritoneal dialysis who were hyperphosphatemic (serum phosphorus
> 5.5 mg/dL) following a two-week phosphate binder washout period were
randomized to receive sevelamer hydrochloride (N=97) or active-control (N=46)
open label for 12 weeks. Average daily sevelamer hydrochloride dose at the end
of treatment was 5.9 g (range 0.8 to 14.3 g). Thirteen patients (14%) in
the sevelamer group and 9 patients (20%) in the active-control group
discontinued, mostly for gastrointestinal adverse reactions. There were
statistically significant changes in serum phosphorus (p < 0.001) for
sevelamer hydrochloride (1.6 mg/dL from baseline of 7.5 mg/dL), similar to the
active-control.
Once A Day Versus Three Times A
Day Dosing
Stage 5 CKD patients on
hemodialysis with a serum phosphate level of > 5.5 mg/dl after washout from
baseline therapies were randomized in a 2:1 ratio to receive either sevelamer
carbonate powder once-daily (N=144) or sevelamer hydrochloride as a tablet with
the dose divided three times per day (N=73) for 24 weeks. The initial dose for
the two groups was 4.8 g/day. At the end of the study, the total daily dose was
6.2 g/day of sevelamer carbonate powder once daily and 6.7 g/day of sevelamer
hydrochloride tablets three times per day. A greater percentage of subjects on
the once daily dose than three times per day regimen discontinued therapy
prematurely, 35% versus 15%. The reasons for discontinuation were largely
driven by adverse events and withdrawal of consent in the once daily dosing
regimen. Serum phosphate levels and calcium-phosphate product were better
controlled on the three times per day regimen than on the once daily regimen.
Mean serum phosphorus decreased 2.0 mg/dL for sevelamer carbonate powder once
daily and 2.9 mg/dL for sevelamer hydrochloride tablets three times per day.