CLINICAL PHARMACOLOGY
Mechanism Of Action
Pantoprazole is a proton pump
inhibitor (PPI) that suppresses the final step in gastric acid production by
covalently binding to the (H+, K+)-ATPase enzyme system
at the secretory surface of the gastric parietal cell. This effect leads to
inhibition of both basal and stimulated gastric acid secretion irrespective of
the stimulus. The binding to the (H+, K+)-ATPase results
in a duration of antisecretory effect that persists longer than 24 hours for
all doses tested (20 mg to 120 mg).
Pharmacodynamics
Antisecretory Activity
The magnitude and time course
for inhibition of pentagastrin-stimulated acid output (PSAO) by single doses
(20 to 120 mg) of PROTONIX I.V. for Injection were assessed in a single-dose,
open-label, placebo-controlled, dose-response study. The results of this study
are shown in Table 2. Healthy subjects received a continuous infusion for 25
hours of pentagastrin (PG) at 1 mcg/kg/h, a dose known to produce submaximal
gastric acid secretion. The placebo group showed a sustained, continuous acid
output for 25 hours, validating the reliability of the testing model. PROTONIX
I.V. for Injection had an onset of antisecretory activity within 15 to 30
minutes of administration. Doses of 20 to 80 mg of PROTONIX I.V. for Injection
substantially reduced the 24-hour cumulative PSAO in a dose-dependent manner,
despite a short plasma elimination half-life. Complete suppression of
PSAO was achieved with 80 mg within approximately 2 hours and no further
significant suppression was seen with 120 mg. The duration of action of
PROTONIX I.V. for Injection was 24 hours.
Table 2: Gastric Acid Output (mEq/hr, Mean ± SD) and
Percent Inhibitiona(Mean ± SD) of Pentagastrin-Stimulated Acid
Output Over 24 Hours Following a Single Dose of PROTONIX I.V. for Injectionb
in Healthy Subjects
Treatment Dose |
2 hours- |
4 hours- |
12 hours- |
24 hours- |
Acid Output |
% Inhibition |
Acid Output |
% Inhibition |
Acid Output |
% Inhibition |
Acid Output |
% Inhibition |
0 mg (Placebo, n=4) |
39 ±21 |
NA |
26 ±14 |
NA |
32 ±20 |
NA |
38 ±24 |
NA |
20mg (n=4-6) |
13 ±18 |
47 ± 27 |
6 ± 8 |
83 ± 21 |
20 ±20 |
54 ± 44 |
30 ±23 |
45 ± 43 |
40 mg (n=8) |
5 ± 5 |
82 ± 11 |
4 ± 4 |
90 ± 11 |
11 ±10 |
81 ± 13 |
16 ±12 |
52 ± 36 |
80 mg (n=8) |
0.1 ±0.2 |
96 ± 6 |
0.3 ±0.4 |
99 ± 1 |
2 ± 2 |
90 ± 7 |
7 ± 4 |
63 ± 18 |
a Compared to individual subject baseline prior to treatment
with PROTONIX I.V. for Injection. NA = not applicable.
b Inhibition of gastric acid output and the percent inhibition of
stimulated acid output in response to PROTONIX I.V. for Injection may be higher
after repeated doses. |
In one study of gastric pH in
healthy subjects, pantoprazole was administered orally (40 mg enteric coated
tablets) or intravenously (40 mg) once daily for 5 days and pH was measured for
24 hours following the fifth dose. The outcome measure was median percent of
time that pH was ≥ 4 and the results were similar for intravenous and
oral medications; however, the clinical significance of this parameter is
unknown.
Serum Gastrin Effects
Serum gastrin concentrations
were assessed in two placebo-controlled studies.
In a 5-day study of oral
pantoprazole with 40 and 60 mg doses in healthy subjects, following the last
dose on day 5, median 24-hour serum gastrin concentrations were elevated by 3-4
fold compared to placebo in both 40 and 60 mg dose groups. However, by 24 hours
following the last dose, median serum gastrin concentrations for both groups
returned to normal levels.
In another placebo-controlled, 7-day
study of 40 mg intravenous or oral pantoprazole in patients with GERD and a
history of erosive esophagitis, the mean serum gastrin concentration increased
approximately 50% from baseline and as compared with placebo, but remained
within the normal range.
During 6 days of repeated administration of PROTONIX I.V.
for Injection in patients with Zollinger-Ellison Syndrome, consistent changes
of serum gastrin concentrations from baseline were not observed.
Enterochromaffin-Like (ECL) Cell Effects
There are no data available on the effects of intravenous
pantoprazole on ECL cells.
In a nonclinical study in Sprague-Dawley rats, lifetime
exposure (24 months) to pantoprazole at doses of 0.5 to 200 mg/kg/day resulted
in dose-related increases in gastric ECL-cell proliferation and gastric
neuroendocrine (NE)-cell tumors. Gastric NE-cell tumors in rats may result from
chronic elevation of serum gastrin concentrations. The high density of ECL
cells in the rat stomach makes this species highly susceptible to the
proliferative effects of elevated gastrin concentrations produced by proton
pump inhibitors. However, there were no observed elevations in serum gastrin
following the administration of pantoprazole at a dose of 0.5 mg/kg/day. In a
separate study, a gastric NE-cell tumor without concomitant ECL-cell
proliferative changes was observed in 1 female rat following 12 months of
dosing with pantoprazole at 5 mg/kg/day and a 9 month off-dose recovery [see Nonclinical Toxicology].
Pharmacokinetics
Pantoprazole peak serum concentration (Cmax) and area
under the serum concentration-time curve (AUC) increase in a manner
proportional to intravenous doses from 10 mg to 80 mg. Pantoprazole does not
accumulate and its pharmacokinetics are unaltered with multiple daily dosing.
Following the administration of PROTONIX I.V. for Injection, the serum
concentration of pantoprazole declines biexponentially with a terminal
elimination half-life of approximately one hour. In CYP2C19 extensive metabolizers
[see CLINICAL PHARMACOLOGY] with normal liver function receiving a 40 mg
dose of PROTONIX I.V. for Injection by constant rate over 15 minutes, the peak
concentration (Cmax) is 5.52 ±1.42 mcg/mL and the total area under the plasma
concentration versus time curve (AUC) is5.4 ±1.5 mcg• hr/mL. The total
clearance is 7.6-14.0 L/h.
Distribution
The apparent volume of distribution of pantoprazole is
approximately 11.0-23.6 L, distributing mainly in extracellular fluid. The
serum protein binding of pantoprazole is about 98%, primarily to albumin.
Metabolism
Pantoprazole is extensively metabolized in the liver
through the cytochrome P450 (CYP) system. Pantoprazole metabolism is
independent of the route of administration (intravenous or oral). The main
metabolic pathway is demethylation, by CYP2C19, with subsequent sulfation;
other metabolic pathways include oxidation by CYP3A4. There is no evidence that
any of the pantoprazole metabolites have significant pharmacologic activity.
CYP2C19 displays a known genetic polymorphism due to its deficiency in some
sub-populations (e.g., 3% of Caucasians and African-Americans and 17-23% of
Asians). Although these sub-populations of slow pantoprazole metabolizers have
elimination half-life values from 3.5 to 10.0 hours, they still have minimal
accumulation ( ≤ 23%) with once daily dosing.
Excretion
After administration of a single intravenous dose of 14C-labeled
pantoprazole to healthy, extensive CYP2C19 metabolizers, approximately 71% of
the dose was excreted in the urine with 18% excreted in the feces through
biliary excretion. There was no renal excretion of unchanged pantoprazole.
Geriatric
After repeated I.V. administration in elderly subjects
(65 to 76 years of age), pantoprazole AUC and elimination half-life values were
similar to those observed in younger subjects. No dosage adjustment is
recommended for elderly patients.
Gender
After oral administration there is a modest increase in
pantoprazole AUC and Cmax in women compared to men. However, weight-normalized
clearance values are similar in women and men. No dosage adjustment is
warranted based on gender.
Renal Impairment
In patients with severe renal impairment, pharmacokinetic
parameters for pantoprazole were similar to those of healthy subjects. No
dosage adjustment is necessary in patients with renal impairment or in patients
undergoing hemodialysis.
Hepatic Impairment
In patients with mild to severe hepatic impairment
(Child-Pugh A to C cirrhosis), maximum pantoprazole concentrations increased
only slightly (1.5-fold) relative to healthy subjects when pantoprazole was administered
orally. Although serum half-life values increased to 7-9 hours and AUC values
increased by 5- to 7-fold in hepatic-impaired patients, these increases were no
greater than those observed in CYP2C19 poor metabolizers, where no dosage
adjustment is warranted. These pharmacokinetic changes in hepatic-impaired
patients result in minimal drug accumulation following once-daily,
multiple-dose administration. No dosage adjustment is needed in patients with
mild to severe hepatic impairment. Doses higher than 40 mg/day have not been
studied in hepatically impaired patients.
Drug-Drug Interactions
Pantoprazole is metabolized mainly by CYP2C19 and to
minor extents by CYPs 3A4, 2D6 and 2C9. In in vivo drug-drug interaction
studies with CYP2C19 substrates (diazepam [also a CYP3A4 substrate] and
phenytoin [also a CYP3A4 inducer]), nifedipine, midazolam, and clarithromycin
(CYP3A4 substrates), metoprolol (a CYP2D6 substrate), diclofenac, naproxen and
piroxicam (CYP2C9 substrates) and theophylline (a CYP1A2 substrate) in healthy
subjects, the pharmacokinetics of pantoprazole were not significantly altered.
Clopidogrel is metabolized to its active metabolite in
part by CYP2C19. In a crossover clinical study, 66 healthy subjects were
administered clopidogrel (300 mg loading dose followed by 75 mg per day) alone
and with pantoprazole (80 mg at the same time as clopidogrel) for 5 days. On
Day 5, the mean AUC of the active metabolite of clopidogrel was reduced by approximately
14% (geometric mean ratio was 86%, with 90% CI of 79 to 93%) when pantoprazole
was coadministered with clopidogrel as compared to clopidogrel administered
alone. Pharmacodynamic parameters were also measured and demonstrated that the
change in inhibition of platelet aggregation (induced by 5 μM ADP) was
correlated with the change in the exposure to clopidogrel active metabolite.
The clinical significance of this finding is not clear.
In vivo studies also suggest that pantoprazole does not
significantly affect the kinetics of other drugs (cisapride, theophylline,
diazepam [and its active metabolite, desmethyldiazepam], phenytoin, warfarin,
metoprolol, nifedipine, carbamazepine, midazolam, clarithromycin, naproxen, piroxicam
and oral contraceptives [levonorgestrel/ethinyl estradiol]). Dosage adjustment
of such drugs is not necessary when they are co-administered with pantoprazole.
In other in vivo studies, digoxin, ethanol, glyburide, antipyrine, caffeine,
metronidazole, and amoxicillin had no clinically relevant interactions with
pantoprazole.
Based on studies evaluating possible interactions of
pantoprazole with other drugs, no dosage adjustment is needed with concomitant
use of the following: theophylline, cisapride, antipyrine, caffeine,
carbamazepine, diazepam (and its active metabolite, desmethyldiazepam),
diclofenac, naproxen, piroxicam, digoxin, ethanol, glyburide, an oral
contraceptive (levonorgestrel/ethinyl estradiol), metoprolol, nifedipine,
phenytoin, warfarin, midazolam, clarithromycin, metronidazole, or amoxicillin.
There was also no interaction with concomitantly
administered antacids.
There have been postmarketing reports of increased INR
and prothrombin time in patients receiving proton pump inhibitors, including
PROTONIX, and warfarin concomitantly [see DRUG INTERACTIONS].
Although no significant drug-drug interactions have been
observed in clinical studies, the potential for significant drug-drug
interactions with more than once daily dosing with high doses of pantoprazole
has not been studied in poor metabolizers or individuals who are hepatically
impaired.
Other Effects
In a clinical pharmacology study, pantoprazole 40 mg
given orally once daily for 2 weeks had no effect on the levels of the
following hormones: cortisol, testosterone, triiodothyronine (T3), thyroxine (T4),
thyroid-stimulating hormone, thyronine-binding protein, parathyroid hormone,
insulin, glucagon, renin, aldosterone, follicle-stimulating hormone,
luteinizing hormone, prolactin and growth hormone.
Pharmacogenomics
CYP2C19 displays a known genetic polymorphism due to its
deficiency in some subpopulations (e.g., approximately 3% of Caucasians and
African-Americans and 17% to 23% of Asians are poor metabolizers). Although
these subpopulations of pantoprazole poor metabolizers have elimination
half-life values of 3.5 to 10.0 hours in adults, they still have minimal
accumulation ( ≤ 23%) with once-daily dosing. For adult patients who are
CYP2C19 poor metabolizers, no dosage adjustment is needed.
Similar to adults, pediatric patients who have the poor
metabolizer genotype of CYP2C19 (CYP2C19 *2/*2) exhibited greater than a 6-fold
increase in AUC compared to pediatric extensive (CYP2C19 *1/*1) and intermediate
(CYP2C19 *1/*x) metabolizers. Poor metabolizers exhibited approximately 10-fold
lower apparent oral clearance compared to extensive metabolizers.
Animal Toxicology And/Or Pharmacology
Studies in neonatal/juvenile and adult rats and dogs were
performed. The data from these studies revealed that animals in both age groups
respond to pantoprazole in a similar manner. Gastric alterations, including increased
stomach weights, increased incidence of eosinophilic chief cells in adult and
neonatal/juvenile rats, and atrophy of chief cells in adult rats and in
neonatal/juvenile dogs, were observed in the fundic mucosa of stomachs in
repeated-dose studies. Decreases in red cell mass parameters, increases in
cholesterol and triglycerides, increased liver weight, enzyme induction, and
hepatocellular hypertrophy were also seen in repeated-dose studies in rats
and/or dogs. Full to partial recovery of these effects were noted in animals of
both age groups following a recovery period.
Reproductive Toxicology Studies
Reproduction studies have been performed in rats at oral
doses up to 450 mg/kg/day (88 times the recommended human dose based on body
surface area) and rabbits at oral doses up to 40 mg/kg/day (16 times the
recommended human dose based on body surface area) and have revealed no
evidence of impaired fertility or harm to the fetus due to pantoprazole.
Clinical Studies
Gastroesophageal Reflux Disease (Gerd) Associated With A
History Of Erosive Esophagitis
A multicenter, double-blind, two-period
placebo-controlled study was conducted to assess the ability of PROTONIX® I.V.
(pantoprazole sodium) for Injection to maintain gastric acid suppression in
patients switched from the oral dosage form of pantoprazole to the intravenous
dosage form. Gastroesophageal reflux disease (GERD) patients (n=65, 26 to 64
years; 35 female; 9 Black, 11 Hispanic, 44 White, 1 other) with a history of
erosive esophagitis were randomized to receive either 20 or 40 mg of oral
pantoprazole once per day for 10 days (period 1), and then were switched in
period 2 to either daily intravenous pantoprazole or placebo for 7 days,
matching their respective dose level from period 1. Patients were administered
all test medication with a light meal. Maximum acid output (MAO) and basal acid
output (BAO) were determined 24 hours following the last day of oral medication
(day 10), the first day (day 1) of intravenous administration and the last day
of intravenous administration (day 7). MAO was estimated from a 1 hour
continuous collection of gastric contents following subcutaneous injection of
6.0 μg/kg of pentagastrin.
This study demonstrated that, after 10 days of repeated
oral administration followed by 7 days of intravenous administration, the oral
and intravenous dosage forms of PROTONIX 40 mg are similar in their ability to
suppress MAO and BAO in patients with GERD and a history of erosive esophagitis
(see Table 3). Also, patients on oral PROTONIX who were switched to intravenous
placebo experienced a significant increase in acid output within 48 hours of
their last oral dose (see Table 3). However, at 48 hours after their last oral
dose, patients treated with
PROTONIX I.V. for Injection had a significantly lower
mean basal acid output (see Table 3) than those treated with placebo.
Table 3: ANTISECRETORY EFFECTS (mEq/h) OF 40 mg
PROTONIX I.V. for INJECTION AND 40 mg ORAL PROTONIX IN GERD PATIENTS WITH A
HISTORY OF EROSIVE ESOPHAGITIS
Parameter |
PROTONIX Delayed-Release Tablets DAY 10 |
PROTONIX I.V. for Injection DAY 7 |
Placebo I.V. DAY 7 |
Mean maximum acid |
6.49 |
6.62 |
29.19* |
output |
n=30 |
n=23 |
n=7 |
Mean basal acid |
0.80 |
0.53 |
4.14* |
output |
n=30 |
n=23 |
n=7 |
* p < 0.0001 Significantly
different from PROTONIX I.V. for Injection. |
To evaluate the effectiveness
of PROTONIX I.V. (pantoprazole sodium) for Injection as an initial treatment to
suppress gastric acid secretion, two studies were conducted.
Study 1 was a multicenter,
double-blind, placebo-controlled, study of the pharmacodynamic effects of
PROTONIX I.V. for Injection and oral PROTONIX. Patients with GERD and a history
of erosive esophagitis (n=78, 20-67 years; 39 females; 7 Black, 19 Hispanic, 52
White) were randomized to receive either 40 mg intravenous pantoprazole, 40 mg
oral pantoprazole, or placebo once daily for 7 days. Following an overnight
fast, test medication was administered and patients were given a light meal
within 15 minutes. MAO and BAO were determined 24 hours following the last day
of study medication. MAO was estimated from a 1 hour continuous collection of
gastric contents following subcutaneous injection of 6.0 μg/kg of
pentagastrin to stimulate acid secretion. This study demonstrated that, after
treatment for 7 days, patients treated with PROTONIX I.V. for Injection had a
significantly lower MAO and BAO than those treated with placebo (p < 0.001),
and results were comparable to those of patients treated with oral PROTONIX
(see Table 4).
Table 4: ANTISECRETORY EFFECTS (mEq/h) OF INITIAL
TREATMENT WITH 40 mg PROTONIX I.V. for INJECTION AND 40 mg ORAL PROTONIX IN
GERD PATIENTS WITH A HISTORY OF EROSIVE ESOPHAGITIS
Parameter |
PROTONIX I.V. for Injection DAY 7 |
PROTONIX Delayed-Release Tablets DAY 7 |
Placebo DAY 7 |
Maximum acid output |
8.4 ± 5.9 |
6.3 ± 6.6 |
20.9 ± 14.5* |
(mean ± SD) |
n=25 |
n=22 |
n=24 |
Basal acid output |
0.4 ± 0.5 |
0.6 ± 0.8 |
2.8 ± 3.0* |
(mean ± SD) |
n=25 |
n=22 |
n=23 |
* p < 0.001 Significantly
different from PROTONIX I.V. for Injection. |
Study 2 was a single-center,
double-blind, parallel-group study to compare the clinical effects of PROTONIX
I.V. for Injection and oral PROTONIX. Patients (n=45, median age 56 years, 21
males and 24 females) with acute endoscopically proven reflux esophagitis
(Savary/Miller Stage II or III) with at least 1 of 3 symptoms typical for
reflux esophagitis (acid eructation, heartburn, or pain on swallowing) were
randomized to receive either 40 mg intravenous pantoprazole or 40 mg oral
pantoprazole daily for 5 days. After the initial 5 days, all patients were
treated with 40 mg oral pantoprazole daily to complete a total of 8 weeks of
treatment. Symptom relief was assessed by calculating the daily mean of the
sums of the average scores for these 3 symptoms and the daily mean of the
average score for each of the symptoms separately. There was no significant
difference in symptom relief between PROTONIX I.V. and oral PROTONIX therapy
within the first 5 days. A repeat endoscopy after 8 weeks of treatment revealed
that 20 out of 23 (87%) of the PROTONIX I.V. plus oral PROTONIX patients and 19
out of 22 (86%) of the oral PROTONIX patients had endoscopically proven healing
of their esophageal lesions.
Data comparing PROTONIX I.V.
for Injection to other proton pump inhibitors (oral or I.V.) or H2 receptor
antagonists (oral or I.V.) are limited, and therefore, are inadequate to
support any conclusions regarding comparative efficacy.
Pathological Hypersecretion
Associated With Zollinger-Ellison Syndrome
Two studies measured the
pharmacodynamic effects of 6 day treatment with PROTONIX I.V. for Injection in
patients with Zollinger-Ellison Syndrome (with and without multiple endocrine
neoplasia type I). In one of these studies, an initial treatment with PROTONIX
I.V. for Injection in 21 patients (29 to 75 years; 8 female; 4 Black, 1
Hispanic, 16 White) reduced acid output to the target level ( ≤ 10 mEq/h)
and significantly reduced H+ concentration and the volume of gastric
secretions; target levels were achieved within 45 minutes of drug
administration.
In the other study of 14 patients (38 to 67 years; 5
female; 2 Black, 12 White) with Zollinger-Ellison Syndrome, treatment was
switched from an oral proton pump inhibitor to PROTONIX I.V. for Injection.
PROTONIX I.V. for Injection maintained or improved control of gastric acid
secretion.
In both studies, PROTONIX I.V. for Injection 160 or 240
mg per day in divided doses maintained basal acid secretion below target levels
in all patients. Target levels were 10 mEq/h in patients without prior gastric
surgery, and 5 mEq/h in all patients with prior gastric acid-reducing surgery.
Once gastric acid secretion was controlled, there was no evidence of tolerance
during this 7 day study. Basal acid secretion was maintained below target
levels for at least 24 hours in all patients and through the end of treatment
in these studies (3 to 7 days) in all but 1 patient who required a dose
adjustment guided by acid output measurements until acid control was achieved.
In both studies, doses were adjusted to the individual patient need, but
gastric acid secretion was controlled in greater than 80% of patients by a
starting regimen of 80 mg q12h.