Division of Pharmaceutical Evaluation-II
Office of Clinical Pharmacology and Biopharmaceutics
NDA: 21-332 Relevant IND: 39,897
Brand Name: Symlin™ Generic Name: Pramlintide Acetate
Concentrations: Vial – 0.6 mcg/mL sterile injection in 5 mL vials
Cartridge – 1.0 mcg/mL sterile injection in 1.5 mL cartridges
Sponsor: Amylin Pharmaceuticals, Inc.
9373 Towne Centre Drive, San Diego, CA 92121
Submission Date: 7-DEC-2000 Division Due Date: 6-JUN-2001
5-APR-2001
Advisory Committee: 26-JUL-2001 PDUFA Date: 7-OCT-2001
CPB Reviewer: Steven B. Johnson, Pharm.D.
CPB Team Leader: Hae-Young Ahn, Ph.D.
Acknowledgements: Daniel Davis, M.D.; S.W. Johnny Lau, Ph.D.; Todd Sahlroot, Ph.D.
EXECUTIVE SUMMARY
On December 7, 2000, Amylin Pharmaceuticals submitted NDA 21-332 in support of Symlin™ (pramlintide acetate) injection. Pramlintide is the synthetic analogue of the 37-amino acid polypetide, amylin. The proposed mechanism of pramlintide action is complex, with regulation of postprandial glucagon concentrations and altered gastric emptying rate being the most well described. Two formulations of Symlin™ have been proposed for marketing, a 0.6 mg/mL (vial) formulation that will be administered by syringe and a 1.0 mg/mL (cartridge) formulation that will use a “pen” system for administration. Symlin™ has been proposed for use as adjunctive therapy to insulin in patients with type 1 or insulin-requiring type 2 diabetes mellitus (DM).
Included in this application were 28 clinical pharmacology and biopharmaceutics related studies or reports. Of these studies, 19 were used to make the CPB recommendation. Many of the early studies were found to be unacceptable for review due to formulation and/or assay issues. Common to the studies that were utilized in this review included: a formulation pH of 4.0 and/or the use of the current immunoenzymetric assay (IEMA) for pramlintide pharmacokinetic (PK) studies.
The following is a brief description of Symlin™ attributes. First of all, there is a high degree of inter-subject variability for all PK parameters, except t˝ and Tmax. This drug is absorption rate limited, has a time to maximum pramlintide plasma concentration (Tmax) of approximately 20 minutes, and a half-life of about 50 minutes. Pramlintide is metabolized to des-lysine pramlintide, which has 100% of the activity as pramlintide, and other none reactive fragments. There is no apparent drug accumulation following multiple doses in either type 1 or type 2 diabetes patients.
In order to take full advantage of pramlintide’s delayed gastric emptying effect, Symlin™ should be administered about 15 minutes before a meal – this timing would correspond with the pramlintide Tmax. Symlin™ should be administered subcutaneously into the tissue of the anterior abdominal wall only, with a maximum dose of 360 mcg/day – divided BID, TID, or QID.
During the course of this review, a series of questions were generated to address pertinent issues that were thought to be key for the approval of this application. The most prominent of these questions are:
1)
Is the analytical method used to detect pramlintide in human
plasma precise and accurate?
Yes, the immunoenzymetric assay used to detect human plasma pramlintide exhibits precision and accuracy estimates that are acceptable. However, it should be noted that the samples used in the quality control analysis were sufficiently far enough away from the calibration limits and the lower limit of quantitation as to create some concern about the plasma concentrations that fall between the LLOQ and the lowest quality control sample.
2)
Is there any assay interference from endogenous substances
or metabolites?
Yes, this assay is susceptible to interference by endogenous amylin, the des-lysine pramlintide metabolite, and human anti-mouse antibody (HAMA). Also, the values reported as pramlintide concentrations are actually pramlintide, the pramlintide metabolite, and amylin.
3)
What is the absolute bioavailability of Symlin™?
The bioavailability of a subcutaneously administered dose of Symlin™, relative to an equivalent intravenously administered dose of Symlin™, is approximately 37%. Pramlintide exhibits absorption rate limited pharmacokinetics.
4)
What effect does pH, mixing, volume, or concentration have
on the bioavailability of Symlin?
The formulation pH has a significant effect on the bioavailability of Symlin™. A formulation pH of 4.7 was shown to exhibit a 25% reduction in bioavailability compared to the to-be-marketed pH 4.0 formulation.
Compatibility studies, that would describe what substances could be mixed with pramlintide, were not performed. However, in interaction studies where pramlintide and insulins were mixed in the same syringe, pramlintide and sometimes insulin pharmacokinetics were significantly altered.
Volume and concentration had no apparent effect on Symlin™ bioavailability.
5)
Does Symlin™ exhibit dose proportionality over the entire
proposed dosing range, 30 mcg to 180 mcg?
No, Symlin™ does not exhibit dose proportionality over the entire proposed dosing range. However, studies in healthy volunteers and patients with type 1 and type 2 diabetes demonstrate a dose-related exposure. Apparent clearance in normal healthy subjects ranged from 2.36 L/min to 2.87 L/min for the dosing range of 30 mcg to 120 mcg.
6)
Given that Symlin™ will be available in two concentrations,
are these formulations bioequivalent?
Bioequivalence was established between the cartridge formulation administered by a pen system and the vial formulation administered with a syringe. Ninety-five percent confidence limits were within the 80% to 125% boundaries for both Cmax and AUC.
7)
Since there will be three suppliers of pramlintide material
for Symlin™, are there any PK-related concerns about using multiple sources of
this protein?
No, there are no outstanding concerns related to the multiple sources of pramlintide. Information submitted in the form of a BE study was sufficient to conclude that pramlintide material from UCB-Bioproducts and Bachem were equivalent. Material from both Bachem and Mallinckrodt was used throughout the development program and was not considered different.
8)
Are there any differences between the pramlintide PK
profiles of type 1 and type 2 diabetes patients?
Yes, there is a difference between the pramlintide PK profiles of type 1 and type 2 diabetes patients. In the studies evaluated in this application, patients with type 2 diabetes exhibited lower relative pramlintide plasma concentrations than did patients with type 1 diabetes. This fact is reflected in the proposed diabetes type-specific dosing regimens.
9)
Pramlintide is renally eliminated, what effect does renal
insufficiency have on pramlintide PK?
The exact effect that renal insufficiency has on pramlintide PK cannot be stated with absolute certainty due to the design limitations of the renal study (e.g., parallel design with 3 to 8 subjects per group and inherent inter-subject variability). However, there was no observed trend in the data to suggest that renal insufficiency adversely effects pramlintide PK. It should be kept in mind that pramlintide dosing in humans has spanned 30 mcg to 10 mg in single dose studies.
10) Can pramlintide be
mixed with insulin(s)?
No, pramlintide should not be mixed in the same syringe with any insulin. The sponsor evaluated mixing effects of pramlintide with rapid, short, intermediate, and long-acting insulins. The results suggest that pramlintide PK, and sometimes insulin PK, is compromised when these agents are mixed.
11) Since pramlintide
delays gastric emptying time, what effect does Symlin™ have on orally
administered medications?
Two studies evaluated the effect Symlin™ has on the PK of Lo/Ovral, an oral contraceptive, and ampicillin, a relatively acid-stable antibiotic. Results indicate that norgestrel, the progestin component of Lo/Ovral, achieves significantly lower and delayed Cmax values when administered 15 minutes after a dose of Symlin™. However, there was no difference in the extent of norgestrel exposure.
Conversely, pramlintide appeared to have no effect on ampicillin AUC or Cmax. However, Tmax was increased by approximately one hour.
The conclusion drawn from these studies would suggest that orally administered drugs that are expected to have a rapid onset of action, or those that are adversely affected (e.g., degraded) by prolonged gastric retention times, should be administered at least one hour prior to dosing pramlintide.
12) What effect does a
morning dose of pramlintide have on the gastric emptying of a lunchtime meal?
There was no observed interference of a morning dose of pramlintide on a lunchtime meal eaten approximately 4 hours after pramlintide administration. This is consistent with pramlintide’s attributes of a relatively short half-life of pramlintide, ~ 50 minutes, and the fact that there is no indication of pramlintide accumulation.
Based upon the results of the studies that answer the above questions, it has been concluded that Amylin, Inc. has supplied sufficient information to the PK section for Symlin™, NDA 21-332, to have been adequately evaluated.
RECOMMENDATION
The Office of Clinical Pharmacology and Biopharmaceutics has reviewed NDA 21-292 for Symlin™ (pramlintide acetate) and finds the application acceptable, pending the indicated labeling changes (see Comments to Sponsor and Labeling Changes).
TABLE of CONTENTS
EXECUTIVE
SUMMARY.................................................................................................................. 1
RECOMMENDATION....................................................................................................................... 3
TABLE of CONTENTS...................................................................................................................... 3
APPENDIX INDEX............................................................................................................................ 4
BACKGROUND – (from
sponsor)...................................................................................................... 4
TERMS and ABBREVIATIONS......................................................................................................... 5
DRUG CHARACTERISTICS.............................................................................................................. 5
ANALYTICAL.................................................................................................................................. 6
HUMAN PK –
BIOAVAILABILITY/BIOEQUIVALENCE......................................................................... 7
HUMAN PK –
BIOEQUIVALENCE................................................................................................... 10
HUMAN PK – TARGET
POPULATION............................................................................................. 12
HUMAN PK – PLASMA/BLOOD..................................................................................................... 17
HUMAN PK – EX VIVO –
Placental Transfer..................................................................................... 17
PHARMACODYNAMICS................................................................................................................ 17
LABELING.................................................................................................................................... 19
COMMENTS TO THE SPONSOR.................................................................................................... 19
APPENDIX INDEX
|
Study # |
Title |
Page # |
|
137-125 |
An open-label, randomized, four-period cross-over study in normal volunteers of the bioavailability of selected concentrations of pramlintide in two different formulations. |
|
|
137-142 |
An open-label, randomized, two-period crossover study in healthy volunteers of the bioequivalence of two different formulations and dosage forms of pramlintide. |
|
|
137-126 |
An open-label, randomized, four-period cross-over study of the proportionality of four subcutaneous doses of pramlintide (AC137) administered at a constant volume in normal volunteers. |
|
|
137-127 |
An open-label, single-dose, pharmacokinetic study of pramlintide in type 1 diabetics with renal impairment. |
|
|
137-133 |
A randomized, double-blind, placebo-controlled, single-dose, two-period cross-over study to evaluate the effect of pramlintide on the pharmacokinetics of ethinyl estradiol and norgestrel in healthy female subjects receiving the oral contraceptive ageng Lo/Ovral®. |
|
|
137-134 |
A randomized, double-blind, placebo-controlled, single-dose, two-period cross-over study to determine the effect of pramlintide on the pharmacokinetics of ampicillin in healthy subjects. |
|
|
137-130 |
A randomized, double-blind, single-dose, two-period cross-over study of the safety of pramlintide and lispro insulin administered as two separate subcutaneous inject5ions in conjunction with NPH, Lente, or Ultralente insulin in patients with type 1 diabetes mellitus. |
|
|
137-115 |
An open-label, randomized, cross-over study in type 1 diabetes mellitus of the pharmacokinetics of subcutaneous pramlintide (AC137) and 70/30 insulin mixed together and as separate single injections. |
|
|
137-119 |
An open-label, randomized, five-period cross-over study of the pharmacokinetics of subcutaneous pramlintide (AC137) versus placebo plus NPH and regular insulin mixed together and as separate single injections in patients with type 1 diabetes mellitus. |
|
|
137-145 |
An open-label, randomized, two-period cross-over study in healthy volunteers to test the bioequivalence of pramlintide supplied by two different manufacturers. |
|
|
137-143 |
An open-label assessment of the single dose and multiple dose pharmacokinetic profiles of pramlintide in subjects with type 1 diabetes mellitus. |
|
|
137-144 |
An open-label assessment of the single dose and multiple dose pharmacokinetic profiles of pramlintide in subjects with type 2 diabetes mellitus. |
|
|
137-120 |
An open-label, randomized, five-period cross-over study of the pharmacokinetics of subcutaneous pramlintide (AC137) versus placebo plus isophane and soluble insulin mixed together and as separate single injections in patients with type 1 diabetes mellitus. |
|
|
137-118 |
The effect of single doses of pramlintide on the gastric emptying of two meals. |
|
|
137-137 |
A study to determine the effect of pramlintide on the gastric emptying of subjects with type 2 diabetes mellitus currently requiring insulin. |
|
|
REST 98049 |
Characterization of pramlintide metabolites following bolus subcutaneous administration in type 1 diabetic subjects. |
|
|
REST 98044 |
Characterization of binding of pramlintide to components from rat, dog, rabbit, mouse, and human blood. |
|
BACKGROUND – (from sponsor)
In people without diabetes, plasma glucose concentrations are tightly regulated by the co-secretion of the hormones amylin and insulin from the pancreatic b-cells in response to nutrient intake, and by the glucagon secretion from pancreatic a-cells in response to a variety of stimuli, including hypoglycemia and elevated concentrations of amino acids. In people with type 1 diabetes, the pancreatic b-cells are usually destroyed by an autoimmune process, leaving patients deficient in both insulin and amylin. In people with type 2 diabetes, insulin resistance leads to an increased demand for insulin, and initially results in increases in b-cell secretion of both insulin and amylin. Over time, b-cell secretion fails, and relative deficiencies of both insulin and amylin occur in conjunction with inappropriate fluctuations in glucose concentrations, overt hyperglycemia, and increased risk of hypoglycemia.
Results of nonclinical and clinical studies indicate that the 37-amino acid polypeptide amylin and the amylin analogue pramlintide contribute to glucose regulation through several mechanisms including reducing the postpranidal rise in glucagon concentrations without impeding the glucagon response to insulin-induced hypoglycemia, and regulating the rate of nutrient delivery to the small intestine via an effect on gastric emptying. It has been proposed that amylin’s effect on gastric emptying may be exerted via a central mechanism involving specific binding sites in the area postrema of the brain, with outflow through the efferent pathways of the vagus nerve to the gastrointestinal system, rather than by direct action on the stomach. Elevated glucagon concentrations favor increased rates of hepatic glucose release, and a reduction in postprandial glucagon concentrations should result in lower rates of hepatic glucose output during the postprandial period, thus favoring lower postprandial glucose concentrations. It has been demonstrated that hypoglycemia overrides these effects.
Immunoassay of amylin in healthy human volunteers indicates fasting concentrations between 4 and 8 pmol/L, increasing two- to three-fold following ingestion of a mixed meal or an oral glucose load. In patients with type 1 diabetes mellitus, amylin concentrations are near or below the limit of quantitation under fasting conditions and do not increase in response to nutrient stimuli. In patients with type 2 diabetes mellitus or with impaired glucose tolerance, fasting amylin concentrations are comparable to those seen in healthy human subjects. However, the postprandial responses vary considerably. The postprandial responses tend to be decreased in relation to the prevailing level of glycemia and are virtually absent in patients with type 2 diabetes who have progressed to insulin therapy. Amylin deficiency in patients with diabetes mellitus may contribute to impaired glucoregulation.
TERMS and ABBREVIATIONS
|
AA --------------------------------- Agency --------------------------- AUC ------------------------------- BA --------------------------------- BE --------------------------------- BMI --------------------------------- Cmax ------------------------------- DMEDP -------------------------- OCPB ----------------------------- NDA ------------------------------- Tmax -------------------------------- t1/2 ---------------------------------- |
Amino acid(s) Food and Drug Administration Area under the plasma-concentration-time curve Bioavailability Bioequivalence Body Mass Index Maximum drug concentration Division of Metabolic and Endocrine Drug Products Office of Clinical Pharmacology and Biopharmaceutics New Drug Application Time of maximum drug concentration (Cmax) Drug elimination half-life |
DRUG CHARACTERISTICS
Drug Chemistry
Pramlintide acetate is a synthetic analogue of the endogenous human polypeptide, amylin. Pramlintide differs from amylin in its replacement of amino-acid (AA) residues at 25 (alanine), 28 (serine), and 29 (serine) of the 37-AA amylin peptide, with proline residues. These substitutions are purported to increase pramlintide’s solubility, and decrease the propensity for aggregation and adhesion, which has been reported with amylin. Pramlintide acetate is an odorless white powder, is soluble in water, has a molecular weight of 3949.9, and a molecular formula of C171H267N51O53S2*xC2H4O2, where x is variable. The structural formula is shown below, and includes the disulfide bridge between the two cysteine residues:
Lys-Cys-Asn-Thr-Ala-Thr-Cys-Ala-Thr-Gln-Arg-Leu-Ala-Asn-Phe-Leu-Val-His-Ser-Ser-
Asn-Asn-Phe-Gly-Pro-Ile-Leu-Pro-Pro-Thr-Asn-Val-Gly-Ser-Asn-Thr-Tyr-NH2 acetate
Drug Formulation
Multiple formulations (i.e., vial = 26; cartridge = 3) have been described in the development of Symlin™. Of these formulations, AC-0137-F22 (vial) and AC-0137-F28 (cartridge) were chosen for marketing. The formulations for both dosage units are presented in TABLE 1:
TABLE 1: Symlin™ Formulations
|
|
Vial – F22 |
|
Strength |
0.6 mcg/mL (5 mL) |
1.0 mcg/mL (1.5 mL) |
|
pH |
4.0 |
4.0 |
|
Pramlintide Acetate Mannitol Metacresol Acetic Acid Sodium Acetate Trihydrate Water for Injection |
0.60 g/L 30 mM 43 g/L 2.25 g/L 1.53 g/L 0.61 g/L QS to 1.0 L or 1.015 kg |
1.00 g/L 30 mM 43 g/L 2.25 g/L 1.53 g/L 0.61 g/L QS to 1.0 L or 1.015 kg* |
|
*Meets
both the European Pharmacopeia (EP) and United States Pharmacopeia (USP)
monographs |
||
Early pharmacokinetic studies utilized formulations other than those shown above that differed mainly in their relative pH values – those studies were not reviewed. The data that provided the basis for the Clinical Pharmacology and Biopharmaceutics recommendation was generated using the above to-be-marketed formulations.
Additionally, the sponsor is using three suppliers of pramlintide in the manufacture of Symlin™, Bachem, Mallinckrodt, and UCB-Bioproducts (see HUMAN PK – BIOEQUIVALENCE).
ANALYTICAL
Is the analytical method used to detect
pramlintide in human plasma precise and accurate?
Is there any assay interference from
endogenous substances or metabolites?
The detection of pramlintide is dependent upon a validated immunoenzymetric assay (IEMA) method that relies on two monoclonal mouse antibodies (Ab): a capture Ab (F024-4.4) and a detection Ab (F025-27.4). Neither Ab is specific for amylin or pramlintide. Antibody F024-4.4 binds near the amino terminus of pramlintide and Ab F025-27.4 binds to the amidated carboxy terminus of pramlintide. The F025-27.4 Ab is conjugated to alkaline phosphatase and a fluorescent substrate, 4-methylumbelliferyl phosphate (4-MUP). This method is able to detect bound, conjugated antibody, using a microplate fluorometer. Relative fluorescence units (RFU) are correlated with concentration using a calibration curve defined in the same assay. This assay uses the Tripro-amylin EIA kit produced by PerSeptive Diagnostics, Inc, and a microplate fluorometer from Dynatech, Chantilly, VA.
In TABLE 2, the quality control samples used in the assays for studies 137-142 and 137-145 are presented. These two studies were chosen because they were the two pivotal bioequivalence studies submitted with this application. Both accuracy and precision were within accepted parameters for these studies. However, there is a concern related to the quality control samples.
Quality control samples were measured at the sponsor defined values of low, middle, and high. However, because the extreme values were far away from the limits of the calibration curve, there exists some doubt about the values obtained at the extremes, especially those plasma pramlintide values that fall between the LLOQ and the lowest quality control sample value. Therefore, because of this issue and the cross-reactivity with endogenous amylin, pharmacokinetic analysis will be confined to Cmax and AUC0-t.
Assay interference was documented for endogenous amylin and for des-lysine pramlintide with 35% and 100% cross-reactivity, respectively. This cross-reactivity results in a total pramlintide concentration that is actually a combination of amylin, des-lysine pramlintide, and pramlintide. Since under fasting conditions endogenous amylin concentrations are usually undetectable, and the fact that the des-lysine pramlintide metabolite is equipotent with pramlintide, these findings are not likely to undermine the value of the assay.
TABLE 2 – Assay Quality Control Results from Two Pivotal Bioequivalence Studies
|
Study |
137-142 |
137-145 |
|
|
LLOQ (pmol/L) |
4.5 |
4.5 |
|
|
Calibration
Range |
5.4 – 111.1 |
5.4 – 111.1 |
|
|
Precision
(%CV) 12.7 40.6 40.1 74.9 79.5 |
3.7 2.9 4.1 |
4.7 4.1 5.0 |
|
|
Accuracy (%) 12.7 40.6 40.1 74.9 79.5 |
104.4 102.4 105.2 |
104.2 101.2 101.1 |
|
|
Stability |
5 freeze/thaw cycles |
||
|
Storage |
1 year @ either –20°C or –70°C |
||
|
Crossreactivity |
35% – amylin; 100% – des-lysine pramlintide |
||
|
Homology |
92% – amylin;
97% – des-lysine pramlintide |
||
One important point. This IEMA utilizes monoclonal antibodies from a murine source – and, many humans carry the human anti-mouse antibody (HAMA). HAMA, present in plasma, binds to the mouse antibodies in the assay, which can result in a false signal, either positive or negative. Strategies for reducing this interference include: immunosuppressant therapy, and the use of humanized, polyethylene glycolated, or Fab fragments of antibody agents. The sponsor chose to reduce the HAMA interference by using a diluent that contained a high concentration of non-specific mouse IgG which competes with the specific mouse monoclonal antibodies for the human anti-mouse antibody binding sites.
The above point was raised because several subjects were determined to be unevaluble in several PK studies due to this assay interference. The Agency strongly encourages the sponsor to develop an assay that does not utilize murine antibodies.
HUMAN PK – BIOAVAILABILITY/BIOEQUIVALENCE
Symlin is a parenterally (i.e., subcutaneously) administered sterile solution. As such, knowing the absolute bioavailability is crucial. It is also imperative that there is a good understanding of the effect that physiochemical alterations have on the product’s bioavailability. Therefore, there are two primary questions that should be asked:
What is the absolute bioavailability of Symlin™?
What effect does pH, mixing, volume, or concentration have
on the bioavailability of Symlin?
Absolute Bioavailability
The absolute bioavailability for Symlin was determined in an open-label, randomized, four-period crossover study (137-125) in 40 (39 completed[i]) healthy male subjects between 18 and 41 years of age. The four treatments consisted of: A) 60 mcg (0.1 mL) pH 4.7 pramlintide administered subcutaneously (formulation F11); B) 60 mcg (0.1 mL) pH 4.0 pramlintide administered subcutaneously (formulation F22); C) 60 mcg (0.2 mL) pH 4.0 pramlintide administered subcutaneously (formulation F21); and D) 60 mcg (0.1 mL) pH 4.0 pramlintide administered intravenously (formulation F22). Each of the treatments was separated by a 1-week washout period.
Results, presented in TABLE 3 and PLOT 1, show that the absolute bioavailability (f) of a 60 mcg dose of pramlintide, in a volume of 0.1 mL, administered to healthy volunteers under fasting conditions, is 37%. However, because the sampling times for the IV administered pramlintide did not include a sufficient number of early time points, the absolute bioavailability of pramlintide may be overestimated.
TABLE 3 – Pramlintide Plasma Concentrations: SC vs. IV Administration
|
Parameter |
Units |
Tx B: 60 mcg (0.1 mL) SC pH 4.0 |
Tx D: 60 mcg (0.1 mL) IV pH
4.0 |
||||
|
Mean |
SD |
%CV |
Mean |
SD |
%CV |
||
|
Cmax Tmax AUC0-t AUC0-inf t1/2 |
pmol/L minutes pmol*min/L pmol*min/L minutes |
89.23 20.5 6234 6803 43.6 |
24.01 6.51 2154 2253 13.6 |
26.9 31.9 34.6 33.1 31.2 |
-- -- 17,950 18,420 33.4 |
-- -- 6834 6795 7.94 |
-- -- 38.1 36.9 23.8 |
|
Cmax / BMI AUC0-t / BMI AUC0-inf / BMI |
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