Clinical Pharmacology for ChiRhoStim
Mechanism Of Action
The primary action of ChiRhoStim® is to stimulate pancreatic ductal cells to secrete pancreas fluid in large volumes that contain bicarbonate.
Secretin is a hormone that is normally released from the duodenum upon exposure of the proximal intestinal lumen to gastric acid, fatty acids and amino acids. Secretin is released from enterochromaffin cells in the intestinal mucosa. Secretin receptors have been identified in the pancreas, stomach, liver, colon and other tissues. When secretin binds to secretin receptors on pancreatic duct cells it opens cystic fibrosis transmembrane conductance regulator (CFTR) channels, leading to secretion of bicarbonate-rich-pancreatic fluid. Secretin may also work through vagal-vagal neural pathways since stimulation of the efferent vagus nerve stimulates bicarbonate secretion and atropine blocks secretin-stimulated pancreatic secretion.
Pharmacokinetics
The pharmacokinetic profile for synthetic human secretin was evaluated in 12 healthy subjects following a single-dose of human secretin administered as a 0.4 mcg/kg intravenous bolus. The plasma concentrations of human secretin declined to baseline concentrations within 90 to 120 minutes. The elimination half-life of synthetic human secretin is 45 minutes. The clearance of synthetic human secretin is 580.9 ± 51.3 mL/min and the volume of distribution is 2.7 liters.
Clinical Studies
Stimulation Of Pancreatic Secretions, Including Bicarbonate To Aid In The Diagnosis Of Exocrine Pancreas Dysfunction
ChiRhoStim® administered intravenously stimulates the exocrine pancreas to secrete pancreatic juice, which can assist in the diagnosis of exocrine pancreas dysfunction. Normal ranges for pancreatic secretory response to intravenous secretin in patients with defined pancreatic disease have been shown to vary. One source of variation is related to the inter-investigator differences in operative technique.
In two studies, a total of 18 patients with a documented history of chronic pancreatitis were given 0.2 mcg/kg synthetic human secretin (sHS), 0.2 mcg/kg synthetic porcine secretin (sPS), and 1 CU/kg (equal to 0.2 mcg/kg for biologically derived secretin (bPS)) in a crossover design. The results appear in Figures 1 and 2. In another study, 35 healthy subjects were given sHS at a dose of 0.2 mcg/kg. The results appear in Figures 1 and 2.
FIGURE 1
FIGURE 2
The values obtained for Figures 1 and 2 were performed by investigators skilled in performing secretin stimulation testing and are to be taken only as guidelines. These results should not be generalized to results of secretin stimulation testing conducted in other laboratories. However, a volume response of less than 2 mL/kg/hr, bicarbonate concentration of less than 80 mEq/L, and a bicarbonate output of less than 0.2 mEq/kg/hr are consistent with impaired pancreatic function.
A physician or institution planning to perform secretin stimulation testing as an aid to the diagnosis of pancreatic disease should begin by assessing enough normal subjects (greater than 5) to develop proficiency in proper techniques and to generate normal response ranges for the commonly assessed parameters for pancreatic exocrine response to ChiRhoStim®.
In three crossover studies evaluating 21 different patients with a documented history of chronic pancreatitis, sHS was compared to sPS and bPS at a dose of 0.2 mcg/kg for each drug. All of the patients treated with these drugs had peak bicarbonate concentrations of less than 80 mEq/L.
Pancreatic secretory response to intravenous synthetic human secretin in 35 healthy subjects demonstrated a mean peak bicarbonate concentration of 100 mEq/L and a mean total volume over one hour of 260.7 mL. All 35 subjects had peak bicarbonate concentrations greater than or equal to 80 mEq/L.
Stimulation Of Gastrin Secretion To Aid In The Diagnosis Of Gastrinoma
ChiRhoStim® administered intravenously stimulates gastrin release in patients with gastrinoma (Zollinger-Ellison Syndrome), whereas no or only small changes in serum gastrin concentrations occur in healthy subjects and in patients with duodenal ulcer disease. Discriminant analysis was used to establish secretin stimulation testing as an aid in the diagnosis of gastrinoma. An increase from basal levels of greater than or equal to 110 pg/mL was the optimal point separating positive and negative tests. This gastrin response is the basis for the use of secretin as a provocative test in the evaluation of patients in whom gastrinoma is a diagnostic consideration.
In a three way crossover study, 6 patients with tissue confirmed gastrinoma received synthetic human secretin (ChiRhoStim®), synthetic porcine secretin and biologically derived porcine secretin at a dose of 0.4 mcg/kg for each drug. Serum gastrin levels were reported to be greater than 110 pg/mL for all secretin products tested after stimulation. Testing of ChiRhoStim® in 12 healthy subjects demonstrated completely negative results for gastrinoma.
Stimulation Of Pancreatic Secretion To Facilitate Identification Of The Ampulla Of Vater And The Accessory Papilla During Endoscopic Retrograde Cholangiopancreatography (ERCP)
In a randomized, placebo controlled crossover study in 24 patients with pancreas divisum undergoing ERCP, ChiRhoStim® at a dose of 0.2 mcg/kg resulted in 16 of 24 successful cannulations of the minor duct compared to 2 of 24 for placebo.
REFERENCES
1. Gardner TB, Purich ED and Gordon SR. Pancreatic Duct Compliance After Secretin Stimulation. A Novel Endoscopic Ultrasound Diagnostic Tool for Chronic Pancreatitis. Pancreas. 2012 Mar;41(2):290-94.
2. Jorpes, E. and Mutt V. On the biological assay of secretin. The reference standard. Acta Physiol Scand. 1966 Mar;66(3):316-25.