Sincalide

Sincalide is a synthetic octapeptide that corresponds to the C-terminal 8 amino acids of the 33-amino acid hormone cholecystokinin (CCK). This C-terminal fragment contains the biologically active sequence of CCK and retains its full pharmacological activity for stimulating gallbladder contraction, pancreatic enzyme secretion, and relaxation of the sphincter of Oddi. Sincalide has approximately 10 times the potency of the natural 33-amino acid CCK on a molar basis.

The primary clinical application of sincalide is in hepatobiliary scintigraphy (HIDA scan) to quantitatively assess gallbladder function. When administered as a slow intravenous infusion during HIDA scanning, sincalide stimulates gallbladder contraction, and the gallbladder ejection fraction (GBEF) is calculated by comparing pre- and post-stimulation radiotracer activity in the gallbladder. A GBEF below 35-40% (depending on the protocol used) is considered abnormal and suggestive of gallbladder dyskinesia (functional gallbladder disorder).

The sincalide-stimulated GBEF has become a crucial diagnostic tool in the evaluation of patients with biliary-type symptoms (right upper quadrant pain, nausea, food intolerance) who have a normal ultrasound with no gallstones. Cholecystectomy in patients with low GBEF has been reported to relieve symptoms in 80-90% of cases in some studies, though the predictive value of GBEF remains debated and varies with the infusion protocol used.

Sincalide has additional diagnostic applications including accelerating transit of barium through the small bowel for radiographic studies, stimulating pancreatic secretion for collection and analysis, and emptying the gallbladder before hepatobiliary imaging to improve gallbladder visualization. Standardization of the infusion protocol (typically 0.02 mcg/kg over 30-60 minutes) has been emphasized as critical for reproducible GBEF measurements.