GUCY2C and irritable bowel syndrome: In January 2017, the FDA approved Trulanc® (plecanatide), a GC-C (guanylate cyclase-C) agonist with linaclotide, for CIC (Chronic Idiopathic Constipation).479,480 Plecanatide is as effective as linaclotide in the treatment of CIC but not as effective as linaclotide in the treatment of IBS-C.481 In terms of structure, Plecanatide and Linaclotide are both small molecule monopeptide, but with one less disulfide bond, which is easier to synthesize.