Ursodiol is a hydrophilic bile acid that can increase the metabolic conversion of cholesterol to bile acids, thus reducing the fractional reabsorption of cholesterol by intestines [5]. Its mechanisms of action in PBC are not clearly defined, but the proposed mechanisms include increasing the hydrophilicity in the circulating bile acid pool, stimulating hepatocellular and ductal secretions, protecting against bile acid- and cytokine-induced injury, and exerting immunodulating and anti-inflammatory effects [5, 6]. Although ursodiol has been the standard of care for patients with PBC for years, up to 40% of patients fail to respond to it with inadequate biochemical improvement and thus are still at risk of progression to end-stage liver disease [7]. Although we do not know how our patient would have responded to ursodiol following desensitization from the liver standpoint, the worsening of her PBC while being on obeticholic acid prior to desensitization warranted her to switch to ursodiol.
Ursodiol is generally well tolerated and shown to improve pruritus in patients with PBC [6]. Paradoxically, exacerbation of pruritus after ursodiol administration has also been reported [4]. Our patient who developed pruritus after desensitization likely experienced a medication side effect as opposed to an allergic reaction in the absence of objective findings. Further, although delayed hypersensitivity reaction to ursodiol, manifesting as skin rash with biopsy-proven lichenoid reaction, has been reported [8], an immediate hypersensitivity has not been reported in the literature.
To our knowledge, this is the first reported case of an immediate allergic reaction followed by successful oral desensitization to ursodiol. We propose that this 12-step desensitization protocol to ursodiol can be safely implemented when alternative options are not available or have proven inferior in efficacy.