Dow, Elizabeth N.

e569 Background: O is a PARP inhibitor that has received breakthrough designation for use in mCRPC based on a study in which a subset of 16 patients with DNA repair defects had an 80% response rate. O is an oral tablet taken twice daily. Studies have demonstrated that compliance with oral agents is often poor, and the less frequent contact with medical staff increases the risk of toxicities when compared to IV therapies. This is compounded by a bias where oral medications are thought of as less toxic than IV medications. The toxicities of O include myelosuppression, nausea, vomiting, and fatigue. Our practice employs a pharmacist to conduct weekly phone calls for toxicity management, monitor patient adherence, and monitor for drug-drug interactions. We report our experience with patient adherence, toxicities, and response with O in mCRPC. Methods: A single institution, retrospective review was performed on 14 mCRPC patients treated with O from November 2015 - October 2016. Adherence and toxicity data were assessed and documented via phone calls conducted by a clinical pharmacist. The primary outcomes were number of missed doses, incidence of toxicities, and dose modifications. The secondary outcome was response rate, defined as a 50% reduction in PSA or radiographic response according to RECIST 1.1 for a duration of greater than 3 months. Results: Patients reported taking 99% of the prescribed doses. The toxicities observed most commonly were fatigue (64%), nausea (57%) and anemia (57%). As a result of toxicities, four patients required a dose reduction to 300 mg BID, three patients required a dose reduction to 200 mg BID and two patients were initiated on 200 mg BID and maintained on that dose until progression. Partial responses were seen in 6 of 14 patients. Conclusions: Our pharmacist led adherence program facilitated timely dose adjustments and high patient adherence. Response rates were comparable to published data.