Late dosing of luteinizing hormone-releasing hormone agonists (LHRH) and testosterone (T) levels >20 ng/dL in prostate cancer (PCa).

31 Background: LHRH agonists are the most frequently used drugs for the delivery of androgen deprivation therapy (ADT) for PCa. Evidence suggests achieving and sustaining T levels ≤20 ng/dL with ADT is desirable and correlates with improved disease-specific survival in advanced PCa patients. However, T levels may rise above castration level (50 ng/dL) between injections, especially if a subsequent dose is delayed. Increase in prostate-specific antigen (PSA) level on ADT may represent true disease progression to castration resistant PCa, or may be a result of late ADT dosing and inadequate T suppression. Current study evaluated timeliness of LHRH agonist dosing, subsequent rate of T breakthroughs and frequency of T/PSA testing prior to dosing in PCa patients. Methods: A retrospective review of electronic medical records and associated claims data (1/1/07-6/30/16) of LHRH agonist injections (n=85,030) evaluated the frequency of late dosing (defined as occurring after day 32, 97, 128, 194 for 1-, 3-, 4-, 6-month formulations, respectively), T tests >20 ng/dL and frequency of T/PSA tests prior to dosing. Results: 26.9% of injections were late: 14.4% were ≤1 week late, 3.1% were between 1-2 weeks late and 9.4% were >2 weeks late. 43% of T values exceeded 20 ng/dL for late injections; while only 21% exceeded this level for early/on-time injections. 83% of LHRH injections had a PSA value drawn prior to dosing; however, only 13% had a similarly timed T assessment. Conclusions: Overall, >25% of injections were late. For late injections, the proportion of T tests with T >20 ng/dL was higher compared to when the dosing was early/on-time. Late injections correlated with ineffective T suppression (>20 ng/dL) over 40% of the time. For all injections, T levels were not monitored as frequently as PSA levels. Considering the potential clinical benefits of maintaining effective T suppression throughout the course of ADT, clinicians should ensure treatments are delivered within approved dosing instructions, routinely monitor T levels and consider prescribing treatments with proven efficacy through the dosing interval to maintain T ≤20 ng/dL.