Background/Purpose: Oral bisphosphonates adherence has been reported as less than 50% at one year. With patients frequently having refill gaps greater than 30 days. Zoledronic acid (ZA) is a once yearly injectable bisphosphonate anti-osteoporosis medication (AOM) with 100% adherence for 12 months. We evaluated what proportion of patients who continued ZA after the first infusion and for those receiving a second dose how close to 365 days that dose was administered.

Methods: We identified new ZA users using billing data between January 1, 2010 and December 2012 from a large healthcare system based on healthcare procedure codes J3488 and Q2051 and linked to electronic medical record data. Included patients had at least two rheumatology office visits and first receipt of ZA was in or after 2010. We excluded patients who had received ZA before the study period but not other AOM. Results are presented as mean (standard deviation [SD]) or %.

Results: There were 771 patients who met inclusion criteria. A second ZA infusion was given to 489 patients (63.4%) and 6.5% not continuing ZA were prescribed another AOM. Women (89.5%) and Caucasian (89.0%) race were the majority of the cohort with a mean age of 68.1 (10.9). The mean number of AOMs used prior to ZA was 1.7 (1.3) with 18.7% not having an AOM prescribed within the health system. Previous fractures were present in 20.4%, mean Charlson Comorbidity score of 1.9 (2.5), and 29.7% had GERD or gastric ulcers at first ZA administration. Persistence of ZA is presented in Table 1. Of the 489 patients who received a second ZA infusion 307 (63%) were within 365 ±30 days (a care gap of >30 days is defined as lack of persistence with oral agents). By 180 days 445/489 (91%) and 365 days 486 (99%) had received a second ZA infusion.

Conclusion:

Although ZA adherence is by definition superior to oral BPs at one year, 36.6% of patients in our cohort did not receive a second infusion. Of those receiving a second infusion only 63% do so within the first 30 days although 99% had a second infusion at 365 days. Considering recent data suggesting that a single dose of ZA may reduce fracture for longer than one year, a  gap of >30 days may be too strict a criterion for lack of persistence. ZA is approved for use at 24 month intervals for prevention. Since 36% of patient did not receive a second ZA dose, reasons for discontinuation and delay in a second infusion should be further investigated. Additionally, physician offices should have a method for scheduling yearly ZA infusions as a quality metric.

Table 1. Zoledronic Acid Treatment Gaps
Treatment Gap	% Treated
±30 days	62.8%
+60 days	77.7%
+90 days	85.7%
+120 days	87.5%
+150 days	90.0%
+180 days	91.0%
+365 days	99.4%
ZA: Zoledronic Acid; 2nd ZA administration was assessed at 365 days after first administration

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/continued-zoledronic-acid-use-in-a-large-healthcare-system/