The utilization review approval rate for opioids for injured workers in California has declined 3.5% since the state’s prescription drug formulary took effect on Jan. 1, according to a preliminary analysis by the California Workers’ Compensation Institute.

In October 2015, Gov. Jerry Brown signed A.B. 1124 mandating the adoption of an evidence-based formulary for medications prescribed to California injured workers and calling on the state Division of Workers’ Compensation to incorporate the formulary into its Medical Treatment Utilization Schedule. The legislation’s intent was to ensure that medications provided to injured workers meet evidence-based standards and to reduce delays and frictional costs associated with pharmaceutical utilization and independent medical review, the Oakland-based institute said Friday in a statement.

The organization’s findings show that the proportion of utilization review decisions involving prescription drug requests fell to 40.7% in the first five months of 2018 from 44.5% in the preformulary period, a relative decline of 8.5%. At the same time, the percentage of utilization review decisions in which a prescription drug request was denied was unchanged at 14.6%, while 85.4% were either approved as submitted or approved with a modification.

Utilization review decisions involving opioid requests showed little change, edging down to 30.0% after the formulary took effect from 30.6% in the preformulary period, but the utilization review approval rate for opioids showed a sharper decline, falling to 68.8% from 72.3%, according to the analysis.

Meanwhile, the percentage of independent medical review decisions involving utilization review modifications or denials of opioids increased to 33.6% under the formulary from 29.2% prior to the formulary’s implementation, while the independent medical review uphold rate for opioid modifications or denials showed a modest increase, rising to 91.4% from 90.1%.

The CWCI analysis used data from 141,643 pharmaceutical requests and utilization review decisions from the first five months of 2017 and 2018, and 58,604 independent medical review decisions from the first four months of those same two years to measure and compare pre- and post-formulary outcomes.

The institute cautioned that the study represents only a preliminary look at data from the first few months as stakeholders were transitioning into the formulary, with more time needed to identify changes in prescribing patterns and other aspects of the formulary regulations that could impact utilization review and independent medical review disputes. The institute is planning to publish an expanded study on first-year formulary outcomes in 2019.