Association Between Children Prescription Drug Costs for New Medications and Their Parent's Adherence to Chronic Medication

Background: The adverse impact of high prescription drug costs on medication non-adherence and health has been well-described for individual patients. However, many families share financial resources. Thus, medication costs for one family member could lead to cost-related non-adherence in another, but these family effects have not been explored.

Objectives: We evaluated whether the initiation of medication by a child affected their parent's adherence to their own existing medications and whether the magnitude of these effects varied by how expensive the child's medication was.

Methods: We conducted an interrupted time-series analysis using administrative claims from 2010-2020 from a large national US health commercial insurer. To do so, we identified children <18 years initiating a medication ("index date") and linked family members on the same insurance plan. We classified individuals ≥15 years older than the child as a parent and restricted to those parents who filled a medication intended for long-term use in the prior year. The exposure was the cost of the child's initiated medication and whether the medication for acute or long-term use. Child medication cost was classified as high (≥90th percentile) or low ( <10th percentile) based on out-of-pocket spending. The primary outcome was parental adherence to medication assessed by the proportion of days covered metric, measured in 30-day increments 360 days before and after the child's index date. We used propensity score matching on baseline covariates and adherence trend and used generalized estimating equations to compare the impact of a child initiating a high-cost vs. low-cost medication, for acute and long-term use, on parental adherence.

Results: Our parent cohort consisted of 309,682 child-parent dyads. In children initiating a medication intended for long-term use, high-cost medications resulted in an immediate 1.9% (95%CI: -3.8%, -0.9%) greater decrease in their parent's adherence than a low-cost medication; this immediate drop persisted in lower adherence over follow-up. Similarly, a child initiating an acute high-cost medication led to an immediate 0.6% (95%CI: -1.3%, -0.1%) decrease in parental adherence relative to controls, with no subsequent change in slope. Sensitivity analyses of other ways of classifying exposure and family units led to similar findings.

Conclusions: The cost of a new medication by a child may have a small but meaningful immediate impact on adherence to chronic disease medications by their parent. This effect persisted regardless of whether the child's medication was expected to be used acutely but was greater for medications intended for long-term use. Healthcare systems, insurers, and clinicians may need to more globally consider household level spending in order to improve healthcare outcomes by all members.