For their study, published online Feb. 19 in, , of the University of Michigan, Ann Arbor, and colleagues looked at claims records from a large national private insurer to identify new cases of dementia, Parkinson’s disease, and neuropathy between 2001 and 2016, along with pharmacy records following diagnoses.
The researchers identified more than 52,000 patients with neuropathy on gabapentinoids and another 5,000 treated with serotonin-norepinephrine reuptake inhibitors for the same. They also identified some 20,000 patients with dementia taking cholinesterase inhibitors, and 3,000 with Parkinson’s disease taking dopamine agonists. Dr. Callaghan and colleagues compared patient adherence over 6 months for pairs of drugs in the same class with similar or equal efficacy, but with different costs to the patient.
Such cost differences can be stark: The researchers noted that the average 2016 out-of-pocket cost for 30 days of pregabalin, a drug used in the treatment of peripheral neuropathy, was $65.70, compared with $8.40 for gabapentin. With two common dementia drugs the difference was even more pronounced: $79.30 for rivastigmine compared with $3.10 for donepezil, both cholinesterase inhibitors with similar efficacy and tolerability.
Dr. Callaghan and colleagues found that such cost differences bore significantly on patient adherence. An increase of $50 in patient costs was seen decreasing adherence by 9% for neuropathy patients on gabapentinoids (adjusted incidence rate ratio [IRR] 0.91, 0.89-0.93) and by 12% for dementia patients on cholinesterase inhibitors (adjusted IRR 0.88, 0.86-0.91, P less than .05 for both). Similar price-linked decreases were seen for neuropathy patients on SNRIs and Parkinson’s patients on dopamine agonists, but the differences did not reach statistical significance.
Black, Asian, and Hispanic patients saw greater drops in adherence than did white patients associated with the same out-of-pocket cost differences, leading the researchers to note that special care should be taken in prescribing decisions for these populations.
“When choosing among medications with differential [out-of-pocket] costs, prescribing the medication with lower [out-of-pocket] expense will likely improve medication adherence while reducing overall costs,” Dr. Callaghan and colleagues wrote in their analysis. “For example, prescribing gabapentin or venlafaxine to patients with newly diagnosed neuropathy is likely to lead to higher adherence compared with pregabalin or duloxetine, and therefore, there is a higher likelihood of relief from neuropathic pain.” The researchers noted that while combination pills and extended-release formulations may be marketed as a way to increase adherence, the higher out-of-pocket costs of such medicines could offset any adherence benefit.
Dr. Callaghan and his colleagues described as strengths of their study its large sample and statistical approach that “allowed us to best estimate the causal relationship between [out-of-pocket] costs and medication adherence by limiting selection bias, residual confounding, and the confounding inherent to medication choice.” Nonadherence – patients who never filled a prescription after diagnosis – was not captured in the study.
The American Academy of Neurology funded the study. Two of its authors reported financial conflicts of interest in the form of compensation from pharmaceutical or device companies. Its lead author, Dr. Callaghan, reported funding for a device maker and performing medical legal consultations.
SOURCE: Reynolds EL et al. Neurology. 2020 Feb 19.