Stone patients are poorly adherent with medical prophylaxis

New findings based on pharmacy claims data show just how adherent patients are to a thiazide, alkali citrate, and allopurinol.

New Orleans-Numerous studies have shown poor adherence with preventive medications prescribed for patients with various chronic medical conditions, and now research conducted by urologists at the University of Michigan show this problem applies to patients prescribed medical prophylaxis for kidney stones.

The investigators used national pharmacy claims data from a recent 5-year period (2002-2006) to identify commercially insured adults who had one or more prescriptions filled for a thiazide, alkali citrate, or allopurinol after receiving a physician-coded diagnosis of nephrolithiasis. Medication adherence was evaluated using the validated proportion of days covered formula. Defining adherence as >80% proportion of days covered during the first 6 months after the index kidney stone claim, only 50% of the nearly 22,000 patients included in the cohort were adherent with their regimen.

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While year-by-year analyses showed a trend for adherence improving over time, the overall adherence rate was still below 55% in the last year of the study.

Logistic regression analysis was also performed to evaluate patient factors associated with adherence. Not surprisingly, the results showed that being on combination therapy or having a less generous insurance plan independently predicted lower adherence. In addition, males were significantly more likely to be adherent than females as were Midwesterners compared with patients from other parts of the country.

“To our knowledge, this is the first study examining patient adherence to medication prescribed for kidney stone prevention, and the findings are important for urologists considering that non-adherence may mitigate treatment benefit or even cause harm,” said Yooni Yi, MD, urology resident at the University of Michigan, Ann Arbor, who presented the research at the AUA annual meeting in New Orleans.

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Dr. HollingsworthJohn M. Hollingsworth, MD, MS, assistant professor of urology at the University of Michigan, told Urology Times, “Getting a patient to accept a prescribed regimen for kidney stone prevention and adhere to it may be difficult since a benefit of treatment is not obviously apparent to someone who is asymptomatic between stone events. Our study reinforces the need to spend time counseling patients on the importance of adherence and suggests possible targets for quality improvement in the secondary prevention of kidney stones.”

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He noted that in addition to reinforcing the need for medication adherence through in-office education efforts, practitioners can suggest the use of a variety of aids, such as medication assistance programs or free mobile apps that remind patients to take their medications and keep track of their dosing schedule.

In investigating the issue of adherence to medical therapy for nephrolithiasis prevention, the study focused on medications recommended by the AUA Guideline on the Medical Management of Kidney Stones to be trialed in patients with selected metabolic abnormalities. Looking at patterns of use, the data showed that 83% of patients were prescribed a monotherapy regimen with thiazide monotherapy being most common (58% of the total population).

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In examining adherence rates for the individual medications, the study identified marked variability with adherence being best for thiazide monotherapy (42%) and lowest for alkali citrate monotherapy (~3%).

NEXT: Reasons for low adherence

“Reasons to explain the very low adherence to citrate include the dosing frequency of a citrate supplementation regimen, its side effects, and cost. These findings highlight a potential barrier faced by providers who care for patients with hypocitraturia and low urine pH,” Dr. Hollingsworth said.

The investigators noted their study has limitations. Its use of a convenience sample limits the ability to generalize the results. In addition, there is the potential for misclassification bias since it cannot be excluded that the investigated medications were prescribed for some other indication.

Importantly, while the study identified a problem with adherence, it did not investigate its consequences on clinical outcomes.

“Now we are actively investigating the impact that non-adherence has on outcome measures, including hospital admissions, emergency department visits, and stone-directed surgery among others,” Dr. Hollingsworth said.