Study: Cancer Diagnosis Impacts Adherence to Diabetes Medications

According to a recent study, following a cancer diagnosis, patients with diabetes are less like to adherence to diabetes medications [Diabetologia. 2015; DOI:10.1007/s00125-015-3497-8]. In addition, compliance with diabetes medications may negatively affect survival and could potentially explain the established higher cancer mortality seen in patients with diabetes.

In the study the researchers found a 6.3% decline in medication possession ratio for glucose-lowering drugs among 3281 patients who were taking them upon subsequent cancer diagnosis compared with 12,891 users of diabetes medications who did not develop cancer. The control group was used to account for the decline

The study population included a total 52,228 patients from a pharmacy database in the southern Netherlands who were ≥30 years of age, with a mean age of 68 years, and those who had been dispensed glucose-lowering medications between 1998 and 2011.

Using data linked to a cancer registry, the authors matched up 3281 patients diagnosed with cancer during follow-up to 4 control patients each for age, sex, duration of follow-up, type of glucose-lowering drug (including metformin, sulfonylureas, insulin, etc), and year of first dispensing. The follow-up time for the controls was matched to the time of cancer diagnosis in the cases.

The average time between the start of use of the glucose-lowering agent and the diagnosis of cancer was 3.7 years for both groups, and the total duration of follow-up was 6.6 years for cases and 6.5 for controls.

Before the cancer diagnosis, the medication possession ratio was increasing by about 0.1% per month. The 6.3% decline at the time of the cancer diagnosis compared with the controls translates to approximately 2 days per month attributable to cancer that the person is not using the glucose-lowering drug, the authors noted.

After the time of the cancer diagnosis, the medication possession ratio declined further by about 0.20% per month. When specific cancers were examined, no declines in diabetes medication adherence were seen among patients diagnosed with prostate or breast cancer. However, significant declines in compliance that were greater compared with controls were seen among patients diagnosed with esophageal, stomach, pancreas, or liver cancers (12.5%) and pulmonary cancers (15.2%). Among those patients, subsequent further monthly drops in medication possession ratio were approximately 0.5% per month.

Declines in medication adherence also increased with more advanced cancer, with an medication possession ratio drop of 10.7% at the time of diagnosis of stage 4 disease, declining an additional 0.64% per month thereafter.

The impact of a cancer diagnosis on adherence was strongest among patients using sulfonylureas in combination with metformin for glucose lowering and in those using insulin alone or in combination.

The authors noted that an medication possession ratio of more than 80% is considered adherent, so the declines of less than 20% seen here may or may not be considered clinically important, though they added that studies have suggested that even a small change in medication possession ratio can impair glycemic control.—Kerri Fitzgerald