For patients receiving renally cleared cancer medications, therapeutic drug levels are higher and adverse events were more frequent for those whose cystatin C-based estimated glomerular filtration rate (eGFR) was more than 30% lower than their serum creatinine–based eGFR, a recent study suggests.
The cohort study included 1869 adult patients with cancer who had simultaneous serum creatinine–based eGFR (eGFRcr) and cystatin C-based eGFR (eGFRcys) measured.
The primary exposure was eGFR discordance, defined as an eGFRcys > 30% lower than the eGFRcr.
The primary outcome was risk of medication-related adverse events associated with vancomycin, trimethoprim-sulfamethoxazole, baclofen, or digoxin.
Roughly 29% of patients (n = 543) had eGFRcys more than 30% lower than their eGFRcr.
These patients were more likely to experience medication-related adverse events, including supratherapeutic vancomycin levels (24% vs 9% of patients), trimethoprim-sulfamethoxazole-related hyperkalemia (22% vs 12%), baclofen toxic effect (26% vs 0%), and high digoxin levels (29% vs 0%).
Even after adjusting for age, sex, race and ethnicity, baseline comorbidities, laboratory studies, and medication use, patients with an eGFRcys more than 30% lower than the eGFRcr had a significantly increased risk of 30-day mortality (adjusted hazard ratio, 1.98).
“We found a considerably higher rate of supratherapeutic drug levels and [adverse events] associated with select renally cleared medications and increased risk of death in patients with an eGFRcys that was more than 30% lower than the eGFRcr compared with patients with a concordant eGFR or those whose eGFRcys was more than 30% higher than the eGFRcr,” the authors reported.
This study, led by Paul Hanna, MD, with Massachusetts General Hospital, Boston, was published online July 5 in JAMA Network Open.
The study likely overestimated the rate of eGFR discordance and used a one-time assessment of serum creatinine and cystatin C, which may not reflect a steady state at the time of measurement.
The authors report no relevant financial relationships. The study reported no specific funding.
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