Inorganic phosphorus low in common CKD medications
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Data from a single-center, cross-sectional study showed medications commonly prescribed to patients with chronic kidney disease were low in inorganic phosphorus, with most phosphorus coming from excipients.
“CKD patients often present with multiple comorbidities such as diabetes mellitus, hypertension, hyperlipidemia, anemia, and so on,” Rowena Lim, BSc, of the department of pharmacy at the National University of Singapore, and associates wrote. “Polypharmacy is therefore an issue among such patients. If most of the chronic medications consumed by CKD patients frequently contain phosphorus, this may contribute significantly to their daily dietary phosphorus intake.”
Abnormally high serum phosphate levels – hyperphosphatemia – pose health threats to patients with CKD, including increased cardiovascular burden, morbidity and mortality, according to the study published in Journal of Renal Nutrition.
Lim and colleagues collected data on recently prescribed outpatient or discharge medications and dosages for 200 patients with CKD stage 3A, 3B, 4, 5 or 5D at an academic public tertiary care hospital in Singapore. When information on excipients or the amount of phosphorus in each medication was not provided, researchers contacted the manufacturer. Data were logged in a brand-specific library of the phosphorus contents of common CKD medications.
Researchers identified 204 medications and supplements, the most common being omeprazole (54%), atorvastatin (54%), frusemide (52%), aspirin (48%), amlodipine (32%), epoetin beta (30%), bisoprolol (29%), cholecalciferol (29%), calcium acetate (26%) and renal vitamin (26%).
They reviewed 399 formulations; 58 formulations (15%) contained phosphorus (with unknown amounts in 15) and 313 (78%) did not contain phosphorus. Because 44 of 70 manufacturers responded with information, the phosphorus content of 28 formulations (7%) remained unknown.
At least one formulation with phosphorus was prescribed to 169 patients (84.5%) for daily use. Assuming the 158 prescriptions with missing information contained 0 mg of phosphorus, the median daily intake of phosphorus from medications was 1.28 mg in all CKD stages, with no significant differences between stages.
For general phosphorus intake, patients with CKD stage 5D had a median daily intake of 4.09 mg of phosphorus, significantly higher than the intake among patients with CKD stages 3 to 5. Lim and colleagues suggested a higher pill burden and higher proportion of patients with stage 5D CKD prescribed phosphorus-containing medications could explain this difference.
Among 42 prescriptions with no missing information, the median daily phosphorus intake was 0.64 mg.
Though phosphorus intake was low, Lim and colleagues wrote inorganic phosphates are more significant physiologically compared with organic phosphorus because of high bioavailability (greater than 90% vs. 40% to 60% for animal-based phosphates and 20% to 50% for plant-based phosphates).
The researchers suggested future studies include larger populations and collect information on serum phosphate levels.
“In the meantime, physicians may consider prescribing medications with formulations that are known to be phosphorus free in patients with persistent hyperphosphatemia, despite strict dietary restrictions and use of phosphate binders, in order to reduce additional phosphorus burden from medications,” they wrote.
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