Abstract
Background and study aims Colonoscopy is a widely used diagnostic procedure which requires prior cleansing
of the bowel. Many different bowel cleansing preparations have been developed, all
of which have specific advantages and disadvantages. This review compares two low-volume
high-osmolarity bowel cleansing preparations, oral phosphate salts and oral sulphate
salts, with a particular focus on risk of nephrotoxicity.
Patients and methods An electronic search of the Medline database was performed using the search terms
“(phosphates OR sulfates) AND cathartics [MeSH Term] AND kidney” restricted to humans
with a cut-off date of December 31, 2016.
Results Introduction of oral phosphate salts offered the advantage of low intake volume and
low risk of bowel irritation compared to previous options. However, phosphate salts
have been associated with renal toxicity (acute phosphate nephropathy [APN]), thought
to arise due to perturbations of calcium and phosphate homeostasis as a consequence
of increases in serum phosphate. This results in high concentrations of calcium phosphate
in the distal tubule and collecting ducts of the kidney, where it may precipitate.
Although APN is rare, it may lead to permanent kidney damage. For this reason, phosphate
salts are contraindicated in vulnerable patient groups. As an alternative to phosphate
salts, oral sulphate salts have recently been introduced. Because sulphate absorption
from the intestinal tract is saturable, serum sulphate concentrations increase only
minimally after ingestion. Furthermore, excretion of sulphate in the kidney is not
accompanied by calcium excretion and urine calcium levels are unchanged. For these
theoretical reasons, use of sulphate salts as bowel cleansing solutions is not expected
to lead to calcium precipitation in the nephron.
Conclusions Oral phosphate salts are no longer recommended for routine use as bowel cleansing
preparations as they carry significant risk of kidney damage and a safer alternative
is available in the form of oral sulphate solutions. To date, use of sulphate salts
has not been associated with elevations in serum creatinine or other markers of renal
impairment, nor with clinical manifestations of kidney injury. Nonetheless, experience
with sulphate salts in everyday practice is limited and physicians should be vigilant
in detecting potential safety issues.
