I don’t know how to segue from high art to the lower bowel, so I’ll just do it. Americans have always been obsessed with their bowels – I’ve told my students many times that if they were to learn only one class of drug it should be laxatives – but lately this fixation has gone big time. About 14 million colonoscopies are done in the US each year – let no bowel be unscoped. This means that there have to be 14 million bowel preps.
Bowel preparation is usually achieved using either polyethylene glycol (eg Golytely) or oral sodium phosphosoda (eg Fleets Phosphosoda). If your doctor prescribes Golytely, you (the one on the action side of the colonoscope) have to drink about a gallon of vile tasting liquid over four hours. If you can get the stuff down it has the desired effect of cleaning out your colon so the endoscopist can get a good look. But the experience is so unpleasant that many patients refuse to do it more than once in the event that a second colonoscopy is needed. Though this prep is extremely distasteful it is safe.
Phosphosoda preps are much better tolerated requiring much less fluid intake. But as always there’s a price for everything. Since 2003 a number of patients have been described who developed acute renal failure after taking phosphosoda. Worse, the loss of renal function may be permanent. The renal injury seems due to tubular precipitation of calcium phosphate. Two papers and an editorial in the December issue of the Journal of the American Society of Nephrology examine the incidence and predisposing factors for this disorder.
The incidence appear to be very low, perhaps one in a thousand or less. But if half of the 14 million colonoscopies done each year use a phosphosoda prep, that’s 7,000 cases. Predisposing factors include increased age, drugs which blockade the renin-angiotensin system, diuretics, heart failure, preexisting renal disease, female sex, dehydration, and a decreased effective arterial blood volume.
Increased physician and patient awareness about this problem should minimize the incidence of acute phosphate nephropathy. First, and most important – avoid phosphosoda preps in patients at increased risk. The manufacturers of phosphosoda laxatives have reduced the phosphate concentration in their products which may decrease the liklihood of phosphate deposition in the kidney. Adequate hydration should be ensured by having the patient drink a minimum of 72 ounces of clear liquids along with the phosphosoda. Of course this obviates one of the reasons for using phosphosoda preps, but the patient can drink a fluid that’s not as distasteful as polyethylene glycol. This is a problem with a solution already at hand.
1. Towards the Incidence of Acute Phosphate Nephropathy:
Glen S. Markowitz, Jai Radhakrishnan, and Vivette D. D’Agati
J Am Soc Nephrol 18: 3020-3022.
2. Association of Oral Sodium Phosphate Purgative Use with Acute Kidney Injury:
Frank P. Hurst, Erin M. Bohen, Eric M. Osgard, David K. Oliver, Nealanjon P. Das, Sam W. Gao, and Kevin C. Abbott
J Am Soc Nephrol 18: 3192-3198.
3. Risk of Kidney Injury Following Oral Phosphosoda Bowel Preparations:
Steven M. Brunelli, James D. Lewis, Meera Gupta, Sherif M. Latif, Mark G. Weiner, and Harold I. Feldman
J Am Soc Nephrol 18: 3199-3205.