Two readers offer alternatives to preventing kidney stones:
Q: The article “Kidney stones: helping patients avoid the pain” (July/August 2008) by Edgar V. Lerma, MD, was a good general review, but it didn't mention medical expulsion therapy (MET) of renal stones using alpha blockers. This is an off-label use, but the literature seems to favor a trial of medical therapy (Lancet. 2006;368:1171-1179; J Urol. 2007;177:983-987; Ann Emerg Med. 2007;50:552-563; Evid Based Med. 2008;13:111). A medical approach would be safer and less invasive than surgical therapy.
—Jerry Goddard, MD, Carbondale, Ill.
Q: I have my recurrent stone patients take magnesium oxide 400 mg daily and vitamin B6 100 mg daily. Isn't there science to support the use of these supplements?
—Karl Sandberg, MD, Ola, Ark.
A: As noted in the article, the likelihood of spontaneous passage of a kidney stone is highly dependent on its size and location. MET has been demonstrated in several studies to be a useful adjunct to medical observation in patients with distal ureteral stones <4 mm in diameter. In some studies, stones as large as 8 mm have also been removed in this manner. Several medications have been described to achieve this effect: antispasmodic agents, calcium channel blockers (nifedipine), and, as Dr. Goddard alluded to, alpha1 blockers (tamsulosin), which have been used with or without corticosteroids (J Urol. 2005;174:167-172 and 2007;177:983-987 and Ann Emerg Med. 2007;50:552-563). The mechanism has been ascribed to the presence of alpha1 receptors in the ureter, especially the distal portion. One major requirement prior to MET is that the patient be comfortable with medical observation and that there be no urgency in immediate stone removal, e.g., hypotension or moderate-to-severe hydronephrosis. In addition to being safer and less invasive than surgical therapy, cost-effectiveness of MET for the management of distal ureter stones as compared with surgical intervention has been evaluated (Eur Urol. 2008;53:418-419).Only a handful of studies have looked at the use of magnesium oxide and pyridoxine (vitamin B6) in the prevention of kidney stones (J Urol. 1974;112:509-512 and Urol Res. 1994;22:161-165). None of these is well-controlled or convincing; some are anecdotal case reports. Moreover, magnesium-related side effects are significant limitations of such treatment. The use of vitamin B6 in preventing stones has been described in those with primary hyperoxaluria as underlying disease (Kidney Int. 2005;67:1704-1709). Certainly, this is an agent that could be studied more in general, that is, outside primary hyperoxaluria.
—Edgar V. Lerma, MD, Chicago, Ill.