Horse Chestnut extract may reduce indinavir kidney sludge

An extract of the Horse Chestnut used in the treatment of chronic venous insuffiency may reduce the risk of indinavir crystals forming in the kidneys. The condition, known as nephrolithiasis results in the accumulation of crystallised indinavir in the kidneys, resulting in severe pain, as well as the passing of razor sharp crystals into the bladder and urinary tract. Nephrolithiasis occurred in around 4% of those who received indinavir in early trials of the drug, but a recent Spanish study of twice daily ritonavir/indinavir reported a rate in the region of 13%.

The Horse Chestnut extract, escin, was tested in a 16 week crossover study in which 47 patients with stable viral load below 200 copies for more than six months were randomised to receive 50mg of escin twice daily or a placebo, then crossed over to the opposite treatment after eight weeks, and then resumed their original treatment at week 12.

Escin significantly increased the crystallisation time of indinavir, hopefully delaying the formation of crystals until the indinavir has passed out of the kidney tubules, where it is most likely to crystallise owing to a higher risk of an alkaline environment. A strict vegetarian diet increases the risk of creating an alkaline environment in the kidneys, according to Professor Felix Grases of the Universidad da Las Islas Baleares, Mallorca. Low fluid intake, especially in hot weather, also increases the risk that crystals will not be flushed from the proximal renal tubules.

The study did not report any cases of nepholithiasis in either arm, so it is not possible to assess whether escin directly reduces the risk of this adverse event.

Three patients discontinued treatment due to gastrointestinal side effects caused by estin, and more than a quarter of participants were lost to follow up or left the study.

A larger clinical endpoint study is now planned to test the effect of escin on the incidence of nephrolithiasis.