Pharmacokinetic studies of alizarin in man

Alizarin, a constituent of the madder root, is employed in phytotherapy to prevent recurrences of calcium-containing urinary stones. Pharmacokinetic studies were carried out in human subjects during the development of a pharmaceutical product containing alizarin. After giving a single oral dose of 210 mg of alizarin there were two maxima in the serum concentration curves, the first at 2-4 h and the second at 6-8 h. Alizarin and its glucuronide conjugate were detected in both maxima by TLC. The mean elimination half-life was 12 h. The amounts excreted in the urine within 6 days ranged from 18.1 to 36.3%, and the amounts in the faeces from 21.6 to 33.0% (total recovery: 40-60%). In bile from a patient who had undergone cholecystectomy only 0.6% of the dose was recovered. To exclude any possibility that alizarin might be bound to calcium ions in bone, bone trephine specimens were examined from patients with oxalate stones who had previously been treated with alizarin for several years. No alizarin was detectable in these samples. When alizarin is mixed with fresh human faeces and incubated anaerobically it undergoes rapid bacterial decomposition. This in vitro experiment indicates that when alizarin is given orally a large proportion is broken down by bacterial action in the intestine.