6-Thioguanine: High-dose 2-H infusions in goats

Abstract

6-Thioguanine (6TG) is poorly absorbed after oral administration. Bolus injections of 6TG result in high peak concentrations with relatively short-lived plasma concentrations. In vitro studies have shown the importance of prolonged exposure to 6TG. Therefore we administered 6TG by infusion at a dose rate of 2 mg/h over 2 h. In three goats we determined the plasma concentration-time curves of 6TG and its riboside (6TGR). A steady state was reached for 6TG and was almost reached for 6TGR within the 2 h of infusion. In one experiment we obtained several samples of CSF and observed good penetration of 6TG and 6TGR into CSF. Urinary excretion of 6TG and 6TGR was also quantitated. The amount of drug and metabolite excreted later than 4 h after the end of the infusion was negligible. By infusing 6TG, the problems of both erratic absorption after oral administration and acute renal toxicity after bolus injection, can be averted. In our opinion prolonged infusions of 6TG may be of advantage in humans suffering from actively proliferating malignant diseases, and thus should be studied.

Plasma pharmacokinetics and cerebrospinal fluid penetration of thioguanine in children with acute lymphoblastic leukemia: a collaborative Pediatric Oncology Branch, NCI, and Children's Cancer Group study

“…The mean steady-state TG CSF concentration was 0.5 lM during CIVI, a concentration that is approximately tenfold higher than the in vitro IC 50 values in human lymphoblastic cell lines [2]. The CSF penetration of 18% observed in our study is similar to the estimated 25% penetration previously observed in an animal model [18]. The CSF penetration of TG is comparable to the CSF penetration of MP [3].…”