51. Human Pharmacokinetics of 5-Formyl Tetrahydrofolate
- Author
-
Bruce Kenneth Birmingham
- Subjects
Chromatography ,biology ,medicine.drug_class ,Metabolite ,Central compartment ,Serum albumin ,chemistry.chemical_element ,Calcium ,Antimetabolite ,chemistry.chemical_compound ,chemistry ,Pharmacokinetics ,Toxicity ,medicine ,biology.protein ,Methotrexate ,medicine.drug - Abstract
The purpose of this study wa~ to deteraine the pharaacokinetics of calcium leucoYorin in nor•al subjects and in patients undergoing High-Dose methotrexa~e therapy for the treat•ent of neoplastic diseaseBy characterizing the disposition of leucovorin it was hoped that the the efficacy of the aethotrexate therapy might be i•proved, while at the sa•e time, the incidence of toxicity could be di•inished. An assay for the separation and quantification of leucovorin in serua was developed. The reduced folate vas extracted from seru• using re•erse-phase chromatographic •inicoluans and a paired-ion reagent. Leucovorin was eluted from this systea in methanol and e•aporated to dryness under nitrogen. The extracted samples were stable for 3 days vhen stored at -4oc. Bigh pressure liquid chroaatoqraphy vas used to separate leuco•orin from the extracted Rerua coaponents using a reverse-phase, paired-ion mode. Aamonium phosphate, dibasic, vas found to be a suitable pairing agent. The recently developed radially coapressed reverse-phase coluans vere found to provide superior resolution of serua components than vas possible with conventional stainless steel columns. The effects of flov rate, pH, column teaperature, and buffer concentration on the separation of leucoYorin vere investigated. Electrochemical detection vas used to quantify the reduced folate in the extracted serum samples. An applied potential of 0.8 volts vas used to produce a sensitive and selective aeans of detecting leucovorin. The apparent lover limit of sensitivity under the conditions employed vas 12 ng leuco•orin. The effects of pH, buffer concentration, methanol concentration, and mobile phase flow rate on detector response vere investigated. The protein binding of leucovorin and its major aetabolite 5-aethyltetrahydrofolate to hu•an serum albumin was determined. Over the concentration range of 5.0x10-78 to 1x10-•K neither folate saturated the available binding sites. Leucovorin binding was a constant 701, vhile aethyltetrahydrofolate decreased slightly over this range. When both folates vere present in the albumin solution, there was a significant decrease in the degree of binding of each. ftethotrexate did not affect the binding of leucovorin or its metabolite. The pharaacokinetics of leucovorin vas determined in 6 noraal subjects and in 5 cancer patient s. There were no siqnif icant differences in the kinetic parameters calculated fro• either group. The disposition of leucovorin is best characterized by a two coapartment open aodel. ln initial half-life of 8.79 ± 4.44 minutes and a second, slower elimination phase of 231.46 ± 31.76 minutes vas determined. The volume of the central compartment vas calculated as 5.49 ± 3.53 Liters. Leucovorin serum concentrations in 3 cancer patients receiving HighDose methotrexate vere deterained to be 3 to 11 times greater than vas predicted using methotrexate pharmacokinetic paraaeters. This study clearly deaonstrates that there are significant differences in the pharmacokinetics of leucovorin and methotrexate. The data presented in this study suggests that it aight be possible to reduce the aaount of leucovorin administered to patients being treated vith met.hotrexate. This may be expected to improve the efficacy of the antimetabolite therapy without additional risk of toxicity. ( ABSTRACT ACKNOilLEDGEftENT TABLE OF CONTENTS LIST OP TABLES LIST OP FIGURES
- Published
- 2020