An investigation involving a comparison between the hydrolytic degradation of lovastatin and simvastatin using HPLC

Abstract

Lovastatin (LV) and Simvastatin (SV) are known by their common general name of Statins. They are hypolipedemic drugs used for the treatment of hypercholesterolemia. Both statins are administrated as prodrugs that require metabolic activation to form the active acid forms, namely lovastatin hydroxy acid (LVA) and simvastatin hydroxy acid (SVA). Both statins possess similar chemical structures and the only differences is the presence of a 2-methylbutryloxy side chain moiety for LV compared to SV that consists of a 2, 2-dimethylbutryloxy side chain. Various studies have reported the hydrolysis of the lactone ring and not the methylbutryloxy side chain of these statins.
The aim of the study was to measure the rate of hydrolysis of the methylbutryloxy side chain esters of both these statins that jroduce monacolin J, which is a metabolite common to both statins in question using porcine liver esterase (PLE), cholesterol esterase (CE), esterases present in human plasma and standard alkaline conditions, monitored by HPLC.
A validated HPLC method was used to measure the compounds of interest at 254 nm. The mobile phase consisted of acetonitrile: water: acetic acid in the ratio of 70: 30: 0.5 (v/v/v). The column used was a Phenomenex Luna C18 (2) 150x4.60
mm column and the flow rate used for the analysis of all the compounds was I mi/mm. LV, SV, LVA and SVA were eluted at retention times (RT) of 7.80, 9.40, 3.67 and 4.75 mm, respectively. Linearity was determined ranging from 78.12 .tg% to 10 mg% for LV, 31.25 g% to 10 mg% for SV, and 1-Im mg% for LVA and SVA, respectively. The correlation coefficient for LV, SV, LVA and SVA were 1.000 0.9993, 0.9920 and 0.9989, respectively. The relative standard deviation (RSD) for the repeatability determinations of LV, SV, LVA and SVA were found to be 0.1209, 0.6194, 1.5972 and 3.0015, respectively. The RSD for the reproducibility determinations of LV, SV, LVA and SVA were 0.5284, 0.4030, 2.1480 and 1.6426, respectively. The limit of detection for LV, SV, LVA and SVA were 1.22, 3.90, 3.90 and 15.62 pig/mI, respectively, whereas, the limit of quantification for LV, SV, LVA and SVA were 2.44, 7.81, 7.81 and 31.25 pig/mi, respectively.
Both LV and SV were readily hydrolysed to the corresponding LVA and SVA. The hydrolysis of LV by PLE also showed the formation of a product at RT of approx. 2.48 mm. LVA and SVA showed a significant decrease in peak areas when incubated with PLE, CE and human plasma, however, these reactions failed to produce any peaks. The rate of decrease in peak area of LVA was found to be greater than that of SVA.
The results suggest that the rate of hydrolysis of the side chain moiety of SV is slower than that of LV. The additional methyl group in the side chain moiety of SV increases the efficacy of the statin since its role is to protect the ester from excessive hydrolysis to the monacolin J metabolite.