Pharmacokinetics, metabolism, bioavailability, tissue distribution and excretion studies of 16α-hydroxycleroda-3, 13(14) Z -dien-15, 16-olide-a novel HMG-CoA reductase inhibitor.

The present study was designed to investigate the oral bioavailability, metabolism, tissue disposition and excretion of 16α-hydroxycleroda-3, 13(14) Z -dien-15, 16-olide (4655K-09), a novel HMG-CoA reductase inhibitor in male Sprague Dawley (SD) rats. Tissue distribution, oral bioavailability and excretion studies of 4655K-09 were carried out in male SD rats through oral administration at active dose of 25 mg/kg. In vitro metabolism studies were carried out in different rat tissues S9 fractions to evaluate primary organs responsible for conversion of parent 4655K-09 to its major active metabolite K-9T. The quantification of both parent and metabolite in different biological matrices was performed using LC-MS/MS method. The oral bioavailability of 4655K-09 was found to be 30% in male SD rats. The biodistribution study was illustrated in terms of tissue to plasma area under curve (AUC)0-∞ ratio (Kp) revealed the preferential distribution of 4655K-09 and K-9T to target site, i.e. liver. In vitro tissue S9 fraction stability assay demonstrated the rapid and extensive metabolic conversion of 4655K-09 to K-9T, primarily through liver and kidney. Very low amount of parent and metabolite were excreted unchanged in urine and faeces. The present studies established 4655K-09 bioavailability, tissue disposition, excretion and tissue-specific metabolic conversion to K-9T which could assist in its further development as antihyperlipidemic drug.

Identification and characterization of fluvastatin metabolites in rats by UHPLC/Q-TOF/MS/MS and in silico toxicological screening of the metabolites.

The present study reports the in vivo and in vitro identification and characterization of metabolites of fluvastatin, the 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitor, using liquid chromatography-mass spectrometry (LC-MS). In vitro studies were conducted by incubating the drug with human liver microsomes and rat liver microsomes. In vivo studies were carried out by administration of the drug in the form of suspension to the Sprague-Dawley rats followed by collection of urine, faeces and blood at different time points up to 24 h. Further, samples were prepared by optimized sample preparation method, which includes freeze liquid extraction, protein precipitation and solid phase extraction. The extracted and concentrated samples were analysed using ultrahigh-performance liquid chromatography-quadruple time-of-flight tandem mass spectrometry. A total of 15 metabolites were observed in urine, which includes hydroxyl, sulphated, desisopropyl, dehydrogenated, dehydroxylated and glucuronide metabolites. A few of the metabolites were also present in faeces and plasma samples. In in vitro studies, a few metabolites were observed that were also present in in vivo samples. All the metabolites were characterized using ultrahigh-performance liquid chromatography-quadruple time-of-flight tandem mass spectrometry in combination with accurate mass measurement. Finally, in silico toxicity studies indicated that some of the metabolites show or possess carcinogenicity and skin sensitization. Several metabolites that were identified in rats are proposed to have toxicological significance on the basis of in silico evaluation. However, these metabolites are of no human relevance. Copyright © 2017 John Wiley & Sons, Ltd.

Voltammetric oxidation and determination of atorvastatin based on the enhancement effect of cetyltrimethyl ammonium bromide at a carbon paste electrode.

An electrochemical method has been described for the voltammetric oxidation and determination of an antihyperlipoproteinemic drug, atorvastatin (ATOR), at a carbon paste electrode (CPE) in the presence of an enhancing agent, cetyltrimethyl ammonium bromide (CTAB) using cyclic and differential pulse voltammetry (DPV). The results indicated that the voltammetric response of ATOR was improved distinctly in the low concentration of CTAB, suggesting that CTAB exhibits noticeable enhancement effect to the determination of ATOR. The dependence of current on pH, concentration and scan rate were investigated to optimize the experimental conditions for the determination of ATOR. The anodic peak was characterized and the process was adsorption-controlled. The number of electrons transferred in the oxidation process was calculated and a plausible oxidation mechanism was proposed. In the range of 0.05-10 µM, the current measured by DPV presents a good linear property as a function of the concentration of ATOR with a detection limit of 4.08 nM with good selectivity and sensitivity. The proposed method was successfully applied to ATOR determination in pharmaceutical samples and urine as a real sample. This method can be employed in clinical analysis, quality control and routine determination of drugs in pharmaceutical formulations.

Determination of rosuvastatin in urine by spectrofluorimetry after liquid-liquid extraction and derivatization in acidic medium.

Statins are a class of drugs mostly used for treating hyperlipidemia, and rosuvastatin is the newest drug in the market belonging to this class. In this present work, a method was developed based on the molecular fluorescence technique, with the objective to quantify rosuvastatin in urine samples. For this purpose, the study of several parameters was made to achieve the maximum analytical signal (under reaction with sulfuric acid during 40 min). Also, a previous step to avoid matrix interference was carried out (liquid-liquid extraction). The limit of detection (LOD) and the limit of quantification (LOQ) were 0.38 and 1.28 mg L(-1), respectively. Linear relationship between rosuvastatin concentration and it's fluorescence intensity was found until 5.0 mg L(-1). The proposed method was tested in several samples spiked with rosuvastatin and recovery was found in the range of 90 ± 10%.

Investigation of the rate-determining process in the hepatic elimination of HMG-CoA reductase inhibitors in rats and humans.

Elucidation of the rate-determining process in the overall hepatic elimination of drugs is critical for predicting their intrinsic hepatic clearance and the impact of variation of sequestration clearance on their systemic concentration. The present study investigated the rate-determining process in the overall hepatic elimination of the HMG-CoA reductase inhibitors pravastatin, pitavastatin, atorvastatin, and fluvastatin both in rats and humans. The uptake of these statins was saturable in both rat and human hepatocytes. Intrinsic hepatic clearance obtained by in vivo pharmacokinetic analysis in rats was close to the uptake clearance determined by the multiple indicator dilution method but much greater than the intrinsic metabolic clearance extrapolated from an in vitro model using liver microsomes. In vivo uptake clearance of the statins in humans (pravastatin, 1.44; pitavastatin, 30.6; atorvastatin, 12.7; and fluvastatin, 62.9 ml/min/g liver), which was obtained by multiplying in vitro uptake clearance determined in cryopreserved human hepatocytes by rat scaling factors, was within the range of overall in vivo intrinsic hepatic clearance (pravastatin, 0.84-1.2; pitavastatin, 14-35; atorvastatin, 11-19; and fluvastatin, 123-185 ml/min/g liver), whereas the intrinsic metabolic clearance of atorvastatin and fluvastatin was considerably low compared with their intrinsic hepatic clearance. Their uptake is the rate-determining process in the overall hepatic elimination of the statins in rats, and this activity likely holds true for humans. In vitro-in vivo extrapolation of the uptake clearance using a cryopreserved human hepatocytes model and rat scaling factors will be effective for predicting in vivo intrinsic hepatic clearance involving active uptake.

Solid-phase extraction and liquid chromatography/tandem mass spectrometry assay for the determination of pitavastatin in human plasma and urine for application to Phase I clinical pharmacokinetic studies.

A sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed and evaluated for the determination of pitavastatin in human plasma and urine. Samples were extracted using solid-phase extraction (SPE). The major benefit of the present method was the high sensitivity, with a lower limit of quantification (LLOQ) of 0.08 ng/mL. Pitavastatin and internal standard (IS, rosuvastatin) were separated on a C(18) column with a mobile phase consisted of methanol/water (75:25, v/v) with 0.05% formic acid. Drug and IS were detected by LC/MS/MS with positive electrospray ionization (ESI). Accuracy and precision for the assay were determined by calculating the intra- and inter-batch variation of quality control (QC) samples at three concentration levels, with relative standard deviations (R.S.D.s) of less than 15%. The developed method was successfully applied to determine pitavastatin in human plasma and urine, and was proved to be suitable for use in Phase I clinical pharmacokinetic study after oral administration of pitavastatin (1, 2 and 4 mg) in healthy Chinese volunteers.

The application of microbore UPLC/oa-TOF-MS and 1H NMR spectroscopy to the metabonomic analysis of rat urine following the intravenous administration of pravastatin.

The metabonomic effects of hepatotoxic doses of pravastatin on the urinary metabolic profiles of female rats have been investigated using ultra performance liquid chromatography (UPLC)-oa-TOF-MS and, independently, by (1)H NMR spectroscopy. UPLC was performed using a 1 mm microbore column packed with 1.7 microm particles. Examination of the data obtained from the individual animals, aided by statistical interpretation of the data, made it possible to identify potential markers for toxicological effects, with both NMR and UPLC-MS analysis highlighting distinct changes in the urinary metabolite profiles. These markers, which included elevated taurine and creatine, as well as bile acids, were consistent with hepatotoxicity in some animals, and this hypothesis was supported by histopathological and clinical chemistry findings. The analytical data from both techniques could be used to define a metabolic "trajectory" as toxicity developed and to provide an explanation for the lack of hepatotoxicity for one of the animals. The two analytical approaches (UPLC-MS and NMR) were found to be complementary whilst the use of a 1mm i.d. x 100 mm column reduced the amount of sample required for analysis to 2 microL, compared with 10 microL for a 2.1mm i.d. x 100 mm column. The 1mm i.d. column also provided increased signal-to-noise without loss of chromatographic efficiency.

Effects of organic anion transporting polypeptide 1B1 haplotype on pharmacokinetics of pravastatin, valsartan, and temocapril.

OBJECTIVE: Recent reports have shown that genetic polymorphisms in organic anion transporting polypeptide (OATP) 1B1 have an effect on the pharmacokinetics of drugs. However, the impact of OATP1B1*1b alleles, the frequency of which is high in all ethnicities, on the pharmacokinetics of substrate drugs is not known after complete separation of subjects with OATP1B1*1a and *1b. Furthermore, the correlation between the clearances of OATP1B1 substrate drugs in individuals has not been characterized. We investigated the effect of genetic polymorphism of OATP1B1, particularly the *1b allele, on the pharmacokinetics of 3 anionic drugs, pravastatin, valsartan, and temocapril, in Japanese subjects. METHODS: Twenty-three healthy Japanese volunteers were enrolled in a 3-period crossover study. In each period, after a single oral administration of pravastatin, valsartan, or temocapril, plasma and urine were collected for up to 24 hours. RESULTS: The area under the plasma concentration-time curve (AUC) of pravastatin in *1b/*1b carriers (47.4 +/- 19.9 ng.h/mL) was 65% of that in *1a/*1a carriers (73.2 +/- 23.5 ng.h/mL) (P = .049). Carriers of *1b/*15 (38.2 +/- 15.9 ng.h/mL) exhibited a 45% lower AUC than *1a/*15 carriers (69.2 +/- 23.4 ng.h/mL) (P = .024). In the case of valsartan we observed a similar trend as with pravastatin, although the difference was not statistically significant (9.01 +/- 3.33 microg.h/mL for *1b/*1b carriers versus 12.3 +/- 4.6 microg.h/mL for *1a/*1a carriers [P = .171] and 6.31 +/- 3.64 microg.h/mL for *1b/*15 carriers versus 9.40 +/- 4.34 microg.h/mL for *1a/*15 carriers [P = .213]). The AUC of temocapril also showed a similar trend (12.4 +/- 4.1 ng.h/mL for *1b/*1b carriers versus 18.5 +/- 7.7 ng.h/mL for *1a/*1a carriers [P = .061] and 16.4 +/- 5.0 ng.h/mL for *1b/*15 carriers versus 19.0 +/- 4.1 ng.h/mL for *1a/*15 carriers [P = .425]), whereas that of temocaprilat (active form of temocapril) was not significantly affected by the haplotype of OATP1B1. Interestingly, the AUC of valsartan and temocapril in each subject was significantly correlated with that of pravastatin (R = 0.630 and 0.602, P < .01). The renal clearance remained unchanged for each haplotype for all drugs. CONCLUSION: The major clearance mechanism of pravastatin, valsartan, and temocapril appears to be similar, and OATP1B1*1b is one of the determinant factors governing the interindividual variability in the pharmacokinetics of pravastatin and, possibly, valsartan and temocapril.

Disposition of oral and intravenous pravastatin in MRP2-deficient TR- rats.

The aim of this study was to characterize the role of the efflux transporter Mrp2 (Abcc2) in the pharmacokinetics of orally and intravenously administered pravastatin in rats. Eight Mrp2-deficient TR- rats and eight wild-type rats were given an oral dose of 20 mg/kg pravastatin. Four TR- animals and four wild-type animals were studied after intravenous administration of pravastatin (5 mg/kg). The TR(-) rats showed a 6.1-fold higher mean area under the plasma concentration-time curve (AUC) of pravastatin (p < 0.001) after oral administration and a 4.7-fold higher AUC (p < 0.01) after intravenous administration of pravastatin as compared with the wild-type animals. The mean systemic (total) clearance of pravastatin was 4.6-fold higher (39.2 versus 8.50 l/h/kg, p < 0.001) and the mean V 4.3-fold higher (14.1 versus 3.29 l/kg, p < 0.01) in the wild-type rats. The mean renal clearance of pravastatin in the TR(-) rats was 16.5-fold increased as compared with the wild-type animals (0.695 versus 0.042 l/h/kg, p < 0.05). The increased systemic exposure to oral pravastatin in the TR- rats was associated with a greater inhibitory effect on 3-hydroxy-3-methylglutaryl CoA reductase, as shown by smaller lathosterol to cholesterol concentration ratios. These results suggest that the reduced biliary pravastatin excretion in the Mrp2-deficient TR- rats is partly compensated for by increased urinary excretion of pravastatin. Furthermore, intestinal Mrp2 does not appear to play a major role in the oral absorption of pravastatin in normal rats.

Quantification of pravastatin in human plasma and urine after solid phase extraction using high performance liquid chromatography with ultraviolet detection.

A high performance liquid chromatography (HPLC) method for the estimation of pravastatin in human plasma and urine samples has been developed. The preparation of the samples was performed by automated solid phase extraction using clonazepam as internal standard. The compounds were separated by isocratic reversed-phase HPLC (C(18)) and detected at 239 nm. The method was linear up to concentrations of 200 ng/ml in plasma and 2000 ng/ml in urine. The intra-assay variability for pravastatin in plasma ranged from 0.9% to 3.5% and from 2.5% to 5.3% in urine. The inter-assay variability ranged from 9.1% to 10.2% in plasma and from 3.9% to 7.5% in urine. The validated limits of quantification were 1.9 ng/ml for plasma and 125 ng/ml for urine estimation. These method characteristics allowed the determination of the pharmacokinetic parameters of pravastatin after administration of therapeutic doses.

Evidence for inverse effects of OATP-C (SLC21A6) 5 and 1b haplotypes on pravastatin kinetics.

OBJECTIVE: We compared the pharmacogenetic effects of OATP-C (organic anion transporting polypeptide C) *1a, *1b (A388G), and *5 (T521C) haplotypes on single-dose pharmacokinetics of pravastatin in white subjects. METHODS: Thirty healthy white male subjects were grouped according to their OATP-C haplotype. Each group contained 10 individuals who were either homozygous or heterozygous carriers of the *1a, *1b, or *5 haplotype. After a single oral dose of 40 mg pravastatin, we analyzed kinetic parameters of pravastatin disposition. RESULTS: Values for the area under the plasma concentration-time curve from time 0 to 6 hours [AUC(0-6)] in *1a/*1a, *1a/*1b or *1b/*1b, and *1a/*5 individuals were 114.5 +/- 68.6 microg. L(-1). h, 74.8 +/- 35.6 microg. L(-1). h, and 163.0 +/- 64.6 microg. L(-1). h, respectively, with highly significant differences across all 3 study groups (P =.006) and between subjects carrying the *1b and *5 haplotype (P =.002). Strikingly, values of AUC(0-6) from the OATP-C *1b group were more than 60% lower than those derived from carriers of the wild-type OATP-C *1a haplotype, although this difference failed to reach statistical significance. However, the amount of pravastatin excreted into the urine from time 0 to 12 hours [Ae(0-12)] was significantly diminished in the OATP-C *1b haplotype group (1729 +/- 907 microg) compared with *1a wild-type control subjects (2974 +/- 1590 microg) (P =.049). CONCLUSION: There was a significant effect of tested OATP-C variant haplotypes on pravastatin disposition. Whereas *5 expression delayed the hepatocellular uptake of pravastatin, *1b expression seemed to accelerate OATP-C-dependent uptake of the drug.

Metabolism, excretion, and pharmacokinetics of rosuvastatin in healthy adult male volunteers.

BACKGROUND: Rosuvastatin is a 3-hydroxy-3-methylglutaryl coenzyme A-reductase inhibitor, or statin, that has been developed for the treatment of dyslipidemia. OBJECTIVE: This study assessed the metabolism, excretion, and pharmacokinetics of a single oral dose of radiolabeled rosuvastatin ([14C]-rosuvastatin) in healthy volunteers. METHODS: This was a nonrandomized, open-label, single-day trial. Healthy adult male volunteers were given a single oral dose of [14C]-rosuvastatin 20 mg (20 mL [14C]-rosuvastatin solution, nominally containing 50 microCi radioactivity). Blood, urine, and fecal samples were collected up to 10 days after dosing. Tolerability assessments were made up to 10 days after dosing (trial completion) and at a follow-up visit within 14 days of trial completion. RESULTS: Six white male volunteers aged 36 to 52 years (mean, 43.7 years) participated in the trial. The geometric mean peak plasma concentration (C(max)) of rosuvastatin was 6.06 ng/mL and was reached at a median of 5 hours after dosing. At C(max), rosuvastatin accounted for approximately 50% of the circulating radioactive material. Approximately 90% of the rosuvastatin dose was recovered in feces, with the remainder recovered in urine. The majority of the dose (approximately 70%) was recovered within 72 hours after dosing; excretion was complete by 10 days after dosing. Metabolite profiles in feces indicated that rosuvastatin was excreted largely unchanged (76.8% of the dose). Two metabolites-rosuvastatin-5S-lactone and N-desmethyl rosuvastatin-were present in excreta. [14C]-rosuvastatin was well tolerated; 2 volunteers reported 4 mild adverse events that resolved without treatment. CONCLUSIONS: The majority of the rosuvastatin dose was excreted unchanged. Given the absolute bioavailability (20%) and estimated absorption (approximately 50%) of rosuvastatin, this finding suggests that metabolism is a minor route of clearance for this agent.

Determination of simvastatin-derived HMG-CoA reductase inhibitors in biomatrices using an automated enzyme inhibition assay with radioactivity detection.

A robust, automated enzyme inhibition assay method was developed and validated for the determination of HMG-CoA reductase inhibitory activities in plasma and urine samples following simvastatin (SV) administration. The assay was performed on Tecan Genesis 150 and 200 systems equipped with 8-probe and 96-well plates. Plasma samples containing HMG-CoA reductase inhibitors were treated with acetonitrile for protein precipitation before being incubated with HMG-CoA reductase, [14C]-HMG-CoA, and NADPH for a fixed length of time at a fixed temperature. The product, [14C]-mevalonic acid, was lactonized and separated from excess substrate via a small ion exchange resin column, and radioactivity was counted on a scintillation counter. HMG-CoA reductase inhibitors were measured before and after base hydrolysis. The two values obtained for each sample are referred to as 'active' and 'total' HMG-CoA reductase inhibitor concentrations. Simvastatin acid (SVA), the beta-hydroxy acid of SV, was used as a standard to generate a calibration curve of HMG-CoA reductase activity versus SVA concentration (ng/ml). Three calibration ranges, 0.4-20, 2-50, and 50, 100 ng/ml, in human and animal plasma and urine were validated. The assay precision was less than 8.5%, CV in plasma and less than 10.4% in urine. The assay accuracy was 93.6-103.0 and 98.1-103.9% for the 0.4 20 and 2-50 ng/ml calibration ranges, respectively, in human plasma, and was 97.3-105.1, 94.4- 105.2, and 90.2-95.7%, for calibration range 5-100 ng/ml in rat plasma, dog plasma and human urine, respectively.

Gemfibrozil increases plasma pravastatin concentrations and reduces pravastatin renal clearance.

BACKGROUND: Gemfibrozil increases the plasma concentrations of active acid forms of cerivastatin, lovastatin, and simvastatin. Pravastatin pharmacokinetics differs from those of these 3 statins, which are extensively metabolized. Our aim was to study the effects of gemfibrozil on the pharmacokinetics of pravastatin. METHODS: A randomized, placebo-controlled, 2-phase crossover study was carried out. Ten healthy volunteers took gemfibrozil (1200 mg/d) or placebo for 3 days. On day 3, each subject ingested a single 40-mg dose of pravastatin. The concentrations of pravastatin and gemfibrozil in plasma and the cumulative excretion of pravastatin into urine were measured up to 24 hours. RESULTS: During the gemfibrozil phase, the mean total area under the plasma concentration-time curve (AUC) of pravastatin from 0 hours to infinity was 202% (range, 40%-412%) of the corresponding value during the placebo phase (P <.05), but there was no difference in the half-life between the phases. The renal clearance of pravastatin was reduced from 25 L/h to 14 L/h by gemfibrozil (P <.0001), but the cumulative excretion of pravastatin into urine did not change significantly. The increase in the AUC of pravastatin from 0 to 24 hours correlated significantly with the decrease in the renal clearance of pravastatin (r = 0.72, P =.02). However, the change in renal clearance was only a minor contributor to the increase in pravastatin AUC. CONCLUSIONS: Gemfibrozil increases plasma concentrations of pravastatin. This is partly but not solely the result of the reduced renal clearance of pravastatin. The increase in pravastatin AUC from 0 hours to infinity by gemfibrozil may represent an interference with a transport protein.

Molecular basis of 3-hydroxy-3-methylglutaric aciduria.

3-Hydroxy-3-methylglutaric aciduria is a human autosomal recessive metabolic disorder that usually appears within the first year of life. The causes of this aciduria are lethal mutations in the gene encoding for 3-hydroxy-3-methylglutaryl coenzyme A lyase (HL). HL is a mitochondrial matrix enzyme that catalyzes the last step of ketogenesis and leucine catabolism. This gene has been mapped to chromosome 1 at locus 1pter-p33 and its genomic organisation comprises 9 exons whose sizes vary between 64-678 bp. The human cDNA sequence was reported in 1993 with the first genetic study of two Acadian-French Canadian siblings. To date, 24 mutations in 36 patients have been described; most of them are single-base substitutions causing amino acid replacements and a variety of splicing defects. In the population studied two mutations appear predominant: g.122GA (8 patients and 15 alleles) frequent in Saudi Arabia, and g.109GT (6 patients and 12 alleles), prevalent in Spain. At least seven mutations are clustered in the second half of exon 2 affecting aminoacids E37, R41 and D42 and conforming a possible hot spot. The genotype-phenotype correlation is difficult to establish since the probands received different treatments, and the onset of an acute episode frequently depends on external factors such as fasting or acute illness.

No effect of rosuvastatin on the pharmacokinetics of digoxin in healthy volunteers.

The effect of rosuvastatin on the pharmacokinetics of digoxin was assessed in 18 healthy male volunteers in this double-blind, randomized, two-way crossover trial. Volunteers were dosed with rosuvastatin (40 mg once daily) or placebo to steady state before being given a single dose of digoxin 0.5 mg. Blood and urine samples for the measurement of serum and urine digoxin concentrations were collected up to 96 hours following dosing. The effect of rosuvastatin was assessed by constructing 90% confidence intervals (CIs) around the treatment ratios (rosuvastatin + digoxin/placebo + digoxin) for digoxin exposure. The geometric least square mean AUC(0-t) and Cmax of digoxin were only 4% higher when the drug was coadministered with rosuvastatin compared to placebo. The 90% CIs for both treatment ratios (AUC(0-t) = 0.88-1.24; Cmax = 0.89-1.22) fell within the prespecified margin of 0.74 to 1.35; therefore, no significant pharmacokinetic interaction occurred between rosuvastatin and digoxin. The geometric mean amount of digoxin excreted into the urine and its renal clearance were similar with rosuvastatin and placebo. These results demonstrate that rosuvastatin has no effect on the pharmacokinetics of digoxin. Coadministration of rosuvastatin and digoxin was well tolerated.

Glucuronidation of statins in animals and humans: a novel mechanism of statin lactonization.

The active forms of all marketed hydroxymethylglutaryl (HMG)-CoA reductase inhibitors share a common dihydroxy heptanoic or heptenoic acid side chain. In this study, we present evidence for the formation of acyl glucuronide conjugates of the hydroxy acid forms of simvastatin (SVA), atorvastatin (AVA), and cerivastatin (CVA) in rat, dog, and human liver preparations in vitro and for the excretion of the acyl glucuronide of SVA in dog bile and urine. Upon incubation of each statin (SVA, CVA or AVA) with liver microsomal preparations supplemented with UDP-glucuronic acid, two major products were detected. Based on analysis by high-pressure liquid chromatography, UV spectroscopy, and/or liquid chromatography (LC)-mass spectrometry analysis, these metabolites were identified as a glucuronide conjugate of the hydroxy acid form of the statin and the corresponding delta-lactone. By means of an LC-NMR technique, the glucuronide structure was established to be a 1-O-acyl-beta-D-glucuronide conjugate of the statin acid. The formation of statin glucuronide and statin lactone in human liver microsomes exhibited modest intersubject variability (3- to 6-fold; n = 10). Studies with expressed UDP glucuronosyltransferases (UGTs) revealed that both UGT1A1 and UGT1A3 were capable of forming the glucuronide conjugates and the corresponding lactones for all three statins. Kinetic studies of statin glucuronidation and lactonization in liver microsomes revealed marked species differences in intrinsic clearance (CL(int)) values for SVA (but not for AVA or CVA), with the highest CL(int) observed in dogs, followed by rats and humans. Of the statins studied, SVA underwent glucuronidation and lactonization in human liver microsomes, with the lowest CL(int) (0.4 microl/min/mg of protein for SVA versus approximately 3 microl/min/mg of protein for AVA and CVA). Consistent with the present in vitro findings, substantial levels of the glucuronide conjugate (approximately 20% of dose) and the lactone form of SVA [simvastatin (SV); approximately 10% of dose] were detected in bile following i.v. administration of [(14)C]SVA to dogs. The acyl glucuronide conjugate of SVA, upon isolation from an in vitro incubation, underwent spontaneous cyclization to SV. Since the rate of this lactonization was high under conditions of physiological pH, the present results suggest that the statin lactones detected previously in bile and/or plasma following administration of SVA to animals or of AVA or CVA to animals and humans, might originate, at least in part, from the corresponding acyl glucuronide conjugates. Thus, acyl glucuronide formation, which seems to be a common metabolic pathway for the hydroxy acid forms of statins, may play an important, albeit previously unrecognized, role in the conversion of active HMG-CoA reductase inhibitors to their latent delta-lactone forms.

Influence of erythromycin pre- and co-treatment on single-dose pharmacokinetics of the HMG-CoA reductase inhibitor cerivastatin.

OBJECTIVE: Cerivastatin is a novel, synthetic, highly potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor that effectively reduces serum cholesterol levels at very low doses. It is exclusively cleared from humans via cytochrome P450-mediated biotransformation (demethylation M1; hydroxylation M23) and subsequent biliary/renal excretion of the metabolites. The influence of concomitant administration of erythromycin, a potent CYP3A4 inhibitor, on cerivastatin bioavailability and pharmacokinetics was investigated. METHODS: Twelve healthy young male subjects received single oral doses of 300 microg cerivastatin alone or on the 4th day of a 4-day pre- and co-treatment with erythromycin 500 mg t.i.d. in a randomised, non-blind crossover study. Plasma and urine samples were analysed for cerivastatin and its major metabolites by validated specific high-performance liquid chromatography assays. RESULTS: Cerivastatin was safe and well tolerated. No clinically relevant treatment-emergent changes in laboratory parameters were observed. The pre- and co-treatment with erythromycin 500 mg t.i.d. had a modest influence on cerivastatin clearance, leading to a mean increase in the maximum plasma concentration (Cmax) of 13% and a slightly increased terminal half-life (approximately 10%), resulting in a mean elevation of the area under the curve (AUC) of 21%; time to peak (tmax) remained unchanged. While the mean AUC of the metabolite M1 following the combined dosing was decreased by 60% compared with mono-dosing, the mean AUC of M23 exhibited an increase of approximately 60%. The respective Cmax results paralleled these pronounced effects, whereas the influence on mean terminal half-lives was small (i.e. for M23, an approximate 20% increase) or not observable (i.e. for M1). CONCLUSIONS: Concomitant administration of erythromycin 500 mg t.i.d. affects, to a certain extent, the metabolism of cerivastatin, administered as a single oral dose of 300 microg, resulting in a slightly increased exposure of the parent drug and active metabolites which, however, does not need dose adjustment. In addition, the small increase in cerivastatin half-life does not predict an accumulation beyond steady state. The pharmacokinetic data for the major metabolites suggest that the M1 metabolic pathway is more sensitive to CYP3A4 inhibition than the parallel M23 pathway, supporting recent in vitro findings that further cytochrome P450 isozymes are differently involved in the metabolic pathways of cerivastatin.