Simultaneous determination and determination of sildenafil and its active metabolite in human plasma using LC-MS/MS method.

A sensitive and selective high-performance liquid chromatography-tandam mass spectrometry (LC-MS/MS) method was developed and validated for the simultaneous quantification of sildenafil and its metabolite N-desmethyl sildenafil in human plasma. Sildenafil-d8 was used as an internal standard. The analytes were extracted by precipitation extraction and chromatographed on a C18 column using mobile phase A of water (containing 0.1% formic acid) and mobile phase B of acetonitrile (containing 0.1% formic acid) with gradient elution. Quantification was done using multiple reaction monitoring mode to monitor the precursor-to-product ion transitions of m/z 475.4 → m/z 283.3 for sildenafil, m/z 461.4 → m/z 283.2 for N-desmethyl sildenafil and m/z 483.3 → m/z 108.1 for IS in positive ionization mode. The calibration curve was established over the range of 2.00-1,000 ng/ml and the correlation coefficient was >0.99. The intra-day and inter-day relative standard deviations were <6.5% for sildenafil and 6.3% for N-desmethyl sildenafil respectively. Accuracy determinaed at four concentrations was 86.50-105.67% for sildenafil and 96.83-114.40% for N-desmethyl sildenafil. This method was successfully applied to a pharmacokinetic description of sildenafil and the effect of food intake on the pharmacokinetics of sildenafil was also demonstrated in healthy Chinese volunteers.

An improved LC-MS/MS method for determination of cinacalcet in human plasma and its application to the evaluation of food intake effect on the pharmacokinetics of cinacalcet in healthy volunteers.

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of cinacalcet in human plasma was developed and validated. This assay was based on liquid-liquid extraction and cinacalcet-d4 was used as an internal standard (IS). Separation was achieved on a C18 column by the mobile phase A of water (containing 0.1% formic acid) and the mobile phase B of acetonitrile-water (95:5, v/v) (containing 0.2% formic acid) with gradient elution. Quantification was done using multiple reaction monitoring mode to monitor the precursor-to-product ion transitions of m/z 358.2 → m/z 155.2 for cinacalcet and m/z 362.3 → m/z 155.0 for IS at positive ionization mode. The calibration curve was established over the range 0.05-20.0 ng/mL and the correlation coefficient was >0.99. The intra- and inter-day relative standard deviations were <5.8%. Accuracy determined at four concentrations ranged between 96.0 and 106.0%. This method was successfully applied to a pharmacokinetic description of oral dose of cinacalcet and the significant effect of food intake on the pharmacokinetics of cinacalcet was first demonstrated in Chinese healthy volunteers.

Prediction of tacrolimus metabolism and dosage requirements based on CYP3A4 phenotype and CYP3A5(*)3 genotype in Chinese renal transplant recipients.

AIM: To examine how the endogenous CYP3A4 phenotype and CYP3A5(*)3 genotype of Chinese renal transplant recipients influenced the dose-corrected trough concentration (C0/D) and weight-corrected daily dose (D/W) of tacrolimus. METHODS: A total of 101 medically stable kidney transplant recipients were enrolled, and their blood and urine samples were gathered. The endogenous CYP3A4 phenotype was assessed by the ratio of 6ß-hydroxycortisol and 6ß-hydroxycortisone to cortisol and cortisone in urine. CYP3A5(*)3 genotype was determined using PCR-RELP. RESULTS: In overall renal transplant recipients, a multiple regression analysis including the endogenous CYP3A4 phenotype, CYP3A5(*)3 genotype and post-operative period accounted for 60.1% of the variability in C0/D ratio; a regression equation consisting of the endogenous CYP3A4 phenotype, post-operative period, body mass index, CYP3A5(*)3 genotype, gender, total bilirubin and age explained 61.0% of the variability in D/W ratio. In CYP3A5(*)3/(*)3 subjects, a combination of the endogenous CYP3A4 phenotype, post-operative period and age was responsible for 65.3% of the variability in C0/D ratio; a predictive equation including the endogenous CYP3A4 phenotype, post-operative period, body mass index, gender and age explained 61.2% of the variability in the D/W ratio. Base on desired target range of tacrolimus trough concentrations, individual daily dosage regimen was calculated, and all the observed daily doses were within the predicted range. CONCLUSION: This study provides the equations to predict tacrolimus metabolism and dosage requirements based on the endogenous CYP3A4 phenotype, CYP3A5(*)3 genotype and other non-genetic variables.

Pharmacodynamic analysis of intravenous recombinant urate oxidase using an indirect pharmacological response model in healthy subjects.

AIM: Pharmacodynamic analysis of intravenous recombinant urate oxidase produced by Escherichia coli was performed in healthy subjects using a pharmacokinetic/pharmacodynamic (PK/PD) model. METHODS: A randomized, single-blind, placebo-controlled study was performed in 40 healthy Chinese subjects (4 groups of 10 subjects each, placebo 4:1 ratio) who received infusions of uricase (single doses of 0.1, 0.2, and 0.3 mg/kg; multiple doses of 0.2 mg·kg(-1)·d(-1) for 7 d). PK profiles were determined through plasma uricase activity, and PD profiles were established using uric acid levels in plasma and urine. The plasma PD parameter was estimated as changes in plasma uric acid levels as the effect in the indirect response model. Adverse events were also monitored. RESULTS: A two-compartment PK model with constant iv input and first-order output was used to describe the kinetic process of plasma uricase. The low value (2.8 U/L) of drug concentration that achieved 50% of maximum effect (EC50) indicated that low plasma uricase concentrations were sufficient to produce pharmacological effects. A strong relationship (r(2)=0.9991) between the mean uric acid concentration in blood and the mean uric acid excretion rate in urine in the range of 11 to 30 h after single dosing was found. Infusions of uricase were well tolerated in all subjects. CONCLUSION: The PK/PD model predicted the effective dose to be 0.1 mg/kg in healthy subjects. The excretion rate of uric acid in urine may be used as a new index for pharmacological effects in further clinical trials.

Effect of amlodipine on the pharmacokinetics of tacrolimus in rats.

1. The immunosuppressant tacrolimus (TAC) is a substrate of cytochrome P450 3A2 (CYP3A2) and P-glycoprotein (P-gp) in rats. Amlodipine (AML) is an inhibitor of CYP3A2 in rats. We investigated the effect of AML on the pharmacokinetics of TAC in rats. 2. When co-administered with TAC orally or intravenously, AML decreased the oral clearance and raised the blood concentration of TAC in rats, but the T1/2 of TAC was not significantly affected by AML. Upon oral administration of TAC, the effect of 15 mg/kg of AML on the AUC of TAC was lower than that seen with 5 or 10 mg/kg. However, upon intravenous TAC administration, the effect of 15 mg/kg of AML on the AUC of TAC was higher than that seen with 5 mg/kg. 3. AML is an inhibitor of P-gp and CYP3A2 in rats. If AML and TAC are co-administered orally, AML elicits greater inhibition in P-gp than CYP3A2 during first-pass metabolism. If AML is given orally and TAC given intravenously concurrently, AML mainly inhibits CYP3A2 activity and increases the blood concentration of TAC. There are significant pharmacokinetic interactions between TAC and AML. AML raises the blood concentration of TAC in rats probably by inhibiting P-gp and CYP3A2.

Metabolism and Mass Balance in Rats Following Oral Administration of the Novel Antifibrotic Drug Fluorofenidone.

Objective: Fluorofenidone (AKF-PD) is a novel antifibrotic small-molecule compound. The purpose of this study was to investigate the metabolic and excretory pathways of AKF-PD in rats. Methods: High-performance liquid chromatography with mass spectrometric (HPLC-MS) detection was used to analyze the metabolites in rat urine. The metabolites were separated by chromatography and their structure was confirmed. HPLC was used to determine the contents of the parent compound and its metabolites in feces and urine after quantitative administration to study the excretion pathway. Results: AKF-PD was mainly oxidized to the carboxyl group after methyl hydroxylation. After oral administration, the total amount of the prototype drug and its hydroxylated metabolites and carboxylated metabolites excreted from the urine and feces of rats was 87%. However, most of them are excreted in urine and feces in the form of carboxylated metabolites, and rarely excreted in the form of prototype drugs and hydroxylated metabolites. Which is that the urinary discharge of hydroxylated metabolites, fluorine ketones, and carboxylated metabolites were 0.2%, 1.1%, and 75.2%, respectively, while the fecal discharge were 0.2%, 0.3%, and 10.1%, respectively. Conclusion: AKF-PD is mainly oxidized into 2-hydroxymethyl and 5-carboxyl AKF-PD through the Phase I metabolic reaction in rats. AKF-PD is a highly permeable compound classified by biopharmaceutics and is mainly excreted from the urine in the form of metabolites.

Association of GSTM1 null polymorphism with isosorbide-5-mononitrate cardiovascular response and involvement of CGRP in healthy Chinese male volunteers.

OBJECTIVES: To determine whether functional polymorphisms of glutathione S-transferase µ type 1 (GSTM1) and aldehyde dehydrogenase-2 (ALDH2) affect the isosorbide 5-mononitrate (IS-5-MN) response, and the role of the calcitonin gene-related peptide (CGRP) in IS-5-MN response in healthy volunteers. METHODS: A two-phase, placebo-controlled study was carried out in 24 healthy Chinese volunteers with their ALDH2 and GSTM1 genotypes known. During each phase, either 20-mg IS-5-MN tablet or placebo was orally administered; blood pressure (BP), heart rate, and plasma concentration of CGRP was determined before and at several time points after drug administration. Pharmacokinetic parameters of IS-5-MN were determined. RESULTS: GSTM1 null individuals showed significantly lower systolic BP (SBP) and diastolic BP (DBP), and higher degree of decreases in SBP (ΔSBP) and DBP (ΔDBP) after IS-5-MN administration. GSTM1 null individuals showed significantly decreased IS-5-MN area under the plasma concentration-time curve than GSTM1 wild-type individuals (P<0.05). Plasma concentration of CGRP was increased significantly at 0.5 (P<0.01), 1 (P<0.05), and 2 h (P<0.05) after IS-5-MN administration in GSTM1 null individuals but not wild-type individuals. GSTM1 null individuals also showed significantly higher degree of percentage increase in the plasma concentration of CGRP than GSTM1 wild-type individuals at 1 h after IS-5-MN administration (P<0.05). IS-5-MN upregulated CGRP I and CGRP II mRNA expressions in cultured peripheral blood mononuclear cells, and the IS-5-MN-induced CGRP II mRNA expression was inhibited by GSTs inhibitor, ethacrynic acid. No difference in the IS-5-MN response was observed between ALDH2 genotypes. CONCLUSION: We suggest that GSTM1, but not ALDH2, may interfere with the bioactivation of IS-5-MN, and CGRP contributes to the IS-5-MN response in a GSTM1 genotype-dependent manner.

Carnosic acid alleviates depression-like behaviors on chronic mild stressed mice via PPAR-γ-dependent regulation of ADPN/FGF9 pathway.

RATIONALE: The pathway of adiponectin (ADPN)/fibroblast growth factor 9 (FGF9) was recently thought as a key role in the development of depression. ADPN is crucially regulated by peroxisome proliferator-activated receptor-gamma (PPAR-γ). Natural material carnosic acid (CA) has been applied for therapeutics of mental disorders. OBJECTIVES: To evaluate the antidepressive effect of CA in stress-treated mice and define whether its effects is involved in the regulation of ADPN/FGF9 pathway. METHODS: In vivo study, the levels of ADPN and FGF9 in both serum and hippocampus tissues, the expressions of ADPN receptor 2 (AdipoR2) in hippocampus and PPAR-γ in abdominal adipose, as well as the pathological changes of hippocampus were determined in 28-day period of chronic unpredictable mild stress (CUMS)-induced depression model of male ICR (Institute of Cancer Research) mice or adipo-/- mice. In vitro study, the level of ADPN and the mRNA expressions of both ADPN and PPAR-γ were determined in mouse 3T3-L1 preadipocytes. RESULTS: In vivo study, treatment with CA (50 or 100 mg/kg per day) for 21 days markedly suppressed depressive-like behaviors, the elevating levels of FGF9 and decreasing levels of ADPN in both serum and hippocampus tissues, the downregulating protein and mRNA expressions of AdipoR2 in hippocampus and PPAR-γ in abdominal adipose, as well as the pathological injury of hippocampus induced by CUMS in male ICR mice. The antidepressive effects of CA were markedly attenuated in male CUMS-treated adipo-/- mice. In vitro study, incubation with CA (3-30 µmol/L) for 24 h could concentration-dependently upregulate the mRNA expressions of both PPAR-γ and ADPN as well as increase the level of ADPN. The experiments using PPAR-γ-specific inhibitor GW9662 and transient transfection with mutated PPAR-γ-binding site promotor constructs showed that the activation of PPAR-γ mediated CA-induced ADPN expression in adipocytes. CONCLUSIONS: CA could significantly improve stress-induced depressive disorder, which may be related to regulating the dysfunction of ADPN-FGF9 pathway via activating PPAR-γ in adipocytes.

The correlation between adiponectin and FGF9 in depression disorder.

Adiponectin (ADPN) and fibroblast growth factor 9 (FGF9) has been reported as anti-depressive and pro-depressive factor, respectively. However, it is unknown whether there is directly interaction between ADPN and FGF9 in depression. The present study aims to investigate the correlation between ADPN and FGF9 in depression disorder. Firstly, the decreased level of ADPN and the increased level of FGF9 in plasma of depressive patients compared with non-depressive subjects were observed. Furthermore, these is a significant negative correlation between the ratio of ADPN to FGF9 and the total score of Hamilton Depression Scale in total investigated subjects. The similar changes of ADPN and FGF9 were also observed in elder adiponectin gene knockout (Adipo-/-) mice with an increasing trend to depressive-like behaviors. Secondly, the decreasing level of ADPN and increasing level of FGF9 in plasma and hippocampus tissues were observed in chronic unpredictable mild stress (CUMS)-induced depression in ICR mice with significant depressive-like behaviors and hippocampus damage, which attenuated by injection of recombinant ADPN or FGF9 antibody into lateral ventricle. In Adipo-/- mice, injection of FGF9 antibody into lateral ventricle also attenuated CUMS-induced depressivelike behaviors. The protein expression of FGF receptor 3 (FGFR3), the main receptor of FGF9, was significantly down-regulated in hippocampus tissues of CUMS-treated mice, which could be attenuated by treatment with either recombinant ADPN or anti-FGF9. In summary, the present results suggest that ADPN maybe a key negative regulator of FGF9/FGFR3 in depressive disorder and the dysfunction of ADPN-FGF9 pathway plays a key role in stress-induced depression.

Evaluation of CYP3A activity in humans using three different parameters based on endogenous cortisol metabolism.

AIM: Currently, there is considerable debate as to which method is more accurate for measuring the activity of CYP3A in vivo: cortisol 6beta-hydroxylation clearance (Cl(m(6beta))) or the urinary ratio of 6beta-OHF to F (6beta-OHF/F). Furthermore, the value of measuring endogenous levels of cortisol over a 24 h period (AUC(F)) needs to be confirmed. The aim of the present study was to determine which method was most effective at measuring changes in the in vivo activity of CYP3A: AUC(F), Cl(m(6beta)), or 6beta-OHF/F. METHODS: A two phase, cross-over design was adopted in this study. A total of 24 subjects (12 males and 12 females) were randomly assigned to one of two groups: the test group subjects were given 250 mg clarithromycin tablets twice a day for a period of 4 d, whereas the control group received a placebo twice daily for a similar period. On d 5 of the study, the last dose of either clarithromycin or placebo was supplemented with an oral dose of 7.5 mg midazolam (MDZ); blood and urine samples were then collected at various times. All samples collected at the same sampling times on d 4 were used to evaluate the effects of MDZ administration on cortisol levels and metabolism. The ratio of 1-hydroxymidazolam (1-OHMDZ) concentration to MDZ concentration at 1 h (MR) was taken as a measure of the in vivo CYP3A activity. AUC(F), Cl(m(6beta)), and 6beta-OHF/F were also used as biomarkers for CYP3A activity. RESULTS: No correlations were found (either before or after inhibition) between CYP3A activity and any of the following measures: AUC(F), Cl(m(6beta)), or 6beta-OHF/F (r<0.4, P>0.05). After 4 d of clarithromycin administration, CYP3A activity (MR) decreased by 75% (P=0.000), whereas AUC(F) increased by 19% (P=0.040), and Cl(m(6beta)) and 6beta-OHF/F decreased by 54.2% (P=0.000) and 50% (P=0.003), respectively. No significant changes in AUC(F) (P=0.178), or in the amount of urinary 6beta-OHF (P=0.169), or in F (P=0.391) were found over a 24 h time period, either with or without MDZ administration. CONCLUSION: Although Cl(m(6beta)) and 6beta-OHF/F can reflect the decline in CYP3A activity, the impression they provide is neither accurate nor complete. AUC(F) is completely ineffective for evaluating variations in CYP3A activity. MDZ administration had no evident effects on either cortisol metabolism or excretion over a period of 24 h.

Effect of sinomenine on human cytochrome P450 activity.

BACKGROUND: Cytochrome P450s superfamily expressed widely in organisms are known to play an important role in the biotransformation of many endogenous and exogenous substances. Inhibition or induction of cytochrome P450 isozymes is one of the major causes for clinical drug-drug interactions. Sinomenine can be metabolized to at least 2 metabolites in human, rat in vivo and in human liver microsomes. The major metabolite was identified to be N-demethylsinomenine. However, which CYP450 isozymes mediated by sinomenine in vivo and in vitro is not known. METHOD: In vitro study, 6 probe drugs were incubated with or without sinomenine respectively to study the effect of sinomenine on different cytochrome P450s activities in human microsomes. In vivo study, a 5-drug cocktail approach was used to study the inhibitive and inducing effect of sinomenine at normal clinical dose on cytochrome P450s activities. RESULTS: Sinomenine (50 micromol/l) had no significant effects on the activities of CYP1A2, CYP3A4, CYP2C9, CYP2E1, and CYP2D6, but it decreased the activity of CYP2C19 by 69% (p=0.012) in human microsomes. In vivo, sinomenine showed almost no significant effects on the activities of CYP1A2, CYP3A4, CYP2E1, and CYP2D6, but enhanced the elimination of mephenytoin by 73% (p=0.032). CONCLUSION: Sinomenine (50 micromol/l) inhibited the activity of CYP2C19 in human microsomes, but in vivo sinomenine at normal clinical dose enhanced the elimination of mephenytoin.

Pharmacokinetic interaction between cefaclor and bromhexine in healthy Chinese volunteers.

OBJECTIVE: To determine the pharmacokinetic interaction between cefaclor and bromhexine in healthy Chinese volunteers. METHODS: Twelve subjects received a cefaclor (CEF) treatment, a bromhexine (BHX) treatment, and a co-treatment of CEF and BHX with a 3 x 3 Latin square design. The wash-out time between periods was 14 days. The plasma and urine drug concentrations of CEF and BHX were detected by HPLC-UV and LC/MS, respectively. RESULTS: All the 12 volunteers completed the study. There were no significant differences in AUC 0-t and Cmax of CEF in logarithm between the single administration group of CEF and the co-administration group of CEF with BHX. Two one sided t-test showed that CEF was bioequivalent in the 2 groups. There were no significant differences in tmax, MRT, t1/2, and Clr between the 2 groups. Vd/F was significantly lower in the single CEF group than in the co-administration group of CEF and BHX. There were no significant differences of AUC 0-t and Cmax of BHX in logarithm between the single administration group of BHX and the co-administration group of BHX with CEF. Two one sided t-test showed that BHX was bioequivalent in the 2 groups. There were no significant differences in tmax, MRT, t1/2, Vd/F, and Clr between the 2 groups. CONCLUSION: There is no significant pharmacokinetic parameter change in the drug absorption, metabolism, and excretion, but Vd/F of CEF significant increases in the co-administration of CEF with BHX. The co-administration of CEF and BHX has no adverse drug interaction. The increase of Vd/F may be a favorable drug interaction, which may be the mechanism of the synergistic effect of the 2 drugs.

[Inhibition of 1,3,8-trihydroxy-5-methoxyxanthone on cytochrome P450s].

OBJECTIVE: To explore the inhibitive effects of 1,3,8-trihydroxy-5-methoxyxanthone (TMX) on cytochrome P450s (CYP450s) in human liver microsomes. METHODS: Probe drugs were incubated with and without adding TMX to determine the changes of enzyme activities. The concentration ratio of metabolites to probe drugs was used to present enzyme activities. Concentrations of the probe drugs and their metabolites in the incubated mixture were detected by high performance liquid chromatography. RESULTS: The variations (mean, 95%CI) of the activities of CYP1A2, CYP2C9, CYP2C19, CYP2E1 and CYP3A4 were 2.95 x 10(-3) (2.03 x 10(-3), 3.88 x 10(-3)), 3.14 x 10(-2) (1.87 x 10(-2), 4.42 x 10(-2)), 2.27 x 10(-3) (-1.4 x 10(-2),1.81 x 10(-2)), 7.72 x 10(-2) (-0.83 x 10(-2), 0.2374), and -0.2548 (-2.9802, 2.4707), respectively. The activities of CYP1A2 and CYP2C9 were significantly reduced in the present of TMX. CONCLUSION: TMX (10 micromol/L) has significant inhibitive effect on the activities of CYP1A2 and CYP2C9, but no significant inhibitive effect on the activities of CYP2C19, CYP2E1 and CYP3A4.

Determination of sinomenine in human plasma by HPLC/ESI/ion trap mass spectrum.

BACKGROUND: Sinomenine is a pure alkaloid with a variety of pharmacological actions including anti-inflammation, immuno-suppression, analgesia, antihypertension, and antiarrhythmia. Methods have been developed to measure sinomenine in rats and rabbits through high-performance liquid chromatography (HPLC). But only one report described a method for determination of sinomenine in humans. METHOD: We developed a method to quantitate sinomenine in human plasma based on liquid chromatography-ion trap mass spectrometry coupled with electrospray ionization (HPLC/ESI/ion trap mass spectrum). RESULTS: The calibration curve (r2=0.9993) of sinomenine was established with standard solutions. The mean inter-day and intra-day CVs<15%. The limit of detection for sinomenine was 0.5 ng/ml. The relative recovery of high, middle and low concentration was 99%, 103%, and 118%, respectively. CONCLUSION: The method is simple, rapid, sensitive, specific, and accurate enough for determination of sinomenine in human plasma and may be used to investigate the metabolism and pharmacokinetics of sinomenine.

[Pharmacokinetics of erythromycin stinoprate capsule].

OBJECTIVE: To determine the pharmacokinetics of erythromycin stinoprate capsules and to provide guidance for clinical research. METHODS: Thirty healthy volunteers (15 men and 15 women) were divided into 3 groups randomly, each including 5 men and 5 women. Single oral doses of 250, 500 and 750 mg were given to each volunteer. The concentrations of erythromycin propionate and erythromycin base in the plasma were determined by HPLC-MS. RESULTS: All 30 volunteers completed the experiment without adverse reactions. Using 3P87 we analyzed the model and calculated the pharmacokinetic parameters. Three dose groups taking high, middle and low dose were all single compartment model. The pharmacokinetic parameters of erythromycin propionate after taking erythromycin stinoprate capsules were as follows: Low dose group: Ka (2.007 +/- 1.281 )/h, tmax ( actual value) (1.9 +/- 0.6) h, Cmax (437.0 +/- 295.0) microg/L, AUC0-14 (trapezoid area) (1840.2 +/- 1476.87) microg x h/L, Ke (0.329 +/- 0.119)/h, T1/2 (2.45 +/- 0.9) h. Middle dose group: Ka (1.451 +/- 0.380)/h, tmax (1.7 +/- 0.3) h, Cmax (923.1 +/- 217.5) microg/L, AUC0-14 (4542.44 +/- 1579.4) microg x h/L,Ke (0.237 +/- 0.057)/h, T1/2 (3.1 +/- 1.1) h; High dose group: Ka (2.076 +/- 1.559)/h, tmax (1.7 +/- 0.3) h, Cmax (1336.5 +/- 366.0) microg/L, AUC0-14 (7481.5 +/- 2496.2) microg x h/L, Ke (0.266 +/- 0.051)/h, T1/2 (2.7 +/- 0.5) h. The pharmacokinetic parameters of erythromycin were as follows: Low dose group: Ka (1.410 +/- 0.626)/h, tmax (1.8 +/- 0.5) h, Cmax (197.5 +/- 227.6) microLg/L, AUC0-14 (766.4 +/- 981.0) microg x h/L, Ke (0.519 +/- 0.240)/ h, T1/2 (1.6 +/- 0.8) h. Middle dose group: Ka (1.900 +/- 1.049)/h, tmax (1.6 +/- 0.2) h,Cmax (488.3 +/- 216.7) microg/L, AUC0-14( 488.3 +/- 216.7) microg/L, Ke (0.329 +/- 0.057)/h, T1/2(2.2 +/- 0.4) h; High dose group: Ka (1.934 +/- 0.794)/h, tmax (1.7 +/- 0.3) h, Cmax (749.3 +/- 387.2) microg/L, AUC0-14(3820.1 +/- 1966.4) microg x h/L, Ke (0.373 +/- 0.174)/h, T1/2( 2.2 +/- 0.7) h. AUC of both erythromycin propionate and erythromycin base was linearly correlated to the doses; T1/2 was not correlated to the doses, so they followed the first order processes. The pharmacokinetic parameters of erythromycin The erythromycin stinoprate propionate and erythromycin base had no gender differences. Conclusion was absorbed as erythromycin propionate. Cmax reached at about 1.6 h. T1/2 of elimination was 2.4-3.1 h. The active component of erythromycin propionate was erythromycin. Cmax of erythromycin is 1.8, T1/2 is 2.4-3.1 h. In the range of oral dose of 250 to 750 mg, both erythromycin propionate and erythromycin base accorded the first order processes. The pharmacokinetic parameters were different with those reported in foreign documents while the gender difference did not exist in Chinese adults.

Development of a new LC-MS/MS based enzyme activity assay for recombinant urate oxidase in plasma and its application to pharmacokinetics in human.

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the determination of recombinant urate oxidase in human plasma. This assay was based on the determination of enzyme reaction product, (15)N-allantoin, and phenacetin was used as an internal standard (IS). Separation was achieved on a C18 column by the mobile phase of 30% water (containing 0.5% formic acid) and 70% methanol. Quantification was done using multiple reaction monitoring (MRM) mode to monitor the precursor-to-product ion transitions of m/z 161 → m/z 118 for (15)N-allantoin and m/z 180 → m/z 110.1 for IS at positive ionization mode. The calibration curve was established over the range of 2.077-42.06 U/l and the correlation coefficient was larger than 0.99. The intra-day and inter-day relative standard deviations were less than 10.6%. Accuracy determined at three concentrations ranged between 98.6% and 109.2%. This method was successfully applied to a pharmacokinetic study of intravenous recombinant urate oxidase produced from Escherichia coli in Chinese healthy volunteers.

Association between common CYP1A2 polymorphisms and theophylline metabolism in non-smoking healthy volunteers.

This study was designed to investigate the impact of cytochrome P450 (CYP) 1A2 polymorphisms on theophylline metabolism in a non-smoking healthy male Chinese population. Four polymorphisms CYP1A2 1C (G-3860A), G-3113A, CYP1A2 1F (C-163A) and CYP1A2 1B (C-5347T) were screened in 238 unrelated male volunteers. Then, a single oral 200-mg dose of theophylline was administered to 37 volunteers, who were selected from 238 volunteers based on the CYP1A2 genotype. CYP1A2 activities were evaluated by plasma 1,7-dimethylxanthine/caffeine ratios (17X/137X) after administration of 100-mg caffeine. The plasma concentrations of theophylline, 17X and 137X were determined by high-performance liquid chromatography. The activity of CYP1A2 was lower in volunteers with the -3113 AA genotype compared with those with the -3113 AG genotype (0.35 ± 0.04 versus 0.48 ± 0.07, p = 0.016) or the -3113 GG genotype (0.35 ± 0.04 versus 0.58 ± 0.22, p = 0.037). CYP1A2 1F polymorphisms were associated with increased CYP1A2 activity in volunteers with -3860G/-3113G/5347C homozygosity (0.66 ± 0.24 versus 0.46 ± 0.05, p = 0.034). However, theophylline metabolism showed no difference among volunteers carrying different haplotype pairs. CYP1A2 genetic polymorphisms influenced CYP1A2 enzyme activity as measured by caffeine, but CYP1A2 gene polymorphisms appeared to have limited influence on theophylline metabolism in our study.

Effect of CYP3A5*3 polymorphism on pharmacokinetic drug interaction between tacrolimus and amlodipine.

The objective of this study was to evaluate the effect of the CYP3A5*3 allele on the pharmacokinetics of tacrolimus and amlodipine, and drug-drug interactions between them in healthy subjects. Pharmacokinetic drug interactions between tacrolimus and amlodipine were evaluated in a randomized, 3-period, 6-sequence crossover study in healthy Chinese volunteers according to CYP3A5 genotype. A single-dose and multiple-dose study were designed. A 96-h pharmacokinetic study followed either tacrolimus or amlodipine dose, and the washout periods between the study phases were 14 days. In the single-dose study, apparent oral clearance (CL/F) of tacrolimus (5 mg) in CYP3A5 expressers was 3.8-fold (p = 0.008) higher than that in CYP3A5 non-expressers. Amlodipine decreased mean tacrolimus CL/F in CYP3A5 expressers by 2.2-fold (p = 0.005), while it had no effect on that in CYP3A5 non-expressers. The CL/F of amlodipine in CYP3A5 non-expressers was 2.0-fold (p = 0.001) higher than that in CYP3A5 expressers. Tacrolimus increased mean amlodipine CL/F in CYP3A5 expressers by 1.4-fold (p = 0.016) while it had no effect on that in CYP3A5 non-expressers. Tacrolimus slightly reduced the AUC0-∞ of amlodipine in both CYP3A5 expressers and non-expressers. Dose adjustment of tacrolimus should be considered according to CYP3A5*3 genetic polymorphism when tacrolimus is coadministered with amlodipine.

Endogenous cortisol 6 beta-hydroxylation clearance is not an accurate probe for overall cytochrome P450 3A phenotyping in humans.

BACKGROUND: We determined if endogenous cortisol 6 beta-hydroxylation clearance [CL(m(6 beta))] could be used as a reliable index for in vivo CYP3A phenotyping (including both hepatic and intestinal CYP3A activities). METHODS: In this study, 16 healthy volunteers received a single 7.5 mg oral dose of midazolam (MDZ). Blood samples were drawn up to 24 h after dosing. Urine samples were collected at various time periods after dosing. MDZ, 1-hydroxymidazolam (1-OHMDZ), cortisol (F) and 6 beta-hydroxycortisol (6 beta-OHF) in plasma or urine were determined by high-performance liquid chromatography with ultraviolet absorbance detection (HPLC-UV). RESULTS: CL(m(6 beta)) was poorly correlated (P>0.2) with MDZ oral clearance [CL(oral(MDZ))] and the ratio of AUC(0-infinity(1-OHMDZ)) versus AUC(0-infinity(MDZ)) [MR((AUC))]. However, when examining the data obtained from male volunteers exclusively, strong correlations were observed between CL(m(6 beta)) and CL(oral(MDZ)). Larger interindividual and intraindividual variabilities were observed in urinary ratio of 6 beta-OHF/F compared with CL(m(6 beta)). CONCLUSION: CL(m(6 beta)) cannot reflect the overall CYP3A activity accurately and quantitatively in the population.

No effect of MDR1 C3435T polymorphism on oral pharmacokinetics of telmisartan in 19 healthy Chinese male subjects.

BACKGROUND: Considerable interindividual differences in both drug response and pharmacokinetics of telmisartan have been identified. This study was designed to investigate the influence of MDR1 C3435T polymorphism on pharmacokinetics of telmisartan after a single oral dose in healthy Chinese volunteers. METHODS: A total of 61 unrelated male volunteers were genotyped for MDR1 C3435T polymorphism by using the polymerase chain reaction-restriction fragment length polymorphism method. Six 3435CC homozygotes, eight 3435CT heterozygotes, and five 3435TT homozygotes were randomly selected and received a single oral dose of 40 mg telmisartan. Plasma concentrations of telmisartan were determined by the high performance liquid chromatography-mass spectrometry method up to 48 h after telmisartan administration. RESULTS: Interindividual variation for t(max), C(max), t(1/2), AUC(0-48), AUC(0-infinity), and clearance (CL) for telmisartan was approximately 6-, 33-, 16-, 17-, 20-, and 20-fold, respectively. C(max) (p=0.010), t(1/2) (p=0.029) and CL (p=0.010) of telmisartan were not normally distributed. MDR1 3435TT homozygotes seemed to show increases in C(max), t(max), t(1/2), AUC(0-48), and AUC(0-infinity). However, no significant differences in C(max), t(max), t(1/2), AUC(0-48), AUC(0-infinity), and CL among MDR1 C3435T genotypes were observed. CONCLUSIONS: MDR1 C3435T polymorphism does not affect oral pharmacokinetics of telmisartan.