Changes in CYP2D enzyme activity following induction of type 2 diabetes, and administration of cinnamon and metformin: an experimental animal study.

1. Alterations in the activity of hepatic cytochrome P-450 isoenzymes result in changes in the pharmacokinetic behavior of drugs. This study was designed to explore the impact of type II diabetes, metformin and cinnamon on the activity of CYP2D isoenzyme. 2. Streptozotocin-nicotinamide-induced diabetic and normal rats were gavaged by cinnamon and/or metformin for 14 days. Using isolated perfusion of rat livers, the metabolic activity of CYP2D in the study groups was evaluated based on the oxidative biotransformation of tramadol hydrochloride. 3. The metabolic ratios of O-desmethyltramadol, the product of CYP2D-mediated metabolism of tramadol, in normal and diabetic control rats were found to be 0.33 ± 0.12 and 0.29 ± 0.07, respectively. Cinnamon significantly reduced the mentioned ratio in both normal and diabetic rats (0.13 ± 0.05 and 0.15 ± 0.04) and metformin increased the reduced activity in diabetic rats (0.37 ± 0.09 versus 0.29 ± 0.07). 4. In conclusion, it is evident that this study has shown the significant inhibitory effect of cinnamon on CYP2D. This finding suggests that it should be taken into consideration the possible metabolism-related pharmacokinetic drug-cinnamon interactions. 5. Additionally, type 2 diabetes condition reduced the enzyme activity and metformin consumption reversed this reduction; however, the significance of the latest is not clear.

Study of the pharmacokinetic changes of Tramadol in diabetic rats.

BACKGROUND: Besides the pathological states, diabetes mellitus may also alter the hepatic biotransformation of pharmaceutical agents. It is advantageous to understand the effect of diabetes on the pharmacokinetic of drugs. The objective of this study was to define the pharmacokinetic changes of tramadol and its main metabolites after in vivo intraperitoneal administration and ex vivo perfused liver study in diabetic rat model.Tramadol (10 mg/kg) was administered to rats (diabetic and control groups of six) intraperitoneally and blood samples were collected at different time points up to 300 min. In a parallel study, isolated liver perfusion was done (in diabetic and control rats) by Krebs-Henseleit buffer (containing 500 ng/ml tramadol). Perfusate samples were collected at 10 min intervals up to 180 min. Concentration of tramadol and its metabolites were determined by HPLC. RESULTS: Tramadol reached higher concentrations after i.p. injection in diabetics (Cmax of 1607.5 ± 335.9 ng/ml) compared with control group (Cmax of 561.6 ± 111.4). M1 plasma concentrations were also higher in diabetic rats compared with control group. M2 showed also higher concentrations in diabetic rats. Comparing the concentration levels of M1 in diabetic and control perfused livers, showed that in contrast to intact animals, the metabolic ratios of M1 and M5 (M/T) were significantly higher in diabetic perfused liver compared to those of control group. CONCLUSIONS: The pharmacokinetic of tramadol and its three metabolites are influenced by diabetes. As far as M1 is produced by Cyp2D6, its higher concentration in diabetic rats could be a result of induction in Cyp2D6 activity, while higher concentrations of tramadol can be explained by lower volume of distribution.

Fundamentals and Applications of Isolated Perfused Lung (IPL) Model in the Development of Pulmonary Drug Delivery.

Estimating parameters such as pulmonary drug disposition and deposited dose, as well as determining the influence of pulmonary pharmacokinetics (PK) on drug efficacy and safety, are critical factors for the development of inhaled drug products and help to achieve a better understanding of the drugs' fate in the lungs. Pulmonary disposition and PK have remained poorly understood due to the difficulty to access pulmonary fluids, compared to other biological fluids, such as plasma, for direct or surrogate measurement of the concentration of the active compounds and their metabolites in the lung. The use of the isolated perfused lung model (IPL) has become more common, and it is considered a useful tool to increase understanding in this area since it offers the possibility of controlling the administration and easier sampling of perfusate and lavage fluid. The model also provides an opportunity to study the relationship between PK and pharmacodynamics. This review describes the fundamentals of the IPL model, such as preparation and setting up the method, species selection, drug administration, and lung viability investigation. Besides, different applications of the IPL model like pharmacodynamic studies, pharmacokinetic parameters studies such as absorption, distribution, and metabolism, and evaluation of inhaled formulation have also been reviewed.

Evaluation of important human CYP450 isoforms and P-glycoprotein phenotype changes and genotype in type 2 diabetic patients, before and after intensifying treatment regimen using Geneva cocktail.

The present study evaluates the influence of type 2 diabetes (T2D) on important CYP450 (CYP) isoforms and P-glycoprotein (Pgp) transporter activities before and 3 months after an intensifying treatment regimen involving 40 patients. Results have been compared with 21 non-T2D healthy participants (the control group). CYPs and Pgp activities were assessed after administering the Geneva cocktail. The mean metabolic ratios (MR) for CYP2B6 (1.81 ± 0.93 versus 2.68 ± 0.87), CYP2C19 (0.420 ± 0.360 versus 0.687 ± 0.558) and CYP3A4/5 (0.487 ± 0.226 versus 0.633 ± 0.254) significantly decreased in T2D patients compared to the control group (p < 0.05). CYP2C9 (0.089 ± 0.037 versus 0.069 ± 0.017) activities slightly increased in diabetic patients, and no difference was observed regarding CYP1A2 (0.154 ± 0.085 versus 0.136 ± 0.065), CYP2D6 (1.17 ± 0.56 versus 1.24 ± 0.83), and Pgp activities in comparison to the control group. Three months after the intensifying treatment regimen, MRs of CYP2C9 (0.080 ± 0.030) and CYP3A4/5 (0.592 ± 0.268) improved significantly and were not statistically different compared to the control group (P > 0.05). Several covariables, such as inflammatory markers (IL-1ß and IL-6), genotypes, diabetes and demographic-related factors, were considered in the analyses. The results indicate that chronic inflammatory status associated with T2D modulates CYP450 activities in an isoform-specific manner.

Impact of Obesity and Bariatric Surgery on Metabolic Enzymes and P-Glycoprotein Activity Using the Geneva Cocktail Approach.

The inter-individual variability of CYP450s enzyme activity may be reduced by comparing the effects of bariatric surgery on CYP-mediated drug elimination in comparable patients before and after surgery. The current research will use a low-dose phenotyping cocktail to simultaneously evaluate the activities of six CYP isoforms and P-gp. The results showed that following weight reduction after surgery, the activity of all enzymes increased compared to the obese period, which was statistically significant in the case of CYP3A, CYP2B6, CYP2C9, and CYP1A2. Furthermore, the activity of P-gp after surgery decreased without reaching a statistical significance (p-value > 0.05). Obese individuals had decreased CYP3A and CYP2D6 activity compared with the control group, although only CYP3A was statistically important. In addition, there was a trend toward increased activity for CYP1A2, CYP2B6, CYP2C9, and CYP2C19 in obese patients compared to the control group, without reaching statistical insignificance (p-value ≥ 0.05). After six months (at least), all enzymes and the P-gp pump activity were significantly higher than the control group except for CYP2D6. Ultimately, a greater comprehension of phenoconversion can aid in altering the patient's treatment. Further studies are required to confirm the changes in the metabolic ratios of probes after bariatric surgery to demonstrate the findings' clinical application. As a result, the effects of inflammation-induced phenoconversion on medication metabolism may differ greatly across persons and drug CYP pathways. It is essential to apply these results to the clinic to recommend dose adjustments.

Variations in the Frequencies of Polymorphisms in the CYP450s Genes in Eight Major Ethnicities of Iran: A Review of the Human Data.

Genetic polymorphisms in cytochrome P450 genes can cause variation in metabolism. Thus, single nucleotide variants significantly impact drug pharmacokinetics, toxicity factors, and efficacy and safety of medicines. The distribution of CYP450 alleles varies drastically across ethnicities, with significant implications for personalized medicine and the healthcare system. We combined whole-genome and exome sequencing data to provide a review of CYP450 allele polymorphisms with clinical importance. Data were collected from 800 unrelated Iranians (100 subjects from 8 major ethnicities of Iran), more than 32,000 unrelated Europeans (other than Caucasian), and four Middle Eastern countries. We analyzed the frequencies and similarities of 17 CYP450 frequent alleles related to nine important CYP450 isoenzymes and homozygous and heterozygous genotypes based on these alleles in eight major Iranian ethnics by integrating these data with population-specific linkage information and compared these datasets with mentioned populations.

Frequency of Important CYP450 Enzyme Gene Polymorphisms in the Iranian Population in Comparison with Other Major Populations: A Comprehensive Review of the Human Data.

Genetic polymorphisms in cytochrome P450 genes can cause alteration in metabolic activity of clinically important medicines. Thus, single nucleotide variants (SNVs) and copy number variations (CNVs) in CYP genes are leading factors of drug pharmacokinetics and toxicity and form pharmacogenetics biomarkers for drug dosing, efficacy, and safety. The distribution of cytochrome P450 alleles differs significantly between populations with important implications for personalized drug therapy and healthcare programs. To provide a meta-analysis of CYP allele polymorphisms with clinical importance, we brought together whole-genome and exome sequencing data from 800 unrelated individuals of Iranian population (100 subjects from 8 major ethnics of Iran) and 63,269 unrelated individuals of five major human populations (EUR, AMR, AFR, EAS and SAS). By integrating these datasets with population-specific linkage information, we evolved the frequencies of 140 CYP haplotypes related to 9 important CYP450 isoenzymes (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4 and CYP3A5) giving a large resource for major genetic determinants of drug metabolism. Furthermore, we evaluated the more frequent Iranian alleles and compared the dataset with the Caucasian race. Finally, the similarity of the Iranian population SNVs with other populations was investigated.

Evaluation of phenoconversion phenomenon in obese patients: the effects of bariatric surgery on the CYP450 activity "a protocol for a case-control pharmacokinetic study".

Personalized therapy suggests the appropriate drug at the right dose for the first time through genotype-based individualized therapy, instead of prescribing medicines by the traditional one-size-fits-all manner, thereby claiming that it will make medicines safer and more effective. Accordingly, polymorphisms of drug metabolizing enzymes (DMEs), which induce inter-individual variability in the pharmacokinetics of a drug, have attracted great interest in the context of personalized medicine. Obesity is one of the most common chronic diseases in the world, including Iran, and the prevalence is increasing according to predictions. The remarkable role of P450 cytochromes has been verified in the metabolism of numerous drugs, toxins, carcinogen compounds, and the synthesis of some intrinsic compounds, such as steroid hormones. Thus, evaluating the activity of these enzymes is of great importance because any functionality variation can lead to failure in the treatment or unwanted side effects of some drugs. Therefore, any change in the activity of these enzymes in obese patients can also be problematic in the treatment process of these patients in comparison to normal weighted ones. Since only a few human studies have examined the role of inflammation in altering the function of these enzymes, it seems to be necessary to investigate the effect of obesity on the expression and activity of these enzymes; in which the role of inflammatory processes has been proven. Most importantly, it is worth evaluating changes in the activity levels of cytochrome P450 (CYP450) and the inflammatory cytokines after a course of post-surgical treatment and weight loss. To evaluate the activity of CYPs, a multi-drug cocktail is prescribed to obese patients before and after obesity surgery, as well as to healthy volunteers, to provide simultaneous evaluation of different isoforms. A complete demographic data, medical examinations, laboratory tests, and the CYPs genotype of all participants can be extremely important during this investigation.

Evaluation of hepatic CYP2D1 activity and hepatic clearance in type I and type II diabetic rat models, before and after treatment with insulin and metformin.

INTRODUCTION: Conversion in the metabolism of drugs occurs in diabetes mellitus. Considering the importance of metabolic enzymes' activities on the efficacy and safety of medicines, the changes in liver enzymatic activity of CYP2D1 and its related hepatic clearance, by using Dextromethorphan as probe in the animal model of type I and type II diabetes, before and after treatment, was assessed in this study. METHODS: Male Wistar rats were randomly divided into 6 groups. Seven days after induction of diabetes type I and type II, treatment groups were received insulin and metformin daily for 14 days, respectively. In day 21, rats were subjected to liver perfusion by Krebs-Henseleit buffer containing Dextromethorphan as CYP2D1 probe. Perfusate samples were analyzed by HPLC fluorescence method in order to evaluate any changes in CYP2D1 activity. RESULTS: The average metabolic ratio of dextromethorphan and hepatic clearance were changed from 0.012 ± 0.004 and 6.3 ± 0.1 in the control group to 0.006 ± 0.0008 and 5.2 ± 0.2 in the untreated type I diabetic group, and 0.008 ± 0.003 and 5.0 ± 0.6 in the untreated type II diabetic rats. Finally, the mean metabolic ratio and hepatic clearance were changed to 0.008 ± 0.001 and 5.4 ± 0.1, and 0.013 ± 0.003 and 6.1 ± 0.4 in the treated groups with insulin and metformin, respectively. CONCLUSION: In type I diabetic rats, corresponding treatment could slightly improve enzyme activity, whereas the hepatic clearance and enzyme activity reached to the normal level in type II group. Graphical abstract .

Evaluating the effect of type 2 diabetes mellitus on CYP450 enzymes and P-gp activities, before and after glycemic control: A protocol for a case-control pharmacokinetic study.

Cytochrome P450s (CYP450) family is one of the most critical factors in the metabolism process. Hence, the present study aims to characterize the activity of CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP3A4/5, and P-glycoprotein (P-gp) pump in patients with type 2 diabetes (T2DM). This characterization was performed before and after good glycemic control versus non-diabetic subjects following the administration of a substrate probe drug cocktail. This single-center clinical study proposes the characterization of T2DM impacts on major CYP450 drug-metabolizing enzyme and P-glycoprotein (P-gp) activities. The main propose of the present study is evaluating any alternation in major CYP450 enzymes and P-gp activities in patients with T2DM, before (A1C>7%) and after (A1C≤7%) good glycemic control along with comparing the activities versus non-diabetic subjects. The phenotypes will be assessed following the oral administration of a drug cocktail containing caffeine (CYP1A2), bupropion (CYP2B6), flurbiprofen (CYP2C9), omeprazole (CYP2C19), dextromethorphan (CYP2D6), midazolam (CYP3A4/5), and fexofenadine (P-gp) as probe substrates. Furthermore, the influence of variables such as glycemia, genetic polymorphisms, and inflammation on the metabolism process will be evaluated. The first patient has entered the study in Dec 2018.

Pharmacokinetic changes of tramadol in rats with hepatotoxicity induced by ethanol and acetaminophen in perfused rat liver model.

Tramadol is an opioid agonist with activation monoaminergic properties. It can be administered orally, rectally, intravenously, or intramuscularly as a centrally acting analgesic. Liver injury can lead to changes in the metabolism of tramadol. In this study, the rate of tramadol metabolism in rats with damaged liver induced by ethanol and acetaminophen was assessed in a recirculation perfusion system. Acetaminophen is a mild analgesic and antipyretic agent, which can cause centrilobular hepatic necrosis in toxic doses, whereas alcohol causes death due to liver diseases. Alcoholic liver disease (ALD), such as alcoholic fatty liver, alcoholic hepatitis, and alcoholic fibrosis, is the most common liver disease. The aim of this study was to investigate the alteration in tramadol metabolism in different hepatotoxicity conditions in animal models. Male rats were randomly assigned to three groups. The control group received normal saline, group 2 received acetaminophen at the dose of 250 mg/kg/day, and group 3 received ethanol at the beginning dose of 3 g/kg/day, which was slowly increased to 6 g/kg/day. Tramadol was added to the perfusion solution at the concentration of 500 ng/mL. Samples were collected during 180 min, and analyte concentrations were determined by the High-Performance Liquid Chromatography (HPLC) method. The concentration of tramadol and its three main metabolites, O-desmethyltramadol (M1), N-desmethyltramadol (M2), and N,O-didesmethyltramadol (M5), were determined in perfusate samples. Ethanol and acetaminophen significantly affected the pattern of weight gain and liver weights before perfusion and caused a significant increase in enzyme activities. Moreover, histopathologic examination revealed that ethanol and acetaminophen caused liver damage. An increase in the elimination half-life and reduced clearance rate of tramadol were seen in the acetaminophen and ethanol groups, in comparison to the control group. Additionally, significant reductions in the Area Under the Curve (AUC) of metabolites of tramadol (M1, M2, and M5) were observed in the acetaminophen and ethanol groups in the perfused rat liver model. Liver damage caused by ethanol and acetaminophen during 45 days in animals leads to a significant reduction in the level of tramadol metabolites. Therefore, in patients with liver damage caused by ethanol and acetaminophen, caution needs to be considered when prescribing tramadol.

Enantioselective determination of tramadol and its main phase I metabolites in human plasma by high-performance liquid chromatography.

A sensitive and relatively rapid reversed-phase HPLC method was applied to the enantiomeric separation of tramadol and its two main metabolites, O-desmethyltramadol (M1) and N-desmethyltramadol (M2) in plasma samples. Chromatography was performed on an AGP column containing alpha1-acid glycoprotein as chiral selector with a mobile phase of 30 mM diammonium hydrogen phosphate buffer-acetonitrile-triethylamine (98.9:1:0.1, v/v), adjusted to pH 7 by phosphoric acid, and a flow rate of 0.5 ml/min. The fluorescence of analytes was detected at excitation and emission wavelengths of 200 and 301 nm, respectively. The sample preparation was a simple extraction with ethyl acetate using fluconazol as internal standard (IS). The enantiomers of all analytes and IS peaks eluted within 32 min, without any endogenous interference. The calibration curves were linear (r(2) > 0.993) in the concentration range of 2-200, 2.5-100 and 2.5-75 ng/ml for tramadol, M1, and M2 enantiomers, respectively. The within- and between-day variation determined by the measurement of quality control samples at four tested concentrations, showed acceptable values. The lower limit of quantitation was 2 ng/ml for tramadol enantiomers and 2.5 ng/ml for M1 or M2 enantiomers. Mean recoveries of enantiomers from plasma samples were > 81% for all analytes. The procedure was applied to assess the pharmacokinetics of the enantiomers of tramadol and its two main metabolites following oral administration of single 100-mg doses to healthy volunteers.

Improved liquid chromatographic method for the simultaneous determination of tramadol and its three main metabolites in human plasma, urine and saliva.

Tramadol, an analgesic agent, and its main metabolites O-desmethyltramadol (M1), N-desmethyltramadol (M2) and O,N-didesmethyltramadol (M5) were determined simultaneously in human plasma, saliva and urine by a rapid and specific HPLC method. The sample preparation was a simple, one-step, extraction with ethyl acetate. Chromatographic separation was achieved with a Chromolith Performance RP-18e 100 mm x 4.6 mm column, using a mixture of methanol:water (19:81, v/v) adjusted to pH 2.5 by phosphoric acid, in an isocratic mode at flow rate of 2 ml/min. Fluorescence detection (lambda(ex) 200 nm/lambda(em) 301 nm) was used. The calibration curves were linear (r(2)>0.996) in the concentration ranges in plasma, saliva and urine. The lower limit of quantification was 2.5 ng/ml for all compounds. The within- and between-day precisions in the measurement of QC samples at four tested concentrations were acceptable in all analyzed body fluids The developed procedure was applied to assess the pharmacokinetics of tramadol and its main metabolites following administration of 100mg single oral dose of tramadol to healthy volunteers.

Inhibition of mirtazapine metabolism by Ecstasy (MDMA) in isolated perfused rat liver model.

BACKGROUND: Nowadays MDMA (3,4-methylendioxymethamphetamine), known as ecstasy, is widely abused among the youth because of euphoria induction in acute exposure. However, abusers are predisposed to depression in chronic consumption of this illicit compound. Mirtazapine (MRZ), an antidepressant agent, may be prescribed in MDMA-induced depression. MRZ is extensively metabolized in liver by CYP450 isoenzymes. 8-hydroxymirtazapine (8-OH) is mainly produced by CYP2D6. N-desmethylmirtazapine (NDES) is generated by CYP3A4. MDMA is also metabolized by the mentioned isoenzymes and demonstrates mechanism-based inhibition (MBI) in association with CYP2D6. Several studies revealed that MDMA showed inhibitory effects on CYP3A4. In the present study, our aim was to evaluate the impact of MDMA on the metabolism of MRZ in liver. Therefore, isolated perfused rat liver model was applied as our model of choice in this assessment. METHODS: The subjects of the study were categorized into two experimental groups. Rats in the control group received MRZ-containing Krebs-Henselit buffer (1 µg/ml). Rats in the treatment group received aqueous solution of 1 mg/ml MDMA (3 mg/kg) intraperitoneally 1 hour before receiving MRZ. Perfusate samples were analyzed by HPLC. RESULTS: Analyses of perfusate samples showed 80% increase in the parent drug concentrations and 50% decrease in the concentrations of both metabolites in our treatment group compared to the control group. In the treatment group compared to the control group, AUC(0-120) of the parent drug demonstrated 50% increase and AUC(0-120) of 8-OH and NDES showed 70% and 60% decrease, respectively. Observed decrease in metabolic ratios were 83% and 79% for 8-OH and NDES in treatment group compared to control group, respectively. Hepatic clearance (CLh) and intrinsic clearance (Clint) showed 20% and 60% decrease in treatment group compared to control group. CONCLUSION: All findings prove the inhibitory effects of ecstasy on both CYP2D6 and CYP3A4 hepatic isoenzymes. In conclusion, this study is the first investigation of MRZ metabolism in presence of MDMA in isolated perfused rat liver model.

Study the effect of 3,4-Methylenedioxy methamphetamine on cytochrome P450 2E1 activity

Abstract Evaluating the effects of ecstasy on CYP2E1 activity is of great concern, mainly due to growing trends in abuse and co-administration of MDMA with ethanol and the dominant role of this isoenzyme on ethanol metabolism. This study aimed to evaluate the effects of MDMA on CYP2E1 activity. A total of 24 male rats were selected and divided into three groups. The first and second groups consisted of 12 rats and were employed to optimize the perfusion method, and the third group was employed for studying the alteration of CYP2E1 activity after liver exposure to MDMA (300 and 600 ng/ml). The amount of chlorzoxazone and 6-hydroxy chlorzoxazone in a sample obtained from liver perfusion before and after exposure to a buffer containing MDMA was determined by HPLC-FL. The enzymatic activity of rat CYP2E1 decreased after liver perfusion with a buffer containing 600 ng/ml of MDMA. However, no significant changes were observed in chlorzoxazone and 6-hydroxy chlorzoxazone concentration in perfusate before and after liver perfusion with a buffer containing 300 ng/ml of MDMA. Our findings suggest that the activity of CYP2E1 in rats might decrease only after administration of MDMA at a lethal dose. However, further animal and human studies are needed to confirm our assumption.

Simultaneous determination of clobazam and its major metabolite in human plasma by a rapid HPLC method.

A rapid and specific HPLC method has been developed and validated for simultaneous determination of clobazam, the anticonvulsant agent, and its major metabolite in human plasma. The sample preparation was a liquid-liquid extraction with tuloene yielding almost near 100% recoveries of two compounds. Chromatographic separation was achieved with a Chromolith Performance RP-18e 100 mm x 4.6mm column, using a mixture of a phosphate buffer (pH 3.5; 10mM)-acetonitrile (70:30, v/v), in isocratic mode at 2 ml/min at a detection wave-length of 228 nm. The calibration curves were linear (r(2)>0.998) in the concentration range of 5-450 ng ml(-1). The lower limit of quantification was 5 ng ml(-1) for two compounds studied. The within- and between-day precisions in the measurement of QC samples at four tested concentrations were in the range of 0.89-9.1% and 2.1-10.1% R.S.D., respectively. The developed procedure was applied to assess the pharmacokinetics of clobazam and its major metabolite following administration of a single 10mg oral dose of clobazam to healthy volunteers.

An improved HPLC method for rapid quantitation of diazepam and its major metabolites in human plasma.

A rapid and specific HPLC method was developed and validated for simultaneous determination of diazepam and its main active metabolites, desmethyldiazepam, oxazepam and temazepam in human plasma. Plasma samples were extracted using toluene. HPLC system included a Chromolith Performance RP-18e 100 mm x 4.6mm column, using 10mM phosphate buffer (pH 2.5)-methanol-acetonitrile (63:10:27, v/v) as mobile phase running at 2 mL min(-1). UV detector (lambda=230 nm) was used. The calibration curves were linear in the concentration range of 2-800 ng mL(-1) for diazepam and 2-200 ng mL(-1) for the three metabolites (r(2)>0.99). The lower limit of quantification was 2 ng mL(-1) for all analytes. Within and between-day precisions in the measurement of QC samples were in the range of 1.8-18.0% for all analytes. The developed procedure was used to assess the pharmacokinetics of diazepam and its main metabolites following single dose administration of 10mg diazepam orally to healthy subjects.

Investigation on different levels of in vitro-in vivo correlation: gemfibrozil immediate release capsule.

Gemfibrozil is a practically water-insoluble, high-dose drug. It represents a typical drug with dissolution rate controlled bioavailability. The aim of this study was to select a dissolution condition for gemfibrozil immediate release capsules, resulting in the best in vitro/in vivo correlation (IVIVC). Five 300 mg gemfibrozil products, including the innovator and four generic products were selected. In vitro dissolution test methods with a standard paddle, round-bottomed vessel of 1 l capacity, and potassium phosphate buffer as the dissolution medium (referred to as conditions I, II and III, respectively) were developed. The products were administered to 12 healthy volunteers and thereby different pharmacokinetic parameters were calculated. Correlations between the in vitro and in vivo calculated parameters were investigated. Of the single point parameters investigated, the best results were seen in the relation between the percent dissolved in 10, 20 and 45 min and the time to 90% dissolution from the in vitro side and the AUCs and C(max) from the in vivo side. The correlation between MRT and MDT was also investigated, and no significant correlation was found in the three above-mentioned conditions. The Wagner-Nelson method was used to calculate the percent remaining to be absorbed. Superimposition of the percent in vivo absorption and the in vitro dissolution curves was used to investigate a multiple point correlation. A remarkable superimposition between in vivo and in vitro curves in conditions I and II was observed.

A disposition kinetic study of tramadol in rat perfused liver.

A recirculated perfusion system was used to investigate the metabolism of tramadol, an analgesic agent, in the isolated perfused rat liver. Tramadol was added to the perfusion medium at a concentration of 300 ng/ml, and the perfusate samples were collected for 180 min. The concentration of tramadol and its three main metabolites O-desmethyltramadol (M1) and N-desmethyltramadol (M2) and N,O-didesmethyltramadol (M5) were determined in perfusate samples by a rapid HPLC method. All through the study, the phase I metabolism of tramadol led to the formation of M1 metabolite from early sampling points while M5 metabolite was detectable after 50 min in 6 out of 10 perfused livers and the M2 metabolite was not detectable in any experiment. The kinetic parameters of tramadol and two detectable metabolites (M1 and M5) were then calculated in perfusate samples. The tramadol concentration decreased from 297.8 to 159.6 ng/ml, with a mean half-life of 232.4 min and a hepatic clearance of 0.73 ml/min. After 180 min, the mean concentration of M1 reached 59.5 ng/ml, resulting in a metabolic ratio of 16%, while the formation of M5 metabolite continued to a mean concentration of 14.6 ng/ml resulting in a metabolic ratio of 2% using AUC((0-180min)).

Pharmacokinetics of tramadol and its three main metabolites in healthy male and female volunteers.

By using a high-performance liquid chromatography method, the pharmacokinetics of the tramadol (T) and its three main metabolites, O-desmethyltramadol (M1), N-desmethyltramadol (M2) and O,N-didesmethyltramadol (M5) was studied in healthy male and female Iranian volunteers after oral administration of two 50 mg tramadol hydrochloride tablets. The related pharmacokinetic parameters such as C(max), T(max), AUC((0-t)), AUC((0-infinity)), T(1/2) and Cl/F were calculated and compared between the two genders. No significant differences were found in the systemic exposure and pharmacokinetic of tramadol, M1 and M2 while there were significant differences in AUCs of M5 in the two genders. It was concluded that to get a more accurate result, the gender dependency of T and its metabolites might be studied in specific phenotypes.