Gerard Sirois

Rapid high-performance liquid chromatographic assay of acetaminophen in serum and tissue homogenates

The quantitation of a hepatorenal toxic drug, acetaminophen, in blood and target organ tissues is needed for toxicokinetic and distribution studies. A rapid, sensitive and simple method is described to assay acetaminophen in rat serum and liver or kidney homogenates by reversed-phase high-performance liquid chromatography, using an octadecyl (3 micron particle size) Apex column, a mobile phase consisting of a mixture of distilled water-acetonitrile (86:14) and ultraviolet detection at 245 nm. Short retention times of ca. 3.75 and 6.25 min are observed for acetaminophen and the internal standard (sulfamerazine), respectively. A sensitivity of 50 ng/ml is easily achieved for 100-microliter serum and liver or kidney homogenate samples. The proposed method proved to have satisfactory recovery, precision and accuracy. The preliminary results obtained with human plasma of volunteers and of patients treated with various drugs show that the assay, with a sensitivity of 25 ng/ml, would be of considerable interest in clinical monitoring of acetaminophen.

Simultaneous determination of the major metabolites of styrene and acetaminophen, and of unchanged acetaminophen in urine by ion-pairing high-performance liquid chromatography

An improved isocratic high-performance liquid chromatographic method for the quantitative determination of the major urinary metabolites of styrene in urine is described. The high separation efficiency of an ion-pairing system using tetrabutyl ammonium chloride allows also the simultaneous determination of acetaminophen and its three major metabolites with those of styrene in rat urine. Simplicity, reproducibility and a short analysis time provide a useful tool for the toxicokinetic studies of these two hepatorenotoxic xenobiotics after their co-administration. An aliquot of the diluted urine is directly injected into the liquid chromatograph. The limits of sensitivity and detection of the metabolites of styrene are better than those reported before. Preliminary works indicate that the method would also be applicable for analysis of these metabolites in human urine and would therefore be useful in monitoring styrene exposure to workers especially when they take acetaminophen.

Novel Pharmacokinetic Modelling of Transdermal Nitroglycerin

AbstractPurpose. To construct a pharmacokinetic (PK) model and to determine population PK parameters of nitroglycerin (GTN), 1,2-dinitroglycerin (1,2-GDN), and 1,3-dinitroglycerin (1,3-GDN). Methods. Data were obtained in thirty healthy volunteers following a single dose of a GTN reservoir transdermal patch. Blood samples were obtained just before and at 0.5, 1, 2, 3, 4, 6, 8, 12, 14, and 24 hours after the patch application and 1 hour after its removal. GTN, 1,2-GDN, and 1,3-GDN concentrations were determined using HPLC and simultaneously best fitted using a first-pass mixed-order release one-compartment PK model. Individual estimates (ADAPT-II) were used as priors for a population PK analysis (IT2S). Fitted parameters included the percentage (A) of the nitroglycerin dose reaching the systemic circulation that was released from the patch by a first-order process (K1); two absorption (ka1 and ka2), two metabolite formation (kfl and kf2) and one metabolite elimination (k(m)) rate constants; and three volumes of distribution Vc/F, V2/F and V3/F. Results. Nitroglycerin mean population parameter estimates and inter-individual variability (CV%) were: A 35% (65), K1, 0.06 h−1(91), ka1 5 h−1(46), ka2 0.47 h−1 (39), kf1 11 h−1(42), kf2 0.6 h−1(34), k(m) 1.4 h−1(29), Vc/F 6 L(31), V2 /F 73 L(34), and V3 /F 23 L(29). The average elimination half-lives for GTN and the two metabolites were 5 and 32 minutes, respectively. Conclusions. The proposed PK model fitted observed concentrations of GTN, 1,2-GDN and 1,3-GDN very well. This model should be useful to predict drug and metabolite concentrations and to assess bioequivalence of two transdermal formulations.

Population pharmacokinetics of nitroglycerin and of its two metabolites after a single 24-hour application of a nitroglycerin transdermal matrix delivery system.

The purpose of this study was to assess the ability of our previously constructed pharmacokinetic (PK) model to describe nitroglycerin (GTN), 1,2-dinitroglycerin (1,2-GDN), and 1,3-dinitroglycerin (1,3-GDN) plasma concentrations after a single-dose application of a GTN transdermal matrix delivery system. GTN, 1,2-GDN, and 1,3-GDN plasma concentrations were simultaneously fitted using a first-pass, mixed-order release, one-compartment PK model. Population PK parameter values were derived using an iterative two-stage methodology (IT2S). Some of the mean PK parameters estimates and their interindividual variability (CV%) were the percentage of the delivered GTN dose reaching the systemic circulation released by a first-order process A, 53% (44); the 1,2-GDN and 1,3-GDN formation rate constants, k(f1)9 h(-1) (67) and k(f2) 0.5 h(-1) (38), respectively; the metabolite elimination rate constant, k(m) 1 h(-1) (27); GTN, 1,2-GDN, and 1,3-GDN volumes of distribution (Vc/F 6 L [45]), V2/F 78 L [51]), and V3/F 29 L [40]), respectively). Mean calculated elimination half-lives (t1/2+/-standard deviation [SD]) for GTN and the GDN metabolites were 7+/-4 minutes and 33+/-7 minutes, respectively. The proposed PK model fitted the observed plasma concentrations of GTN, 1,2-GDN, and 1,3-GDN very well. This new transdermal matrix delivery system appears to behave pharmacokinetically in the same manner as a transdermal reservoir delivery system (Transderm-Nitro, Ciba-Geigy, Mississauga, Canada).

Ability of a First-pass Pharmacokinetic Model to Characterize Cyclosporine Blood Concentrations After Administrations of Sandimmune or Neoral Formulations

Most recent cyclosporine (CsA) pharmacokinetic (PK) studies have focused on noncompartmental analysis. Because CsA undergoes significant first-pass elimination after oral dosing, the most appropriate compartment model may need to take this process into account for the construction of a valid population PK model for Sandimmune (SAN) and Neoral (NEO) formulations. Twenty patients with cardiac transplants were stabilized for at least 4 weeks on a certain dose of SAN, then changed to the same daily dose of NEO. Blood samples were obtained at times 0, 1, 2, 3, 4, 6 and 12 hours after dosing at steady state. Pharmacokinetic modeling was performed using ADAPT II. Quality of fit was assessed by visual graph inspections, R2 values, and Akaike criterion test. Eight pharmacokinetic models were constructed and evaluated. These included one- and two-compartment with and without a first-pass effect and a time-lag. Neoral and SAN data were consistently best fitted using a two-compartment or the two-compartment first-pass model. However, a time-lag process was found to be necessary for SAN. The use of a two-compartment first-pass with (SAN) or without (NEO) a time-lag process appears to fit CsA concentrations at least as well as a two-compartment model. This first-pass model may be very useful for population pharmacokinetics and Bayesian control analysis.

High-performance liquid chromatography determination of dipotassium clorazepate and its major metabolite nordiazepam in plasma

A rapid and sensitive high-performance liquid chromatographic method is described for the quantitative analysis of dipotassium clorazepate (CZP) and its major metabolite nordiazepam (ND) in fresh human and dog plasma. The method consists of two separate selective ND extractions from a plasma sample without and with conversion of all the CZP to ND. For quantitation, diazepam (DZP) is used as the internal standard. The chromatographic phase utilized in a reversed-phase Hibar EC-RT analytical column prepacked with LiChrosolv RP-18 with a solvent system consisting of acetonitrile-0.05 M sodium acetate buffer, pH 5.0 (45:55). The UV absorbance is monitored at 225 nm using a variable-wavelength detector. The mean assay coefficient of variation over a concentration range of 20-400 ng per ml of plasma is less than 3% for the within-day precision. Recoveries of ND, DZP and CZP (as ND) are essentially quantitative at all levels investigated. The calibration curves of ND are rectilinear (r2 = 0.99) from the lower limit of sensitivity (2 ng/ml) to at least 2000 ng/ml in plasma. Applicability of the method to CZP and ND disposition studies in the anaesthetized mongrel dog is illustrated. When the two separate selective nordiazepam extractions from plasma cannot be performed immediately after blood sampling, an extrapolation kinetic method is suggested for the estimation of CZP concentration. In all previous in vivo studies, CZP has been determined only with gas-liquid chromatographic methods.

Simultaneous Ion-Pairing Liquid Chromatographic Determination of the Major Metabolites of Styrene and Carbamazepine, and of Unchanged Carbamazepine in Urine

Abstract A high-performance liquid chromatographic method for a simultaneous quantitative determination of carbamazepine (CBZ) and of the major metabolites of CBZ (trans-10,11-dihydroxy-10,11-dihydrocarbamazepine, TDC; carbamazepine-10,11-epoxide, CBZ-E) and those of styrene (S) (hippuric acid, HA; mandelic acid, MA; phenylglyoxylic acid, PA) in the rat urine is described. Separation is achieved on a Nova-Pak reverse-phase column by isocratic elution. Excellent resolution was obtained by adding to the acetonitrile-water mobile phase, tetrabutylammonium chloride (0.005 M) and methanol (1%). Detection is effected by UV absorption at 230 nm with a total analysis time of less than 18 min. An aliquot of diluted urine is injected directly onto the liquid chromatographic column. The limits of sensitivity of CBZ, CBZ-E, TDC, HA, MA, and PA are 3.3, 2.0, 1.8, 3.1, 1.2, and 3.1 μg/ml of diluted rat urine, respectively. Precision and accuracy of the method are found to be acceptable. The method can be used for study...

Urinary excretion kinetics of intact quinidine and 3-OH-quinidine after oral administration of a single oral dose of quinidine gluconate in the fasting and non-fasting state

SummaryTo obtain more precise urinary excretion data of intact quinidine (D) and its main metabolite, 3-OH-quinidine (DM), the specific HPLC method of Bonoraet al has been used to follow its urinary excretion kinetics. In a cross-over study, 2 commercial dosage forms of quinidine gluconate, fast- and slow-release, were administered to 18 healthy subjects who had fasted for 10 hours in 3 treatments which were administered during the fasting period (T1), and before (T2) of after (T3) a standard breakfast. The urine was collected at fixed time intervals for 72 hours after the administration of a single dose (405 mg of quinidine base). The difference between the drug release characteristics of the two products was studied by analysing the cumulative amount of D and DM excreted as a function of time, and the time required to reach the maximum value for the urinary excretion rate of intact quinidine. A food effect could be noticed among treatments with the conventional fast-release dosage form when comparing the maximum values of the urinary excretion rate of D (T2>T1). There was no significant difference in the percentage of drug absorbed from the 2 products, according to the data on the cumulative amount of D and DM. The parameters estimated for quinidine and the metabolite were: the apparent half-life of elimination, the urinary excretion rates and the time to reach a maximum value in the urinary excretion rate. The urinary excretion rate constant and the renal clearance were also quantified for quinidine by combining urinary parameters with the corresponding serum data previously reported.