Pharmacokinetics of cefamandole using a HPLC assay

Optimal design of mixed-effects PK/PD models based on differential equations

There is a vast literature on the analysis of optimal design of nonlinear mixed-effects models (NLMMs) described by ordinary differential equations (ODEs) with analytic solution. However, much less has been published on the design of trials to fit such models with nonanalytic solution. In this article, we use the "direct" method to find parameter sensitivities, which are required during the optimization of models defined as ODEs, and apply them to find D-optimal designs for various specific situations relevant to population pharmacokinetic studies using a particular model with first-order absorption and elimination. In addition, we perform two simulation studies. The first one aims to show that the criterion computed from the development of the Fisher information matrix expression is a good measure to compare and optimize population designs, thus avoiding a large number of simulations; In the second one, a sensitivity analysis with respect to parameter misspecification allows us to compare the robustness of different population designs constructed in this article.

Multiple pharmacokinetic parameter prediction for a series of cephalosporins

The goal of quantitative structure-pharmacokinetic relationship analyses is to develop useful models that can predict one or more pharmacokinetic properties of a particular compound. In the present study, a multiple-output artificial neural network model was constructed to predict human half-life, renal and total body clearance, fraction excreted in urine, volume of distribution, and fraction bound to plasma proteins for a series of cephalosporins. Descriptors generated solely from drug structure were used as inputs for the model, and the six pharmacokinetic parameters were simultaneously predicted as outputs. The final 10 descriptor model contained sufficient information for successful predictions using both internal and external test compounds. Descriptors were found to contribute to individual pharmacokinetic parameters to differing extents, such that descriptor importance was independent of the relationships between pharmacokinetic parameters. This technique provides the advantage of simultaneous prediction of multiple parameters using information obtained by nonexperimental means, with the potential for use during the early stages of drug development.

New models for pharmacokinetic data based on a generalized Weibull distribution

We consider the development of the concentration of a drug in the blood after single oral or intravenous administration. We introduce a new nonlinear model capable of describing concentration-time curves following intravenous administration. A similar model is proposed for oral data. Both models have four parameters, of which two regulate the shape of the curve and two determine the scale of the time and concentration axes. All the parameters are closely related to geometric properties of the curve. The scale parameters determine a point in the curve, and the shape parameters can be calculated by using numerical integration. The models can be used when the object of the analysis is to quantify the shape of a concentration-time curve. We discuss the usefulness of the models in bioequivalency trials, in clinical safety and efficacy trials, and in population pharmacokinetics. The models are applied to two previously presented data sets. To reduce the number of parameters, the shape parameters are assumed common for all individuals. Encouraging results are obtained. We also present a new four-parameter Michaelis-Menten model.

Quantitative structure-pharmacokinetic relationships for systemic drug distribution kinetics not confined to a congeneric series

Many attempts have been made to describe quantitative structure-pharmacokinetic relationships within a congeneric series of drug molecules. The goal is to develop a predictive relationship that could predict in vivo results for other drugs within that series. These studies typically evaluate pharmacokinetic parameters that are reflective of both distribution and elimination processes. This work utilizes the results from 17 noncongeneric drugs reported in 18 pharmacokinetic studies. The objective was to determine if drug distribution parameters that were independent of elimination could be predicted from easily measured physicochemical parameters with a data base that included a wide variety of drugs that were not congeners of one another. Regression models utilizing a linear and a quadratic response surface were used to predict the various distribution parameters from physicochemical parameters, including molecular weight, intrinsic solubility, alcohol solubility, protein binding, and the distribution coefficient. Analogous to the extent of absorption, the extent of drug distribution can be predicted reasonably well by the probability that the drug will distribute into the peripheral system before being eliminated and by the volume of distribution at steady state. The duration of distribution, analogous to the rate of absorption, can be predicted by the mean transit time through the peripheral system the mean residence time of the drug in the peripheral system and the intrinsic mean residence time in the peripheral system. The ability to use statistical models to approximate drug distribution parameters without the constraints of working within a congeneric series provides some valuable opportunities.

Simultaneous determination of cefamandole and cefamandole nafate in human plasma and urine by high-performance liquid chromatography with column switching

A high-performance liquid chromatographic method with column switching has been developed for the simultaneous determination of cefamandole and cefamandole nafate in plasma and urine. The plasma and urine samples were injected onto a precolumn packed with Corasil RP C18 (37-50 microns) after simple dilution with an internal standard solution in 0.05 M phosphoric acid. Polar plasma and urine components were washed out using 0.05 M phosphoric acid. After valve switching, the concentrated drugs were desorbed in back-flush mode and separated by a reversed-phase C8 column with methanol-5 mM tetrabutylammonium bromide (45:55, v/v) as the mobile phase. The method showed excellent precision with good sensitivity and speed, and a detection limit of 0.5 microgram/ml. The total analysis time per sample was less than 30 min, and the mean coefficients of variation for intra- and inter-assay were both less than 4.9%. The method has been successfully applied to plasma and urine samples for human volunteers after intravenous injection of cefamandole nafate.

Linear and nonlinear system approaches in pharmacokinetics: how much do they have to offer? II. The response mapping operator (RMO) approach

The description of the relationship between different responses measured simultaneously in the same subject is commonly described in terms of specific pharmacokinetic models such as linear compartmental models. An alternative system approach involving response mapping operators (RMOs) is presented. The theoretical and mathematical basis of the RMO approach are derived. The assumptions, limitations, and practical significance of the RMO approach are discussed. The derivation of the RMO is illustrated with several examples. An algorithm and computer program for implementing the RMO in a routine manner is presented. The usage of the computer programs RMO and MAP presented are demonstrated using the pharmacokinetics of trimazosin and cefamandole in humans as examples. The RMO approach offers a new and powerful tool in pharmacokinetic analysis, which allows the investigator to approach certain problems in an objective, rational way without getting involved in specific pharmacokinetic modeling.

Cefamandole pharmacokinetics during standard and pulsatile cardiopulmonary bypass

The pharmacokinetics of cefamandole during standard or pulsatile cardiopulmonary bypass were studied in 13 adult cardiac surgery patients. All patients received 20 mg/kg of cefamandole intravenously at midnight before surgery, 6 AM on the morning of surgery and just prior to the initiation of cardiopulmonary bypass (CPB) surgery. Serum, skeletal muscle, and fat samples were taken at the beginning of CPB and at 30-minute intervals thereafter and assayed for cefamandole concentration. The average elimination rate constant and elimination half-life for cefamandole in patients undergoing standard CPB were 0.73 +/- 0.09 hour-1 and 0.94 +/- 0.11 hour, respectively. In contrast patients undergoing pulsatile CPB had significantly slower elimination rate constants (0.50 +/- 0.1 hour-1 and 1.4 +/- 0.28 hours, respectively; P less than or equal to .05). Area under the curve (AUC) values for cefamandole in fat and muscle tissue were higher in patients undergoing pulsatile CPB, but the differences were not statistically significant. Prolonged elimination from the serum, skeletal muscle, and adipose tissue, as compared with normal subjects, is seen with both pulsatile and standard CPB but is greater for the pulsatile method. Intraoperative dosing of cefamandole is required to maintain adequate serum and tissue levels for operations lasting longer than 4 or 6 hours in which standard or pulsatile CPB, respectively, are used.

Theorems and implications of a model-independent elimination/distribution function decomposition of linear and some nonlinear drug dispositions. III. Peripheral bioavailability and distribution time concepts applied to the evaluation of distribution kinetics

Disposition decomposition analysis (DDA) is applied to evaluate the rate and extent of drug delivery from the sampling compartment to the peripheral system, i.e., peripheral bioavailability. Four parameters are introduced which are useful in quantifying peripheral bioavailability. The compounded peripheral bioavailability, F comp, is the ratio between the total compounded amount of drug transferred to the peripheral system and the injected dose, D. The AUC peripheral bioavailability, FAUC, is the ratio between the area under the amount vs. time curves for the peripheral system and the sampling compartment. The distribution time td, is the time following an i.v. bolus at which the net transfer of drug to the peripheral system reverses in direction. The maximum peripheral bioavailability, Fmax, is the maximum fraction of an i.v. bolus dose that is present in the peripheral system at any one time. Equations are derived which permit estimation of those parameters from drug concentrations in the sampling compartment. Simple algorithms and a computer program are provided for estimating Fcomp, FAUC, td, Fmax, and other parameters relevant to DDA for drugs that exhibit a linear polyexponential bolus response. Estimates of Ecomp, FAUC, td, and Fmax are presented for several drugs.

Dose linearity testing of intravenous cefpirome (HR 810), a novel cephalosporin derivate

After intravenous injection of single doses of 0.25, 0.5, 1.0, 1.5 and 2.0 g of cefpirome (HR 810) to 46 healthy male volunteers in an open manner, concentrations of unchanged drug were estimated at various times in serum and urine, over 24 h and 48 h, respectively. Cefpirome concentrations were determined using both high pressure liquid chromatography (HPLC) and a microbiological assay. The measurements obtained were compared by linear distribution independent regression, and were found to be equivalent. A linear relationship between dose and AUC00 (r = 0.96) for both HPLC and microbiological assay was demonstrated for the doses tested (0.25 g to 2.0 g). The biological half-life (t1/2,beta) was determined by fitting a two-compartment open model to the data: t1/2,beta was about 2 h (HPLC, median values) and was not relevantly dose dependent. A general twice daily dosing will be recommended for the treatment of infections. Clinically relevant high concentrations of unchanged cefpirome were detected in urine already after the lowest dose (0.25 g) for about 12 h, and after the highest dose (2.0 g) for at least 24 h. General tolerance was good, only slight temporary taste disturbances immediately after injection were claimed by one volunteer after both 0.5 g and 1.0 g doses and by four volunteers receiving 2.0 g of cefpirome; however, no counter-measures were needed.

Single pass mean residence time in peripheral tissues: a distribution parameter intrinsic to the tissue affinity of a drug

The single pass mean residence time in peripheral tissues, tp1, is a characteristic constant of linear pharmacokinetic systems and nonlinear systems with linear distribution kinetics. It is descriptive of distribution kinetics in such systems and is not dependent on elimination kinetics as are other related parameters, e.g., mean residence time in peripheral tissues, tp. Equations are derived which permit estimation of tp1 from experimental data for systems in which no peripheral elimination occurs. The type of data required are systemic drug levels resulting from iv administration. The probability density function for single pass residence time in peripheral tissues is derived. It is shown that tp1 is related to the amount of drug in the peripheral tissues at steady state according to (Ap)ss = CLdCsstp1, where CLd is the distribution clearance, and Css is the steady-state systemic drug level. Values of tp1 are presented for several drugs.

Cefamandole distribution in serum, adipose tissue, and wound drainage in morbidly obese patients

Distribution and elimination of cefamandole 2 g iv were studied in 11 morbidly obese patients during a gastric bypass operation and again on the first postoperative day. Serum, subcutaneous adipose tissue, wound drainage, and urine were analyzed by high performance liquid chromatography for cefamandole and pharmacokinetic parameters from the intraoperative period were compared to those obtained postoperatively. Total body clearance was significantly greater (p less than 0.001) postoperatively (297 ml/min) than intraoperatively (254 ml/min). Volume changes were unpredictable but the elimination rate constant tended to increase postoperatively. Renal clearance and percentage of urinary recovery were significantly increased (p less than 0.01) postoperatively. The patients had a mean (+/- SD) volume of the central compartment of 10.3 (+/- 2.3) L, volume at steady state of 18.3 (+/- 3.9) L, and elimination rate constant of 1.67 (+/- 0.63) h-1. Tissue concentrations of cefamandole were highest during the first hour after drug administration and were less than 1 microgram/g after 3.5 hours. Mean wound drainage concentrations ranged between 10 and 12 micrograms/ml during a dosing interval and dropped to 7 micrograms/ml 12 hours after the last dose. Intraoperative dosing of cefamandole is required to maintain subcutaneous adipose tissue concentrations greater than 1 microgram/g during procedures longer than three hours in morbidly obese patients. A postoperative dose of cefamandole 2 g iv q6h will provide sustained and therapeutic concentrations in the wound drainage of morbidly obese patients.

Pharmacokinetics of cefmetazole administered intramuscularly and intravenously to healthy adults

The pharmacokinetics of cefmetazole, a new parenteral cephalosporin, administered intravenously and intramuscularly at a dose of 30 mg/kg to two groups of seven healthy volunteers were studied. Concentrations in serum were monitored over 8 h by a high-pressure liquid chromatography technique. The plasma concentration-time data were statistically fitted to a biexponential equation for both administration routes, and the data were analyzed by a two- and one-compartment kinetic model, respectively. For the dose range and the administration routes used, the pharmacokinetics of cefmetazole proved to be essentially linear, with clearances from plasma ranging between 3.8 and 12.5 liters/h. The mean maximum concentration in plasma after intramuscular administration of the drug was 90.1 micrograms/ml at 0.7 h. The elimination half-life, about 1.3 h, did not show statistically significant differences for the two routes of administration studied.

Theorems and implications of a model-independent elimination/distribution function decomposition of linear and some nonlinear drug dispositions. II. Clearance concepts applied to the evaluation of distribution kinetics

The disposition decomposition approach is employed to derive clearance parameters descriptive of drug distribution kinetics. The name distribution clearance, CLd, is given to a characteristic constant of linear and some nonlinear pharmacokinetic systems. CLd is the clearance associated with the steady-state rate of drug transfer from the peripheral tissues to the systemic circulation. Also introduced is the elimination clearance, CLe, which is associated with the total drug transfer rate from the systemic circulation in linear systems. Estimates of CLd and CLe are presented for several drugs.

Antibiotic monitoring in body fluids

Analytical procedures recently described for the quantitative determination of antibiotics in body fluids are reviewed. High-performance liquid chromatography (HPLC) and immunoassays appear as an alternative to current microbiological assays. HPLC has been applied to most antibiotics in clinical use and a major part of the review deals with this technique. Attention is given to sample pretreatment, characteristics of chromatography and detection, and limit of sensitivity. Non-isotopic immunoassays have been essentially applied to aminoglycosides and vancomycin and are also reviewed. Advantages and drawbacks of HPLC and immunoassays are presented.

A pharmacokinetic comparison of cephalexin and cefadroxil using HPLC assay procedures

The pharmacokinetics of cephalexin and cefadroxil were compared following single 500 mg oral doses to 12 healthy male volunteers. Doses were administered after an overnight fast according to a crossover design. Plasma and urinary levels of both compounds were determined by HPLC procedures. Cephalexin was absorbed rapidly, achieving a mean peak plasma level of 17.5 micrograms ml-1 at 1 h, compared to 16 micrograms ml-1 at 1.8 h for cefadroxil. Elimination half-lives of cephalexin and cefadroxil were 0.7 and 1.1 h, respectively. The area under the cefadroxil plasma curve was significantly larger than that for cephalexin. However, after allowing for differences in elimination rate constants and assuming equal distribution volumes, plasma data indicated the compounds were equally well absorbed. Only 70 per cent of cefadroxil was recovered in urine compared to 87 per cent of cephalexin during the 12 h following drug administration. The therapeutic significance of the different pharmacokinetic characteristics of cephalexin and cefadroxil, if any, may be a function also of their pharmacologic activity and/or the sensitivity of the target organism.

High-pressure liquid chromatographic method for analysis of cephalosporins

A high-pressure liquid chromatographic method is described for the analysis of a wide range of cephalosporin congeners, using only three reagents for extraction and drug analysis. Plasma was treated with cold methanol-0.1 M sodium acetate to precipitate protein. Cephalosporins were resolved on a C-18 reverse-phase column, utilizing a mobile phase of various percentages of 0.01 M sodium acetate and acetonitrile-methanol. Compounds analyzed included cephalexin, cefamandole, cephalothin, cefotaxime, cefazolin, cephaloridine, cefoxitin, cefaclor, cephapirin, and cefoperazone. Each antibiotic demonstrated excellent linearity throughout the therapeutic range. The method of standard additions revealed recoveries of 93 to 101%, with detection limits ranging from 0.2 to 1.0 micrograms/ml for these drugs. Retention times ranged from 4 to 6 min. This method offers a rapid and simple means by which this group of cephalosporins may be reliably quantitated.

Systematic approach to the determination of cephalosporins in biological fluids by reversed-phase liquid chromatography

The chromatographic behaviour of some cephalosporins as a function of pH and ionic strength of the mobile phase was studied on 10-microns LiChrosorb RP-18. Acidic cephalosporins were retained longest in their neutral form with an acidic eluent. Amphoteric cephalosporins were retained longest in their protonated form with an acidic eluent of low ionic strength. Cefotiam was retained longer with an alkaline mobile phase. LiChrosorb RP-18, Nucleosil C18 and muBondapak C18 gave rise to different selectivities when an acidic eluent, methanol-water (25:75) containing 0.2% of 1.8 M H2SO4 was used. This may be related to interactions with residual silanol groups. The studied cephalosporins (with the exception of cefotiam and cefsulodin) were separated from compounds present in biological fluids on 5-microns LiChrosorb RP-18 using the mobile phase 0.2% of 1.8 M H2SO4 in a mixture of methanol and water with various methanol contents. The determination of cefotiam in biological fluids was performed with an alkaline mobile phase. The preparation of the sample was simple and rapid: precipitation of plasma proteins or dilution of urine. The method was applied to the determination of ceftizoxime in human plasma and urine. Concentrations down to 0.2 micrograms/ml of plasma and 25 micrograms/ml of urine could be determined with good reproducibility and accuracy.

Precise high-performance liquid chromatographic procedure for the determination of cefsulodin, a new antipseudomonal cephalosporin antibiotic, in plasma

A simple and precise high-performance liquid chromatographic (HPLC) procedure was developed for the determination of cefsulodin, a new antipseudomonal cephalosporin antibiotic, in plasma. The analytical procedure involved ultrafiltration of samples that were buffered to prevent cefsulodin degradation, followed by injection into an HPLC system, utilizing a C18 reversed-phase analytical column, a mobile phase of acetonitrile-modified aqueous acetate buffer, and a UV spectrophotometric detector. Because of the simplicity of the procedure, the intraassay (or approximately 2%) and interassay (or approximately 3-4%) coefficients of variation were extremely low. Recoveries of drug were essentially quantitative in freshly buffered specimens and in those stored buffered and frozen for nearly 3 months. Calibration curves were rectilinear from the limit of quantification (or approximately 0.2 microgram/ml) to 200 micrograms/ml, as demonstrated by regression correlation coefficients averaging greater than 0.999 during routine analyses.

Pharmacokinetics of cefonicid, a new broad-spectrum cephalosporin

This study determined the pharmacokinetic disposition of cefonicid. A single dose of 7.5 mg/kg of body weight was administered to five healthy volunteers as a 5-min intravenous infusion. Multiple plasma and urine samples were collected for 48 h. Peak plasma concentrations ranged from 95 to 156 micrograms/ml and fell slowly (mean plasma half-life, 4.4 +/- 0.8 h), so that levels after 12 h were in the range of 6 to 12 micrograms/ml. Urinary concentrations were high but variable and ranged from 100 to 1,000 micrograms/ml for the first 12 h after the dose and averaged 84 micrograms/ml between 12 and 24 h. Plasma and renal clearances were 0.32 +/- 0.06 and 0.29 +/- 0.05 ml/min per kg, respectively. An average of 88 +/- 6% of the dose was excreted unchanged in the urine over 48 h. The mean steady-state volume of distribution was found to be 0.11 +/- 0.01 liters/kg.

Effect of cardiopulmonary bypass on the pharmacokinetics of drugs

The cardiopulmonary bypass apparatus must temporarily substitute for the cardiac and pulmonary function of the patient undergoing heart surgery. In order to meet the metabolic needs of the patient and the technical demands of the surgeon, within the limits of engineering technology, a number of major alterations are made in normal physiology. The patient is typically cooled to 27 degrees C and perfused with a non-pulsatile flow of blood which has been diluted with saline to a haematocrit in the mid-20s. Blood flow and pressure are often considerably less than normal. Blood coagulation is prevented by administration of a massive dose of heparin. Central redistribution of blood flow, elaboration of stress-reactant hormones, and fluid and electrolyte shifts occur in response to these changes. In the postoperative period, these alterations are reversed, and normal physiology is restored. Effects upon the pharmacokinetics of drugs are anticipated. The clearance of many drugs may be reduced. Protein binding is diminished by haemodilution, but may rise above normal in the postoperative period for basic drugs which bind to alpha 1-acid glycoprotein. Changes in volume of distribution depend upon the opposing influences of protein binding and reduced peripheral perfusion. Previous studies on the pharmacokinetics of drugs during and after cardiopulmonary bypass illustrate many of these effects. The clearance of digoxin, fentanyl, and the cephalosporins is reduced after cardiopulmonary bypass, and the volume of distribution of cefazolin is increased during cardiopulmonary bypass. Studies of digitoxin and propranolol are also reviewed. Many of the investigations in this area of study have been limited by logistical and methodological factors. Thus, the effects of cardiopulmonary bypass on the pharmacokinetics of drugs are incompletely understood, and the subject merits further attention.

A very precise high-performance liquid chromatographic procedure for the determination of cefmenoxime, a new cephalosporin antibiotic, in plasma

A simple and very precise high-performance liquid chromatographic procedure has been developed for the determination of cefmenoxime, a new broad spectrum cephalosporin antibiotic, in plasma. The workup procedure involves ultrafiltration of samples which have been treated with sodium dodecyl sulfate to displace the drug from its binding sites on plasma proteins. The ultrafiltrates are then directly injected into a high-performance liquid chromatographic system utilizing a reversed-phase analytical column, and an ultraviolet spectrophotometric detector. The mean assay coefficient of variation over a concentration range of 0.5-200 micrograms/ml is slightly greater than 1% when either p-nitrobenzoic or p-anisic acid is used as the internal standard. Recoveries of drug are essentially quantitative at all levels investigated; hence the calibration curves are rectilinear from the limit of quantification (about 0.05 microgram/ml) to at least 200 micrograms/ml.

Determination of cephalosporins in biological material by reversed-phase liquid column chromatography

Seven cephalosporins (beta-lactam antibiotics), viz. cefazolin, cephalotin, cefoxitin, cefotaxime, cefamandole, cefuroxime and cefoperazone (T 1551) were determined in biological material. The compounds were extracted from acid-treated body fluids into chloroform--1-pentanol (3:1) and re-extracted into a small volume of an aqueous phase at Ph 7, which was injected into the chromatographic column. The chromatographic support was muBondapak C18 (10 micrometer) and the mobile phase was a mixture of 0.01 M acetate buffer (pH 4.8) and methanol or acetonitrile. Detection limits are about 50 ng/ml for extractions from 1 ml of serum and have permitted pharmacokinetic studies of the seven cephalosporins.

Pharmacokinetics of cefuroxime in normal and impaired renal function: comparison of high-pressure liquid chromatography and microbiological assays

The pharmacokinetics of cefuroxime were studied after a single dose of 750 mg was given intravenously to each of 21 male volunteers grouped according to their creatinine clearances; these clearances were 60 to 120, 20 to 59, and less than 20 ml/min per 1.73 m,2 respectively, for groups 1 (12 subjects), 2 (4 subjects), and 3 (5 subjects). Cefuroxime obeyed two-compartment model kinetics in all three groups. Initial serum levels of cefuroxime were approximately 130 microgram/ml in group 1 and 2 and 80 microgram/ml in group 3. the levels then declined rapidly for 0.5 to 1 h after injection. After that time, cefuroxime levels declined more slowly, and the elimination rate became monoexponential. The mean serum half-lives for cefuroxime in groups 2, 2, and 3 were 1.7, 2.4, and 17.6 h, respectively. Mean cefuroxime levels in serum were greater than 8 microgram/ml for 3 h in group 1, for 6 h in group 2, and for 30 h in group 3. Cumulative 24-h urinary excretion accounted for essentially 100% of the dose in group 1 and 2, and for 40% in group 3. Urine levels exceeded the minimal inhibitory concentration for susceptible organisms for more than 12 h in all groups. Cefuroxime distribution characteristics were independent of renal function. In patients with creatinine clearances less than 20 ml/min per 1.73 m2, doses of cefuroxime needs to be reduced. A microbiological disk diffusion assay and a high-pressure liquid chromatography assay for cefuroxime yielded statistically identical results, except for serum levels in uremic patients (group 3).

The clinical pharmacokinetics of buflomedil in normal subjects after intravenous and oral administration

A dose-ranging pharmacokinetic study of buflomedil was carried out in eight subjects to determine the pharmacokinetic parameters of the drug after oral and intravenous administration. Based on AUC infinity analyses, the pharmacokinetics of buflomedil were found to be linear within the dose ranges studied (50 to 200 mg for i. v. injection and 150 to 450 mg for oral administration). In the oral study, the mean biological half-life of the drug was 2.97 h, while after intravenous dose it was 3.25 h. The apparent volume of distribution after the pseudodistribution equilibrium (Fd beta) and volume of distribution at the steady state (Vdss) were 1.43 +/- 0.24 l/kg and 1.32 +/- 0.26 l/kg, respectively. The mean urinary recovery of intact drug and the metabolite, paradesmethyl buflomedil, after intravenous dosing, were 23.6% and 18.7%, respectively, while after oral dosing, they were 18% and 14.8%, respectively. On the average, 72% of the dose was observed into the systemic circulation after oral administration. This level of bioavailability was attributed to the hepatic first-pass effect.