Stepwise determination of multicompartment disposition and absorption parameters from extravascular concentration-time data. Application to mesoridazine, flurbiprofen, flunarizine, labetalol, and diazepam.

When disposition is monoexponential, extravascular concentration-time (C, t) data yield both disposition and absorption parameters, the latter via the Wagner-Nelson method or deconvolution which are equivalent. Classically, when disposition is multiexponential, disposition parameters are obtained from intravenous administration and absorption data are obtained from extravascular C, t data via the Loo-Riegelman or Exact Loo-Riegelman methods or via deconvolution. Thus, in multiexponential disposition one assumes no intrasubject variation in disposition, a hypothesis that has not been proven for most drugs. Based on the classical two- and three-compartment open models with central compartment elimination, and using postabsorptive extravascular C, t data only, we have developed four equations to estimate k10 when disposition is biexponential and two other equations to estimate k10 when disposition is triexponential. The other disposition rate constants are readily obtained without intravenous data. We have analyzed extravascular data of flurbiprofen (12 sets), mesoridazine (20 sets), flunarizine (5 sets), labetalol (9 sets), and diazepam (4 sets). In the case of diazepam intravenous C, t data were also available for analysis. After disposition parameters had been estimated from the extravascular data the Exact Loo-Riegelman method with the Proost modification was applied to the absorptive extravascular data to obtain AT/VP as a function of time. These latter data for each subject and each drug studied were found to be fitted by a function indicating either simple first-order absorption, two consecutive first-order processes, or zero-order absorption. After absorption and disposition parameters had been estimated, for each set of extravascular data analyzed, a reconstruction trend line through the original C, t data was made. The new methods allow testing of the hypothesis of constancy of disposition with any given drug. There is also a need for new methods of analysis since the majority of drugs have no marketed intravenous formulation, hence the classical methods cannot be applied.

Estimation of the amount of alcohol ingested from a single blood alcohol concentration.

Capillary blood alcohol concentrations (BAL) measured in 22 young adult male volunteers each of whom received three different treatments of alcohol (total N = 66) have been related quantitatively to the dose of alcohol ingested. Linear regression with reasonably homogeneous variances have been found when the BAL at 2, 2.5 and 3 hr are divided by the person's body weight and plotted versus the g/kg (D/W) dose. Error analysis indicated that the least error in the predicted dose (D/W) was obtained for BAL measured at 2 hr post dosing. In the latter case the mean absolute error was 6.23%, 59% of the errors were within +/- 5% and 88% of the errors were within +/- 10%.

Intersubject variation in the pharmacokinetics of haloperidol and reduced haloperidol.

Single oral doses (5 mg) of haloperidol were administered to 36 healthy men (26 black, 10 white) of whom 28 (22 black, 6 white) completed the study. Plasma samples harvested over 96 hours were analyzed for haloperidol and reduced haloperidol by means of a new high performance liquid chromatographic method. Reduced haloperidol was detectable in the plasma of only six of the 28 subjects (five blacks, one white). In these individuals reduced haloperidol plasma concentrations were generally much lower than those of the parent drug. This finding in the present single-dose study is in contrast to literature reports that have described levels of reduced haloperidol higher than those of the parent drug in some patients chronically mediated with haloperidol. There was wide intersubject variation in area under the plasma concentration versus time curve and apparent oral clearance values for haloperidol. The distributions of these pharmacokinetic parameters about their respective means were each leptokurtotic and skewed toward higher values. In each case the geometric mean gave a better estimate of central tendency than the arithmetic mean. Wide intersubject variation prevented the detection of significant differences in these pharmacokinetic parameters between black and white subjects or between smokers and nonsmokers.

Parameters Vm' and Km for elimination of alcohol in young male subjects following low doses of alcohol.

Seventy-four (44 under fasting conditions and 30 following oral liquid meals) sets of post-absorptive human capillary blood alcohol concentration-time data were computer-fitted to the integrated form of the Michaelis-Menten equation by numerical integration by nonlinear least squares to provide 74 pairs of the kinetic Vm' and Km parameter values. The parameters were highly correlated (r = 0.915) by orthogonal least squares. Eight of the fasting subjects received four different oral doses of alcohol and fourteen subjects each received three different alcohol treatments. Intra-subject variances of Vm', Km and the ratio Vm' Km were calculated from the multiple treatments. Inter-subject variances were calculated from the 22 mean values of each parameter. Each parameter and the intra-subject variances of the parameters were found to be log normally distributed. The liquid meals (carbohydrate, fat and protein separately) appeared not to affect the parameter values. The computer fittings were all excellent as evidenced by the relatively small standard deviations of the estimated parameters and other statistical measures of fit.

Improved high-performance liquid chromatographic assay for the quantification of 5-bromo-2'-deoxyuridine and 5-bromouracil in plasma.

A sensitive and specific procedure using high-performance liquid chromatography (HPLC) was developed for the quantification of 5-bromo-2'-deoxyuridine (BUdR) and 5-bromouracil (BU) in plasma. BUdR and BU were first extracted with a mixture of ethyl acetate and 2-propanol from plasma presaturated with solid ammonium sulfate. Following evaporation of the organic extract, the remaining residue was reconstituted in saturated ammonium sulfate solution, washed with a mixture of n-pentane-methylene chloride and re-extracted with the original solvent mixture. The organic extract was evaporated, reconstituted in mobile phase and chromatographed on a regular-bore ODS HPLC column using ultraviolet absorbance detection. The BUdR and BU quantification limits were both 0.1 microM, the mean intra-assay coefficients of variation were 5.0 and 5.6%, respectively, and the mean inter-assay coefficients of variation were 5.4 and 10.7%, respectively. This method was used to determine steady-state femoral arterial and hepatic venous plasma concentrations of BUdR and BU in a patient receiving a continuous intravenous infusion of BUdR (20 mg/kg per day).

Sensitive and specific high-performance liquid chromatographic assay for the quantification of sulforidazine and two diastereomeric sulforidazine-5-sulfoxide metabolites in plasma.

A sensitive and specific procedure using high-performance liquid chromatography for the quantification of sulforidazine and two diastereomeric sulforidazine-5-sulfoxide metabolites in plasma was developed. Sulforidazine was first extracted from basified plasma using a mixture of pentane and 2-propanol. Sulforidazine-5-sulfoxide metabolites were then extracted from the same basified plasma using a second solvent mixture consisting of methylene chloride, pentane and 2-propanol. Each organic extract was subsequently back-extracted separately with 0.1 M hydrochloric acid, basified and re-extracted with the original solvent mixtures. In order to avoid interferences due to hydroxylated metabolites co-eluting with sulforidazine-5-sulfoxides in the more polar extract, this extract was derivatized with N-methyl-(tert.-butyldimethylsilyl) trifluoroacetamide. The two extracts were separately chromatographed on a narrow-bore nitrile column using ultraviolet detection. The quantification limits for sulforidazine and two diastereomeric sulforidazine-5-sulfoxide metabolites were 1.0 ng/ml with mean intra-assay coefficients of variation less than 10%. These methods were applied to the analysis of plasma from a dog following the administration of a single oral dose (25 mg of the base) of sulforidazine hydrochloride.

Identification in in vivo acetylation pathway for N-dealkylated metabolites of doxylamine in humans.

1. Metabolites of doxylamine in human urine were separated by g.l.c. and h.p.l.c. and tentatively identified by their mass spectrometric behaviour. 2. N-Desmethyldoxylamine, N,N-didesmethyldoxylamine and their N-acetyl conjugates were identified. This is believed to be the first report of acetylation in vivo of primary and secondary aliphatic amines in man.

Doxylamine metabolism in rat and monkey.

Metabolites of doxylamine obtained with rat-liver homogenate in vitro and from urine of Wistar rats and squirrel monkeys in vivo were examined. The metabolites were separated by g.l.c., h.p.l.c. and t.l.c., and tentatively identified through interpretation of their mass-spectrometric behaviour. N-Desmethyldoxylamine was identified in vitro while both N-desmethyl and N,N-didesmethyldoxylamine were detected in rat and monkey urine. The N-acetyl conjugates of N-desmethyl and N,N-didesmethyldoxylamine were tentatively identified both in rat urine and in vitro. Only the N-acetyl conjugate of N,N-didesmethyldoxylamine was detected in monkey urine. In addition, nine other metabolites were tentatively identified in rat urine: N,N-dimethyl-2-[1-(?-hydroxyphenyl)-1-(2-pyridyl)ethoxy]ethanamine; N-methyl-2-[1-(?-hydroxyphenyl)-1-(2-pyridyl)ethoxy]ethanamine; 1-phenyl-1-(2-pyridyl)ethanol; 1-(?-hydroxyphenyl)-1-(2-pyridyl)ethanol; 1-phenyl-1-(2-pyridyl)ethane; 1-(?-hydroxyphenyl)-1-(2-pyridyl)ethane; 2-phenyl-2-(2-pyridyl)ethanol; N,N-dimethyl-2-[1-phenyl-1-(2-pyridyl)-2-hydroxyethoxy]ethanamine; doxylamine pyridine N-oxide. The excretion of doxylamine aliphatic N-oxide in rat urine was confirmed by comparison with the authentic synthetic compound.