Urinary excretion kinetics for evaluation of drug absorption. I. Solution rate limited and nonsolution rate limited absorption of aspirin and benzyl penicillin; absorption rate of sulfaethylthiadiazole

The design and analysis of parallel experiments to produce structurally identifiable models

Pharmacokinetic analysis in humans using compartmental models is restricted with respect to the estimation of parameter values. This is because the experimenter usually is only able to apply inputs and observations in a very small number of compartments in the system. This has implications for the structural identifiability of such systems and consequently limits the complexity and mechanistic relevance of the models that may be applied to such experiments. A number of strategies are presented whereby models are rendered globally identifiable by considering a series of experiments in parallel. Examples are taken from the pharmacokinetic literature and analysed using this parallel experiment methodology. It is concluded that considering a series of pharmacokinetic experiments where some, but not all, of the parameters may be shared across the experiments can improve the identifiability of some compartmental models.

in vitro and in vivo Properties of Aloxiprin: A New Aluminium Derivative of Acetylsalicylic Acid

The rates of solution of aspirin from aloxiprin, an aluminium derivative of acetylsalicyclic acid, in buffer solutions of pH 2–8 were found to be lower than those of aspirin B.P., particularly in the more acid buffers.

The excretion of salicylate in the urine of 11 human subjects who received aloxiprin was more delayed than that from a corresponding dose of aspirin B.P. Little difference was found in the total amount of salicylate excreted in 24 hr.

Continuous transepidermal drug collection: basis for use in assessing drug intake and pharmacokinetics

Continuous transepidermal drug collection (CTDC) has been proposed for use in assessing ethanol intake and in monitoring compliance with therapeutic regimens. Exploration of a theoretical basis for use of CTDC in these circumstances and for its use in assessing other aspects of drug disposition kinetics was undertaken. Effects of single and multicompartmental drug disposition models, single dose and multiple dose regimens, with regular and irregular doses and dosing intervals, and zero-order, first-order, and Michaelis-Menten excretion patterns were explored. First-order transepidermal drug transfer was assumed with and without back transfer from the collection device. These analyses suggest that the utility of CTDC is severely restricted when back transfer from the collection device is substantial. With back transfer minimized, CTDC may be a useful tool for assessing amount of drug exposure, compliance with therapeutic regimens, and relative bioavailability, but offers little advantage over discrete sampling of other body fluids in the study of other aspects of drug disposition kinetics.

Analysis of drugs by pyrolysis. II--An improved method for the determination of carpronium chloride in plasma by selected ion monitoring

A sensitive and specific method has been devised for the determination of carpronium chloride, a parasympathomimetic agent, in plasma. The method is based on selected ion monitoring combined with the pyrolysis reaction of (3-isopropoxycarbopropyl)trimethylammonium chloride derived by transesterification of the drug. Carpronium chloride-[2H9] is used as an internal standard. The drug and the internal standard are separated from deproteinized plasma by ion pair extraction, and converted into isopropyl ester derivatives. The derivatives are pyrolysed to produce the respective isopropyl N,N-dimethyl-gamma-aminobutyrates available for selected ion monitoring. Measurement is carried out in the electron impact mode by monitoring the fragment ion [M-OC3H7]+ (m/z 114, 120). The method is applicable to 5 ng ml-1 plasma with about 10% coefficient of variation, and has been utilized successfully for the pharmacokinetics of carpronium chloride in man.

Statistical moments in pharmacokinetics

Statistical moments are parameters that describe the characteristics of the time courses of plasma concentration (area, mean residence time, and variance of residence time) and of the urinary excretion rate that follow administration of a single dose of a drug. The relationship between the moments of a time-course curve and pharmacokinetic profiles of drug disposition, i.e., absorption, distribution, metabolism, and excretion, is described. The moments are related to the extent and rate of bioavailability, and it is shown that they can be effectively applied to the deconvolution operation.

Solid-state dispersions employing urethan

The dissolution rates of a number of drug-urethan solid-state dispersion systems were studied. A marked enhancement of the initial dissolution rates of several poorly water-soluble drugs was found when they were incorporated into a urethan matrix by heat fusion. These differences were considerable when pure substances such as griseofulvin, hydrocortisone, chloramphenicol, and acetaminophen were compared to the urethan-drug solid dispersion. Physical mixtures of the medicinal agents with urethan also gave a marked increase in the amount of drug in solution, with the value in most cases being over one-half that of the solid-state dispersion. Data are given, comparing ultrafiltration with samples filtered through cotton, regarding drug content remaining in solution.