ABSTRACT
In vitro dissolution kinetics of Methotrexate have been analysed at different temperatures in water at pH 1.5. After giving rise to the dissolution reaction, it has been possible to follow up the kinetic of dissolution and calculate energy activation. The pH variation allows us also to appreciate the constant behaviour of dissolution at temperature 310 K (37 degrees). Weilbull equation is valid with success for dissolution reaction as well during temperature variation and different values of pH. In both cases the Weibull constant b has been calculated and compared to constant dissolution K.
Subject(s)
Methotrexate/pharmacokinetics , Hydrogen-Ion Concentration , In Vitro Techniques , Solubility , Temperature , WaterABSTRACT
The absorption of sodium valproate was studied in 5 rabbits. Each animal received the drug (70 mg/kg) via 3 routes: intravenous, gastric and duodenal. For the 2 extravascular routes, the absolute bioavailability F, maximal plasma concentrations Cmax, times to peak Tmax and absorption coefficients Kabs were the same. Absolute bioavailability was always close to unity. This indicated that valproic acid was absorbed from the intestine as well as from the whole gastrointestinal tract. The other pharmacokinetic parameters such as terminal plasma half-life, total clearance and volume of distribution remained unchanged whatever the route of administration.
Subject(s)
Valproic Acid/pharmacokinetics , Animals , Catheterization , Duodenum/metabolism , Gastric Mucosa/metabolism , Injections, Intravenous , Intestinal Absorption , Male , Rabbits , Valproic Acid/administration & dosageABSTRACT
Determination of changes in plasma concentration of ioxaglate in patients with renal failure made it possible to demonstrate that distribution and clearance of this contrast medium, as in the case of classic uroangiographic products, conform to an open two-compartment model with clearance from the central compartment. Various pharmacokinetic parameters were calculated. The metabolic clearance of ioxaglate was lower for all 6 patients studied, as compared with results for 3 normal subjects tested, but less marked than with iodamide, a contrast medium involving tubular secretion.
Subject(s)
Ioxaglic Acid/blood , Kidney Failure, Chronic/blood , Adult , Aged , Aged, 80 and over , Humans , Kinetics , Mathematics , Metabolic Clearance Rate , Middle Aged , Models, Biological , Osmolar ConcentrationABSTRACT
A dynamic study of the kinetics of theophylline adsorption in aqueous medium by two adsorbent resins is proposed. The adsorption process involves Van der Walls pattern physical bonds. An in vitro haemoperfusion apparatus was schematized and data describing the adsorption-desorption process was obtained. A mathematical treatment led to the conclusion that first-order adsorption and desorption rates are involved, results which led to the consideration of a model of in vivo haemoperfusion in the case of first-order adsorption and desorption, with first-order corporeal elimination. The results indicate that one of the resins used, Amberlite XAD4, already known as a haemocompatible resin, is useful in eliminating theophylline.
Subject(s)
Hemoperfusion/methods , Models, Biological , Theophylline/poisoning , Adsorption , Anion Exchange Resins , Evaluation Studies as Topic , Humans , In Vitro Techniques , Kinetics , Polystyrenes , Polyvinyls , Resins, Synthetic , Theophylline/blood , Theophylline/isolation & purificationABSTRACT
A general theory of haemoperfusion for drugs obeying the one-compartment pharmacokinetics model is proposed. The following theoretical cases are investigated: First case Adsorption and desorption are first-order reactions without biotransformation, and elimination rate is first-order. Two particular cases are examined: no desorption and alpha = beta. Second case: Adsorption and desorption rates are first-order, without biotransformation, and elimination rate is zero-order. Third case: Adsorption rate is first-order and desorption rate is zero-order, without biotransformation, and elimination is either first-order or zero-order. Fourth case Adsorption rate is zero-order and desorption rate is first-order, without biotransformation, and elimination is either first-order or zero-order. Fifth case: Adsorption and desorption rates are first-order, with biotransformation. In all these pharmacokinetics models for haemoperfusion, theoretical computations lead to the values of adsorbed amount and plasma level, in relation to time. Clearances are also computed. In most cases, haemoperfusion must be performed quickly because of the desorption phenomenon. Parameters modulating the adsorption process are: surface area, blood flow, drug concentration in blood, adsorbent nature and adsorbent quantity.
Subject(s)
Hemoperfusion , Models, Biological , Poisoning/therapy , Adsorption , Biotransformation , Humans , In Vitro Techniques , Kinetics , Metabolic Clearance Rate , Poisoning/bloodSubject(s)
Pharmaceutical Preparations/metabolism , Biotransformation , Humans , Kinetics , Models, BiologicalABSTRACT
Drug absorption during vaginal administration. A method is described (systems approach to vaginal delivery of drugs and development of in situ vaginal drug absorption procedure) and is able to show vaginal absorption of drugs. Some drugs are rapidly and largely absorbed through vaginal epithelium: Metronidazole (Flagyl), Prostaglandins, Estrogens, Polyvidone-iodine (Betadine), Chloroquinadol (Gynotherax), d-Methadone, Hexachlorophene (Phisohex et Ultralan), Insulin and Triclosan. Other drugs are poorly absorbed: Amphotericin B (Fungizone, Amphocycline), Econazole (Pevaryl) and Trimethoprim. At least, some drugs are not absorbed: Nystatine (Mycostatine) and Furazolidone (Tricofuron).
