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Biomedical subjects

F Theeuwes

Publications and source records attributed to F Theeuwes.

8 recordsLinked to original sources
PubMed1978

Gastrointestinal therapeutic system for acetazolamide. Efficacy and side effects.

Acetazolamide has been formulated in a new gastrointestinal therapeutic system that delivers the drug at an essentially constant rate of 15 mg/hr (GITS 15/125). We compared the therapeutic effect, magnitude of plasma concentration fluctuations, and incidence of side effects produced by the GITS 15/125 with conventional 250-mg acetazolamide tablets on eight glaucomatous patients randomly assigned to a different regimen each week. One or two GITS 15/125 twice a day (bid) were found as effective in reducing intraocular pressure as one 250-mg acetazolamide tablet. Plasma concentration fluctuations with the GITS 15/125 were decreased, compared with acetazolamide tablets, and, as a result, the incidence of drowsiness, tingling feet, tingling hands, and confusion was substantially reduced.

Acetazolamide↗
PubMed1977

Dosage form index: an objective criterion for evaluation of controlled-release drug delivery systems.

A dimensionless parameter, the dosage form index (DLtau) is proposed for evaluating the performance of drug delivery systems. The index is defined as the ratio of the maximum to minimum concentrations of the drug in plasma within each interdose interval (in hours), tau, during repetitive administration of the dosage form in the quasisteady state. Dosage form indexes can be averaged among subjects or within subjects at successive time periods to arrive at a mean value. As an example, two GI therapeutic systems--the 15- and 20-mg/hr acetazolamide systems that deliver drug at constant rates for 6 and 12 hr and contain 125 and 250 mg, respectively--were compared in normal subjects with a commercial sustained-release product containing 500 mg of acetazolamide. The dosage form index, DI24, was 4.9 for the sustained-release dosage form and 3.2 for the 20-mg/hr system; DI12 was 1.6 for the 15-mg/hr system.

Acetazolamide↗
PubMed1976

Programmed diffusional release rate from encapsulated cosolvent system.

The programmed diffusional release rate of an active agent through a rate-controlling membrane from a cosolvent system is discussed. At initial conditions, the drug is present below saturation in solution in a solvent mixture, enclosed by the rate-controlling membrane; the solvent is composed of the main solvent and a consolvent, which increases the drug solubility in the main solvent. During operation, the active agent and cosolvent diffuse from the capsule at a rate controlled by the membrane. Equations were derived describing the release rate of the active agent as a function of the permeability of the cosolvent and agent, the capsule dimensions, and the system's initial conditions. A great variety of release rate profiles can be programmed from declining to increasing delivery rate patterns as a function of time. Experimental data are presented for the drug progesterone in solution in cyclohexane with methyl, heptyl, or cetyl alcohol as the cosolvent in a polyethylene capsule. The theory qualitatively predicts the theory qualitatively predicts the experimental results.

Alcohols↗
PubMed1975

Elementary osmotic pump.

The elementary osmotic pump is a new delivery system for drugs or other active agents; it delivers the agent by an osmotic process at a controlled rate. Control resides in the: (a) water permeation characteristics of a semipermeable membrane surrounding the formulated agent, and (b) osmotic properties of the formulation. In its simplest embodiment, the system is constructed by coating an osmotically activie solid agent with the rate-controlling, semipermeable membrane. This membrane contains an orifice of critical size through which solubilized agent is dispensed. The system can contain the agent in solid form at loading higher than 90% of the total volume, and the agent can be delivered at rates several orders of magnitude higher than can be achieved by solution diffusion through polymeric membranes. The delivery rate, the fraction of total content delivered at zero order, and the system's delivery portal size have been calculated for delivery of a single compound. Experimental work verified the theory. The release rate from the system was found to be independent of outside agitation when the system is not deformed by shaking action, the pH of the environment, and delivery portal size for sizes within a specified range. The delivery rate from this system in vitro and in the GI tract of dogs was found to be equal.

Animals↗