Controlled release osmotic pumps

Ozdemir N, Sabin J. Design of a controlled release osmotic pump system of ibuprofen. Int ] Pharm 1997 158 91-97. 

It is worthwhile to mention that (SB P-CD also makes controlled drug delivery more feasible for water-insoluble compound. It is well known that the release from controlled porosity osmotic pump tablets is limited due to its low aqueous solubility. However, Okimoto et al. (1999) successfully developed osmotic pump tablets for testosterone by using StjSBJD. Because each (SBEVm-P-CD molecule has an average of seven negative charges and seven sodium ions, it can act as... 

Habib, B.A., Rehim, R.T.A., El-Nour, S.A., 2014. Feasibility of optimizing trimetazidine dihydrochloride release from controlled porosity osmotic pump tablets of directly compressed cotes. Journal of Advanced Research 5, 347—356. 

Makhija, S.N. Vavia, R.R. Controlled porosity osmotic pump-based controlled release systems of pseudoephedrine. I. Cellulose acetate as a semipermeable membrane. J. Control. Release 2003, 89 (1), 5-18. 

In open fibers the fiber wall may be a permselective membrane, and uses include dialysis, ultrafiltration, reverse osmosis, Dorman exchange (dialysis), osmotic pumping, pervaporation, gaseous separation, and stream filtration. Alternatively, the fiber wall may act as a catalytic reactor and immobilization of catalyst and enzyme in the wall entity may occur. Loaded fibers are used as sorbents, and in ion exchange and controlled release. Special uses of hoUow fibers include tissue-culture growth, heat exchangers, and others. 

Fig. 6. Schematic representation of the elementary osmotic pump containing a reservoir of dmg for controlled release and an immediately available overcoat...

DG Pope, PK Wilkinson, JR Egerton, J Conroy. Oral controlled release delivery of ivermectin in cattle via an osmotic pump. J Pharm Sci 74 1108-1110, 1985. 

The rectal milieu is quite constant as its pH is about 7.5, and the temperature is usually 37°C. It is normally empty and the pressure varies between 0 and 50 cm. This makes this route suitable for the (controlled) delivery of drugs by applying adequate (controlled release) dosage forms such as osmotic pumps and hydrogels, since the classical suppositories are, in general, not the most suitable dosage form to achieve a reproducible rate and extent of drug absorption. 

Controlled release dosage forms typically have one of three different dissolution profiles square root of time or matrix diffusion, zero-order delivery as for erosional dosage forms or osmotic pumps, and zero-order delivery with depletion of the driving force as for a membrane-controlled system. For many controlled release dosage forms, zero-order release may be the holy grail. ... 

The principal application of these small osmotic pumps has been as implantable controlled release delivery systems in experimental studies on the effect of continuous administration of drugs. The devices are made with volumes of 0.2-2 mL. Figure 12.18 shows one such device being implanted in a laboratory rat. The delivery pattern obtained with the device is constant and independent of the site of implantation, as shown by the data in Figure 12.19. 

Cellulose esters (e.g., cellulose triacetate, cellulose diacetate, cellulose propionate, and cellulose butyrate) are prepared by initially treating cellulose with glacial acetic acid (or propionic acid and butyric acid) followed by the corresponding acid anhydride with a trace of strong acid as a catalyst in chlorinated hydrocarbon. Complete esterification reactions result in the formation of a triester, which undergoes water hydrolysis to form a diester. Cellulose acetate alone or in combination with cellulose triacetate or cellulose butyrate is used as a semipermeable membrane for osmotic pumping tablets, primarily in controlled release systems. The permeability of the membrane can be further modulated by adding water-soluble excipients to the cellulose esters. 

The driving force for drag release from a pump is a pressure difference that causes the bulk flow of a drag, or drug solution, from the device at a controlled rate. This is in contrast to the polymeric controlled release systems described above, where the driving force is due to the concentration difference of the drag between the formulation and the surrounding environment. Pressure differences in an implantable pump can be created by osmotic or mechanical action, as described below. 

Okimoto, K., Rajewski, R. A., and Stella, J. V. (1999), Release of testosterone from an osmotic pump tablet utilizing (SBE)7m-B-cyclodextrin as both a solubilizing and an osmotic pump agent, /. Controlled Release, 58, 29-38. 

Zhang, Y., Zhang, Z., and Wu,F. (2003), A novel pulsed-release system based on swelling and osmotic pumping mechanism,/. Controlled Release, 89,47-55. 

In another study, Wu et al. from China used a neural network to model the formulation of salbutanol sulfate osmotic pump tablets, using the amount of hydroxypropyl methyl cellulose and polyethylene glycol present in the cellulose acetate coating, in addition to the coating weight, as control factors. Using the model, the authors predicted the release parameters for 1000 formulations, from which they selected an optimum with the desired release pattern. 

Cellulose acetate is used as a semipermeable coating on tablets, especially on osmotic pump-type tablets and implants. This allows for controlled, extended release of actives. Cellulose acetate films, in conjunction with other materials, also offer sustained release without the necessity of drilling a hole in the coating as is typical with osmotic pump systems. Cellulose acetate and other cellulose esters have also been used to form drug-loaded microparticles with controlled-release characteristics. 

Abrahamsson, B., M. Alpsten, B. Bake, U. E. Jonsson, M. Lepkowska-Eriksson, and A. Larsson. (1998b). Drug absorption from nifedipine hydrophilic matrix extended-release (ER) tablet—Comparison with an osmotic pump tablet and effect of food./. Controlled Release 52 301-310. 

The principle of a purely osmotically controlled drug delivery was disclosed some 15 years ago [147]. The so-called elementary osmotic pump consists of a core containing the drug (and if necessary an osmotic agent) and a CA semipermeable membrane with a micro-orifice drilled usually by a laser beam. Drug release is activated by the transport of water through the semipermeable... 

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