Osmotic pump drug delivery systems

Theeuwes and Higuchi1 applied the principle of osmotic pressure to a new generation of controlled drug delivery devices with many advantages over other existing controlled drug delivery systems. The first of these devices, the elementary osmotic pump, is considered a typical delivery system that operates on osmotic principles. 

The invention that positioned osmosis as a major driving force for controlled drug delivery was the elementary osmotic delivery system. ALZA has developed elementary osmotic delivery systems under the name OROS. A successful modification that overcame the disadvantages of the elementary osmotic pump was the Push-Pull osmotic drug delivery system. The following sections are devoted to the principal features of these systems. 

There are several variants to this apparatus, which is based on a sample holder that oscillates up and down in the medium vessel. The sample holder may take the form of a disk, cylinder, or a spring on the end of a stainless steel or acrylic rod, or it may simply be the rod alone. The sample is attached to the outside of the sample holder either by virtue of being self-adhesive (e.g., transdermal delivery system) or is glued in place using a suitable adhesive. This apparatus may be used for transdermal products, coated drug delivery systems, or other suitable products (e.g., osmotic pump devices). It is prescribed for the drug-release testing of Psuedoephedrine hydrochloride extended-release tablets USP where the tablets are enclosed in a 5x5 cm of nylon, which is then attached to the rod. 

Fig. 19 (A) Cross-sectional view of the Alzet osmotic pump, an osmotic pressure-activated drug-delivery system. (B) The effect of 7 days of subcutaneous delivery of antidiuretic hormone (vasopressin) on the daily volume of urinary excretion and urine osmolality in the Brattleboro rats with diabetes insipidus.

Numerous other examples of the use of solubility to control the delivery profile of drugs from the elementary osmotic pump can be found in the literature, especially the patent literature [35-40], These systems apply to drugs of moderate to high aqueous solubility where either the excipient or the salt form of the drug was used to control the drug solubility within the core formulation. 

OROS Push-Pull system. After the introduction of commercial products based on EOP technology in the early 1980s, numerous attempts were made to apply the osmotic concept to a broader range of drugs. Since the elementary osmotic pump is limited to the delivery of relatively soluble drugs with solubilities greater than about 2 to 10 wt%, depending on dose, other modifications were necessary to expand the utility of the EOP... 

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. 

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