Reservoir devices

Several narcotic antagonists, including naloxone, naltrexone, L-methadone, and cyclazocine, have been incorporated in lactide homopolymers and lactide/glycolide copolymers. Cyclozocine was incorporated in poly(L-lactide) in the form of films (81,82). Lamination of drug-polymer films with a drug-free film created a reservoir device and eliminated the burst observed with the monolithic films originally tested. 

The use of polylactides for delivery of insect hormone analogs and other veterinary compounds (115,116) has been studied. Microspheres, pellets, and reservoir devices based on polyglycolide, poly-(DL-Iactide), poly(L-lactide), and various copolymers have been used to deliver methoprene and a number of juvenile hormone analogs. ... 

FIGURE 14 In vitro rate of release of testosterone from a PCL capsule (reservoir device), illustrating rate control by drug dissolution when the polymer membrane thickness is small. (From Ref. 68.)... 

FIGURE 16A Daily rate of release of naltrexone from a poly-e-caprolactone-co-lactic acid capsule (reservoir device) under in vitro conditions. (From Ref. 89.)... 

FIGURE 17 Use of a porous PCL membrane to achieve diffusion-controlled zero-order deliveiry of a LHRH analog from a reservoir device. (From Ref. 72.)... 

Diffusion systems are characterized by the release rate of a drug being dependent on its diffusion through an inert membrane barrier. Usually this barrier is an insoluble polymer. In general, two types or subclasses of diffusional systems are recognized reservoir devices and matrix devices. These will be considered separately. 

Reservoir devices, as the name implies, are characterized by a core of drug, the reservoir, surrounded by a polymeric membrane. The nature of the membrane determines the rate of release of drug from the system. A schematic description of this process is given in Fig. 4, and characteristics of the system are listed in Table 3. 

Fig. 6 Plot showing the approach to steady state for a reservoir device that has been stored for an extended period (the burst effect curve) and for a device that has been freshly made (the lag time curve). (From Ref. 29.)...

Advantages Easier to produce than reservoir devices Can deliver high molecular weight compounds... 

B.Huet de Barochez, F.Lapeyre and A.Cuinne, Oral sustained release dosage forms. Comparison between matrices and reservoir devices, 4th Int. Pharmaceutical Technology Symp., Ankara, 12-14, September 1988. 

The Ocusert system illustrated in Figure 12.7 is one example of a diffusion-controlled reservoir device. Another is the steroid-releasing intrauterine device (IUD) shown in Figure 12.9. Inert IUDs of various shapes were widely used for... 

The CYPHER stent employs two nonerodible polymers polyethylene-co-vinyl acetate (PEVA) and poly-n-butyl methacrylate (PBMA), The combination of sirolimus and these two polymers constitutes the basecoat formulation that is applied to a stent treated with paryleneC. In addition, a drug-free topcoat of PBMA polymer is applied to control the release kinetics of sirolimus (59), making this a diffusion-controlled reservoir device. The chemical structure of the polymers used in the CYPHER stent is shown in Figure 4,... 

Before the establishment of a steady state, the membrane-reservoir device will exhibit initial release rate higher or lower than the steady state value, depending on the prior history of the device. Thus, immediately after fabrication, a finite time lag will be required to establish the steady-state concentration profile... 

Diffusion-controlled reservoir devices are used in a wide variety of routes including those shown in Table 3.1. 

Reservoir devices Parenteral Norplant subdermal implant... 

Outline the differences between a reservoir device and a matrix device. 

In both cases, drug release is governed by diffusion, i.e. the drug moiety must diffuse through the polymer membrane (for a reservoir device) or the polymeric matrix (for a matrix device), in order to be released. 

As for the non-porous reservoir device, in the microporous system, both ... 

Reservoir/matrix hybrid-type non-degradable polymeric implants are also available. Such systems are designed in an attempt to improve the M t1/2" release kinetics of a matrix system, so that release approximates the zero-order release rate of a reservoir device. Examples of these types of systems include ... 

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