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Background Information of Current Systems

Controlled Release systems

            A controlled release system is a device for controlled the release time of a chemical, and/or the release rate. In the field of drug delivery, the amount delivered over a certain time frame is critical depending on the therapeutic purpose and the patient. If drug concentrations are below this specific range, then there is no therapeutic benefit for the patient. However, if drug concentrations are too much, then the drug can have toxic effects and can possibly pose substantial danger or death to the patient.
            Conventional drug delivery systems include tablets of injections that commonly result in a bolus release of drugs followed by a general decrease in drug concentrations. In a drug delivery profile this can be seen as a sharp peak much larger than the therapeutic concentration range within the initial stages of delivery that immediately decreases below the therapeutic concentration range (Figure a. below taken from [1]). An ideal form of drug delivery would be a sustained or “controlled” form of drug release that can be kept constant within the therapeutic range.

conventional drug profile Picture Rights belong to [1]

            Figure: A comparison of conventional drug delivery profile versus a controlled drug release profile, in which c is drug concentration and t is time. (Picture Rights belong to [1]) 

            A common example of a sustained drug release system is one that utilizes polymers to constantly diffuse drug from within through gradual degradation. The systems can exist as oral tablets, polymer implants or microspheres. Commercially available products include Gliadel and Lupron Depot [2,3]. Another example of sustained drug release systems include transdermal delivery through the skin that can be used through such lipophillic drug molecules such as estradiol and nitroglycerin. The limitation to drug application through the skin however is the establishment of a stable concentration of drug in the blood stream.
            Pulsatile release is another form of drug release, which as opposed to constant sustained release methods, delivers a pulse of drugs at variable time intervals (Figure b. below taken from [1]). This method of delivery is theoretically preferred by the body due to the similarity in which naturally forming compounds, such as insulin and growth hormones, are secreted by the body in pulses [4]. In some cases, such as women suffering from hormonal deficiencies, the applications of continuous drug delivery to assist this deficiency can have negative effects on the body, such as suppression of naturally occurring hormone production. Pulsatile release however, may provide a reduction in hormonal deficiencies that more closely mimics functions of the body.

pulsatile drug profile Picture Rights belong to [1]

            Figure:. A comparison of sustained drug release versus pulsatile release, in which r is the rate of drug release and t is time. (Picture Rights belong to [1]) 

            Pumps and catheters are another form of release that rivals pulsatile drug delivery. Pumps can also be programmed to apply pulsatile drug delivery through a catheter within the patient. The problem with pumps and catheter delivery systems are the inconvenience, large size, expense, and discomfort or infections experienced at the catheter site.

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