Drugs controlled release type

Controlled release, although resulting in a zero-order delivery system, may also incorporate methods to promote localization of the drug at an active site. In some cases, a controlled-release system will not be sustaining, but will be concerned strictly with localization of the drug. Site-specific systems and targeted-delivery systems are the descriptive terms used to denote this type of delivery control. 

Historically, the oral route of administration has been used the most for both conventional and novel drug-delivery systems. There are many obvious reasons for this, not the least of which would include acceptance by the patient and ease of administration. The types of sustained- and controlled-release systems employed for oral administration include virtually every currently known theoretical mechanism for such application. This is because there is more flexibility in dosage design, since constraints, such as sterility and potential damage at the site of administration, axe minimized. Because of this, it is convenient to discuss the different types of dosage forms by using those developed for oral administration as initial examples. 

Rapid-release products are another class of con-trolled-release drug-delivery systems of growing interest to pharmaceutical scientists. For this type of product rapidity of response is the key parameter. If a conventional non-controlled-release product gives the therapeutic response in one hour, a rapid-release product might be designed so as to yield such a response in 20 minutes. 

To develop an HPLC stability-indicating method for Type I or II dissolution, the linearity must be wide enough, in combination with good sensitivity and minimal interference, to accommodate concentrations from low (possibly LOQ) to very high end, as the samples drawn represent the cumulative drug amount dissolved over time. As for an FiPLC method that is designed for Type VII dissolution, the linearity should accommodate the lower concentrations since it is a drug measurement of a controlled-release system. 

The eoneept of mueoadhesion in drug delivery was introduced in the field of controlled-release drug delivery systems in the early 1980s [2,3]. Thereafter, several researchers have focused on the investigations of the interfacial phenomena of mucoadhesive hydrogels (and of other type mucoadhesive compounds) with the mucus. Several techniques of studying these interactions were evaluated both in vitro and... 

Another aspect related to control release of drugs concerns the type of structures that currently appear to be working. Not unexpectedly, because of compatibility and degradation purposes, most of the effort on the control release formulations includes polymers that have both a hydrophobic and hydrophilic portion with the material necessarily containing atoms in addition to carbon. Another concern is that the products of degradation are not toxic or do not form toxic materials. It has also been found that amorphous materials appear to be better since they are more flexible and permit more ready entrance of potential degrad-ative compounds. 

This book is a companion volume to Pharmaceutical Technology Controlled Drug Release, Volume 1, edited by M.H.Rubinstein and published in 1987. It focused on the different types of polymeric materials used in controlled release. This book extends these concepts to include drug properties, design and optimization, coating, the effect of food and pharmacokinetics. It also reflects the growing interest in biodegradable polymers in oral and topical formulations and the use of sterile implants. 

The widespread applicability of di-O-methylisosorbide as a medium for chemical reactions or as a solvent for pharmaceutical formulations is well documented. In some cases, an additive synergism of the solvent and the solute was observed. Some typical examples mentioned include that it acts as a solvent for muscle-relaxant drugs, which are otherwise difficultly soluble,226 and is used for topical and other types of pharmaceutical formulations,227,228 transdermal controlled-release films229 and tapes,230 anthelmintic solutions,231 antimycotic emulsions,232 and for the treatment of skin disorders, such as eczema.233... 

FIGURE 22.15 Pharmacokinetic parameters for the Spherazole CR tablet, 100 mg, compared with the Sporanc IR capsule. (Note Types A and B differed in levels of rate-controlling excipients.) (Adapted from Jacob, J. Gastroretentive, bioadhesive drug delivery system for controlled release of itraconazole pharmacokinetics of Spherazole CR in healthy human volunteers. Controlled Release Society 34th Annual Meeting and... 

Intramuscular. The large quantity of skeletal muscle in the body allows this route to be an easily accessible site for parenteral administration. Intramuscular injections can be used to treat a problem located directly in the injected muscle. For example, botu-linum toxin and other substances can be injected directly into hyperexcitable muscles to control certain types of muscle spasms or spasticity (see Chapter 13).7,78 Alternatively, intramuscular injection can be used as a method for a relatively steady, prolonged release of the drug into the systemic circulation to control conditions such as psychosis,2 or to administer certain vaccines. 

The regulation of drug input into the body is the core tenet of controlled release drug delivery systems. With advances in engineering and material sciences, controlled release delivery systems are able to mimic multiple kinetic types of input, ranging from instantaneous to complex kinetic order. In this section three of the most common input functions found in controlled release drug delivery systems will be discussed— instantaneous, zero order, and first order. 

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