Sustained release dosage forms

A. Biological Factors Influencing Oral Sustained-Release Dosage Form Design... 

Degim T, Eglen B, and Ocak O (2006) A sustained release dosage form of acyclovir for buccal application An experimental study in dogs. J. Drug Target 14 35-44. 

Absorption - Theophy ne is well absorbed from oral liquids and uncoated plain tablets maximal plasma concentrations are reached in 2 hours. Rectal absorption from suppositories is slow and erratic, the oral route is generally preferred. Enteric-coated tablets and some sustained-release dosage forms may be unreliably absorbed. 

Do not crush or chew sustained-release dosage forms... 

Ritschel, W.A. Hardt, T.J. (1983) Pharmacokinetics of coumarin, 7-hydroxycoumarin and 7-hydroxycoumarin glucuronide in the blood and brain of gerbils following intraperitoneal administration of coumaxm. Arzneim.-Forsch., 33, 1254-1258 Ritschel, W.A. Hoffmann, K.A. (1981) Pilot study on bioavailability of coumarin and 7-hydroxycoumarin upon peroral administration of coumarin in a sustained-release dosage form. J. din. Pharmacol., 21, 294-300... 

Granulation particle size did not impact the release rate. In addition, tableting at various compression forces had no significant impact on the release rate of the tablets. This knowledge that variability in tablet manufacture resulted in a uniform sustained release dosage form provided an advantage for further process optimization and scale-up, as shown in Figure 23. 

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 aim of this investigation was to create a sustained release dosage form to provide a constant blood level pattern for up to 12 h after oral administration of ketoprofen. Three different techniques for delaying drug release from hydrophilic matrices of hydroxyproplmethylcellulosc were evaluated. 

Table 5 Typical Factors That Affect Release Kinetics for Parenteral, Polymer Sustained-Release Dosage Forms...

Thus polymers serve as key excipients in oral and parenteral CR formulations. Other excipients used in sustained release dosage forms have been covered in other chapters within this book. For example, parenteral CR dosage forms involving polymers would still have other excipients as discussed in the chapter on injectable excipients (Chapter 16). Similarly oral dosage forms will require consideration of other excipients depending on the nature of the drug, as discussed in Chapter 12. This chapter reviews some of the promising polymers used in this application. 

C. Castan, M. Cicquel, R. Meyrueix, et al. Genvir The first sustained release dosage form of acyclovir. Proc. Int. Symp. Contr. Rel. Bioact. Mater. 27 1198—1199, 2000. 

On the way to multiple-unit dosage forms, a demand is seen for flexible polymers. These polymers can be summed up in a new class of polymers that have at least two main functions They have the functionality for enteric targeting and they show physicochemical properties necessary to obtain the desired flexibility. A new market can be seen in this field for the manufacture of coating materials, because the functionality of these polymers should not be limited to enteric targeting but also be applicable to other fields of controlled release, like transdermal applications or oral sustained-release dosage forms. 

Polyvinylacetate (PVAc) has not been used in the pharmaceutical held until recently. During the polymerization, especially at high conversion, free radicals are transferred to dead polymers, resulting in the formation of branched polymers. These branched polymers are susceptible to deterioration. Because the PVAc latex particles are produced by an emulsion polymerization technique, this provides a good process for the water-based dispersion in him coatings. The main purpose of this polymer is the him coating of sustained release dosage forms. The polymer is used as a precursor in the production of polyvinylalcohol (PVA), which cannot be prepared directly by polymerization due to the unstable, isomeric monomer of acetaldehyde. 

Our first stereospedfic bioequivalence evaluation using verapamil formulations was a pilot study conducted in 24 healthy male volunteers. The study compared the bioavailability of two sustained-release dosage forms and an immediate release formulation of racemic verapamil in a three-way cross-over study. Table 2 summarizes the results observed for verapamil. Table 3 the results for norverapamil. First, pharmacokinetic... 

Very limited drug absorption due to the lack of microvilli and the more viscous and semisolid nature of the lumen contents. A few drugs such as theophylline and metoprolol are absorbed in this region. Drugs that are absorbed well in this region are good candidates for an oral sustained-release dosage form... 

Many review articles and many more research studies have been written on the use of systems involving the congealing and cooling of solid mixtures or solutions to produce both fast-release and sustained-release dosage forms. There are many reasons for using... 

Sustained-Release Dosage Forms Made Using Melt-Congealing Processes... 

The mechanism of absorption must always be evaluated when a sustained-release dosage form is considered. A drug that is passively absorbed throughout the GI tracts is an ideal candidate for sustained release. Drugs such as riboflavin, folic acid, aminopenicillins, amino-p-lactams and nucleoside analogs, which have windows of absorption due to site-specific and/or active transport processes, may have incomplete bioavailability when formulated in oral, sustained-release dosage forms. 

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