Sustained release dosage forms capsule, sample

The key consideration in the analysis of any sustained release dosage form as previously discussed (see Sections II.A, II.B, II.C.l, and II.C.2rg) is to determine what solvent or solvent system will be most appropriate to assure the dissolution of the drug and its excipients to make it amenable to HPLC analysis. Aqueous solubility of weak acids and bases is governed by the pfCa of the compound and the pFI of the medium. In an acidic or low pFI medium, weak acids will be unionized and will be more soluble in organic solvents. The reverse is the case for basic compounds as previously discussed in Section II.B. Because the formulation of sustained release dosage forms tend to rely on the use of insoluble plastics (i.e., methyl acrylate-methyl methacrylate, polyvinyl chloride, and polyethylene), hydrophilic polymers (i.e., methylcellulose, hydroxypropyl-methylcellulose, sodium carboxymethyl cellulose, and carbopol 934), and fatty compounds (i.e., waxes such carnauba wax and glyceryl tristearate), similar hydro-organic solvents and sample preparation steps that have been discussed for tablets and capsules can also used for their analysis by HPLC (see Sections II.A, II.B, II.C.l, and II.C.2). 

Initially, the dose given is very low, then a blood sample is taken, and the dosage is increased gradually until the desired concentration is reached. When therapy is initiated, blood samples are taken every three or four days, then once a week, progressing to every two weeks, once a month, then perhaps every three or four months. In order to maintain the desired level, the medication is usually taken periodically throughout the day, depending upon the dosage. Slow-release and sustained-release tablets and capsules have been developed that make the administration of lithium medication easier. It is sometimes taken in liquid form as well. 

A. Sample Preparation Procedure for a Sustained Release Capsule Dosage Form... 

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