PubMed · 4644644
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H M Fales. 1972. Newer physicochemical methods useful in bioavailability studies.. https://doi.org/10.1159/000136330
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Development of a rice variety enriched in provitamin A, the accumulation of polyhydroxybutyrate polyester in Arabidopsis nuclear transgenic plants (with enzymes targeted to chloroplasts in both), and the expression of bacterial operons via the chloroplast genome are recent landmark achievements in multigene engineering. Hyper-expression of transgenes has resulted in the formation of insecticidal protein crystals or inclusion bodies of pharmaceutical proteins in transgenic chloroplasts, achieving the highest level of transgene expression ever reported in transgenic plants. These achievements illustrate the potential of multigene engineering to realize benefits of the post-genomic revolution.
The current BSC guidance issued by the FDA allows for biowaivers based on conservative criteria. Possible new criteria and class boundaries are proposed for additional biowaivers based on the underlying physiology of the gastrointestinal tract. The proposed changes in new class boundaries for solubility and permeability are as follows: 1. Narrow the required solubility pH range from 1.0-7.5 to 1.0-6.8. 2. Reduce the high permeability requirement from 90% to 85%. The following new criterion and potential biowaiver extension require more research: 1. Define a new intermediate permeability class boundary. 2. Allow biowaivers for highly soluble and intermediately permeable drugs in IR solid oral dosage forms with no less than 85% dissolved in 15 min in all physiologically relevant dissolution media, provided these IR products contain only known excipients that do not affect the oral drug absorption. The following areas require more extensive research: 1. Increase the dose volume for solubility classification to 500 mL. 2. Include bile salt in the solubility measurement. 3. Use the intrinsic dissolution method for solubility classification. 4. Define an intermediate solubility class for BCS Class II drugs. 5. Include surfactants in in vitro dissolution testing.
Despite having pharmacodynamic or target activity, many drugs fail in the drug development process due to poor bioavailability, and presently marketed conventional dosage forms of poorly soluble drugs employ high doses leading to potential toxicity. The introduction of the Biopharmaceutic Classification System (BCS) has provided a basis to categorize drugs based on the two major parameters affecting absorption, solubility and permeability. Several techniques can be employed to enhance the absorption and bioavailability of poorly soluble and poorly permeable drugs based on the BCS concept. This article is an attempt to summarize the development of various formulation approaches that are currently employed to enhance bioavailability of orally administered poorly soluble drugs.