Bioavailability delivery

Co-administration of ofloxacin and chitosan in eyedrops increased the bioavailabUity of the antibiotic [290]. Trimethyl chitosan was more effective because of its solubility (plain chitosan precipitates at the pH of the tear fluid). On the other hand, N-carboxymethyl chitosan did not enhance the corneal permeability nevertheless it mediated zero-order ofloxacin absorption, leading to a time-constant effective antibiotic concentration [291]. Also W,0-carboxymethyl chitosan is suitable as an excipient in ophthalmic formulations to improve the retention and the bioavailability of drugs such as pilocarpine, timolol maleate, neomycin sulfate, and ephedrine. Most of the drugs are sensitive to pH, and the composition should have an acidic pH, to enhance stability of the drug. The delivery should be made through an anion exchange resin that adjusts the pH at around 7 [292]. Chitosan solutions do not lend themselves to thermal sterilization. A chitosan suspension, however. 

Polymeric microparticles have been studied and developed for several years. Their contribution in the pharmacy field is of utmost importance in order to improve the efficiency of oral delivery of drugs. As drug carriers, polymer-based microparticles may avoid the early degradation of active molecules in undesirable sites of the gastrointestinal tract, mask unpleasant taste of drugs, reduce doses and side effects and improve bioavailability. Also, they allow the production of site-specific drug targeting, which consists of a suitable approach for the delivery of active molecules into desired tissues or cells in order to increase their efficiency. 

Drug delivery problems associated with pilocarpine, most notably low ocular bioavailability and short duration of action, continue to be significant (44). In an effort to prolong delivery and to avoid undesirable effects, an investigation was carried out on the incorporation and in vitro release of pilocarpine from a soluble film... 

Because of its convenience and good patient compliance, oral administration is the most preferred drug delivery form. As a result, much of the attention of in silico approaches is focused on modeling drug oral absorption, which mainly occurs in the human intestine. In general, drug bioavailability and... 

Chan, O. H., Stewart, B. H. Physicochemical and drug-delivery considerations for oral drug bioavailability. Drug Discov. Today 1996, 1, 461 73. 

Intravenous antibiotic administration is the most common delivery method for surgical prophylaxis. Intravenous administration ensures complete bioavailability while minimizing the impact of patient-specific variables. Oral administration is also used in some bowel operations. Non-absorbable compounds like erythromycin base and neomycin are given up to 24 hours prior to surgery to cleanse the bowel. Note that oral agents are used adjunctively and do not replace IV agents. 

Welling, P.G. Deobrinska, M.R. "Dosing considerations and bioavailability assessment of controlled drug delivery systems" In Controlled Drug Delivery Robinson, J.R., Lee, V.H.L., Eds. Drugs and the Pharmaceutical Sciences M. Dekker, New York, NY, 1987, Vol. 29, pp. 253-292. 

A number of other peptide molecules are currently being explored for delivery via inhalation (6). Very recently, a much smaller peptide (leuprolide, about 9 amino acid residues) has been delivered by metered dose inhaler (MDI) in a characterized fashion to humans (7). This work revealed that about 50% of a dose deposited in the lung could be bioavailable. This value is much greater than those reported for nasal bioavailabilities of this and similar molecules (8). These results, and ours in the rat lung (9), imply that inhalation administration of some peptide and polypeptide molecules is perfectly feasible. 

GIT, is considered to be lost from the absorption site, as is metabolic clearance and sequestration in various cell types and membranes (72,14). It is clear from Scheme I that the relative rates of the various processes will define the bioavailable fraction of the dose and understanding those factors which control pulmonary absorption kinetics is obviously the key to enhancing bioavailability via the lung. In a recent book (75) the molecular dependence of lung binding and metabolism was considered alongside the parallel processes of absorption, clearance and dissolution in the lung (14). Some key features of this work will be repeated as it relates to the systemic delivery of polypeptides. 

In conclusion, it should be apparent from this discussion of the absorption mechanisms that, although the major features influencing drug absorption are well known, implementation of a coherent delivery strategy is highly specific for any compound, and many variables need to be adjusted for their significant influence on absorption and more importantly, on bioavailability. In addition, from the suggestion of the role of... 

A Adjei, J Garren. Pulmonary delivery of peptide drugs effect of particle size on bioavailability of... 

Sustained- and controlled-release devices for drug delivery in the vaginal and uterine areas are most often for the delivery of contraceptive steroid hormones. The advantages in administration by this route—prolonged release, minimal systemic side effects, and an increase in bioavailability—allow for less total drug than with an oral dose. First-pass metabolism that inactivates many steroid hormones can be avoided [183,184],... 

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