Drug delivery systems toxicity reduction

Topical heparin eyedrops were effective for long-term reduction of fibrotic posterior capsule opacification after extracapsular cataract extraction with intraocular lens implantation (93). Implantation of a heparin drug delivery system into the posterior chamber of experimental animals maintained a significantly higher heparin level in the aqueous humor for a long period of time, suggesting the potential for effective prevention of posterior capsular opacification after phacoemulsification of the lens with no toxic or side effects (94). 

An important aspect in all drug delivery is the toxicity of the drug as well as that of the drug carrier. Therefore, toxicity has to be assessed also for microemulsion formulations. In microemulsion systems, the main concern regarding toxicity has to do with the cosurfactants used. For example, the majority of the work on the pharmaceutical application of microemulsions has involved the use of short- or medium-chain alcohols, e.g., butanol. In a range of studies it has been shown that these cause toxic side effects. For example, inhalation studies of the toxicity of 1-butanol, 2-butanol, and / -butanol in rats showed a dose-dependent reduction in fetal weight [56]. Furthermore, aqueous solutions of ethanol, propanol, and butanol were shown to result in elongated mitochondria in hepatocytes after 1 month of exposure [57]. (In addition to the toxicity aspects of these alcohols, microemulsions formed in their presence are often destabilized on dilution of the continuous phase.) Furthermore, many studies so far have involved aliphatic or aromatic oils, such as hexane or benzene, which obviously are unsuitable for pharmaceutical use. Moreover, ionic surfactants could in themselves be toxic and irritant [58]. 

The delivery system is one of the most important aspects to consider when molecules used as contrast agents or therapeutic drugs are injected into the blood stream. Encapsulation is a common strategy used for the protection of molecules against in vivo degradation, reduction of potentially toxic side effects that occur with the direct administration of the solution, to avoid repetitive bolus injections or the use of perfusion pumps and pharmacokinetic improvements (Vrignaud et al., 2011). Delivery systems currently under investigation are based on liposomes, smart polymers, viral... 

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