Drug release prolonged retention

A recent approach to ocular inserts was presented by Chetoni et in a study of cylindrical devices for oxytetracycline, made from mixtures of silicone elastomer and grafted on the surface of the inserts with an interpenetrating mueoadhesive polymeric network of polyacrylic acid or polymethacrylic acid. The inserts were tested for drug release and retention at rabbit eyes. It was shown that some of the inserts are able to maintain prolonged oxytetracycline concentrations in the lacrimal fluid for 36 h. 

The use of pharmaceuticals in form of emulsions is of special interest. Thus, for example, o/w emulsions stabilised by surfactants, such as mono- and diglycerides, are successfully used as pseuo-doxime-proxetil protection from intestinal lumen hydrolysis through oral administration [128]. Multiple w/o/w emulsions stabilised by Tween 20/Span 20 or Tween 80/Span 80 mixtures contributed to a prolonged retention of cytarabine in one of the phases, and its gradual release ensured a prolonged action of the drug [129]. 

To sustain drug release and prolong therapentic activity, the coUoidal particles must be retained in the ocular cul-de-sac after topical administration, and the entrapped drug released from the particles at an appropriate rate. To enhance particle retention in the ocnlar cul-de-sac, it is highly recommended to manufacture or coat the particles with bioadhesive materials. These dosage forms can then bioadhere to the conjunctival epithelinm and therefore increase contact time between these tissues and the drugs adsorbed or encapsulated into these carrier systems. 

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