Polyacrylic acid is considered to be a first mucoadhesive polymer and the protonated form at an acidic pH is responsible for mucoadhesion. It is used as artificial tears to treat dry eye syndrome. Polyacrylic acid forms the hydrogen bond between its –COOH groups and sialic –COOH groups of the mucin glycoprotein. This bond formation leads to an increase in the viscosity. Thus, these acrylic compounds can also be used as hydrogels to treat ocular irritations (Wagh et al., 2008). A controlled release of the drug can be achieved when administered through thiolated poly(acrylic acid) based inserts, which are not soluble and possesses excellent cohesive properties. The in vivo study showed that thiolated poly(acrylic acid) based inserts provide a fluorescein concentration for more than 8 h compared with the aqueous eye drops or inserts based on unmodified poly(acrylic acid). Thus, it suggests that thiolated poly(acrylic acid) could be used as promising solid devices for ocular drug delivery (Hornof et al., 2003).
Cao et al. developed a poloxamer/carbopol-based in situ gelling system of azithromycin as a novel method for ophthalmic delivery using poloxamer and carbopol. Poloxamer is hydrophilic, nonionic triblock copolymers of polyoxyethylene and polyoxypropylene. Carbopol is a hydrophilic polymer of acrylic acid cross-linked with polyalkenyl ethers or divinyl glycol. Poloxamer 407 and poloxamer 188 used as gelling agents and Carbopol 974P used to increase the solubility of azithromycin were also added to the gelling systems. Carbopol 974P also increases the mucoadhesive property of the gelling systems. The developed formulation shows a 24 h sustained release of azithromycin. In vivo study reveals an increase in AUC0–12 of azithromycin in rabbit tears by 1.78-fold for in situ gel as compared with eye drops. At 12 h, tear concentrations increase minimum inhibitory concentration breakpoint for most common causative pathogens of bacterial conjunctivitis by 2.8-fold. Thus, these data indicate that formulated droppable gel is better for ocular delivery of azithromycin than eye drops (Cao et al., 2010).
Acrylic polymers such as N-butyl-2-cyanoacrylate (NBCA) are not ideal sclerosing agents for VMs. In addition to their high cost, they are absorbed slowly, and a firm painful mass is left in the soft tissues for many months. They are useful when rapid occlusion and minimal swelling are desired, such as for outflow occlusion in conjunction with injection of sclerosant or for hemostasis before resection. NBCA opacified with oily contrast medium in a ratio of 1:4 to 1:6 appears to be effective in controlling bleeding and improving localization of VMs during resection. Risks include unintended occlusion of major veins and pulmonary embolization. Intraoperative injection of tissue adhesive (NBCA) immediately before surgical excision of VMs of the orbit has been reported.
