Design and Evaluation of Ophthalmic Delivery Formulations

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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.

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The RV Inverter Guide for Beginners What's an RV inverter and do you need one? How do you choose the right inverter for your RV and how do you go about installing it? We were able to consult RV expert, Gary Brinck, on this topic to put together this concise guide for you. You may have noticed that the 120v wall outlets in your RV only work when plugged into shore power or when using a generator. That probably includes the microwave and TV as well. That means your RV is not equipped with an inverter. To find out more about RV inverters, keep reading. What’s An RV Inverter? The inverter is an electronic module that gives the capability to power things that normally require 120VAC shore power (when not using a generator). Having an inverter is hugely convenient if you like to camp off the power grid but still want to watch TV or charge up your phone. Mid- and high-end RVs often come with inverters already installed. They serve just a few items or maybe even all the outlets in the RV. The good news is that if your RV doesn’t have an inverter, you can add one! Sounds attractive, right? However, except for the simplest needs, adding an inverter is a major change in how the 120VAC system in your RV works. In most cases, it's not what you would call a “plug ‘n play” upgrade. How Does An RV Inverter Work? An inverter uses the RV’s 12v batteries to supply the power and inverts the battery 12VDC to become 120VAC power for the outlets. In theory, you can power everything with a large enough inverter, even the air conditioning. However, the inverter cannot provide more power than the battery bank that supplies it. The laws of electricity are that increasing the power output from 12v to 120v (a factor of 10x increase) causes a 10x increase in the input amps (current) as well. That means a high wattage appliance like an AC unit or hair dryer that draws a lot of amps will pull a huge amperage from the batteries. For example, a 1500 watt appliance uses 12.5 amps @ 120v, so it will draw a minimum of 125 amps from the batteries when inverting from 12v to 120v. There is also a power loss of around 10% when inverting. A rule of thumb is that the inverter will draw about 10% more battery amps than actually needed by the power conversion. This is called the efficiency of the inverter and 90%-95% is typical. Since a typical RV battery can supply only 50-70 amps for a mere hour, you can see that batteries quickly become the bottleneck if you try to do too much. The cost, weight, and space needed for a large battery bank are prohibitive for most RVers. For practical purposes, you will want to limit what things you expect to power.

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