Ocular-specific anti-viral management options are limited even as viral pathogens that invade the eye are also somewhat limited to three types. Most viral infections are etiologically adenoviral, herpetic, or zoster in origin, with the potential for serious vision loss in affected patients. There is no doubt that treatment and management of viral infections should be aggressive in nature, as the possibility of permanent damage to eye structures can result in devastating consequences (Labetoulle, 2009).
Iodine has broad anti-microbial properties and low toxicity to tissues. It is known to disrupt enzymes and proteins in bacteria, viruses, and fungi. This oxidizing characteristic makes iodine a very potent broad-spectrum antimicrobial agent. A solution containing 50ppm of iodine kills bacteria in one minute and spores in 15 minutes.
Iodine Formulations and Uses
Iodine is poorly soluble in water but readily dissolves in ethanol, which enhances its antibacterial activity (Apt et al, 1984). Iodophors are a combination of iodine and a vehicle or solubilizing agent. The two most common combinations in iodophors are povidone-iodine and poloxamer-iodine, which are more stable and water soluble compared to older formulations.
There are various iodophor formulations. Iodine tincture contains 2% iodine and 2.4% sodium iodide (NaI) dissolved in 50% ethanol, which is used as a skin disinfectant. Strong iodine tincture contains 7% iodine and 5% potassium iodide (KI) dissolved in 95% ethanol. This more potent formulation is also more irritating compared to tincture of iodine. Iodine solution contains 2% iodine and 2.4% NaI dissolved in aqueous solution; it is mostly used as an abrasion and wound antiseptic. Strong iodine solution (Lugol’s solution) contains 5% iodine and 10% KI in aqueous solution.
These antimicrobial formulations are widely used as skin disinfectants, particularly before surgery. They do not sting or permanently stain (Sibbald et al, 2011).
A Formulation for Ocular Use
Among the more recent treatment options for adenoviral conjunctivitis is a drug combination of 0.4% povidone-iodine and 0.1% dexamethasone, which may prove to be effective. Clinical trials have been conducted to test the effectiveness of this combination in the treatment of adenoviral conjunctivitis (Clement et al, 2011; Pelletier et al, 2009; Pinto et al, 2015).
As mentioned previously, the mechanism of action of povidone-iodine involves disrupting the enzymes and proteins in microbes; it is both efficient and has a potent, broad-spectrum antimicrobial activity (Sibbald et al, 2011). Dexamethasone is a well-known-to-eye-care anti-inflammatory corticosteroid that inhibits phospholipase A2, leading to inhibition of cyclooxygenase and lipoxygenase pathways and inhibiting inflammatory prostaglandin synthesis. This activity also makes dexamethasone effective in treating certain types of ocular inflammation (Goldman et al, 2011).
A study was conducted by Clement et al (2011) using the drug combination of 0.4% povidone-iodine and 0.1% dexamethasone in rabbit corneas. Twenty rabbits used in the study were randomly assigned into four groups: FST-100 (0.4% povidone-iodine + 0.1% dexamethasone), 0.5% cidofovir, tobramycin/dexamethasone ophthalmic suspension, and balanced salt solution (BSS). Of the four groups, the group treated with FST-100 attained the lowest score of clinical symptoms; in addition, FST-100 was proven to be effective in lowering viral titers.
Pelletier et al (2009) also conducted a study to assess the effectiveness of the combination of 0.4% povidone-iodine and 0.1% dexamethasone in treating adenoviral keratoconjunctivitis in human subjects. The study evaluated the treatment for signs of toxicity and for effectiveness in cases of adenovirus infection verified using the Rapid Pathogen Screening (RPS) Adeno Detector. Nine eyes of six patients were enrolled in the study that concluded with resolution of symptoms after three to four days of treatment. A significant reduction in adenoviral titers were observed after three to five days. One limitation of the study was that it was not a placebo-controlled trial.
Pinto et al (2015) conducted a randomized, masked, and controlled trial that included 122 patients diagnosed with viral conjunctivitis. The population was randomly assigned into the treatment and control groups. The treatment group was provided with a combination of topical ophthalmic 0.4% povidone-iodine and 0.1% dexamethasone applied four times daily for seven days, and the control group was given a placebo of artificial tears applied four times daily for seven days. Symptoms were recorded on day 0 and after treatment; subsequent follow-up visits occurred on days 5, 10, and 30 post-treatment. The results of this clinical trial demonstrated that the combination treatment resulted in faster resolution of symptoms by exhibiting shorter conjunctivitis durations of 9.4 ± 4.6 days as opposed to the control group, which had a longer conjunctivitis duration of 11.8 ± 4.9 days (p = 0.009), thereby exhibiting the effectiveness of the combination of 0.4% povidone-iodine and 0.1% dexamethasone in the treatment of viral conjunctivitis.
A New and Promising Use for an Old Antiviral Agent
Viruses are a common infectious entity encountered in eye care that have the potential to culminate in adverse visual outcomes for affected individuals (Labetoulle, 2009). With limited options in ocular viral infection management, innovative uses of familiar products might just be an effective and well-received idea. CLS
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