A Steroid For All Seasons

BY WILLIAM TOWNSEND, O.D.
MAR. 1996

Corticosteroids have been a mainstay in moderating the discomfort and cellular damage associated with ocular inflammation since their introduction 45 years ago. However, one of the common complications of current steroid preparations, such as dexamethasone, betamethasone and prednisolone is the induction of intraocular tension elevation. Although medrysone and fluorometholone induce less tension elevation, their ability to inhibit "deep" inflammation such as uveitis or surgically-induced inflammation is limited. For those of us who routinely manage such conditions, Vexol (rimexolone), a new corticosteroid treatment from Alcon, is a welcome addition to our clinical armamentarium.

ALCON'S VEXOL DEMONSTRATES DECREASED PRESSURE ELEVATION.

The most important feature of Vexol is its low propensity for elevation of IOP. Chemically, Vexol is similar to prednisolone acetate, but modification of the chemical structure of the molecule makes it far less likely to cause pressure elevation. Although Vexol causes some increase in intraocular tension, the elevation is similar to that induced by fluorometholone. Clinical studies comparing IOP rise with Vexol and with prednisolone acetate 1% showed that prednisolone users were 2.6 times more likely to experience a clinically significant rise than those using Vexol. In another study, after four weeks of treatment, known steroid responders showed a final mean IOP of 30.4mm Hg in prednisolone users while the mean IOP of those using Vexol was 21mm Hg.

IT'S ALL IN HOW YOU SHAKE IT

Another benefit of Vexol is its ability to maintain suspension much longer than comparable drugs. Many ophthalmic steroid preparations must be shaken vigorously before each use to adequately resuspend the active ingredients. If patients fail to do this, they may not receive the desired amount of drug. A container of Vexol suspended in 1993, however, showed only 10 percent settling over a period of 497 days.

Other non-approved uses for Vexol include conditions such as GPC where steroid treatment may be required for long periods of time. Patients with severe epidemic keratoconjunctivitis occasionally develop dense central corneal infiltrates that reduce visual acuity. They may also benefit from Vexol. But remember, while Vexol has many positive attributes, like all steroids, it reduces the body's ability to resist infection and may cause cataracts if used for extended periods.

IN REVIEW

Corticosteroids inhibit both the early and late phases of inflammation by reducing vascular permeability thus lessening associated edema and migration of polymorphonuclear neutrophils, macrophages and other leukocytes. They also prevent the release of proteolytic enzymes and other destructive agents by granulocytes. By inhibiting the activity of phospholipase, corticosteroids block the conversion of arachidonic acid into prostaglandin, leukotrienes and other mediators. Thus, they reduce many of the signs and symptoms of long-term inflammation.

ADVERSE SIDE EFFECTS

Because corticosteroids' immune-suppressing effects are nonselective, they increase susceptibility to viral, bacterial and fungal infection. They inhibit wound healing and migration of epithelial cells, which is especially problematic when dealing with a corneal erosion or postsurgical incision. Chronic treatment with both systemic and topical steroids induces posterior subcapsular cataract formation. Another well-known complication of topical corticosteroid use is elevation of intraocular tensions. The exact mechanism by which this occurs is not well understood. One theory is that corticosteroids reduce outflow in the eyes of susceptible individuals. Patients with glaucoma and their blood relatives may develop elevated intraocular tensions as a result of steroid therapy. Other risk factors for development of steroid-induced pressure elevation include diabetes, high myopia and pigment dispersion. CLS

Dr. Townsend is in private practice in Canyon, Texas, and is a consultant at the Amarillo VA Medical Center.