the first time in more than 15 years, a new combination drop is available to clinicians.
Zylet (Bausch & Lomb) is a combination of tobramycin and loteprednol. This
portion of the article will review the research on this new therapeutic agent and
the research behind loteprednol.
Zylet combines tobramycin and
TobraDex is one of the most prescribed
medications in optometry and the main difference in this new drug is the substitution
of dexamethasone for loteprednol etabonate 0.5%. Loteprednol etabonate is a chloromethyl
ester in the 17 beta-position modification of prednisolone; research suggests that
ester molecules are metabolized quicker once inside the eye, preventing receptor
attachment and potential complications. Studies have shown that ketone steroids
such as dexamethasone or prednisolone may be more likely to raise intraocular pressures
(IOPs). A study involving children under 10 years of age showed that those receiving
0.1% dexamethasone six times per day for up to four weeks had a significantly higher
IOP and significantly quicker responses (89% of high responders reached their peak
within 8 days). Ketone-based steroids have also been shown to cause IOP rises after
PRK and LASIK and the IOP elevation might induce an episode of diffuse lamellar
keratitis. Other complications doctors have documented include posterior subcapsular
cataract formation and secondary infections. This becomes significant in chronic
conditions such as dry eye, blepharitis, meibomitis and keratoconjunctivitis
In one study evaluating 0.2% loteprednol
etabonate, 397 patients were followed long-term, including 159 patients who
used the drop continuously for more than 12 months. They were evaluated for IOP
rise, cataract formation and other possible topical steroid-induced adverse events.
There were no adverse events, including no significant pressure rise, no cataract
formation and no secondary infections. In fact, with more than 4 million scripts
of loteprednol prescribed there has been no reported case of cataract formation
to date. Elevated IOP, although not noted with 0.2% in the Ilyas study, can occur
with 0.5% loteprednol and therefore we should continue to take IOP measurements
in all patients using corticosteroids including Zylet. However, the difference with
loteprednol etabonate is a lower incidence of steroid response and less of an IOP
rise in those that do respond. A study by Bartlett compared the use of loteprednol
in known steroid responders and found that the IOP elevation in the loteprednol
group after 42 days was 21.5mm HG, versus 27.1mm HG in the prednisolone group.
While the safety of the steroid component
is one aspect of the drug, tobramycin still plays a role as an effective antibiotic
in both gram-positive and gram-negative organisms. This would make it an effective
medication in contact lens-related sterile keratitis or peripheral infiltrates for
example. The gram negative coverage would play a more significant role in terms
of organisms often associated with contact lens wear. Conditions such as contact
lens-induced sterile infiltrates, as well as chronic conditions such as meibomitis
and blepharitis, may benefit from this new medication. These are some of the most
common conditions encountered by practicing optometrists.
When new therapeutics become available
to the practicing clinician, it's important to look into the research and understand
what we are prescribing and when to best utilize these new medications. Zylet will
make a great addition to the therapeutic formulary based on its application and
safety in contact lens-related and chronic conditions.
Karpecki is Director of Research at Moyes Eye Center in Kansas City and was a principal
investigator in the research on Zylet. Dr. Karpecki is a paid consultant to Bausch
& Lomb but holds no financial interest in any products mentioned in this article.