Beta Adrenergic Receptor Antagonist (Beta Blockers)
The Timbols
Betaxolol
Levobetaxolol
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Timoptic & Timoptic-XE (timolol maleate) and generics
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Betimol (timolol hemihydrate)
Timoptic (Merck) was the first
beta-blocker and came to market in 1978. It is a non-selective
beta receptor antagonist that is available in both a conventional
solution and a gel-based delivery system (marketed as Timoptic-XE
in a gellan gum-based vehicle). Timoptic and Timoptic-XE are
now available generically. It is important to note that the
timolol solutions perform on par with the gel-forming formulations
at a fraction of the cost. We never write for gel-forming products;
their additional expense makes them an unwise choice that would
be unfair to the patient.
 Betimol (Santen Inc.) is a brand name of timolol hemihydrate
which is not generically substitutable, yet is about the same
cost as generic timolol maleate. It is well established that
Betimol is equivalent in efficacy to Timoptic. Betimol, like
Timoptic, is available in both 0.25% and 0.5% concentrations
and is prescribed exactly as traditional timolol. Remember, good
studies have shown that once-daily administration is equally
effective as twice-daily.
Using drugs with long half-lives, like timolol or levobunolol,
once a day instead of twice would cut the price in half, and
undoubtedly reduce the potential for side effects as well.
Betaxolol
 Betaxolol is a unique, beta1 selective beta-blocker,
and is probably the “safest” beta-blocker available. This drug
must also be used q12h. Although beta receptors in the ciliary
body are almost exclusively beta2, the common theory is that
betaxolol is such a profound and potent blocker of beta1 receptors
that it causes override to the beta2 receptors, decreasing
aqueous production. Put another way, beta selectivity is heavily
influenced by the concentration of the beta-blocker. Betaxolol
is available as 0.25% suspension, Betoptic-S (Alcon). Betoptic-S
requires only minimal shaking to maintain the proper concentration.
(The original Betoptic 0.5% solution has been removed from
the market by the manufacturer because of its marked stinging
upon instillation.)
This drug does not decrease IOP as effectively as a non-selective
beta-blocker, but may do an equal or better job of preserving
the visual field. This is, of course, the ultimate goal in glaucoma
therapy. If long-term studies confirm this, betaxolol should
enjoy even more widespread use. Even though it is a beta1 selective
blocker, patients with active chronic obstructive pulmonary disease,
emphysema or asthma should use an alternative, such as latanoprost,
brimonidine or one of the topical CAIs.
Levobetaxolol
Born under the shadow of its sibling, Travatan, we foresee
a relatively small role for Betaxon. This levo-isomer of
betaxolol has a slightly enhanced therapeutic profile over
its prototype betaxolol. Overall, it probably reduces IOP
about 1 or 2 mm more than original betaxolol, and has the
same excellent safety profile. Like betaxolol, it must be
used q12h. While levobetaxolol us an upgrade over its predecessor,
we feel all the flurry over the three prostaglandins will
subdue its clinical use. Levobetaxolol will be marketed as
Betaxon 0.5% ophthalmic suspension (Alcon).
In summarizing the beta-blockers, we quote from Louis Pasquale,
M.D., co-director of the glaucoma service at the Harvard Medical
School’s Massachusetts Eye and Ear Infirmary in the March/April
2002 publication of Vision and Aging. He observed, “The study
evaluated whether patients continued to fill prescriptions
or not. Latanoprost did best in terms of persistency. However,
not too far behind, in second place, were beta-blockers, which
placed far ahead of brimonidine, which was close to last. This
speaks to the relative acceptance of beta-blockers among patients.”
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