DƯỢC LÍ Goodman & Gilman's The Pharmacological Basis of Therapeutics 12th, 2010

1790 subconjunctivally during the postoperative course (Fluorouracil
Filtering Surgery Study Group, 1989). Although both agents work by
limiting the healing process, sometimes this can result in thin,
ischemic, avascular tissue that is prone to breakdown. The resultant
leaks can cause hypotony (low IOP) and increase the risk of infection.
In corneal surgery, mitomycin has been used topically after
excision of pterygium, a fibrovascular membrane that can grow onto
the cornea. Mitomycin can be used to reduce the risk of scarring
after certain procedures to remove corneal opacities and also prophylactically
to prevent corneal scarring after excimer laser surface
ablation (photorefractive and phototherapeutic keratectomy).
Mitomycin also is used to treat certain conjunctival and corneal
tumors. Interferon -2b has been used in the treatment of conjunctival
papilloma and certain conjunctival tumors. Although the use of
mitomycin for both corneal surgery and glaucoma filtration surgeries
augments the success of these surgical procedures, caution is
advocated in light of the potentially serious delayed ocular complications
(Rubinfeld et al., 1992; Hardten and Samuelson, 1999; Bahar
et al., 2009).
Intraocular methotrexate (see Chapter 61) is used to treat
uveitis and uveitic cystoid macular edema. It also has been used to
treat the uncommon complication of lymphoma in the vitreous,
which is an inaccessible compartment for most anti-neoplastic drugs
(Taylor et al., 2009).
SECTION IX
SPECIAL SYSTEMS PHARMACOLOGY
Immunomodulatory Agent. Topical cyclosporine
(cyclosporin A; RESTASIS) is approved for the treatment
of chronic dry eye associated with inflammation.
Cyclosporine is an immunomodulatory agent that
inhibits activation of T cells. Use of cyclosporine is
associated with decreased inflammatory markers in the
lacrimal gland, increased tear production, and improved
vision and comfort (Sall et al., 2000; Perry et al., 2008).
Drugs and Biological Agents
Used in Ophthalmic Surgery
Presurgical Antiseptics. Povidone iodine (BETADINE) is formulated
as a 5% sterile ophthalmic solution for use prior
to surgery to prep periocular skin and irrigate ocular surfaces,
including the cornea, conjunctiva, and palpebral
fornices. Following irrigation, the exposed tissues are
flushed with sterile saline. As for other povidone iodine
uses, hypersensitivity to iodine is a contraindication.
Adjuncts in Anterior Segment Surgery. Viscoelastic substances
assist in ocular surgery by maintaining spaces,
moving tissue, and protecting surfaces. These substances
are prepared from hyaluronate (HEALON, others), chondroitin
sulfate (VISCOAT), or hydroxypropylmethylcellulose
and share the following important physical
characteristics: viscosity, shear flow, elasticity, cohesiveness,
and coatability. Various viscoelastic agents emphasize
certain features that are broadly characterized as
dispersive or cohesive. They are used almost exclusively
in anterior segment surgery. Complications associated
with viscoelastic substances are related to transient elevation
of IOP after the surgical procedure.
Ophthalmic Glue. Cyanoacrylate tissue adhesive
(ISODENT, DERMABOND, HISTOACRYL), while not FDA
approved for the eye, is widely used in the management
of corneal ulcerations and perforations. It is applied in
liquid form and polymerized into a solid plug.
Fibrinogen glue (TISSEEL, EVICEL) is increasingly
being used on the ocular surface to secure tissue such as
conjunctiva, amniotic membrane, and lamellar corneal
grafts. These are FDA approved for use in cardiac, vascular,
and general surgery but not for the eye.
Anterior Segment Gases. Sulfur hexafluoride (SF 6
) and
perfluoropropane gases have long been used as vitreous
substitutes during retinal surgery. In the anterior
segment, they are used in non-expansile concentrations
to treat Descemet’s detachments, typically after cataract
surgery. These detachments can cause mild to severe
corneal edema. The gas is injected into the anterior
chamber to push Descemet’s membrane up against the
stroma, where ideally it reattaches and clears the
corneal edema.
Vitreous Substitutes. The primary use of vitreous
substitutes is reattachment of the retina following vitrectomy
and membrane-peeling procedures for complicated
proliferative vitreoretinopathy and traction retinal
detachments. Several compounds, including gases, perfluorocarbon
liquids, and silicone oil (Table 64–8), are
available. With the exception of air, the gases expand
because of interaction with systemic oxygen, carbon
dioxide, and nitrogen, and this property makes them
desirable to temporarily tamponade areas of the retina.
However, use of these expansile gases carries the risk of
complications from elevated IOP, subretinal gas,
corneal edema, and cataract formation. The gases are
absorbed over a period of days (for air) to 2 months (for
perfluoropropane).
The liquid perfluorocarbons, with specific gravities between
1.76 and 1.94, are denser than vitreous and are helpful in flattening
the retina when vitreous is present. Silicone oil (polydimethylsiloxanes;
ADATOSIL 5000) has had extensive use in both Europe and the
U.S. for long-term tamponade of the retina. Complications from silicone
oil use include glaucoma, cataract formation, corneal edema,
corneal band keratopathy, and retinal toxicity.
Surgical Hemostasis and Thrombolytic Agents. Hemostasis
has an important role in most surgical procedures and
usually is achieved by temperature-mediated coagulation.
In some intraocular surgeries, thrombin has a
valuable role in hemostasis. Intravitreal administration