Therapies

Therapies round-up: IOP-lowering medications

A primer on the drugs commonly prescribed to glaucoma patients.

Mark Hakim, Worcester, Mass.

Most treatments for glaucoma are designed to lower IOP, which can reduce damage to the optic nerve that transmits visual information to the brain. There are 6 different therapeutic classes of glaucoma medications and each class will be further elaborated upon. Glaucoma eye drops often are the first choice over glaucoma surgery and can be very effective at controlling IOP to prevent eye damage.

Parasympathomimetic/Cholinergic agents

Examples: Pilocarpine (Isopto Carpine, Pilopine), Carbachol (Isopto Carbachol, Miostat), Aceclidine (Glaunorm), and Echothiophate (Phospholine Iodide).

MOA: Directly stimulates cholinergic receptors in the eye causing miosis (by contraction of the iris sphincter), loss of accommodation (by constriction of ciliary muscle), and lowering of intraocular pressure (with decreased resistance to aqueous humor outflow).

Uses: Control IOP in narrow-angle glaucoma. Causes pupil to constrict, assisting in opening the narrowed or blocked angle where drainage occurs.

S/E: brow ache, pupil constriction, burning, reduced night vision.

Sympatholytics/Beta-blockers

Examples: Timolol (Betimol, Istalol, Timoptic), Betaxolol (Betoptic-S), Levobunolol (Betagan, AK-beta), Carteolol (Cartrol), Metipranolol (OptiPranolol)

MOA: Blocks both beta 1 and beta 2 adrenergic receptors, reduces IOP by reducing aqueous humor production or possibly outflow; reduces blood pressure by blocking adrenergic receptors and decreasing sympathetic outflow.

S/E: Dry eyes, slight burning sensation, slight reduced corneal sensitivity, reduced heart rate, lung problems (such as emphysema), diabetes, depression and other conditions.

Carbonic Anhydrase Inhibitors

Examples: Acetazolamide, Methazolamide (Diamox, Neptazane), Dichlorphenamide (Daranide), Dorzolamide (Trusopt) and Brinzolamide (Azopt)

MOA: Reversible inhibition of the enzyme carbonic anhydrase resulting in reduction of hydrogen ion secretion at renal tubule and an increased renal excretion of sodium, potassium, bicarbonate, and water. Decreases production of aqueous humor and inhibits carbonic anhydrase in CNS to retard abnormal and excessive discharge from CNS neurons.

Usually used in combination with other anti-glaucoma eye drops and not alone. This classification of drug is also used in oral form.

S/E: Burning, bitter taste, eyelid reactions and eye redness (ocular injection).

About half of patients cannot tolerate oral CAIs due to their systemic side effects, which include fatigue, depression, loss of appetite, weight loss, loss of libido, kidney stones, metallic taste and tingling in fingers and toes (peripheral neuropathies).

Prostaglandins

Examples: Latanoprost (Xalatan), Travoprost (Travatan), Tafluprost (Zioptan), Bimatoprost (Lumigan) and Unoprostone (Rescula)

Best user compliance because they are required only once daily. Many glaucoma specialists now report that prostaglandins have taken the lead in recent years as a first-line therapy for glaucoma (EyeWorld, January 2007).

MOA: Prostaglandin analog believed to reduce IOP by increasing the outflow of the aqueous humor

S/E: Stinging, burning, iris color change due to an increase of pigmentation, lengthening and curling of the eyelashes, muscle, joint, back pain, rash, possible worsening of the disorder among people who have uveitis.

1+: The eyelash growth side effect eventually led to the development of an eyelash-lengthening drug called Latisse.

Alpha-adrenergic agonists

Examples: Epinephrine/Adrenaline (Eppy/N, Glaucon, Epifrin, Epinal), Dipivefrin (Propine, AKPro), Brimonidine (Alphagan P), Clonidine (Catapres, Kapvay, Duraclon) and Apraclonidine (Iopidine)

MOA: Selective agonist for alpha2-receptors; causes reduction of aqueous humor formation and increased uveoscleral outflow

S/E: Include red or blood shot eyes, upper lid elevation, dilated pupil, itching, increase in blood pressure or heart rate and abnormal heart rhythm

Combination therapies

Examples: Dorzolamide and Timolol (Cosopt), Brimonidine and Timolol (Combigan), Travoprost and Timolol (DuoTrav), and timolol and latanoprost (Xalacom)

Study results show that half of individuals with glaucoma require more than one type of medication to control IOP.

The advantage for the patient is that only one bottle of eye drops is used instead of two or three; additionally, the number of drops instilled is fewer and subsequently the quantity of preservatives applied to the eye is greatly reduced as well.

Pre-operative care

Glaucoma medications need to be instilled in the eye up to the morning of glaucoma surgery. Patients who are taking glaucoma pills (Diamox/acetazolamide or Neptazane/ Methazolamide), unless instructed otherwise should take the morning dose with a small sip of water.

Unless instructed otherwise, discontinue Xalatan, Travatan, or Lumigan 5 days before surgery only in the eye undergoing surgery.

Beginning 5 days before surgery start Pred forte, Econopred plus, or prednisolone acetate in operative eye one drop 4 times a day.

Post-operative care

Antibiotic drops every 4 hours for the first week. Steroid drops every 2 hours for the first month, followed by taper. Steroids may be tapered sooner following tube shunt surgery or if a concern is raised about steroid response. Cycloplegics may be used in cases of shallow anterior chamber or hypotony.

Anti-metabolite Fluorouracil and Alkylating agent Mitomycin are more commonly used.

Fluorouracil is inexpensive and has a better safety margin than Mitomycin however, it is not as effective as Mitomycin, requires multiple injections and has a higher incidence of corneal toxicity. OP

This article has been reviewed by Joel M. Solano, MD. Dr. Solano practices at Vance Thompson Vision in Sioux Falls, SD.

Mark Hakim is a student in the School of Optometry at MCPHS University (Massachusetts College of Pharmacy and Health Sciences), Worcester, Mass. Has a passion for neuro-optometry and sports vision.