Nearly all glaucoma medications are prescribed for reducing eye pressure.
BETA-BLOCKERS (TIMOLOL AND OTHERS)
Topical beta adrenoceptor blockers (commonly called beta-blockers) are the drugs most often prescribed to treat glaucoma. They lower the pressure inside the eye by inhibiting the production of aqueous humor.
Brands. These drugs are categorized as either nonselective or selective beta-blockers:
- Nonselective adrenoceptor beta-blockers. Timolol (
Timoptic, Betimol) has been the standard beta-blocker for years. Newer nonselective drugs include levobunolol ( Betagan), carteolol ( Ocupress), and metipranolol ( OptiPranolol). A few studies suggest some are more beneficial than timolol with similar side effects.
- Selective beta1-adrenoceptor blockers. Betaxolol (
Betoptic) and levobetaxolol ( Betaxon) are selective beta-blockers. These drugs appear to have fewer adverse effects on the heart than the nonselective beta-blockers, although they still have widespread effects. Studies also suggest that they slow progression more than timolol, although timolol is more effective at lowering IOP. Selective beta-blockers may also have nerve-protecting properties.
All beta-blockers work well and generally well tolerated. Because they cause less eye irritation than many other glaucoma medications, they are often prescribed for patients who also have cataracts.
Side Effects and Complications. After the beta-blocker is administered, only a tiny amount of the drug is absorbed by the cornea. Most of it enters in the bloodstream. These drugs, therefore, can cause side effects in parts of the body other than the eyes (“systemic” side effects):
- Systemic side effects may include reduced sexual drive, fatigue, depression, anxiety, and breathing difficulties.
- Beta-blockers affect the heart. They lower heart rate and reduce blood pressure.
- Beta-blockers can worsen severe asthma or other lung diseases.
- A patient switching to a beta-blocker from other glaucoma medication may feel a sudden rise in eye pressure. It is important that the pressure be checked shortly after the other drug has been withdrawn.
- When beta-blockers are used to treat one eye, the other (contralateral) eye also experiences a lesser, but still significant reduction in IOP.
Interactions with Other Medications. The effects of the eye medication can interact with other oral medications, such as oral beta-blockers, calcium-channel blockers, or the antiarrhythmic drug quinidine. People with diabetes who take insulin or hypoglycemic medications should realize that beta-blocker side effects may mask the symptoms of hypoglycemia (low blood sugar).
Prostaglandins are hormone-like substances that help open blood vessels. Drugs that resemble prostaglandins increase outflow of aqueous humor (the watery substance in the eye). Drainage of aqueous humor helps reduce intraocular pressure.
Brands. Latanoprost (
Xalatan) and unoprostone ( Rescula) are the standard brands. Latanoprost was the first prostaglandin to be approved as first-line treatment for elevated eye pressure. Two newer prostaglandins, travoprost ( Travatan) and bimatoprost ( Lumigan), may help some patients who do not respond to latanoprost. These drugs may also benefit patients with normal-tension glaucoma.
Side Effects. These drugs do not slow down the heart rate and also appear to be safe for people with asthma. Side effects include itching, redness, and burning during administration. Muscle and joint pain may also occur. All of these drugs may permanently change eye color from blue or green to brown.
CARBONIC ANHYDRASE INHIBITORS
Carbonic anhydrase inhibitors (CAIs) decrease eye pressure by reducing the fluid in the chambers of the eye (aqueous humor). These drugs are used for glaucoma when other drugs do not work. They may be combined with other medications.
CAIs may also improve blood flow in the retina and optic nerve (beta-blockers do not). Improving blood flow can keep the disease from getting worse.
Brands and Side Effects. CAIs are available in the following forms:
- Eye-drop CAIs include dorzolamide (
Trusopt) and brinzolamide ( Azopt). About 10% of patients report fatigue, stinging in the eye, and loss of appetite using dorzolamide. Taste changes can occur. Brinzolamide is a newer medication that may cause less stinging than dorzolamide.
- Forms taken by mouth (oral) include acetazolamide (
Diamox), methazolamide ( Neptazane), and dichlorphenamide ( Daranide). Although they are more effective than eye drops, they have significantly more side effects and are rarely used for long-term treatment. The oral forms have very unpleasant side effects, including frequent urination, depression, stomach problems, fatigue, weight loss, sexual dysfunction, and, in infants, failure to thrive. Long-term use of the oral forms, in rare cases, can cause serious anemia and kidney problems, including the risk for stones. They can also produce a toxic reaction when taken with large doses of aspirin.
Adrenergic agonists activate muscles in the eye that dilate pupils and, therefore, increase outflow of aqueous fluid. Newer variations called alpha 2-adrenergic agonists reduce production of aqueous humor and also increase outflow through the uveoscleral pathway (the alternative channel to the trabecular meshwork).
Apraclonidine (Iopidine) and brimonidine (
Alphagan) are alpha 2-adrenergic agonists. These are generally been used before glaucoma surgery, but may be useful as primary therapy when used in combination with beta-blockers or other standard drugs.
Brimonidine is proving to be particularly effective for long-term therapy. (Apraclonidine is used for the short term.) It also may have nerve-protecting properties and may be safer than other drugs during pregnancy and for patients with asthma.
The most common side effects of brimonidine and apraclonidine are dry mouth and altered taste. They also commonly trigger an allergic reaction that causes red and itching eyes and lids,. Brimonidine causes less of an allergic response than apraclonidine. Unlike apraclonidine, however, it can cause lethargy and mild low blood pressure.
MIOTICS (PILOCARPINE AND OTHERS)
Miotics, also called cholinergic agonists, narrow the iris muscles and constrict the pupil. This action pulls the iris away from the trabecular meshwork and allows the aqueous humor to flow out through the drainage channels, reducing the pressure inside the front of the eye.
Brands. Pilocarpine (Pilocar, Adsorbocarpine, Almocarpine,
Isoptocarpine, Ocusert) was the most widely used anti-glaucoma drug before timolol was introduced. It is the preferred miotic. Because pilocarpine is used up by the body fairly quickly, however, patients must take it several times a day; many people, therefore, fail to take their medication regularly. A combination of timolol or latanoprost with pilocarpine is more effective than either drug used alone. Carbachol is another miotic.
Epinephrine and its derivatives are the older anticholinergics. Epinephrine is now rarely prescribed because of side effects.
Dipivefrin (Dipivefrin), a newer form of epinephrine, remains inactive until it reacts with enzymes in the cornea. It is effective in low doses and causes few systemic side effects.
Side Effects. Side effects include:
- Teary eyes, brow-aches, eye pain, and allergic reactions.
- A miotic narrows the pupil and so can cause nearsightedness. Vision can also become dim and it may difficult to see in darkened rooms or at night, when driving could be hazardous.
- Anticholinesterase miotics increase the risk of cataract development and are therefore used mostly in patients in whom cataracts have already been removed. Retinal detachment is an uncommon but dangerous side effect in susceptible individuals. Excessive use of these miotics may cause toxic reactions, including convulsions, muscular paralysis, and even death from respiratory failure.
- Epinephrine can produce burning in the eyes, enlarged pupils, and allergic reactions. Occasionally it can cause anxiety and headaches. Rare side effects include high blood pressure and disturbances in heart rhythm. It is rarely prescribed now. Although dipivefrin, the newer form of epinephrine, has fewer systemic side effects, it still causes problems in the eyes similar to those of epinephrine.
MANAGING DRUG REGIMENS
Studies indicate that many patients skip doses of their glaucoma medications, sometimes because of side effects and sometimes because of confusing or time-consuming regimens. Skipping even a few doses can greatly increase the risk of visual loss. It is essential that patients tell their doctor if they are not regularly taking their medication. Otherwise, the doctor may increase the dosage, thereby causing unwelcome side effects.
Patients who do not regularly take their glaucoma medication are at high risk for blindness. If you have problems taking your medications or sticking to the dosing regimen, talk with your doctor.
Hints for Managing a
- Pharmaceutical manufacturers use colored tops, yellow for timolol, for example, and green for pilocarpine, to help prevent mix-ups. Creating a chart scheduling each drug by color can be helpful.
- Small electronic timers are available that will signal times for taking the medications. The timing of these combinations is important.
- Some patients may be candidates for single medications that combine two drugs, such as
Cosopt, which contains both dorzolamide and timolol. This medication requires only one drop twice per day. Patients who need additional glaucoma drugs, however, will need to take these two drugs separately.
- When using any drug for a long period of time, side effects are a potential problem. If they become intolerable, patients should discuss with the doctor reducing the dosage or trying other drugs.
Administering Eye Drops. A common reason that medicine does not work is that patients do not take it correctly. Patients should ask the ophthalmologist to watch while they place the drops in their own eyes to make sure the procedure is being done correctly. The following are some recommended steps:
- If you use both ointments and eye drops, take the eye drops first.
- Wash your hands before applying eye drops.
- Hold the bottle upside down.
- Tilt your head back and, with one hand, pull the lower eyelid down to form a pocket.
- With your other hand, hold the bottle as close as possible to your eye. Don’t let the bottle directly touch your eye or eyelid.
- After you have placed the drop, close your eye or press your index finger against the corner of the eye near your nose. Gently move the lower lid upward until the eye is closed. Keep your eye closed for at least 1 minute. This prevents the drop from draining out.
- Wait at least 5 minutes before applying another drop or a different medication