Its always important to consider possible drug interactions when prescribing treatment for ocular conditions. At no time is this more true than when treating glaucoma. Glaucoma patients may have a variety of concurrent conditions that require systemic medications. Many glaucoma medications have the potential to create systemic side effects and/or interact with other prescribtion medications. Here, well look at some commonly prescribed glaucoma drugs and their potential to interact with your treatments.

Topical Beta-blockers.
If you choose a topical beta-blocker such as Timoptic (timolol maleate, Merck), Betagan (levobun-olol, Allergan), or Ocupress (carteolol, Novartis Ophthalmics), there are several classes of systemic drugs that may interact with these including; systemic beta-blockers, calcium channel blockers, hypoglycemics, beta-adrenergic agonists, adrenergic psychotropic drugs, and cathecholamine depleting drugs.

Antihypertensives are the most likely to interact with topical beta- blockers. These include diuretics, beta-blockers, angiotension converting enzyme (ACE) inhibitors and calcium antagonists (calcium channel blockers). Systemic beta-blockers can exacerbate hypotension or bradycardia when combined with a topical beta-blocker. Monitor blood pressure and heart rate in glaucoma patients. Also, use beta-blockers with caution in patients with cerebrovascular insufficiency. Evaluate patients complaining of vertigo, syncope or postural hypo-tension for possible hypotension or bradycardia.

Conditions Contraindicated With Glaucoma Meds

Cerebrovascular Insufficiency
Type II Diabetes
Renal Disease
ACE inhibitors like Vasotec (enalapril maleate, Merck), Accupril (quinapril, Parke Davis) and Altace (ramipril, Mon-arch) are used to treat hypertension and have the potential to create hypo-tension. Calcium channel blockers such as Norvasc (amlodipine, Pfizer), Cardizem CD (diltiazem, Biovail) and Calan (verapamil, Searle) may interact with topical beta-blockers and can cause irregular heart beat. Cardiac glycosides combined with calcium channel blockers and beta-blockers can also slow heart rate.

Hypoglycemics like Glucophage (metformin, Bristol Meyers Squibb), Glucotrol (glipizide, Pfizer), or Avandia (rosiglitazone, GlaxoSmithKline) are contraindicated in patients with non-insulin dependant or type II diabetes. Beta-blockers have the potential to mask hypoglycemia in these patients.

Adrenergic agonists like Proventil (albuterol, Schering) are prescribed to help control ashtma. Beta-blockers can directly compete with these and may antagonize bronchodilation.
Other Glaucoma Meds
Prostaglandin anaologs like Lumigan (bimataprost, Allergan), Travatan (travoprost, Alcon) and Xalatan (latanoprost, Pfizer) rarley interact with systemic medications. However, if your patient is on hypolipidemic medication, alert the patients primary care physician. Regular blood work is the standard of care for these patients to monitor liver function. Prostaglandins may show a false positive for liver abnormalities. Medications in this class include: Lipitor (atorvastitin, Parke Davis), Zocor (simvastatin, Merck) and Lescol (fluvastatin, Novartis).

Alpha-2 adrenergic agonists like Alphagan and Alphagan-P (brimonidine, Allergan) may produce hypotension or bradycardia. Again, use caution with all beta-blockers, antihypertensives and cardiac glycosides.

Carbonic anhydrase inhibitors like Trusopt (dorzolamide, Merck) and Azopt (brinzolamide, Alcon) are sulfonamides. The same types of adverse reactions attributable to sulfonamides may occur with topical administration. CAIs are contraindicated in patients with renal disease because they are excreted mainly through the kidneys.

One final pearl: Inform your patients primary care provider, in writing, of any chronic medications you prescribe. This provides the primary physician with important information for future therapeutic considerations and provides two sources to monitor potential side-effects or interactions. 

Vol. No: 140:07Issue: 7/15/03