BLOG: ‘Doc, can I take this drug if I have glaucoma?’

In the mid-1990s, the FDA relaxed regulations regarding direct-to-consumer pharmaceutical advertising that brought ads for medications from the magazine pages (where they were heavily advertised with lots of small print) to the television airwaves.

In 2004, the FDA further eased the rules regarding how the drug companies have to present risks and allowed them to use simplified language that average consumers would understand. The result is that in 2011 the average American television viewer watched up to nine drug advertisements a day, and the total is almost certainly higher today (Ventola).

This direct-to-consumer pharmaceutical advertising (DTCPA) is controversial, but it certainly does make patients more aware of medications and more aware of some potential side effects. We’ve all heard the fast-talking spokesperson say something like: “Patients with certain types of glaucoma should consult their eye doctor before taking this medication.” This month we’ll talk about what you need to know for your glaucoma patients when systemic medications affect the eye.

Most of the time, these ads are referring to a side effect of angle-narrowing, and most of the ads are for drugs with anticholinergic effects. Before we go any further, let’s review the pharmacology of iris innervation.

“Cholinergic” refers to nerve cells that use acetylcholine as a neurotransmitter. The long ciliary nerve that innervates the iris sphincter uses acetylcholine as a transmitter across the synapse from the ciliary nerve to the sphincter muscle cell; thus, the iris sphincter is a cholinergic receptor. Tropicamide is the most obvious anticholinergic drug we use in eye care and it works to prevent iris sphincter activation by binding to acetylcholine receptors on the sphincter, blocking the ability of acetylcholine to activate the muscle cell. This works nicely in our field, because the pupil is unique: it’s in a constant push-pull balance of cholinergic (miosis) and adrenergic (mydriasis with the iris dilator muscle) effects. Limiting one causes the other to become dominant. Of course, we know that pupil dilation is not without risks, and one of the biggest is angle-closure glaucoma.

Thus, when anticholinergic drugs are used systemically, they can have a side effect of blocking acetylcholine from accessing the iris sphincter receptors and, thus, allowing the now-unopposed iris dilator muscle to slightly dilate the pupil. For a patient with narrow angles, this negligible-to-moderate dilation might be all it takes to precipitate an angle closure attack.

So, for patients who we suspect are at risk of angle closure, we should be aware of the systemic meds they take and be on the lookout for one that might have anticholinergic properties.

Some of the most popular anticholinergic drugs that are used systemically outside of eye care include atropine (used for bradycardia); Paxil (paroxetine, GlaxoSmithKline), an SSRI used for depression); Atrovent (ipratropium bromide, Boehringer Ingelheim), an inhaler used for asthma and chronic obstructive pulmonary disease; Dramamine (dimenhydrinate, Prestige), used for motion sickness; Benadryl (diphenhydramine, McNeill), used for allergies and colds; and Cogentin (benztropine, Akorn), used for Parkinson’s. One can easily find documented cases of angle closure for most of these drugs with a quick search of PubMed.

But it’s not just these drugs alone; there are new drugs coming out every year in each of the above classes, especially lately for restrictive lung disease. Cholinergic receptors are all over our bodies, controlling parasympathetic responses in salivation, digestion, urination and mucus secretion, among others. Thus, it’s no surprise that so many DTCPAs have a caveat about an increased risk of glaucoma when taking a certain medication.

We as eye care providers need to understand how anticholinergic drugs can affect the angle of the eye and then triage the risk of the drug to our specific patient. Patient education about the symptoms of angle closure is important for all narrow angle patients on these medications, with closer monitoring and cessation of the drug as options to consider for those patients with high angle closure risk.

So pay attention the next time you see a DTCPA, and listen for any connection to glaucoma. File that drug’s name away in your memory bank, because you might just be asked about it. By the way, the U.S. and New Zealand are the only countries that allow DTCPA that include product claims.

Do you think these ads are helping make the patient more involved in their own health care? Are they frightening patients about possible side effects? Are they pressuring the doctor to prescribe name brand drugs? Click the link below and leave a comment on what you think.

References:

Harvey RA. Pharmacology. 5th ed. Lippincott Williams & Wilkins. 2011.

Humphreys DM. Br J Ophthalmol. 1992;304(6822):320.

Kirwan JF, et al. Br J Ophthalmol. 1997;81:252 doi:10.1136/bjo.81.3.252.

Raj KM, et al. J Pharm Bioallied Sci. 2015;7(Suppl 1):S70-71. doi: 10.4103/0975-7406.155809.

Ventola, CL. Pharmacy and Therapeutics. 2011;36(10):669-674, 681-684.