Ask the Pharmacist

Q: I heard Health Canada has issued a warning regarding antidepressants and glaucoma. What is that all about?

A: This warning was apparently issued after Health Canada found out that the FDA in the United States was investigating a possible connection between angle-closure glaucoma and the consumption of antidepressants.

Angle-closure (also known as narrow-angle) glaucoma is a very serious eye disorder in which the normal fluid drainage which occurs within the eye is blocked, causing the excess fluid to accumulate and exert a pressure within the eye and causing pain and blurred vision. If not treated immediately, angle-closure glaucoma can lead to permanent vision loss.

Glaucoma affects more than 400,000 Canadians although the vast majority of these have open-angle glaucoma which cannot be caused by these drugs.

With a continued increase in the prescribing of antidepressants (their use has risen at an average rate of 5.6 per cent per year since 2009), it is perhaps not surprising (although disappointing, nonetheless) that we are discovering possible new side effects to drugs that have, for the most part, been available for decades.

As of the timing of the warning, Health Canada had received 163 reports of angle-closure glaucoma linked with the use of antidepressants. This may seem like a lot, but when kept in the perspective that 40.5-million prescriptions were filled for antidepressants in Canada in 2013 alone, the incidence is rare. At this point in time, there does not seem to be any single drug in this class that seems to be more or less likely to exert this effect.

Exactly why this happens in some people is still unknown but some experts speculate that it is related to the fact that antidepressants increase the available amount of serotonin within the brain and this, in turn, can dilate (enlarge) the pupils and increase production of the fluid found within the eye. Typically, the glaucomatous attack occurs within the first six months of antidepressant therapy and tends to occur in only one of the eyes.

Individuals at greatest risk from this side effect tend to exhibit one or more of the following characteristics: female, advanced age, Asian or Inuit ethnicity, positive family history, hyperopia (farsightedness), narrow iridocorneal angle and shallow anterior chamber depth (i.e. smaller eyes). It has also been speculated that these attacks are more common in the fall and winter than spring and summer.

While the risk of this occurring is so low it should not dissuade individuals from taking an antidepressant when warranted, patients should be on the alert for the signs of an acute attack and should seek medical treatment promptly should any of the following arise. These symptoms can arise very quickly and include severe eye or head pain plus hazy or blurred vision, the appearance of rainbow-coloured halos or circles around bright lights, nausea or vomiting and sudden sight loss.

Should this occur, treatment usually involves surgery (often via a laser) that helps to unblock drainage channels so that the extra fluid can drain. In general, surgery is successful and long-lasting. The key is early recognition and treatment since the vision loss incurred will be permanent.

Note that antidepressants are not the only drugs that can cause angle-closure glaucoma. Other culprits include antihistamines, incontinence control drugs, amphetamines (used in ADD and narcolepsy), epinephrine, pseudoephedrine (found in many cold tablets), trans-derm V patches (for motion sickness), inhalers used for COPD (such as Spiriva and Atrovent) and a few other drugs.

For the many people who already have glaucoma and use daily drops to control their pressure, none of the drugs mentioned in this article are a problem. Drugs, such as the antidepressants, are related strictly to angle-closure glaucoma for which there are no drops involved in the care.

For more information about this or any other health-related questions, contact the pharmacists at Gordon Pharmasave, Your Health and Wellness Destination. Also check the website at www.gordon-pharmasave.com/ and the Facebook page at www.facebook.com/GordonPharmasave/?fref=ts