Harder, Better, Faster, Dead?

October 30, 2008 6:56 PM

YANMD Filter: I was told recently that my eye drops (Cosopt) could limit my heart rate: is this true?

YANMD, YANAD, Etc.: I was told recently that my eye drops (Cosopt) could limit my heart's BPM. The reason for this is that one of the active ingredients (timolol) is a "non-selective beta-adrenergic receptor blocker." aka Beta Blocker.

I've been riding my bicycle for the past several years (because I don't have good enough vision to drive) and am worried that I could hurt/kill myself if I push my heart to hard. Obviously, I have some questions:

• Does the beta blocker really limit my max heart rate?
• If it does, what happens if I push my body to the point where it needs my heart to be at 160 bpm, but it can only do 130 bpm? (Heart Failure?)
• Finally, will my heart have adjusted (become stronger, etc.) so that when most people would need 160, it can pump at 130 and still keep up? (Just theorizing here...)

I am 16 yr. old, so my max heart rate should be 204 IIRC. Also, if it makes a difference, I'm 6'0", 135 lbs, male.

I'm going to be at the doctor's on Monday–at which point I will ask them–but I'm rather worried about it right now. (Seeing as to how I push myself rather hard when riding my bicycle.)

Thanks!

posted by 47triple2 to health & fitness (5 comments total)

Since nobody's responded yet, here's my absolutely in no way a health professional take on it.

I used to race bicycles very competitively. According to a friend who I raced with who was on heart rate limiting medication for some time, it's more or less self-limiting. In other words, your limited heart rate will limit the amount of blood going to your muscles, which will limit the amount of aerobic/oxidative work you can do with them. That fits with my understanding of the world, though, again, I'm not a biologist or a doctor.

As someone who does science for a living, though, that's awesome. I wish most 16 year olds were that curious and well-informed.

(the 220-[your age] estimate for heart rate is almost entirely crap, by the way. The only reliable way I know of finding out is by, well, finding out)
posted by oostevo at 7:57 PM on October 30, 2008

While it's true that beta-blockers slow your heart rate, I don't think you need to worry because the timolol will not reach therapeutic levels in your systemic circulation, if it even reaches your systemic circulation at all. There is a strong barrier between your eyes and the rest of your body (kinda like the blood-brain barrier?); this is part of why most eye medicines are applied topically instead of by mouth.
posted by cucumberfresh at 8:06 PM on October 30, 2008

@ oostevo

Okay, quick, hypothetical, follow up question: if my eyes were magically healed where I don't need to take the drops, would I be able to (almost) instantly ride my bike faster? Or does the slower heart rate = weaker muscles?
posted by 47triple2 at 9:40 PM on October 30, 2008

The drops are unlikely to affect your heart rate much if at all as others have noted.

If they did modulate your heart rate, it would do you no harm in terms of making exercise a health risk in any way.

Some athlete's who are placed on oral/systemic beta-blockers swear that it has an affect on their endurance or peak output, and I believe most (not all) of the scientific literature supports this though these studies tend to be older (mostly from the 1980s), somewhat poorly designed, and demonstrated a small effect. I notice you mention weaker muscles but that's not the way to think about this. High heart rate during exercise is the body's way of increasing blood flow to hard working muscles. The muscles won't become weaker per se in terms of maximal strength, but they won't be able to endure as much strain during aerobic exercise if you limit blood flow/heart rate because that would essentially put a cap on oxygen delivery with fixed extraction.

If the medication did have an affect (again I don't think the drops will do much), discontinuing it would likely lead to a return to normal endurance within days.

I also like the way you think and the questions you ask. Ever thought about a future in medicine/physiology?
posted by drpynchon at 10:36 AM on November 1, 2008

Thanks for the great answers everybody!

However, I would have to disagree with the topical eye drops not affecting the rest of the body. When my sister was younger (6 yrs. old or so) she was prescribed an eye drop for her glaucoma.

I don't remember which one it was, bit I think it was Alphagan. (It had a purple lid from what I remember.)

Anyway, when she took the drop, she fell asleep shortly after taking it. This wasn't your normal sleep either; she was sleeping so soundly we couldn't wake her.

The same thing happened to my brother when he took it, just not quite as severely.

We learned later that the drop shouldn't be prescribed to children because it could result in death.


Also, my brother took Betagan which resulted in him have severe asthma as long as he was taking it.
posted by 47triple2 at 3:32 PM on November 1, 2008