Blood Brain Barrier question

[Diver Lori]

Doc,

Question. I called DAN regarding ZyrtecD and was given the go ahead for use during diving. I know someone else who called and was told to take caution because it "crossed the blood brain barrier"....what does this mean and why the double-speak?

TIA!

Lori

 

[beche de mer]

Doc,

Question. I called DAN regarding ZyrtecD and was given the go ahead for use during diving. I know someone else who called and was told to take caution because it "crossed the blood brain barrier"....what does this mean and why the double-speak?

TIA!

Lori

There is a physiological barrier which separates the brain from the rest of the body. It's called the blood-brain barrier.

Technically, the brain is protected by three membranes (dura mater, pia mater and arachnoid). The innermost of these, the arachnoid, also coats the small capillaries as they penetrate the brain.

The upshot of this is that substances which circulate in the body outside the brain, are not always able to penetrate into the substance of the brain, because of this blood-brain barrier.

The main issue with antihistamines (such as Zyrtec) is that, if they can cross the blood-brain barrier, they may cause sedation. My understanding of Zyrtec is that it has very little potential to pass into the brain and should not cause sedatation. So it should be suitable for diving. However, different people respond in different ways, to give yourself a test dose first.