Antihistamines...and diving..?

Questions relating to medical issues and treatment. Where possible and appropriate, we will request comment from qualified and reputable NZ-based diving doctors. If your query relates to a personal medical issue, we recommend you contact your GP or relevant medical specialist.

Antihistamines...and diving..?

Postby NEMES1S » Mon Dec 15, 2008 8:58 am

Just wondering as cold and flu medications have affected divers in the past what about Antihistamines...?
I have hayfever and we are well into the season where my sinuses remind me on a regular basis that they absolutely hate me.
So I was wondering just how they affect divers?

Most Antihistamines claim to be "Non-Drowsy" but that means little...

I take TELFAST which contains 180mgs of Fexofenadine Hydrocloride.

Anybody have any information on this...?
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Re: Antihistamines...and diving..?

Postby Gregv » Wed Dec 17, 2008 8:49 am

NEMES1S wrote:Just wondering as cold and flu medications have affected divers in the past what about Antihistamines...?
I have hayfever and we are well into the season where my sinuses remind me on a regular basis that they absolutely hate me.
So I was wondering just how they affect divers?

Most Antihistamines claim to be "Non-Drowsy" but that means little...

I take TELFAST which contains 180mgs of Fexofenadine Hydrocloride.

Anybody have any information on this...?


Antihistamines are one of the three classes of drug most commonly used to facilitate diving; decongestants and anti-motion sickness drugs being the other two. Some of the drugs within these classifications have overlapping modes of action, making any such classification less useful. Many also use combinations in the same pill. This is a long way of saying that you need to know what the pill you are taking contains.

The other key issue with medications used by divers is that there have been very few controlled studies done in this area. Some of the studies that are available are not directly applicable to recreational divers and the depths they dive to. As a result, giving advice on the risk of using 'medication X' underwater is difficult and is invariably informed opinion at best - no guarantee of safety is possible. The safest bet is to avoid medications while diving.

When considering using any medication underwater, you want to consider the following (using antihistamines as an example):
1. Will antihistamines make me more susceptible to DCI? Older sedating antihistamines could exaggerate the effect of nitrogen narcosis in a diver. There is no obvious physiological effect of their action that would make DCI more likely. Poor decision making as a result of impaired cognition however clearly can lead to an accident.
2. Will diving make any side effects of antihistamines worse? Other than potentially exacerbating nitrogen narcosis, no.
3. Will my exercise tolerance or thought processes be affected by use of antihistamines? If using a non sedating antihistamine, probably not.

Regarding the use of Telfast specifically, there has been some limited research done on use of terfenadine in a hyperbaric environment (1) and was found to cause no significant side effects. Fexofenadine is the active metabolite of this drug in vivo.

(1) Kohl RL, Calkins DS, Robinson RE. Control of nausea and autonomic dysfunction with terfenadine, a peripherally acting antihistamine. Aviat Space Environ Med. 1991 May;62(5):392-6.
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Re: Antihistamines...and diving..?

Postby NEMES1S » Wed Dec 17, 2008 9:12 am

Brilliant Greg, many thanks... :D
Hope to see you up at the Poor Knights again sometime, or if you guys are ever in Welly definately look us up for a dive or dive 4x4 trip.. :D
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Re: Antihistamines...and diving..?

Postby Scuba Sam » Wed Dec 17, 2008 6:20 pm

I'm not a medical expert (Cheers GregV for your comments), but have personal experience with diving and antihistamines. I have dived on Teldane for nearly ten years - it is still available, also known by the names Loratidine and Loratabs - I take it daily all year round. I have also dived on stronger sedating antihistamines used as a seasickness preventative (Paihia Bombers - combination of anti nausea, anti histamine and caffeine to combat drowsiness) when on offshore liveaboards. I've always trialled any medication on land first, and then diving cautiously, with an informed and familiar buddy. I felt that for me personally the risks of diving while dehydrated from sea sickness seemed to outweigh the risks of diving with this medication. Five of our divers used Paihia Bombers on our Three Kings trip.

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