First things first: this is not a medicine. It takes quite a bit of digging, but you can just about find on the website where it says in small letters that its a medical device. You can also tell by the trademark, and the "clinically proven" claims splashed liberally all over the website (real medicines don't tend to point out that they're clinically proven as the very fact they have a license does that).
So what is it supposed to do? According to the advert, it has a unique thixotropic formula. That sounds science-y and cool, eh? It basically means that when you shake it, it becomes a liquid, therefore it can be easily sprayed. It'll then thicken up at rest, i.e. on the inside of your nostrils. It's supposed to form a barrier on the inside of your nose to stop the nasty allergens getting through. According to the website, this is a unique approach, the next generation of hayfever treatment. This is totally untrue: for many, many years we've been advising to put Vaseline on your nostrils as a barrier. A product called HayMax which has been around for years claims to be a "natural balm that acts as a barrier to pollen, dust and dander.". This is, in no way, shape or form, a new concept or breakthrough.
Let's look at what's actually in it, shall we? This is actually very difficult to find, as it doesn't appear to tell you anywhere at all on their website. At first I thought it was cellulose-based, given that most of the references they cite for it being "Clinically proven" are about cellulose powder. However, according to Netdoctor, it contains "mixture of inactive ingredients, including bentonite (a form of purified clay), xanthan gum, glycerol stearate and sesame seed oil." So, basically, gunky stuff then. gunky stuff that becomes a bit less gunky so it can be sprayed, but that will dry to be more gunky in your nose (although given the inside of noses are actually fairly moist, it's probably, I should imagine, unlikely to dry completely, which would presumably lessen its ability to form a full barrier). It's basically like PVA glue for your nose and it apparently feels like wallpaper paste when its up there, according to @ianthunderroad. Mmmm, sounds lovely.
The "evidence" they show on their website as proof that it works is frankly laughable. Check out this chart:
'% of patients experience improvement' it reads. Well, how many patients? What do they mean by improvement? Hopefully we'll find the answers in the accompanying text:
"Prevalin™'s efficacy has been proven in 2 clinical studies, where over 9 out of 10 people experienced significant improvement of their allergic symptoms6,7."
Two studies? that's all? Even if they were pretty big studies, I'd be happier if there were more than two of them. What is "over 9 out of 10 people"? Surely that would be 10 people then? Given a person is a discrete being, you can hardly have 9.25 people experiencing significant improvements. And what do they mean by significant- statistically? or, what we would be more interested in, clinically?
The referencing on this page is very odd to say the least. I'm expected a reference for two studies, presented in the usual, standard (formerly Vancouver, or similar) format. I'm presented with this:
6,7. Efficacy of thixotropic nasal spray for seasonal allergic rhinitis assessed by a 4-hour and 3-hour allergen challenge in an environmental exposure unit.
No authors, no information about date, or where it is published, etc etc. A quick google search finds what I assume to be the paper, although I have no way of confirming that due to the very poor referencing. Even the article itself tells you how to reference it, but the makers of Prevalin have happily ignored this
Luond-Valeskeviciute I, Haenggi B, Gruenwald J. Efficacy Of Three Thixotropic Nasal
Spray Preparations On Seasonal Allergic Rhinitis Assessed By Allergen Challenge In An Environmental Exposure Unit . WebmedCentral ALLERGY 2010;1(10):WMC00993
So let's have a look at the three nasal sprays being used in this study then, they are referred to as IQM 11, IQM12, and IQM 13. The first study is a pilot, which uses IQM11. The other two are used in the second study.
Here's the ingredients for IQM 11: liquid paraffin, gylcerol, emulsifier (Glucate SS and Glucamate SSE-20), and water.
It's pretty unclear what the ingredients of the other two are, as they're not fully described. However I think the inference is that they have the same ingredients except for the emulsifier.
See any bentonite in there? any xanthan gum? any of the other ingredients that appear in Prevalin at all? No, me neither. There are other methodological problems with the studies too, but to be honest its not worth going into them now because they are unrelated to the product they are supposed to prove efficacy for.
So in summary: the two studies that the manufacturer's quote are actually the same study, poorly conducted and poorly written up, and about completely different products.
Would I buy this product if I had hayfever? Probably yes initially, because the nice trustworthy pharmacist man on the telly said its good and it works. Would I buy it having looked at the appallingly shaky evidence base for it? abso-blummin-lutely not. This is a shoddy effort, if you ask me, and at a cool £9.95 there is absolutely no way that its worth it.
If any patients ask me whether it works on my locum shifts, I will be very clearly telling them to put their money away and use the vaseline they've probably already got in the house instead.
UPDATE: 10/05/13 I'm reliably informed by a friend who is using this product out of desperation (and in spite of my ranting about it) that this product has an inconvenient habit of dripping back out of your nose at inopportune moments without much warning. Doesn't sound great, does it? In fact it reminds me a bit of the 'flatulence with oily seepage' side effect you can get with orlistat, only from your nose. Distinctly unpleasant.