Sure, but will you be awake to notice the difference???

David Douglas of Reuters Health reported last Friday on the publication of a clinical trial revealing that a one-week trial of Benadryl (diphenhydramine HCl) was superior to Clarinex (desloratadine) in managing symptoms of moderate-to-severe allergic rhinitis, or hay fever. The article was published in the April 2006 issue of Annals of Allergy, Asthma & Immunology (2006;96:606-614)

You can read the results here but Douglas misprinted the Benadryl dose as 500 mg! three times daily. The actual dose, 50 mg, t.i.d., is already high enough to make one so drowsy as to not really care about one's hay fever. (Somnolence was reported in 22.1% of pts on Benadryl as compared with 4.5% for Claritin, and 3.4% for placebo).

At 500 mg (twenty, 25 mg tabs or capsules) even taken once a day will cause disturbing hallucinations due to the central anticholinergic effects of this drug. I fear that some readers of the Reuters story who are really suffering with allergies might try to take the misprinted dose. (Disclaimer: DO NOT attempt taking high doses of Benadryl/diphenhydramine for the purpose of recreational hallucinations; it can be fatal, particularly when taken with other CNS depressants. Diphenhydramine alone can cause paradoxical CNS stimulation, seizures, and death in infants and should not be used in children under age two).

I wrote in to Reuters on Sunday but have yet to get a response or a correction to the article.

As a seasonal allergic rhinitis patient, I can say that diphenhydramine HCl at 25 mg twice daily can manage my symptoms. However, even me at 215 lbs. has to work up to the tolerance of drowsiness that invariably occurs with this old OTC drug. In fact, this is how the non-sedating antihistamines (loratadine, desloratadine) are designed to produce less drowsiness: their physicochemical characteristics make it difficult for the drug to cross the blood-brain barrier whereas diphenhydramine HCl does it much better. However, I also think that since the non-sedating antihistamines cross tissues generally more poorly than diphenhydramine, I tough it out with a little bit of the latter drug instead of the more-expensive, less-effective desloratadine. Frankly, I'm surprised that somnolence was as low as 22.1% in the 50 mg, t.i.d. group - I'd wager that participants self-titrated to a lower dose to avoid drowsiness.

From the abstract:

"Results: The mean reduction from baseline in 24-hour reflective TNSSs [total nasal symptom score] relative to the placebo response was 77.6% for the diphenhydramine group (P < .001) and 21.0% for the desloratadine group (P = .12). A TNSS between-treatment difference of −1.81 (46.7%; P < .001) was observed when comparing diphenhydramine with desloratadine. A similar between-treatment difference was observed for the 24-hour reflective total symptom score comparing diphenhydramine to desloratadine (−3.35; 45.5%; P < .001). Diphenhydramine provided clinically and statistically significant reductions vs placebo and desloratadine in all individual symptoms, including nasal congestion. Desloratadine had a tendency toward improvement compared with placebo for most individual symptom scores. However, a statistically significant result was reached only for sneezing (−0.27; 33.9%; P = .04)."

Oh, by the way, the trial was financed and conducted by the makers of Benadryl. The timing of the publication, April, was also nicely coincidental with the peak of allergy season on the US East Coast.