Antihistamines still worth trying

DEAR DR. ROACH >> You recently wrote that the antihistamine Zyrtec might be helpful for interstitial cystitis (IC). A recently published review found no benefit. Would you readdress your opinion? — D.M.

DEAR READER >> The review that you sent looked at the same studies I did to make its recommendation, but they came to a different conclusion. While the data are the same, I framed my answer a little differently.

The study showed that in patients with IC, the use of antihistamines helped some people — 31% improved with an antihistamine, while 20% improved on a placebo. But the studies could not conclude with 95% confidence that the results may have been due to chance. (They were only 75% sure.) The study only included 61 people, which makes proving a benefit difficult.

It is possible that with a larger trial, the benefit would be powerful enough to reject with a high level of certainty the hypothesis that antihistamines are no better than a placebo. I should note that the same study failed to show a significant benefit of Elmiron, which had 34% of its subjects improve compared to 18% with a placebo. Elmiron costs over $1,000 a month and has a small risk of serious retinal disease with long-term use. Larger studies did confirm the benefit of Elmiron, although it was even lower than the benefit seen in the smaller study.

The review authors chose to say that there is no benefit to antihistamines, but that’s not exactly true. Thirty-one percent of people benefitted, but this was not a large enough proportion to meet statistical significance. Thus, there is no statistically proven benefit, but these small trials ought to at least lead to larger studies to further elucidate whether there really is a benefit.

In the case of an overthe-counter oral antihistamine, even a small possibility of benefit seems worth a try, since the potential for harm is miniscule.

Finally, the main objective for me was not to say that antihistamines are a great treatment, but to bring awareness to a condition that many people aren’t even aware they have.