Antihistamines are the most commonly used medication to treat allergies. You know about generics and brand name drugs. But what about active metabolites? Dr. Jerry Avorn of Harvard Medical School explains this option in his book “Powerful Medicines”.
Most antihistamines cause drowsiness. In fact, many of them are sedating enough to be used for insomnia, motion sickness, anxiety, and even surgical anesthesia (in combination with other drugs). But there is a class of antihistamines, called second generation, that have much less potential for causing drowsiness. The common ones are loratidine (Claritin), desloratidine (Clarinex), fexofenadine (Allegra), and cetirizine (Zyrtec).
Loratidine is available over the counter, both as the brand name Claritin and in generic versions. Dr. Avorn points out that desloratidine, available by prescription as Clarinex, is the active metabolite of loratidine (Claritin). That is, when you take loratidine (Claritin), your liver converts it to desloratidine (Clarinex), and that's what clears up your runny nose and watery eyes. The important difference, according to Dr. Avorn, is the price.
Here are some prices from drugstore.com. All these options are 24-hour pills:
Generic loratidine: $0.53 per pill
Claritin (loratidine): $0.83 per pill
Clarinex (desloratidine): $4.19 per pill
Dr. Avorn says this is one of the tricks the pharmaceutical industry uses to extend patent protection and high profits for its popular products. It's common to make minor chemical changes that do not affect the drug's mechanism of action, get a new patent, and advertise the modified drug as new. We tend to assume newer is better.
The one obvious advantage to Clarinex is that your insurance may pay for it, since it's a prescription drug. If your copay is less than $16 for a one-month supply of a brand name drug, then Clarinex will cost you less than generic loratidine. However, this kind of choice is what motivated the insurance industry to switch to managed care plans, with all their controversies.
Some years back, I saw a news report about an insurance company that refused to pay for two 12-hour prescription antihistamine pills per day.