Very little.

Both Alavert and Claritin contain a non-sedating antihistamine called loratadine. Claritin was one of the leading prescription antihistamines until it was approved for sale over the counter. Almost at the same time, the manufacturer of Claritin lost its patent exclusivity for the product. That means that other manufacturers can ask the U.S. Food and Drug Administration for approval for a generic version. Wyeth Laboratories was the first to do so. Others are in process. As more companies make the product, there should be a gradual drop in the price. Schering Plough, the makers of Claritin, started marketing Clarinex as their prescription antihistamine when they lost their patent exclusivity for Claritin. Clarinex (also known as desloratadine) is actually a byproduct of our body's metabolism of Claritin.

Alavert is similar to Claritin Redi-Tabs and is available as a quick-dissolving tablet. Despite what the ads say, there is no difference in the time for the drug to work with the quick-dissolving tablet as compared to a regular tablet. In order for Alavert (or Claritin) to work, it must be converted in the body to desloratadine. So, it really doesn't make any difference if you take a tablet or the quick-dissolving table, the timing will be the same.