The anti-histamine bandryl won't do anything for inhibiting down regulation of the beta 2 receptors. You want the anti-histamine keotifen.
Ketotifen is a medically used anti-histamine to treat asthma and allergies. Ketotifen has been shown to inhibit the down regulation of the beta 2 receptors caused by clenbuterol. Consequently, you can continue taking clenbuterol for a longer period of time without having to cycle off to regenerate the receptor sensitivity by adding ketotifen. Additionally, it means that you don't need as much clenbuterol to get the same benefits. Although no studies have been done to find the most effective dose of ketotifen for this purpose, most users find a daily dose of 2-3 milligrams (mgs) to be ideal, and this dosage can be split or taken in one sitting. Meanwhile, higher doses are likely to cause drowsiness and increased appetite that can be sometimes severe.