Evaluation of blockbuster drugs under the rule-of-five.

The current drug research techniques, combinatorial synthesis and high throughput screening, enabled the obtaining and pre-evaluation of thousands of compounds in short time. In order to chose the best hits to become leads, observation of drug-likeness tries to optimize this selection. Probably, the most widely used filter is Lipinski's Rule-of-five, which proposes that molecules with poor permeation and oral absorption have molecular weight > 500, Clog P > 5, hydrogen-bond donor > 5 and hydrogen-bond acceptor > 10. In order to evaluate the Rule-of-five, the top pharmaceutical products in 2007 were analyzed. Among 60 drugs, 7 (atorvastatin, montelukast, docetaxel, telmisartan, tacrolimus, leuprolide and olmesartan) did not fit the rule, and 5 failed only one of the threshold values. It was possible to conclude that the rule is very useful to select better compounds in chemolibraries, but it must be used carefully and with criteria, to avoid a possible exclusion of promising compounds.