Drug Action and Shape of Molecules Some years ago two drug c

Drug Action and Shape of Molecules Some years ago two drug companies marketed a drug under the trade names Dexedrine and Benzedrine. The structure of the drug is shown below. The physical properties (C, H, and N analysis, melting point, solubility, etc.) of Dexedrine and Benzedrine were identical. The recommended oral dosage of Dexedrine (which is still available) was 5 mg/day, but the recommended dosage of Benzedrine (no longer available) was twice that. Apparently it required considerably more Benzedrine than Dexedrine to yield the same physiological response. Explain this apparent contradiction.

Solution

Both Dexedrine and Benzedrine have the same structural formula, but there exist some structural difference between these two molecules. Dexedrine comprise of D-amphetamine, whereas Benzedrine is a racemic mixture of F-amphetamine and L-amphetamine. This difference in their structural composition alters their properties such as the rate of absorption and metabolism. This is the reason why Dexedrine is more potent than Benzedrine, and lower dose is needed for Dexedrine.