ABSTRACT
In addition to pharmacological considerations, molecular modifications may be designed to alter selected pharmacokinetic properties of the parent drug. The lack of an appreciation for pharmacokinetic differences arising from minor molecular modifications has led to invalid direct comparisons between structural analogs. The most significant question ultimately is Does the alteration in pharmacokinetic behavior improve therapy with this drug? The interpretation of plasma drug concentration time-course data to compare analogs differs from that used to compare dosage forms. While testing a new drug, a pharmacologist administered equal doses both intramuscularly and subcutaneously to some test animals. Increased rates of oral absorption have been obtained by using salt forms of the parent drug such as potassium salts of penicillins or sodium salts of sulfonamides. Also, the possibility of new biological effects resulting from delivery of drug to new regions of the body must be then considered.
