ABSTRACT To the Editor.— In her letter (1981; 246:2576), Penny W. Budoff, MD, fails to grasp or at least make clear several fundamental points in the use of nonsteroidal anti-inflammatory (NSAI) drugs in the treatment of primary dysmenorrhea.Dr Budoff seems to lump all NSAI drugs together as if they were somehow generically equivalent to each other. The "chemical idiosyncrasy" that she invokes to explain differing degrees of action represents only the difference between drugs derived from different sources (proprionic acid derivatives and anthranilic acid derivatives) with differing mechanisms of action (prostaglandin synthetase inhibitors and synthetasereceptor site blockers). By understanding the pharmacology of these drugs, a drug with specific reactions may be selected to match the specific needs of the patient.A second, more fundamental oversight occurs when Dr Budoff assumes that "resistance" or treatment failure represents an inconvenience requiring little more than generic substitution. Drugs of the NSAI group are