Generic Substitution Issues: Brand-generic Substitution, Generic-generic Substitution, and Generic Substitution of Narrow Therapeutic Index (NTI)/Critical Dose Drugs.

Doctors accuse individual variability or lack of quality of generic drugs for adverse reactions or lack of efficacy. The variability of effect of generic substitution, although accepted by clinicians as possible, is little discussed or even understood by them. The situation is really serious in the case of generic substitution of drugs with narrow therapeutic index (NTI) or critical dose.