Final answer:
Brand name drugs may be preferred over generics in certain cases due to patients' sensitivities to different formulations, or in the case of drugs with a narrow therapeutic index where consistency in drug concentration is crucial.
Step-by-step explanation:
An instance when you might dispense the brand name drug instead of the generic is when the brand name has established clinical effectiveness in a specific patient for whom the generic equivalent may not have the same efficacy or tolerability. For example, some patients may be sensitive to different fillers or excipients in the generic formulation that could affect absorption or cause adverse reactions. Another instance could be in the case of a narrow therapeutic index (NTI) drug, where small variations in the drug concentration can lead to serious therapeutic failures or adverse drug reactions. Brand-name drugs in this category sometimes are preferred because they have a consistent manufacturing process that patients and physicians are familiar with. Generic pharmaceuticals are significantly cheaper than name-brand ones primarily because they do not have to repeat the expensive clinical trials that were required for the branded drugs to gain approval. Additionally, generic drug manufacturers usually do not spend on advertising, marketing, and promotion at the scale of brand-name companies.