During an ICU admission, Tony is given IV ranitidine in appropriate doses to prevent development of stress erosions

 During an ICU admission, Tony is given IV ranitidine in appropriate doses to prevent development of stress erosions. The goal of treatment is to maintain his gastric pH above 4, and this goal is reached quickly after the first dose. However, on day 2 of therapy the drug effect seems to have been lost just as quickly, with Tony's gastric pH consistently measuring 1.5 to 2. this is an example of ______.


Drug disposition tolerance


Drug resistance


Pharmacodynamic tolerance


Tachyphylaxis