M.K. is a 41 year old female who is started on an oral beta-agonist for asthma. While she was initially titrated

M.K. is a 41 year old female who is started on an oral beta-agonist for asthma. While she was initially titrated

to a stable response, her dose requirements have increased lately. Diagnostic tests have ruled out worsening disease. She is compliant with taking her medication. There are no known drug interactions. Her changing dose requirements are possibly explained by the pharmacologic effect known as: