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PCAT Biological Processes – Caffeine Metabolism

A student studying caffeine metabolism learns that one of caffeine’s metabolites in the body is theophylline, which has the effect of relaxing smooth muscles of the bronchi. The student concludes that caffeine could be used to effectively treat asthma. Which of the following is true?

A) The student’s conclusion is correct.
B) The student’s conclusion is most likely correct, as a drug has effects both through its own action and through the action of its metabolites.
C) The student’s conclusion is most likely not correct, as caffeine has other metabolites which are direct antagonists of theophylline.
D) The student’s conclusion cannot be said to be correct or incorrect without more information about caffeine’s other metabolites and effects.


The student isn’t entirely off-track here. Drugs have effects on the body both directly and through the action of their metabolites. However, the student has no information about what percent of caffeine is metabolized into theophylline, nor about what sort of dosages of caffeine or theophylline would be needed to effectively treat asthma. Thus (D) is the correct answer. In fact, only about 4% of caffeine is metabolized into theophylline, although theophylline is actually used as an asthma medication.

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