A patient is seen in the emergency department. The patient had been maintained on theophylline (Theo Dur), and a blood sample reveals the serum theophylline level is subtherapeutic. Which may cause a subtherapeutic serum level?
a. Cimetidine use
b. Drug tolerance
c. Smoking
d. Overuse of the inhaler
ANS: C
The patient is not tolerant to the drug if the serum theophylline levels are too low. Cimetidine would enhance the effects of theophylline, not decrease the effects. Smoking reduces the therapeutic effects of xanthine derivatives, including theophylline. Overuse of the inhaler would cause a high level of serum theophylline.
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