Respiratory Drugs and Medications Q 21
To evaluate the effectiveness of theophylline therapy, which of the following laboratory values must be drawn?
A. Glucose
B. Hematocrit
C. Potassium
D. Theophylline levels
Correct Answer: D. Theophylline levels
Theophylline levels must be drawn to determine if the drug is present in therapeutic amounts in the client’s serum. Theophylline has a very narrow therapeutic window, and its interaction with various other drugs has led to the limitation of its use. The serum theophylline concentrations require monitoring directly to avoid toxicity as the adverse effects of theophylline are related to its plasma concentration and have been observed when plasma concentrations exceed 20 mg/L. Some patients have also experienced adverse effects at low plasma concentrations. The dose gradually increases until achieving therapeutic plasma concentrations. This approach reduces side effects.
Option A: The most common side effects are nausea and vomiting, headache, increased stomach acid secretion, and gastroesophageal reflux, which could be due to PDE inhibition. CNS symptoms (irritability, lightheadedness, and dizziness) can also occur in patients. In severe cases, seizures have also occurred. At high serum concentrations, adenosine A1-receptor antagonism could lead to convulsions and cardiac arrhythmias.
Option B: For patients taking oral treatment, monitor serum concentrations at 6-month intervals for rapidly developing children and at annual intervals for all other patients (if their symptoms are well controlled).
Option C: The serum concentration of theophylline should be checked 30 minutes after the completion of an intravenous loading dose in patients with no theophylline use in the last 24 hours to determine if additional loading may be required (if the serum concentration is less than 10 mcg/mL) or to delay initiating the constant IV infusion (if the serum concentration is greater than 20 mcg/mL).