What is the therapeutic range for theophylline?

• A. 1-5 mg/L
• B. 10-20 mg/L
• C. 20-30 mg/L
• D. 5-15 mg/L

Answer: (B)

Theophylline has a narrow therapeutic index, so therapy is guided by measuring serum levels to balance efficacy with safety. The target range is about 10 to 20 mg/L. Levels within this window tend to provide bronchodilation with an acceptable risk of adverse effects. If levels fall below 10 mg/L, the drug may not be effective enough; if levels rise above 20 mg/L, the risk of toxicity increases, including cardiac arrhythmias, seizures, and gastrointestinal or CNS symptoms. Because theophylline is metabolized in the liver and is affected by many factors, clinicians monitor trough concentrations at steady state and adjust the dose to keep the level within this range. Factors like smoking (which increases clearance) and hepatic impairment or drug interactions (which can raise levels) influence what dose achieves the target range.