Which statement about theophylline is true?

Which statement about theophylline is true?

• A. It has a wide therapeutic window and minimal side effects
• B. It is a diuretic with renal clearance
• C. It is safe in all ages
• D. It has a narrow therapeutic window and risk of severe adverse reactions

Answer: (D)

Theophylline has a narrow therapeutic window, meaning the dose needed for benefit is close to the dose that causes toxicity. Therapeutic blood levels are in the low tens of micrograms per milliliter, and small increases—due to dose changes, drug interactions, or altered metabolism—can push levels into toxicity. Toxic effects include nausea, vomiting, tachycardia, arrhythmias, seizures, and other severe CNS or cardiac symptoms. Metabolism occurs mainly in the liver via CYP1A2 and is influenced by age, liver function, smoking, and drug interactions (for example, certain antibiotics can inhibit clearance and raise levels). Because of this, monitoring blood levels and adjusting dosing is essential. Theophylline is not a true diuretic, its diuretic effect is mild, and it is not safe in all ages. So the statement reflecting its true pharmacology is that it has a narrow therapeutic window and risk of severe adverse reactions.