Which factor can increase the plasma level of theophylline?

• A. Hyperthyroidism
• B. Renal impairment
• C. Liver disease
• D. Heart failure

Answer: (D)

The key idea is that theophylline is cleared mainly by the liver, so anything that reduces hepatic blood flow or liver function slows its metabolism and raises its plasma level. In heart failure, the reduced cardiac output lowers blood flow to the liver, so theophylline is cleared more slowly and accumulates in the bloodstream. That’s why heart failure can increase theophylline levels. By contrast, hyperthyroidism tends to speed up metabolism (lowering levels), and while renal impairment can affect elimination, theophylline clearance is predominantly hepatic, so liver-related factors or reduced hepatic perfusion are the more direct contributors to higher plasma levels.