Medical Surgical Labs Top 5 Toxic Drug Levels #4

Question

Which medication does theophylline increase the risk for toxicity?

Answers

  1. Digoxin
    • Rationale:

      This answer is correct because theophylline increases the risk for digoxin toxicity. Theophylline increases serum potassium, which increases the risk for digoxin toxicity. It speeds up the heart, thus creating low cardiac output. This results in a rise of serum digoxin levels.

  2. Lithium
    • Rationale:

      This answer is not correct because theophylline decreases the effects of lithium due to its diuretic effect. This leads to an increase of lithium clearance in urine and a decrease in amount of lithium in the blood.

  3. Phenytoin
    • Rationale:

      This answer is not correct because theophylline decreases the effects of phenytoin. Theophylline is a methylxanthine, which exacerbates seizure activity and also reduces the effects of anticonvulsant drugs.

  4. Warfarin
    • Rationale:

      This answer is not correct because theophylline may cause the body to process warfarin more quickly. The metabolism of theophylline can be increased when combined with warfarin.

Overview

Theophylline is a bronchodilator given for asthma or COPD. Theophylline increases the risk for digoxin toxicity and decreases the effects of lithium and phenytoin.

Explanation

Learning Outcomes

Theophylline is a bronchodilator given for asthma or COPD. It is in the drug class of methylxanthines. Theophylline increases serum potassium, which increases the risk for digoxin toxicity. It speeds up the heart, thus creating low cardiac output. This results in a rise of serum digoxin levels. Methylxanthines decrease the effects of lithium, phenytoin, and warfarin. Signs of digoxin toxicity are nausea, vomiting, abdominal pain, diarrhea, confusion, loss of appetite, and irregular heartbeat. Visual changes can also occur such as seeing spots, blind spots, blurry vision, or changes in color vision.

Test Taking Tip

Remember digoxin and theophylline should not be taken together. They counteract one another.

Video Rationale