USMLE

Theophylline

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Respiratory Drugs
  1. Cromolyn
  2. Montelukast
  3. Guaifenesin
  4. Ephedrine / Phenylephrine
  5. Theophylline
  6. Acetylcysteine

Summary

Theophylline is a medication that is used to treat asthma and COPD. It is a slow-acting drug and should not be used in emergency situations. Theophylline causes lots of drug interactions, which can contribute to drug level fluctuations above its narrow therapeutic range. Importantly, symptoms of theophylline toxicity start to appear above a dose of 20 micrograms per milliliter. Mild symptoms of toxicity include GI distress and CNS stimulation. To avoid exacerbating the CNS stimulation, patients should avoid caffeine while on treatment. More severe symptoms of toxicity seen at higher doses include seizures and arrhythmias.

Key Points

  • Theophylline
    • Mechanism
      • Belongs to drug class of methylxanthines
      • Bronchodilator
        • Inhibits phosphodiesterase (PDE) enzyme, thus increasing cAMP and relaxing bronchial smooth muscle, resulting in bronchodilation
        • Taking the medication in the morning will allow for maximum bronchodilation during the day
    • Clinical Uses
      • Chronic Asthma
        • Long-term control
        • Used only when other drugs have proved ineffective due to narrow therapeutic range and several adverse reactions
      • COPD
        • Long-term control
        • Used only when other drugs have proved ineffective due to narrow therapeutic range and several adverse reactions
    • Side Effects and Adverse Reactions
      • Drug interactions
        • Increase theophylline levels
          • Beta blockers, cimetidine, fluoroquinolone antibiotics
          • Patients should avoid caffeinated products
            • Worsens side effects (e.g. CNS stimulation, tachycardia, restlessness)
        • Decrease theophylline levels
          • Barbiturates, carbamazepine, phenytoin, rifampin, St. John’s Wort
        • Do not give with beta-2 agonists
          • A synergistic effect can occur that may cause cardiac dysrhythmias
        • Theophylline increases digoxin levels and lowers lithium levels
      • Toxicity symptoms begin > 20 mcg/mL
        • Narrow therapeutic range of 5-15 mcg/m
      • Mild Toxicity
        • GI Distress
          • Anorexia, nausea, vomiting, diarrhea, abdominal pain
        • CNS stimulation
          • Restlessness, irritability, insomnia, headache
          • Worsened by caffeine use
      • Severe Toxicity
        • Seizures
        • Arrhythmias (tachyarrhythmias)
      • Hyperglycemia