Theophylline Poisoning

Basics

Description

  • Theophylline is a methylxanthine, related to caffeine and theobromine
  • Theophylline toxicity has decreased over the years but is still encountered. In 2022, there were 128 case mentions of theophylline and 1 death per the National Poison Data System (NPDS)
  • Clinical uses of theophylline include:
    • Treatment of airway diseases including bronchospasm/asthma and COPD
    • Neonatal apnea
  • Theophylline mechanism of action:
    • Stimulates the release of endogenous catecholamines resulting in stimulation of β1- and β2-receptors
    • Antagonist of adenosine receptor
    • Inhibition of phosphodiesterase (at supratherapeutic levels):
      • Increases intracellular cAMP
      • cAMP augments β-adrenergic stimulation
  • Available in immediate- and sustained-release formulations
  • Peak absorption is 60–90 min with immediate-release and 6–10 hr with sustained-release formulations
  • Half-life is highly variable:
    • In a healthy, nonsmoker adult half-life is typically 4.5 hr
  • Therapeutic serum concentration 5–15 mcg/mL
  • Acute overdose:
    • Ingestion within an 8-hr interval in a patient with no prior theophylline use
  • Acute-on-chronic overdose:
    • Single excessive dose in a patient previously receiving usual therapeutic doses for ≥24 hr
  • Chronic intoxication:
    • Accumulation of theophylline >20 mcg/mL associated with prior therapeutic use for ≥24 hr secondary to:
      • Drug–drug, drug–diet, or drug–disease interactions
    • Use of serial excessive doses

Etiology

  • Acute ingestions require higher concentrations to achieve specific toxic effects compared with acute-on-chronic or chronic overdoses
  • Drug–drug interactions:
    • Inhibiting theophylline metabolism (can lead to toxicity when these drugs are started):
      • H2-receptor antagonists
      • Macrolide antibiotics
      • Fluoroquinolones
      • Allopurinol
      • Influenza vaccine
      • Oral contraceptives
      • Interferons
    • Enhances theophylline metabolism (can lead to toxicity when these drugs are discontinued):
      • Carbamazepine
      • Barbiturates
      • Smoking
      • Rifampin
  • Chronic theophylline accumulation:
    • Uncontrolled CHF
    • Liver disease (cirrhosis or severe hepatitis)
    • Acute viral infections

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