Hypoxia, arterial pH and theophylline disposition

Area of Science:

• Pharmacology
• Pulmonary Medicine
• Toxicology

Background:

• Theophylline is a key bronchodilator for obstructive pulmonary disease.
• Factors like smoking, age, and liver disease affect theophylline clearance.
• Emerging evidence suggests pulmonary obstruction severity, hypoxia, and arterial pH also alter clearance.

Purpose of the Study:

• To evaluate theophylline disposition under varying conditions, particularly hypoxia and altered pH.
• To investigate the impact of pulmonary disease severity on theophylline metabolism.
• To assess the risk of theophylline toxicity in specific patient populations.

Main Methods:

• In vitro studies using isolated rat livers and mouse hepatocytes.
• In vivo studies in rats, rabbits, and dogs assessing theophylline metabolism under hypoxia.
• Analysis of human case reports and observational studies on theophylline disposition during acute illness.

Main Results:

• In vitro, low oxygen increased theophylline concentrations and half-life, decreasing metabolite production.
• Rabbit studies showed hypoxia, hypercapnia, and acidosis reduced clearance and increased plasma levels.
• Animal studies yielded inconclusive results due to methodological variations; human data is limited but suggests decreased clearance in acute illness and elderly patients.

Conclusions:

• Theophylline metabolism and clearance are significantly affected by hypoxia and altered pH, particularly in severe pulmonary disease.
• Elderly patients with COPD and acute exacerbations are at increased risk of theophylline toxicity due to impaired metabolism.
• Clinical caution is advised when dosing theophylline in patients with acute respiratory events and compromised pulmonary function.