Respiratory acidemia and theophylline pharmacokinetics in the awake dog

Recently, respiratory acidemia has been shown to be associated with an altered volume of distribution (Vd) of theophylline in patients during an acute exacerbation of chronic obstructive pulmonary disease. However, many factors other than acidemia could have altered the pharmacokinetics. Our purpose was to study the effects of respiratory acidemia alone. Six awake dogs had normocapnia and hypercapnia induced in a conditioned chamber. After intravenous injection (8 mg/kg), plasma theophylline concentrations were measured for 8 hours by means of quantitative enzyme immunoassay technique. There were no statistically significant effects of respiratory acidosis on Vd and total theophylline clearance. There was no significant correlation between these variables and pH, PCO2, PO2. We conclude that respiratory acidosis, per se, does not effect theophylline pharmacokinetics in dogs.