title: The role of intracellular esterification in budesonide once-daily dosing and airway selectivity.
abstract: BACKGROUND
  Since their introduction in the 1970s, inhaled corticosteroids (ICSs) have been used to control airway inflammation associated with asthma. Budesonide is one of the ICSs recommended as first-line therapy for mild to moderate persistent asthma.
  
  
  OBJECTIVE
  This article describes the esterification of budesonide and how it results in prolonged, location-specific retention of drug in the airways, allowing once-daily dosing.
  
  
  RESULTS
  Studies conducted over the past decade have shown that budesonide forms reversible fatty acid esters within the cells of airway tissue, resulting in the formation of an intracellular depot pool of inactive drug. As the intracellular concentration of free budesonide decreases, these budesonide esters are hydrolyzed back to their active state. This process increases budesonide's retention in the airways, prolongs its duration of action, and lowers the risk of systemic effects.
  
  
  CONCLUSIONS
  By extending budesonide's local anti-inflammatory effect and increasing its airway selectivity, the esterification process appears to contribute to the drug's efficacy, particularly during once-daily administration. Reducing the number of required daily inhalations may increase patient compliance with asthma therapy, although this remains to be evaluated.
authors.affiliation: AstraZeneca R and D Lund, Lund, Sweden. anna.miller-larsson@astrazeneca.com
authors.forename: Ralph
authors.initials: R
authors.lastname: Brattsand
authors.forename: Anna
authors.initials: A
authors.lastname: Miller-Larsson
mesh_terms: D000280:Administration, Inhalation; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology*; D001249:Asthma / Q000188:drug therapy / Q000378:metabolism; D019819:Budesonide / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology*; D004951:Esterification; D006801:Humans; D008168:Lung / Q000378:metabolism
chemical_list: D000893:Anti-Inflammatory Agents; D019819:Budesonide