title: Excipient interaction with cetylpyridinium chloride activity in tablet based lozenges.
abstract: OBJECTIVE
  The purpose of the investigation was to determine the effect of tablet excipients on the activity of cetylpyridinium chloride (CPC) and the relative interaction between excipients and CPC.
  
  
  METHODS
  An analytical assay was developed to evaluate the interaction between CPC and the excipients. In vivo activity was investigated using six volunteers by determining the reduction in colony forming units recoverable from the oropharynx after sucking each proprietary lozenge separately on different days. In vitro determinations investigated the relative antimicrobial activity of aqueous solutions of the lozenges and, the effect of pH and tablet base excipients on that activity against Staphylococcus aureus, Streptococcus pyogenes and Candida albicans.
  
  
  RESULTS
  Both in vivo and in vitro results showed that the tablet based lozenges had markedly reduced antimicrobial activities compared with previous results with a candy based lozenge (in vivo and in vitro) or the same concentration of aqueous CPC (in vitro). Magnesium stearate suspensions in CPC 250 micrograms/ml indicated that magnesium stearate adsorbed CPC and at 0.4% lozenge weight and above significantly reduced the antimicrobial activity of CPC 250 micrograms/ml.
  
  
  CONCLUSIONS
  The reduced activity of CPC in tablet based lozenges resulted from a decreased availability of CPC in solution due to an adsorption of CPC on magnesium stearate. To avoid this reduction in activity tablet based lozenges containing CPC 250 micrograms/ml, or similar concentrations, plus magnesium stearate should contain not more than 0.3% w/w lozenge weight of the lubricant.
authors.affiliation: School of Pharmacy, Robert Gordon University, Schoolhill, Aberdeen, United Kingdom.
authors.forename: R M
authors.initials: RM
authors.lastname: Richards
authors.forename: J Z
authors.initials: JZ
authors.lastname: Xing
authors.forename: K M
authors.initials: KM
authors.lastname: Mackay
mesh_terms: D000284:Administration, Oral; D000891:Anti-Infective Agents, Local / Q000008:administration & dosage / Q000494:pharmacology*; D002176:Candida albicans / Q000187:drug effects; D002594:Cetylpyridinium / Q000008:administration & dosage / Q000494:pharmacology*; D004304:Dosage Forms; D004347:Drug Interactions; D005079:Excipients / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D009960:Oropharynx / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects; D013297:Streptococcus pyogenes / Q000187:drug effects
chemical_list: D000891:Anti-Infective Agents, Local; D004304:Dosage Forms; D005079:Excipients; D002594:Cetylpyridinium