title: Photodegradation of levofloxacin in aqueous and organic solvents: a kinetic study.
abstract: The kinetics of photodegradation of levofloxacin in solution on UV irradiation in the pH range 2.0-12.0 has been studied using a HPLC method. Levofloxacin undergoes first-order kinetics in the initial stages of the reaction and the apparent first-order rate constants are of the order of 0.167 to 1.807×10-3 min-1. The rate-pH profile is represented by a curve indicating the presence of cationic, dipolar and anionic species during the reaction. The singly ionized form of the molecule is non-fluorescent and is less susceptible to photodegradation. The increase in the degradation rate in the pH range 5.0-9.0 may be due to greater reactivity of the ionized species existing in that range. The rate appears to vary with a change in the degree of ionization of the species present in a particular pH range and their susceptibility to photodegradation. Above pH 9, the decrease in the rate of photodegradation may be a result of deprotonation of the piperazinyl group. The levofloxacin molecule is more stable in the pH range around 7, which is then suitable for formulation purposes. The photodegradation of levofloxacin was found to be affected by the dielectric constant and viscosity of the medium.
authors.affiliation: Institute of Pharmaceutical Sciences, Baqai Medical University, Karachi, Pakistan.
authors.forename: Iqbal
authors.initials: I
authors.lastname: Ahmad
authors.forename: Raheela
authors.initials: R
authors.lastname: Bano
authors.forename: Muhammad Ali
authors.initials: MA
authors.lastname: Sheraz
authors.forename: Sofia
authors.initials: S
authors.lastname: Ahmed
authors.forename: Tania
authors.initials: T
authors.lastname: Mirza
authors.forename: Shakeel Ahmad
authors.initials: SA
authors.lastname: Ansari
mesh_terms: D000890:Anti-Infective Agents / Q000737:chemistry / Q000493:pharmacokinetics / Q000528:radiation effects; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D064704:Levofloxacin / Q000737:chemistry / Q000493:pharmacokinetics / Q000528:radiation effects; D009930:Organic Chemicals / Q000737:chemistry / Q000145:classification / Q000494:pharmacology; D010782:Photolysis; D012995:Solubility / Q000528:radiation effects; D012997:Solvents / Q000737:chemistry / Q000494:pharmacology; D014466:Ultraviolet Rays; D014783:Viscosity; D014867:Water / Q000737:chemistry / Q000494:pharmacology
chemical_list: D000890:Anti-Infective Agents; D009930:Organic Chemicals; D012997:Solvents; D014867:Water; D064704:Levofloxacin