title: Preparation of 0.05% FK506 suspension eyedrops and its pharmacokinetics after topical ocular administration.
abstract: OBJECTIVE
  To investigate the stability of FK506 eye suspension and its pharmacokinetics in rabbit aqueous humor, as well as its distribution in eye tissues.
  
  
  METHODS
  Sedimentation rate, flocculation value, redispersion time, rheological study, and accelerated experiment were determined for evaluating the stability of FK506 suspension. In a single-dose pharmacokinetic study, six rabbits were instilled a 25-microL drop of 0.05% FK506 suspension and aqueous humor samples were collected at different intervals after administration. In a multiple-dose pharmacokinetic study, a 25-microL drop of FK506 suspension was instilled into the right eye of six rabbits four times a day for 7 days. On the eighth day, aqueous humor samples were collected before the administration of the first, second, third dose, and at different checkpoints after the third dose. For tissue distribution study, six eyes per time points (18 rabbits in total) were treated with single dose of FK506 suspension, and the eyes were enucleated at 60, 100, and 240 min after treatment, then eye tissues were collected. The concentrations of FK506 in all samples were determined by LC-MS/MS.
  
  
  RESULTS
  The preliminary results indicated that the stability of FK506 suspension was in accord with the standards of Chinese pharmacopoeia. The maximum concentrations of aqueous humor after single dose and multiple dose administrations were 31.40 +/- 9.32 ng/mL and 37.73 +/- 11.25 ng/mL, respectively. The concentration of FK506 in cornea at 60, 100, and 240 min after a single dose were 402.0 +/- 96.8 ng/g, 363.8 +/- 84.5 ng/g, and 220 +/- 62.3 ng/g, respectively. Determination of pharmacokinetic parameters of single-dose and multiple-dose administration, as well as the FK506 concentrations in eye tissues, showed that the FK506 formulation and the dosing regimen ensured the therapeutic concentration of FK506 for treating corneal allograft rejection.
  
  
  CONCLUSIONS
  Based on the stability, single-dose and multiple-dose pharmacokinetics, and tissue distribution, FK506 suspension eyedrops may be a suitable candidate for clinical application in ophthalmology.
authors.affiliation: Zhongshan Ophthalmic Center at Sun Yat-sen University, The State Key Laboratory of Ophthalmology, Sun Yat-sen University, 54 south Xianlie Road, Guangzhou, People's Republic of China.
authors.forename: Jin
authors.initials: J
authors.lastname: Yuan
authors.forename: Jia-jie
authors.initials: JJ
authors.lastname: Zhai
authors.forename: Jia-qi
authors.initials: JQ
authors.lastname: Chen
authors.forename: Cheng-tian
authors.initials: CT
authors.lastname: Ye
authors.forename: Shi-you
authors.initials: SY
authors.lastname: Zhou
mesh_terms: D000287:Administration, Topical; D000818:Animals; D001082:Aqueous Humor / Q000378:metabolism*; D002681:China; D002853:Chromatography, Liquid / Q000379:methods; D003315:Cornea / Q000378:metabolism*; D004334:Drug Administration Schedule; D004355:Drug Stability; D007166:Immunosuppressive Agents / Q000008:administration & dosage / Q000493:pharmacokinetics*; D009883:Ophthalmic Solutions; D010602:Pharmacopoeias as Topic; D011817:Rabbits; D012212:Rheology; D016559:Tacrolimus / Q000008:administration & dosage / Q000493:pharmacokinetics*; D053719:Tandem Mass Spectrometry / Q000379:methods; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D007166:Immunosuppressive Agents; D009883:Ophthalmic Solutions; D016559:Tacrolimus