title: Detection of Raman spectra in ocular drugs for potential in vivo application of Raman spectroscopy.
abstract: OBJECTIVE
  Raman spectroscopy holds potential for the assessment of intraocular pharmacokinetics. Raman spectra of ocular drugs were acquired, to determine the drug-specific Raman signature. The ability of the Raman technique to quantify drug concentrations was also investigated.
  
  
  METHODS
  The experimental setup was based on a High Performance Raman Module 2500 Raman module, designed for 180° "backscatter" signal detection in the wavenumber range of 400-1,800 cm(-1). Excitation source was a diode laser emitting a beam with a wavelength of 785 nm and a power of 10 mW. Laser light was focused in the sample with a long-working-distance microscope objective (25×/0.50). Samples were measured in quartz cuvettes in 10 sequential measurements, with exposure time 30 s. The total number of measured drugs was 49. To determine whether signal intensity and drug concentration correlate, 2 drugs were diluted in water and measured with 120 s exposure time at different concentrations.
  
  
  RESULTS
  An active ingredient-specific Raman signature was detected in 4 glaucoma drugs, 6 mydriatics, 5 antibiotics, 4 anesthetics, 3 anti-inflammatory drugs, 2 types of artificial tears, and 5 other drugs. In 20 drugs, no specific Raman signature was detected. Linear correlation of drug concentration with signal intensity was high (R(2)≥0.94).
  
  
  CONCLUSIONS
  Using low laser powers, Raman signatures for 29 commonly used ocular drugs were detected. Correlation of drug concentration with signal intensity is high, which is essential for monitoring drug concentration in ocular media. The presented results encourage the use of Raman spectroscopy to acquire detailed information on the pharmacokinetics of these ocular drugs.
authors.affiliation: Maastricht University Medical Center, University Eye Clinic Maastricht, Maastricht, The Netherlands. m.elshout@mumc.nl
authors.forename: Mari
authors.initials: M
authors.lastname: Elshout
authors.forename: Roel J
authors.initials: RJ
authors.lastname: Erckens
authors.forename: Carroll A
authors.initials: CA
authors.lastname: Webers
authors.forename: Henny J
authors.initials: HJ
authors.lastname: Beckers
authors.forename: Tos T
authors.initials: TT
authors.lastname: Berendschot
authors.forename: John
authors.initials: J
authors.lastname: de Brabander
authors.forename: Fred
authors.initials: F
authors.lastname: Hendrikse
authors.forename: Jan S
authors.initials: JS
authors.lastname: Schouten
mesh_terms: D060433:Administration, Ophthalmic; D016903:Drug Monitoring / Q000379:methods; D004364:Pharmaceutical Preparations / Q000008:administration & dosage / Q000032:analysis*; D010599:Pharmacokinetics; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013997:Time Factors
chemical_list: D004364:Pharmaceutical Preparations