Detection of Raman spectra in ocular drugs for potential in vivo application of Raman spectroscopy.

Abstract Purpose: 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 degrees "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 (25x/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.