Impact of Flow Rate, Collection Devices, and Extraction Methods on Tear Concentrations Following Oral Administration of Doxycycline in Dogs and Cats

Abstract

Purpose: Compare the precision of doxycycline quantification in tear fluid collected with either Schirmer strips or polyvinyl acetal (PVA) sponges following oral drug administration.Methods: Three dogs and 3 cats were administered doxycycline orally at a dose of 4.2–5 mg/kg every 12 h for 6 consecutive days. At day 5 and 6, blood and tear fluid were sampled to capture doxycycline trough and maximal concentrations. Tear fluid was collected 3 times (spaced 10 min apart) at each session with the absorbent material placed in the lower conjunctival fornix until the 20-mm mark was reached (Schirmer strip, one eye) or for 1 min (PVA sponge, other eye). Tear extraction was performed with either centrifugation or elution in methanol. Doxycycline concentrations were measured with liquid chromatography–mass spectrometry. Low (100 ng/mL) and high (1,000 ng/mL) tear concentrations measured in vivo were spiked into each absorbent material in vitro to evaluate percentage drug recovery.Results: After oral administration of doxycycline, the drug reached the tear compartment at concentrations of 45.1–900.7 ng/mL in cats and 45.4–632.0 ng/mL in dogs, representing a tear-to-serum ratio of 12% and 16%, respectively. Doxycycline tear concentrations were significantly more precise when tear collection was performed with Schirmer strips rather than PVA sponges (P = 0.007), but were not correlated with tear flow rate. In vitro doxycycline recovery was poor to moderate (<75%).Conclusions: Schirmer strips represent a good option for lacrimal doxycycline quantification, although the collection and subsequent extraction have to be optimized to improve drug recovery.

An eye on the dog as the scientist's best friend for translational research in ophthalmology: Focus on the ocular surface

“…Topically and systemically administered drugs can be quantified in tear fluid to determine the clinical efficacy and dosing frequency from fitting of kinetic data. [211][212][213][214][215] Multiple "omics" approaches can also be utilized for analysis of the tear fluid including proteomics, 173,190,191,[216][217][218][219][220] lipidomics, 141,206,221,222 and metabolomics, 222…”

“…41 cellulose filter paper and possess specific characteristics to promote tolerance (5-mm width × 35-mm length, 0.22-mm thick, 20-25 µm porosity, foldable extremity for ease of insertion). 249,257 In addition to their conventional use for aqueous tear assessment, Schirmer strips can retrieve tear fluid for bioanalytical purposes in humans, 182,216,219,220,228,231,258 dogs, 190,209,211,214,215,240,259 and small laboratory species. 244,260,261 For instance, Schirmer strips were used for indepth characterization of proteomics in human 173 and canine tears, 190 and can also successfully recover specific analytes such as cytokines, 200,258 clusterin, 182 and xenobiotics.…”

“…244,260,261 For instance, Schirmer strips were used for indepth characterization of proteomics in human 173 and canine tears, 190 and can also successfully recover specific analytes such as cytokines, 200,258 clusterin, 182 and xenobiotics. 211,[213][214][215]244,262 Absorbent sponges exist in different material types such as cellulose, 234,236,263,264 polyvinyl acetal, 209,214,228,236,244,264-266 polyester, 239,242,266 and polyrurethane. 236 A material with hydrophilic and hydrophobic properties (e.g., polyvinyl acetal and polyurethane) 236,264 is generally preferred to optimize the amount of fluid absorbed and the amount of fluid retrieved from the sponge.…”

“…For tear fluid collection, the sponge is held against the lacrimal lake by the operator (to minimize reflex tearing), 234,239,242,244,266 or placed beneath the lower eyelid for a given period of time. 214,236,264 Tear fluid recovered from absorbent sponges can be assayed for selected tear compounds, similar to Schirmer strips.…”

“…250 On this note, the main limitation of indirect sampling is the "invasiveness" of the technique, at risk of promoting reflex tearing and altering the composition of the tear fluid; indeed, several studies showed variable tear composition between directly and indirectly collected samples, with notable differences in the qualitative and quantitative profiles obtained for tear lipids 221 and tear proteins. 216,220,226,269 Another important drawback is related to the adsorptive properties of Schirmer strips or absorbent sponges, that is, incomplete release of tear compounds following extraction 209,214,257,258,265 ; however, the authors believe this limitation can be minimized/controlled with adequate precautions (see Section 3.3).…”