Table 1.

Median ± Standard Error (95% Range) Trough and Maximal Concentrations of Doxycycline in Tear Fluid of 3 Healthy Dogs and 3 Healthy Cats Receiving 4.2–5 mg/kg Doxycycline Per orally for 6 Consecutive Days

	Schirmer strips		PVA sponges
In vivo Doxycycline concentration	Centrifugation	Methanol elution	Centrifugation	Methanol elution
Ctrough (ng/mL)	279.6 ± 24.2 (143.3–458.2)*	63 ± 57.9 (44.8–543.7)	176 ± 59.2 (119.3–831.8)	65.4 ± 12.7 (33.7–138.8)
Cmax (ng/mL)	441.1 ± 79.2 (308.8–1388.1)*	87 ± 53.9 (53.9–156.6)	278 ± 26.1 (186.4–552.5)*	96.8 ± 57.2 (38.7–650.7)

Tears were collected in vivo with either Schirmer strips or PVA sponges, and fluid was subsequently extracted by centrifugation or methanol elution. For the same absorbent material, significant differences between centrifugation versus methanol are noted with an asterisk (^*).

PVA, polyvinyl acetal.