Objective—To determine magnitude and duration of
the effect of oral administration of methazolamide at
2 dosages on intraocular pressure (IOP) in dogs in single-
dose and multiple-dose trials and to determine
aqueous humor flow rate (AHFR) by use of anterior
segment fluorophotometry before and during treatment.
Animals—25 healthy adult Beagles.
Procedure—Baseline IOPs and AHFRs were determined
on days 0 and 1, respectively. On day 2, the
single-dose trial was initiated with oral administration
of 25 or 50 mg of methazolamide at 7 AM to 2 groups
of 10 dogs each. Five dogs served as controls. In the
multiple-dose trial, the same dogs received 25 or 50
mg of methazolamide at 7 AM and at 3 and 11 PM on
days 3 through 9.
Results—Intraocular pressures varied diurnally with
highest IOPs in the morning. In the single-dose trial,
IOP decreased significantly at 3 to 6 hours after treatment
and then increased significantly at later time
points, compared with baseline values. In the multipledose
trial, dogs in both treatment groups had significantly
lower IOPs during the treatment period at 10 AM
and 1 PM but not at 6 and 9 PM, compared with baseline
values. In both treatment groups morning IOPs
had returned to baseline values by the first day after
treatment. Evening IOPs were significantly increased
by 2 to 3 days after treatment, compared with baseline
values. The AHFRs in both treatment groups were significantly
lower than pretreatment AHFRs.
Conclusions and Clinical Relevance—Oral administration
of methazolamide decreases IOPs and AHFRs
in clinically normal dogs, with effectiveness diminishing
in the evening. (Am J Vet Res 2003;64:183–187)