Furthermore, the patches were evaluated on STZ-induced diabetic and normal-control rats. The patches were applied to the animals'
backs (see Figure 1). The average blood-glucose levels of Group III and IV animals were similar to those in diabetic-control
Group II animals. The plain patch without drug did not alter the glucose levels of animals in Group III and Group IV. Orally
administered rosiglitazone maleate reduced Group VII diabetic animals' blood-glucose level to 140 mg/dl from 250 mg/dl in
12 h. However, the blood-glucose level rose to 220 mg/dl in 24 h. This rise necessitated the additional dose to be given to
maintain the glucose level (see Figure 7). Again, it is worth mentioning that the glucose level was not reduced to the level
of the control animals (i.e., Group I) upon administering the drug orally or transdermally. This suggests that additional
therapy such as insulin analogues may be required because STZ damages islets cells irreversibly. Blood-glucose levels in Group
V and Group VI animals were effectively reduced for 48 h to 150 mg/dl, which suggests that the patches controlled blood-glucose
levels at least for 48 h in the diabetic rats. Formulation I reduced blood-glucose levels more effectively (i.e., in Group
V animals) compared with Formulation II (i.e., in Group VI animals). Although numerical values did not differ greatly, the
differences were persistent and statistically significant.
The location of the patch on humans is an important factor because the thickness of skin differs at different locations on
the body. Different permeation rates were found at different locations when patch-type formulations of scopolamine hydrobromide
were applied behind the ear and on the thigh (24). The steady-state permeation rate of this drug was 10 μg/cm2/h from the patch applied behind the ear, where average skin thickness is 0.084mm. The permeation rate was 4.7 μg/cm2/h from the patch applied on the thigh, where average skin thickness is 0.106 mm. Hence, the authors chose to apply the rosiglitazone
transdermal patch to the neck region behind the ear.
The plasma-drug level was determined using HPLC. Figure 8(a) shows the chromatogram of pure drug and internal standard in
solvent. Figure 8(b) represents the chromatogram of blank plasma. Figure 8(c) represents the chromatogram of rosiglitazone
and pioglitazone in plasma for a standard sample. Figure 8(d) is a representative chromatogram of rosiglitazone in plasma
after 8 h in humans, where pioglitazone was used as an internal standard.