The effect of fractionation of light treatment on necrosis and vascular function of normal skin following photodynamic therapy.

Sparing of normal tissue, mouse tail skin, by fractionation of light treatment in photodynamic therapy has been demonstrated in BDF1 mice injected with 2 mg tetrasodium-meso-tetra(4-sulphophenyl)porphine dodecahydrate i.v. When the time between 2 fractions of 67.5 J cm-2 and 90 J cm-2 was increased to 2 and 4 days respectively the incidence of necrosis fell to that expected after a single fraction. Blood flow in the tail skin 5 days after the second light fraction, as measured by the clearance of an intradermally injected solution of 133xenon in 0.9% saline, returned to control values when the time between 2 fractions was 2 days with 67.5 J cm-2 fractions, and 3 days with 90 J cm-2 fractions. The time course of recovery of normal mouse tail skin from photodynamic therapy, as shown by these split dose experiments, was found to be similar to the time course for the recovery of blood flow following a single light treatment.