An active ingredient comprising a diketopiperazine, or a pharmaceutically acceptable salt thereof, for use in the inhibition of vascular hyperpermeability in an animal that has a disease or condition mediated by vascular hyperpermeability selected from the group consisting of macular edema. diabetic, age-related macular degeneration, myocardial edema, myocardial fibrosis, diastolic dysfunction, diabetic cardiomyopathy, delayed lung development in fetuses of diabetic mothers, vascular hyperplasia in the mesentery, diabetic neuropathy, diabetic nephropathy, diabetic retinopathy, injury Acute pulmonary, acute respiratory distress syndrome, atherosclerosis, choroidal edema, choroiditis, coronary microvascular disease, cerebral microvascular disease, Eales disease, edema caused by injury, edema associated with hypertension, hemorrhagic shock, hypertension, Gass Irvine syndrome, ischem ia, macular edema, nephritis, nephropathies, nephrotic edema, nephrotic syndrome, neuropathy, organ failure due to edema, preeclampsia, pulmonary edema, pulmonary hypertension, renal insufficiency, retinal edema, retinal hemorrhage, retinal venous occlusion, retinitis, retinopathy, infarction silent brain, systemic inflammatory response syndrome, transplant glomerulopathy, vascular filtration syndrome, vitreous hemorrhage and von Hippel-Lindau disease, which comprises administering to the animal an effective amount of the active substance, in which the diketopiperazine is selected from the group consisting of DA-DKP, MR-DKP and YE-DKP.Un principio activo que comprende una dicetopiperazina, o una sal farmacéuticamente aceptable de la misma, para su uso en la inhibición de la hiperpermeabilidad vascular en un animal que tiene una enfermedad o afección mediada por la hiperpermeabilidad vascular seleccionada entre el grupo que consiste en edema macular diabético, degeneración macular relacionada con la edad, edema miocárdico, fibrosis miocárdica, disfunción diastólica, miocardiopatía diabética,
