A compound of Formula for use in the treatment of cerebrovascular disorders associated with insufficient cerebral circulation, wherein, R 1 represents a hydrogen atom, an aryl group, an alkyl group having from 1 to 5 carbon atoms or an alkoxycarbonylalkyl group having from 3 to 6 carbon atoms in total; R 2 represents a hydrogen atom, an aryloxy group, an arylmercapto group, an alkyl group having from 1 to 5 carbon atoms or a hydroxyalkyl group having from 1 to 3 carbon atoms, or R 1 and R 2 taken together may form an alkylene group having from 3 to 5 carbon atoms; and R 3 represents a hydrogen atom, an alkyl group having from 1 to 5 carbon atoms, a cycloalkyl group having from 5 to 7 carbon atoms, a hydroxyalkyl group having from 1 to 3 carbon atoms, a benzyl group, a naphthyl group or a phenyl group, or a phenyl group substituted with from 1 to 3 substituents, which substituent(s) may be the same or different and are selected from the class consisting of alkoxy groups having from 1 to 5 carbon atoms, hydroxyalkyl groups having from 1 to 3 carbon atoms, alkoxycarbonyl groups having from 2 to 5 carbon atoms in total, alkylmercapto groups having from 1 to 3 carbon atoms, alkylamino groups having from 1 to 4 carbon atoms, dialkylamino groups having from 2 to 8 carbon atoms in total, halogen atoms, a trifluoromethyl group, a carboxyl group, a cyano group, a hydroxyl group, a nitro group, an amino group, and an acetamide group, or a pharmaceutically acceptable salt of the compound, and further wherein the dosage of administration is controlled for providing attainment of a therapeutically effective plasma concentration of unchanged form of the compound within a range of from 60 ng/ml to 3200 ng/ml within 3 minutes to 5 minutes after completion of the loading dose administration by intravenous bolus administration, and for providing maintenance of a therapeutically effective plasma concentration of unchanged form of the compound within a range of from 60 ng/ml to 3200 ng/ml up to 2.75 hours after initiation of the administration of the maintenance dose by i.v. infusion, and further wherein the dose of the loading dose administration is from 0.025 to 1.3 mg per kg of the weight of a patient and the dose of the maintenance dose administration is from 0.05 to 2.5 mg/hr per kg of the weight of the patient. R 1 represents a hydrogen atom, an aryl group, an alkyl group having from 1 to 5 carbon atoms or an alkoxycarbonylalkyl group having from 3 to 6 carbon atoms in total; R 2 represents a hydrogen atom, an aryloxy group, an arylmercapto group, an alkyl group having from 1 to 5 carbon atoms or a hydroxyalkyl group having from 1 to 3 carbon atoms, or R 1 and R 2 taken together may form an alkylene group having from 3 to 5 carbon atoms; and R 3 represents a hydrogen atom, an alkyl group having from 1 to 5 carbon atoms, a cycloalkyl group having from 5 to 7 carbon atoms, a hydroxyalkyl group having from 1 to 3 carbon atoms, a benzyl group, a naphthyl group or a phenyl group, or a phenyl group substituted with from 1 to 3 substituents, which substituent(s) may be the same or different and are selected from the class consisting of alkoxy groups having from 1 to 5 carbon atoms, hydroxyalkyl groups having from 1 to 3 carbon atoms, alkoxycarbonyl groups having from 2 to 5 carbon atoms in total, alkylmercapto groups having from 1 to 3 carbon atoms, alkylamino groups having from 1 to 4 carbon atoms, dialkylamino groups having from 2 to 8 carbon atoms in total, halogen atoms, a trifluoromethyl group, a carboxyl group, a cyano group, a hydroxyl group, a nitro group, an amino group, and an acetamide group,