An infusion device capable of administering liquid medication at a continuous flow rate, and upon user demand delivers a controlled volume dosage of liquid medication at a higher dosage flow rate. The dosage reservoir (200) remains empty until the user actuates it by selectively and temporarily removing the pressure source, such as a spring (230). During actuation, fluid rapidly flows from the medication reservoir (100) to fill the dosage reservoir (200). After actuation, the pressure source (230) exerts a higher pressure on the dosage reservoir (200) than the medication reservoir pressure (100), which results in a temporary higher bolus flow rate. Thus, two distinct flow rates are achieved with one flow restrictor element (700).
