The present invention refers to a medical drug infusion system for dosing relatively small quantities of a fluid, comprising a container (1) of the fluid to be dosed, a fluid conduit (2) connected to an infusion catheter or needle (3), a pumping means (4) to transport the fluid to be dosed via fluid conduit (2) to the patient, and a sensor unit (5) which monitors the pressure within said fluid conduit (2). The sensor unit (5) is arranged downstream of the pumping means (4) at a fork (6) from the fluid conduit (2), a valve (7) being arranged between the fluid conduit (2) and the sensor unit (5), said valve (7) enabling at the predetermined pressure, which is higher than the usual pressure in the fluid conduit (2) such as during an occlusion, flow of the fluid to be dosed from said conduit (2) into said sensor unit (5) where the fluid is optically or acoustically detected.
