Very rare side effects • difficulties in passing urine • Sweet's syndrome (plum-coloured, raised, painful lesions on the limbs, sometimes the face and neck, with fever) • water retention in the lungs, bleeding in the lungs, coughing up of blood, lack of oxygen, inflammation of the lungs (which can cause breathlessness, cough, raised temperature); in some cases, this could lead to respiratory failure or adult respiratory distress syndrome (ARDS, a condition causing increased shortness of breath, in very ill patients), which may be fatal • sickle cell crises (acute collapse of red blood cells) in patients with sickle cell disease • rupture of the spleen