This study will compare the administration of ceftazidime by intermittent intravenous injections (29 mg/kg 30min ×3/day) and by continuous infusion (86 mg/kg/24 h, preceded by 29 mg/kg/30 min). The main evaluation criterion of the study is the measure of the time during which ceftazidime concentration is above minimal inhibitive concentration of Pseudomonas aeruginosa in cerebrospinal fluid. This study will be developed in a neurological intensive care department. Inclusion criteria will be essentially, patients aged over 18 years old, hospitalised for a cerebrolesion associated to a hydrocephalus drained by an external ventricular derivation, an acquired pneumopathy under mechanic ventilation since more 7 days in the department of neurological intensive care. This study is a prospective randomised, simple blind and divided in two parts. The first part of the study is a study with parallel group comparing the treatment initiation between a continuous and an intermittent treatment of ceftazidime. The second part of the study is a cross-over study. One patient group will receive a continuous treatment of ceftazidime and the other patient group will receive an intermittent treatment of ceftazidime.