Pharmacokinetics of Ertapenem in Patients Aged Over 75

In geriatric departments, physicians are faced with two difficulties, first the increasing number of infections caused by multiresistant bacteria, especially extended spectrum β-lactamase (ESBL) producing enterobacteria strains and second, the poor venous access frequently encountered in elderly population. Giving antibiotics subcutaneously would be an interesting alternative, all the more as intramuscular injection is contraindicated in case the of anticoagulant therapy. Unfortunately, few data are available about subcutaneous (SC) administration. Ertapenem is a recent long-acting parenteral carbapenem indicated especially in the treatment of ESBL infection. Its subcutaneously administration has been tested in several studies in Intensive Care Units (ICU) and internal medicine wards with promising results regarding clinical and pharmacokinetics data. An alternative to the IV Ertapenem administration is needed because of poor venous access and behavioural abnormalities commonly present in infected elderly population. Ertapenem is currently SC administrated in geriatric departments if no other option is available. Moreover elderly patients often present several comorbdities, polymedication, renal insufficiency, cachexia which may disturb antibiotics pharmacokinetics. The aim of the study is to obtain pharmacokinetic data of SC and IV Ertapenem administration in elderly population, obtain PK/PD parameters adapted to time-dependent antibiotics (T%\>MIC) and descriptive data of occurrence of adverse effects and evolution of signs of infection.

Inclusion Criteria: * Age\> or equal to 75 years * Treatment with ertapenem (1g daily) for at least 48 hours IV or SC (or one then the other) * Subject affiliated or beneficiary of a social security system, * Free Consent, informed and signed by the participant or by the designation of a proxy if delirium and the investigator. Exclusion Criteria: * Age \< 75 years * Criteria for legislation: those under protection of the justice, subject participating in other research, including a period of exclusion still going to pre-inclusion