Pharmacokinetics of Ceftriaxone Free Fraction

Inclusion Criteria: * Men or women over 55 years of age receiving treatment with high-dose ceftriaxone (minimum 4 grams / day) for any clinical indication in the study period. * Creatinine \<1.5 mg / dL * The patient must have received at least 48 hours of treatment with the same previous therapeutic regimen to extraction. * The subject or her representative must give their verbal or written consent to participate in the study. East Consent can be revoked at any time without prejudice to the patient. The consent it will be recorded in your medical record. Exclusion Criteria: * Patients under 55 years of age. * Creatinine\> 1.5 mg / dL * Patient with less than 48 hours of treatment with high-dose ceftriaxone. * Subjects with allergy or hypersensitivity to cephalosporins and penicillins. * Subjects who do not grant or withdraw their consent. * Patients whose concomitant treatment presents possible interactions with the study medication. The possible interactions will be evaluated by staff of the Pharmacy Service.