Adverse drug events (ADE) are one of the major problems affecting quality of care and achievement of therapeutic goals in older adults (OA), increasing re-admissions, hospital stays, resource use, and problems on patient safety. The present study aim is to determine the impact of the clinical pharmacist interventions on the prevention of ADE in OA at 3 months post-discharge compared to usual care.

A randomized clinical trial of two parallel groups 1: 1 (control and intervention) plus a historical control group will be carried out at the Internal Medicine Service (IMS) of the teaching Hospital at the University of Chile. The sample will be of 611 patients (242 per each parallel group and 127 of the historical control group) of 60 years or older, admitted to the IMS for acute pathology or decompensation of chronic pathology, with survival over 6 months, who is under pharmacological therapy and have a caretaker or responsible contact person at discharge.

The historical control group will receive usual care and the parallel control group will also receive training on pharmacogeriatrics. The intervention group will receive the care of a clinical pharmacist during hospitalization, at discharge and post-discharge, through a home visit at 30 days post-discharge and a telephone call at 60 days post discharge.

The intervention plan during hospitalization will consist of daily monitoring of pharmacological efficacy and safety, participating in clinical rounds and patient interviews. To review, assess the indications according to the conditions of each patient and evaluating possible interactions of clinical importance, dose adjustments, potentially inappropriate medication for older adult (OA), adverse effects and omissions of therapy. To make recommendations to the healthcare team regarding pharmacological therapy received during hospitalization and at discharge.

Patient-directed interventions will occur at discharge and post-discharge, focusing on clarifying management regimens, drug use motives, preventing drug-related problems, clarifying doubts and educating on pharmacotherapy, and enhancing adherence to treatment. The selection and recruitment of the patients will be made during the first 48 hours of their admission to the Internal Medicine Service (IMS), where they will be invited to participate and sign the informed consent.

In all groups, a physician, pharmacist, and occupational therapist, blind to treatment assignment, will collect sociodemographic, morbid, pharmacotherapeutic, and functional (Barthel Index and Lawton & Brody Scale), adherence (Morisky & Green Scale), delirium (Confusion Assessment Method, CAM), comorbidity (cumulative illness rating scale in Geriatrics (CIRS-G)), anticholinergic burden (Anticholinergic Burden Scale and Ars Risk Scale), potentially inappropriate medications (Beers Criteria and screening tool of older people's prescriptions & screening tool to alert to right treatment criteria (STOPP & START)) before, during hospitalization, at discharge and post-discharge. Also a follow up by telephone interviews at 30, 60 and 90 days after hospital discharge from the IMS.

Two trained and independent evaluators (geriatrician and clinical pharmacist), blind to treatment assignment, will evaluate the history of each case and by consensus will assign the presence of Adverse Drug Events (ADE), and classify them as preventable or not and according to severity. The Chi-squared or Fisher exact test will be used to test the hypothesis that clinical pharmacist intervention prevents at least 50% of ADE at 3 months post-discharge in OA compared to usual care in the IMS.

Inclusion Criteria:

• Patients attended by the staff of internists of the internal medicine service of the Clinical Hospital of the University of Chile for acute condition or decompensation of chronic pathology.
• Patients with an estimated survival of more than 6 months.
• Patients who are on pharmacological therapy.
• Patients who have a contact person or responsible caregiver, willing to comply with the scheduled care plan.
• Patients who have a contact telephone number

Exclusion Criteria:

• Patients without cognitive autonomy in which it is not possible to establish contact with the caregiver.
• Any other condition that in the judgment of the research team affects the quality of the collection of the information.