INTRODUCTION: Pressure ulcers (PU) are one of the main challenges for nursing in our country. Wound bed preparation and the TIME algorithm provide essential tools for adequately treating these lesions. However, these wounds tend to become chronic due to the bacterial load in their bed. It is now known that bacteria can form complex and diverse structures, named as biofilm, which are difficult to diagnose and much more resistant to antimicrobial action.

Controlling these biofilms is crucial to create the optimal conditions for wound healing. Currently, it is believed that biofilms are present in 60-100% of chronic wounds. Therefore, more studies are needed to evaluate the efficacy of different antimicrobial agents on these structures.

OBJECTIVE: To determine the efficacy of a gel containing polyhexanide and biguanide, alone or in combination with alginate with or without silver, in preventing biofilm in PU, in terms of healing at 4 weeks.

METHODOLOGY: Multicenter clinical trial with a 2x2 factorial design, conducted with patients from Alcoy with category II and III PUs that meet the inclusion and exclusion criteria. A sample of 140 participants is estimated, distributed into four groups of 35 patients. The interventions that will be carried out will be: application of Prontosan gel® and Aquacel Ag+®; Aquacel Ag+®; control group; Prontosan gel®. Data on wound evolution will be collected using RESVECH 2.0. Descriptive statistical analysis and hypothesis testing will be performed.

Inclusion Criteria:

• Bedridden patients, patients with bed-to-chair mobility, or those in a wheelchair.
• Presenting one or more category II-III pressure ulcers.
• Aged over 65 years.
• Patients with laboratory results within normal metabolic values (HbA1c < 7%).
• Patients who, in item 6 "infection/suspected biofilm" of the RESVECH 2.0 index, do not have tissue compatible with biofilm, hypergranulation, or purulent exudate, and never score more than 4 in the other items.
• During follow-up, cases that develop signs and symptoms of local infection according to TILI and/or the RESVECH 2.0 index will be considered therapeutic failures, allowing for clinical rescue, but the patient will remain in the intention-to-treat (ITT) analysis.

Exclusion Criteria:

• Patients who, despite the above, present a deteriorated health status that could influence the outcome, such as terminally ill patients, oncology patients, or those with inflammatory diseases.
• Patients in a state of malnutrition according to the Mini Nutritional Assessment (MNA®) scale who are not receiving nutritional supplements, and/or at risk of malnutrition with nutritional deficits.
• Patients with pressure ulcers in the perineal area and urinary incontinence (except those with a urinary catheter) and/or fecal incontinence.