This study evaluates whether adding melatonin to standard colistin therapy improves outcomes in patients with multidrug-resistant (MDR) Gram-negative bacterial infections. These infections are difficult to treat and are associated with high morbidity and mortality, particularly in critically ill patients.

Colistin is often used as a last-line antibiotic for these infections; however, its effectiveness may be limited, and it is associated with side effects such as kidney injury. Melatonin, a naturally occurring hormone, has antioxidant, anti-inflammatory, and immune-modulating properties that may enhance the effectiveness of antibiotics and reduce treatment-related complications.

In this randomized, double-blind, placebo-controlled study, adult patients receiving colistin will be assigned to receive either melatonin or a placebo in addition to standard care. The study will assess whether melatonin improves oxidative stress, infection control, and clinical outcomes while maintaining safety.

Antimicrobial resistance is a major global health challenge, particularly among Gram-negative bacteria, which have developed resistance to multiple antibiotic classes, including last-line agents such as colistin. These infections are especially prevalent in intensive care units and are associated with poor clinical outcomes.

Given the limited development of new antibiotics, alternative strategies such as the use of adjunctive therapies are being explored. Melatonin (N-acetyl-5-methoxytryptamine) is an endogenous hormone known for its role in circadian rhythm regulation, but it also exhibits antioxidant, anti-inflammatory, and immunomodulatory effects. Emerging experimental evidence suggests that melatonin may enhance antibiotic activity and help overcome resistance mechanisms, including those affecting colistin.

This study is a prospective, randomized, double-blind, placebo-controlled clinical trial conducted in adult patients with confirmed MDR Gram-negative bacterial infections requiring intravenous colistin therapy in the intensive care setting.

Participants will be randomly assigned in a 1:1 ratio to receive either oral melatonin (60 mg once daily) or a matching placebo, initiated concurrently with colistin therapy. All patients will receive standard antimicrobial treatment and supportive care according to institutional protocols.

The primary objective is to evaluate the effect of adjunctive melatonin on oxidative stress, measured by changes in serum malondialdehyde (MDA) levels. Secondary objectives include assessment of microbiological eradication, clinical response, inflammatory markers, renal safety (including the incidence of acute kidney injury), and overall clinical outcomes such as length of stay.

This study aims to determine whether melatonin can serve as a safe and effective adjunctive therapy to improve outcomes and potentially restore the efficacy of colistin in the treatment of multidrug-resistant Gram-negative infections.

Inclusion Criteria:

• • Confirmed diagnosis of infection caused by multidrug-resistant Gram-negative bacteria based on microbiological culture and sensitivity testing

  • Patients receiving intravenous colistin therapy according to institutional protocols
  • Clinical diagnosis of sepsis or severe infection in accordance with established critical care criteria

Exclusion Criteria:

• • Pregnancy or lactation

  • Terminal medical or surgical illness (e.g., advanced malignancy)
  • Severe chronic liver disease or end-stage renal failure
  • Impaired cognitive function or active psychiatric illness under treatment
  • Known hypersensitivity to melatonin
  • Use of melatonin within 48 hours prior to enrollment