INTRODUCTION
COVID-19 is an infectious disease caused by the new coronavirus (SARS-CoV-2), was first reported in Wuhan, China, later reaching pandemic proportions. Patients may present symptoms (fever, dry cough and tiredness), severe (dyspnea, hypoxia and/or great pulmonary involvement) and critical (respiratory failure, systemic shock and/or multiple organ failure) [1]. Respiratory discomfort syndrome, an incident complication, affected 15.6% of patients in a study that collected data from 1,099 patients with COVID-19 in China [2]. Despite the incessant search for effective drugs in their clinical treatment, no drug has yet been validated [3,4]. Several classes of drugs and strategies are being evaluated or developed aiming at the clinical management of COVID-19, such as antibiotics, antiviral, anti-inflammatory, antibodies, anticoagulants, anti-fibrotic, oxygen therapy, and immunomodulation, among others. Possibly, different treatment modalities have different efficiencies according to the stage of the disease and its manifestation [4]. Thus, it is necessary to understand the pathophysiology of the disease, as well as the affected organs and systems, in order to improve the identification of therapeutic targets and, thus, rigorously define the ideal treatment.
In the context of the search for adequate pharmacotherapy, biguanides, buformin (BUF), metformin (MET) and phenformin (PHEN) appear as possible adjuvant therapy for the treatment of COVID-19, due to their comprehensive pharmacological properties [5]. Only MET is used in large scale [6], appearing as the first therapeutic line for type 2 diabetes mellitus (DM2) and one of the most prescribed drugs worldwide [7].
Antihelmintic, antimalarial and antiviral effects of biguanides have been described, the latter being dependent on the administration of high doses [8,9]. Considering recent publications of this pharmacological class, its potential off label use, pharmacological advances that allow the administration of drugs by alternative routes, as well as the demand for new therapeutic tools for COVID-19, this study aimed to review the pharmacological effects of biguanides, as well as its therapeutic potential in viral infections.