From mid-December 2019, the outbreak of the coronavirus disease 2019 (COVID-19) in Wuhan has spread worldwide and become an emergency of major international concerns (Pascarella et al., 2020). Recently, a television report has drawn extensive attention of the public in China. Two frontline doctors of the central hospital of Wuhan, Fan Yi and Weifeng Hu, were unfortunately infected by COVID-19. Cutaneous hyperpigmentation of the two doctors was noticed in the TV interview. Many people expressed grave concerns about the pathogenesis and prognosis of their skin pigmentary disorder. Fan Yi and Weifeng Hu were diagnosed with COVID-19 infection on January 18 and January 28, respectively. The illness progress of the two doctors was very rapid and they were transferred to the intensive care unit for further treatment. Extracorporeal membrane oxygenation (ECMO) was provided as rescue therapy for respiratory failure. Because of prolonged hospital stay, mechanical ventilation, and presence of invasive devices, some critically ill patients suffered from infections caused by multidrug-resistant (MDR) bacteria (Bassetti et al., 2018). Polymyxin B was used in these two doctors for the treatment of MDR infections. Polymyxin B is a cyclic polypeptide antibiotic that regained significant interest due to the inevitable appearance of MDR bacteria (Rigatto et al., 2019). It is even being considered as last resort therapy against some intractable gram-negative bacteria (Manchandani et al., 2018). Acquired skin hyperpigmentation is a common dermatologic complaint, which is attributable to drugs up to 20% of all cases (Nahhas et al., 2019). Many drugs are associated with skin hyperpigmentation such as nonsteroidal anti-inflammatory agents, antihypertensive agents, antibiotics, and psychoactive agents (Gimeńez Garcıá and Carrasco Molina, 2018). Nephrotoxicity and neurotoxicity are common adverse reactions of polymyxin B, while skin hyperpigmentation was also reported as a side effect recently (Li et al., 2020). Reports of polymyxin B associated skin hyperpigmentation in adults were rare, unlike in neonates (Zavascki et al., 2015; Gothwal et al., 2016). Polymyxin B is mainly excreted through the kidney, dosage adjustment is required in patients with lower creatinine clearance (Zheng et al., 2018). The cumulation of polymyxin B might be a possible reason for skin hyperpigmentation in neonates due to their immature kidney function (Gothwal et al., 2016; Li et al., 2020). Kidney involvement is prevalent in patients with COVID-19. Acute kidney injury (AKI) has been reported in approximately 20%-40% of critically ill or deceased COVID-19 patients (Ronco et al., 2020). Several mechanisms are possibly involved in COVID-19 associated AKI, including direct damage action of the virus, hemodynamic alterations, inflammatory cytokines, administration of nephrotoxic drugs, and mechanical ventilation (Gabarre et al., 2020; Martinez-Rojas et al., 2020). According to these findings, we speculate that AKI may be an important factor