Colistin, also known as polymyxin E, is an antibiotic used to treat bacterial infections caused by susceptible Gram-negative bacteria. It is particularly active against difficult-to-treat pathogens.
What is Colistin
Colistin is classified as a polymyxin antibiotic, a group of cationic polypeptides. These antibiotics work by disrupting the bacterial cell membrane, a critical outer layer of Gram-negative bacteria. This disruption changes the membrane’s permeability, leading to bacterial cell death. Colistin was initially discovered in 1947 and saw use in the 1950s.
Its use was largely abandoned in the 1970s with the development of less toxic antibiotics. However, due to the increasing prevalence of multidrug-resistant Gram-negative bacteria and a lack of new antimicrobial agents, Colistin has re-emerged as a treatment option. Only two polymyxins, Colistin and polymyxin B, are currently available.
Why Colistin is Used
Colistin is primarily used as a “last-resort” antibiotic for severe infections caused by multi-drug resistant (MDR) Gram-negative bacteria, including pathogens such as Acinetobacter baumannii, Pseudomonas aeruginosa, and carbapenem-resistant Enterobacteriaceae (CRE). It is considered a last resort because its use is reserved for situations where other, less toxic antibiotics are ineffective.
Colistin can be administered through various routes depending on the infection. It can be injected intravenously or intramuscularly for systemic infections. For pulmonary infections, particularly in patients with cystic fibrosis, it may be administered via inhalation. In specific cases of meningitis or ventriculitis, it can also be given by intraventricular or intrathecal routes.
Key Side Effects and Precautions
Colistin use is associated with several adverse effects, with nephrotoxicity (kidney damage) being a primary concern. Close monitoring of kidney function is essential during treatment, and dose adjustments may be necessary to mitigate this risk.
Neurotoxicity is another potential side effect, which can manifest as temporary neurological disturbances. These may include symptoms such as dizziness, tingling, numbness, or slurred speech. Patients should be advised to avoid activities requiring mental alertness if they experience these effects. General precautions also include informing healthcare providers about any pre-existing conditions or other medications being taken, as some drugs can affect Colistin’s excretion or increase the risk of side effects.
The Challenge of Colistin Resistance
A growing concern is the emergence of resistance to Colistin. This development threatens its effectiveness as a last-resort drug against highly resistant bacteria. One mechanism of resistance involves the mcr-1 gene, which can be transferred between different bacteria, accelerating the spread of resistance.
This poses a challenge to the global fight against antimicrobial resistance. The effectiveness of Colistin is diminishing due to this increasing resistance. Efforts are underway to preserve the effectiveness of Colistin, including judicious use and exploring combination therapies with other antibiotics.