Gramicidin is a mixture of three antibacterial polypeptides that work together to form a channel that spans cell membranes. The antibiotic increases the permeability of the bacterial cell membrane to inorganic cations by forming a network of channels through the normal lipid bilayer of the membrane. Medicinally, gramicidin is often used in a combination with other drugs for treating inflammation of the skin, eyes, and ears. Side effects include local irritation of areas with the applied drug.