Tylosin (trade names Tylocine, Tylan) is a bacteriostat feed additive used in veterinary medicine. It has a broad spectrum of activity against Gram-positive organisms and a limited range of Gram-negative organisms. It is found naturally as a fermentation product of Streptomyces fradiae. It is a macrolide antibiotic. Tylosin is used in veterinary medicine to treat bacterial infections in a wide range of species and has a high margin of safety. Tylosin is certified by the FDA but is only approved for use in livestock such as cattle, chickens, swine, and turkeys. The FDA has prohibited the use of tylosin in dogs and cats, except where it is specifically prescribed by a veterinarian. Tylosin has a bacteriostatic effect on susceptible organisms, caused by inhibition of protein synthesis through binding to the 50S subunit of the bacterial ribosome.

Pirlimycin is an antibiotic which was approved in the US and Europe for the treatment of subclinical mastitis in lactating dairy cattle associated with common mastitis pathogens, mostly Gram-positive bacterias. The drug exerts its action by binding to the 50S ribosomal subunit, therefore hindering the aminoacyl-tRNA binding and inhibiting the peptidyltransferase reaction, which interferes with protein synthesis within the bacteria.

Florfenicol (Nuflor) is a fluorinated synthetic analog of thiamphenicol. Florfenicol is indicated for the treatment of bovine respiratory disease (BRD) associated with Mannheimia (Pasteurella) haemolytica, Pasteurella multocida, and Haemophilus somnus, for treatment of bovine interdigital phlegmon (foot rot, acute interdigital necrobacillosis, infectious pododermatitis) associated with Fusobacterium necrophorum and Bacteroides melaninogenicus. Florfenicol is a broad-spectrum, primarily bacteriostatic, antibiotic with a range of activity similar to that of chloramphenicol, including many gram-negative and gram-positive organisms; however, florfenicol does not carry the risk of inducing human aplastic anemia that is associated with chloramphenicol. It also has activity against some chloramphenicol resistant strains of bacteria, possibly because it is less affected by the major enzyme produced in plasmid-mediated bacterial resistance against chloramphenicol and thiamphenicol. Although the activity of florfenicol against obligate anaerobes is not addressed in the literature, it is likely to be quite effective. Antibiotic principle of Florfenicol is similar to that of chloramphenicol and Thiamphenicol. Florfenicol inhibits protein synthesis by binding to 70S ribosomal 50S subunits of susceptible bacteria, leading to the inhibition of peptidyl transferase and thereby preventing the transfer of amino acids to extending peptide chains and subsequent protein formation. The bacterial receptor that is the site of action for florfenicol is also considered to be the same as that for chloramphenicol and thiamphenicol. Florfenicol has a fluorine atom instead of the hydroxyl group located at C-3 in the structure of chloramphenicol and thiamphenicol. This prevents the acetylation of bacterial acetyltransferase in this site as to allow florfenicol to be less susceptible to deactivation by bacteria with plasmid-transmissible resistance that involves acetylation of the C-3 hydroxyl group in chloramphenicol and thiamphenicol, and prevents their interaction with bacterial ribosomes.

Ceftiofur is an antibiotic of the cephalosporin type (third generation), licensed for use in veterinary medicine only. It was first described in 1987. It is marketed by pharmaceutical company Zoetis as Excenel, Naxcel, and Excede and is also the active ingredient in that company's Spectramast LC (lactating cow formulation) and Spectramast DC (dry cow formulation) product. Ceftiofur has worldwide approvals for respiratory disease in swine, ruminants (cattle, sheep and goats) and horses and has also been approved for foot rot and metritis infections in cattle. Ceftiofur has also been approved in various countries for early mortality infections in day-old chicks and turkey poults. Ceftiofur (NAXCEL) is indicated for treatment of bovine respiratory disease (shipping fever, pneumonia) associated with Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni. NAXCEL is also indicated for treatment of acute bovine interdigital necrobacillosis (foot rot, pododermatitis) associated with Fusobacterium necrophorum and Bacteroides melaninogenicus.

Flucloxacillin is an isoxazolyl penicillin of the β-lactam group of antibiotics, which exerts a bactericidal effect upon many Gram-positive organisms including β-lactamase-producing staphylococci and streptococci. While no longer used in the United States, Flucloxacillin is supplied under a variety of trade names in other countries, including Floxapen, Flopen, Staphylex. Floxapen is indicated for the treatment of infections due to sensitive Gram-positive organisms, including β-lactamase-producing staphylococci and streptococci. Typical indications including, skin and soft tissue infections; respiratory tract infections; other infections caused by floxapen-sensitive organisms, like example, osteomyelitis, urinary tract infection, septicaemia, endocarditis. Floxapen is also indicated for use as a prophylactic agent during major surgical procedures when appropriate; for example cardiothoracic and orthopaedic surgery. Flucloxacillin, by its action on the synthesis of the bacterial wall, exerts a bactericidal effect on streptococci except those of group D (Enterococcus faecalis) staphylococci. It is not active against methicillin-resistant staphylococci. There is evidence that the risk of flucloxacillin induced liver injury is increased in subjects carrying the HLA-B*5701 allele. Despite this strong association, only 1 in 500-1000 carriers will develop liver injury. Consequently, the positive predictive value of testing the HLA-B*5701 allele for liver injury is very low (0.12%) and routine screening for this allele is not recommended. Flucloxacillin diffuses well into most tissue. Specifically, active concentrations of flucloxacillin have been recovered in bones: 11.6 mg/L (compact bone) and 15.6 mg/L (spongy bone), with a mean serum level of 8.9 mg/L. Flucloxacillin diffuses in only small proportion into the cerebrospinal fluid of subjects whose meninges are not inflamed. It is also excreted in small quantities in mother's milk. In normal subjects approximately 10% of the flucloxacillin administered is metabolised to penicilloic acid. The elimination half-life of flucloxacillin is in the order of 53 minutes.

Thiamphenicol is a broad-spectrum antibiotic, which is active against gram-positive and gram-negative organisms. The drug is marketed in Asia and Latin America for the treatment of various infections, including sexually transmitted diseases. As many phenicols, thiamphenicol inhibits the protein synthesis in bacterias by binding to 23S ribosomal subunit. In Europe and USA the drug is used in a veterinary practice.

Cefalonium is a 1st generation cephalosporin with a broad spectrum of actvity against Gram-positive and Gram-negative bacterias. The drug inhibits the bacterial cell wall synthesis by binding to penicillin binding proteins. Cefalonium is approved for routine dry cow therapy to treat existing sub-clinical infections and to prevent new infections which occur during the dry period.

Apramycin is a broad-spectrum aminocyclitol antibiotic produced by a strain of Streptomyces tenebrarius. It has a bactericidal action against many gram-negative bacteria. Apramycin is a structurally unique antibiotic that contains a bicyclic sugar moiety and a monosubstituted deoxystreptamine. It is not approved for use in humans. Apramycin is registered for use in more than twenty countries in cattle, pigs and chickens. The drug exerts its antibacterial effect by inhibiting protein synthesis at the level of peptidyl translocation. It is mostly used for treating gastrointestinal infections. Apramycin is available in soluble powder and feed premix formulations.

Cefquinome is a 4th generation cephalosporin which is active against a broad spectrum of Gram positive and Gram negative bacteria. As many cephalosporin it acts by binding to bacterial PBP and thus inhibiting the cell wall synthesis. Cefquinome is approved for veterinary use in cattles with respiratory tract infections, skin infections, bacterial mastitis and septicaemia.

Colistin sulfate is a polypeptide antibiotic which penetrates into and disrupts the bacterial cell membrane. It is a cyclic polypeptide antibiotic from Bacillus colistinus. It is composed of Polymyxins E1 and E2 (or Colistins A, B, and C). Colistin was first isolated in Japan in 1949 from a flask of fermenting Bacillus polymyxa var. colistinus and became available for clinical use in 1959. The following local adverse events have been reported with topical corticosteroids, especially under occlusive dressings: burning, itching, irritation, dryness, folliculitis, hypertrichosis, etc. Healthcare providers had largely stopped using colistin in the 1970s because of its toxicity. However, with antibacterial resistance on the rise, colistin is increasingly being used today to treat severe, multidrug-resistant Gram-negative bacterial infections, particularly among intensive care-based patients. The problem with re-introducing an older drug, such as colistin, though, is that techniques for evaluating new drugs have evolved since the 1950s, and therefore, little is known about the dose needed to effectively fight infection while limiting the potential emergence of antimicrobial resistance and reducing potentially toxic side effects. More data are needed to guide optimal use of these older medications. An international team of NIAID-funded researchers is making progress in obtaining better dosing information about colistin and how best to use the antibiotic to treat Gram-negative bacterial infections. Resistance to colistin is rare. The first colistin-resistance gene that is carried in a plasmid and can be transferred between bacterial strains was described in 2016. This plasmid-borne mcr-1 gene has since been isolated in China, Europeand the United States.