The types of antibiotics used in dogs vary based on several factors. Certain types of antibiotics are more suitable than others in treating certain types of infections. The primary purpose of antibiotics is to fight bacteria, they are therefore used in treating as well as preventing infections. They work either by killing the bacteria – bactericidaleffect or by stopping its growth – bacteriostatic effect. According to a study published on the Journal of Small Animal Practice, Β-lactamase-resistant combo (amoxicillin/clavulanate) is the most prescribed antibiotic, followed by cephalosporins (cephalexin), enrofloxacin, amoxicillin, and doxycycline. The most important things when it comes to antibiotics would be: using the right type, using the right dose and using it long enough.
The penicillin group of antibiotics work by killing susceptible bacteria (bactericidal effect) by inhibiting the bacterial cell wall biosynthesis (inhibit peptidoglycan synthesis), thus, the bacterial wall becomes compromised, osmotic pressure is uncompensated causing, eventually, cell death.
Natural penicillins are a narrow spectrum type of antibiotics, killing gram-positive bacteria only. They are lactamase sensitive - lactamase destroys it. Lactamase is an enzyme produced by some species of bacteria.
Penicillin G targets susceptible bacteria such as gram-positive anaerobes and aerobes, most beta-hemolytic streptococci, beta-lactamase-negative staphylococci, Actinomyces spp, Corynebacterium spp, and most Clostridium species.
It's indicated for otitis externa (ear infections), bladder infections, superficial skin infections, bacterial pneumonia caused by susceptible bacteria, tooth abscess. There is also penicillin V and penicillin O.
Aminopenicillins are relatively wide spectrum, they work in killing gram-positive and gram-negative bacteria. Ampicillin/Amoxicillin is used for gram-positive bacteria, Streptococcus pneumoniae, Streptococcus pyogenes, some isolates of Staphylococcus aureus ), and some Enterococcus. Gram-negative bacteria include E. coli, Klebsiella, and Haemophilus – not covered with natural penicillins.
Ampicillin/amoxicillin is used for infections caused by Staphylococcus aureus, Streptococcus spp, E. coli, and Proteus mirabilis. Mostly respiratory tract infections like tonsillitis, genitourinary tract infections (cystitis), bacterial gastroenteritis, bacterial dermatitis and soft tissue infections (lacerations, small wounds, and abscesses).
Methicillin is very rarely used because of occurring interstitial nephritis (inflammation of kidneys) as a side effect This drug worked well on gram-positive bacteria such as Staphylococcus aureus, Streptococcus pyogenes, and Streptococcus pneumonia, but is no longer effective due to resistance caused by a gene mutation in bacteria.
Amoxicillin-Clavulanate is the most commonly prescribed antibiotic. This combination of two drugs works well on a wide range of bacteria. This combination has a similar effect to Penicillin, but with a wider spectrum of bacterial activity; Clavulanate works as an inhibitor of beta-lactamase enzyme produced by bacteria, to which Amoxicillin is not resistant.
Susceptible bacteria to amoxicillin include penicillin-sensitive gram-positive microorganisms: streptococci, Clostridia spp. Among gram-negative bacteria, amoxicillin works well on non-lactamase E. coli, some strains of Salmonella and Pasteurella multocida. Clavulanate expands this specter with beta-lactamase producing E.coli, Klebsiella, Proteus spp. and Staphylococcus spp. Indications: periodontal infections, skin and soft tissue infections, urinary tract infections.
Cephalosporins are bactericidal (killing the bacteria). Cephalosporins have the same mechanism of action as the other β-lactam antibiotics such as Penicillins, but are less susceptible to β-lactamases. Cephalosporins disrupt the cell wall by inhibiting the synthesis of peptidoglycan, therefore making the wall unstable.
The first generation type works well for gram-positive bacteria. Antibiotics included in this group are cephapirin, cefazolin, cephalexin, cephradine, cephaloridine and cefadroxil. Susceptible bacteria include many Staphylococci, Streptococci, Moraxella catarrhalis, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Shigella. Cephalexin is most potent against Staphylococcus pseudintermedius, the main cause of superficial bacterial pyoderma.
The second generation type works well on gram-positive microorganisms, and expanded to gram-negative ones, Antibiotics included in this group are cefuroxime, cefamandole, cefoxitin, cefotiam and cefaclor.
The third generation types works on some gram-positive organisms, but not as well as first and second generation. These do not work well on staphylococcal, most gram-negative bacteria are covered. Third generation includes: ceftiofur, cefovecin, cefotaxime, ceftriaxone, cefsulodin and cefepime (4th generation).
Susceptible organisms include E.coli, Klebsiella and Proteus, Pseudomonas spp. and Citrobacter spp. Cefpodoxime and cefovecin are used against Staphylococcus pseudintermedius, the main cause of superficial bacterial pyoderma.
Cefazolin is used for surgical prophylaxis while other first gen cephalosporins are mainly used for skin infections. Other than that, all cephalosporins are used to treat infections of soft tissue and bone. They are used to treat arthritis, prostatitis, and osteomyelitis. There is emerging resistance against cephalosporins, so before using it, it is advised to test for antibiotic sensitivity.
These antibiotics are bactericidal (killing the bacteria) Fluoroquinolones are direct inhibitors of bacterial DNA synthesis. They are binding topoisomerase and gyrase enzymes (necessary for DNA replications) and complex made of DNA-enzymes-antibiotics in stopping the replication process until the damage is irreversible. Antibiotics in this group include: ciprofloxacin, enrofloxacin, marbofloxacin, orbifloxacin and difloxacin.
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Susceptible microorganisms include a wide range of gram-negative organisms and very few gram-positive aerobes. On that list are E.coli, Enterobacter, Proteus, Klebsiella, Salmonella and Pseudomonas aeruginosa (particularly ciprofloxacin). Also, there is modest activity against Brucella spp, Chlamydia spp, and Mycoplasma. Obligate anaerobes are resistant, but with the new generations of these drugs, we have very effective anaerobic spectrum.
These types of antibiotics are used to treat deep infections and intracellular pathogens. They are used for infections of respiratory, urinary, and intestinal systems as well as skin infections, and to treat prostatitis, osteomyelitis, and arthritis.
These antibiotics are also bacteriostatic (they stop bacterial growth). Mode of action of tetracyclines is protein synthesis inhibition; tetracycline molecules bind the ribosomal sub-unit and inhibit the association of aminoacyl-tRNA. Aminoacyl-tRNA delivers amino acid to the ribosome to be incorporated in the newly forming protein chain.
Antibiotics in this group include: doxycycline, tetracycline and oxytetracycline. Tetracyclines have wide broad-spectrum, which includes both aerobic and anaerobic gram-negative and gram-positive bacteria, Rickettsiae, Mycoplasmas, Chlamydia, protozoa (amebae) and Wolbachia.
These antibiotics are used to treat Lyme disease, Rocky Mountain spotted fever, Chlamydia, ehrlichiosis (especially doxycycline), leptospirosis, anaplasmosis, actinobacillosis, nocardiosis (especially minocycline), Wolbachia, haemobartonellosis, gastroenteritis, urinary tract infections.
These antibiotics are classified as bacteriostatic (they stop bacterial growth). Mechanism of action of macrolides is protein synthesis inhibition; they bind reversibly to bacterial ribosome subunit, thereby preventing peptide chain grows as well as inhibiting ribosomal translation.
Macrolide antibiotics include clindamycin, erythromycin, lincomycin, azithromycin and lincomycin. Macrolides work well against most aerobic and anaerobic gram-positive bacteria. They are active against Mycobacterium, atypical mycobacteria, Mycoplasma, Campylobacter, Chlamydia and Rickettsia spp.
Erythromycin is active primarily against gram-positive bacteria such as Staphylococcus and Streptococcus spp, as well as against Mycoplasma, and Campylobacter spp.
Macrolides work may help dogs suffering from Enteritis (Campylobacter), pyoderma, chronic diarrhea, respiratory tract infections (pneumonia, tracheitis, bronchitis), urinary tract infections, arthritis and dental problems.
These antibiotics are bactericidal (killing the bacteria). The mode of action of aminoglycosides is protein synthesis inhibition. Once inside the bacterial cell, aminoglycosides irreversibly bind to the ribosomal sub-unit, causing inaccurate translation, and therefore misreading in the genetic code.
Antibiotics in this class include, amikacin, gentamycin, tobramycin, streptomycin, neomycin and kanamycin.The broad spectrum of these antibiotics includes E.coli, Salmonella, Klebsiella, Enterobacter, Proteus, Pseudomonas aeruginosa (gentamicin, tobramycin, amikacin) and Acinetobacter spp. They are also effective against Pasteurella spp, Leptospira spp, Brucella spp and Mycobacterium tuberculosis (especially streptomycin).
Oxygen is necessary for their action, so caution is advised when it comes to facultative anaerobes or when treating cases in the low-oxygen environment.
These antibiotics are commonly prescribed forbacteriemia, septicemia, bone and joint infections, respiratory tract infections, urinary tract infections, skin and soft tissue infections, uterine infections, topical solution for ear and eye.
Other Types of Antibiotics Used in Dogs
Susceptible bacteria: many gram-positive and gram-negative bacteria including anaerobes (Rickettsia, Chlamydia spp, Bacteroides fragillis)
This type of antibiotic is used against Salmonellosis and Bacteroides sepsis are the most specific indications, and typically for skin and wounds infections, otitis media and interna. As an ointment, it is used as a treatment for conjunctivitis.
Metronidazole is only active against obligatory anaerobes and some protozoa. Susceptible bacteria include: Bacteroides spp, Clostridium spp, and Eubacterium spp. Indications: amebiasis, trichomoniasis, giardiasis, anaerobic bacterial infections.
About the Author
DVM Ivana Vukasinovic is a veterinarian in Belgrade, capital city of Serbia.
She received her B.S from University of Belgrade in 2012, and her master’s degree from Veterinary University, Belgrade.
Before eventually becoming director of Vetanima Doo, company that sells animal food, medicine and supplements, she has worked in many different fields of sales.
After finishing college, she started working as sales person in the biggest Serbian bookshop chain, and being passionate about books, she had reached the position of publisher.
After leaving this field, she started working as a veterinary commercialist, and then landing a job as veterinarian at veterinary pharmacy, in the same company in which she is now acting as director.
When she is not working, she is either glued to some fantasy book or cooking for friends. She currently resides in Belgrade with her cat Mile.