Narrow-spectrum antimicrobials
Please note that the table below is not a complete list.
| Drug name |
Spectrum (good susceptibility) |
Penicillin (V or G)
|
Primarily Gram-positive aerobic organisms: such as b-haemolytic streptococci and Bacillus anthracis. Also anaerobic organisms such as Actinomyces spp., Fusobacterium spp. and Bacteroides |
Meticillin and cloxacillin
|
Antistaphylococcal penicillins (hence meticillin-resistant Staphylococcus aureus, MRSA) |
Aminoglycosides (gentamicin, neomycin, amikacin)
|
Primarily Gram-negative aerobic organisms. Note: amikacin is considered to be a ‘top-shelf’ antimicrobial |
|
Metronidazole
|
Gram-positive and Gram-negative anaerobic organisms. Note: they also have antiprotozoal activity, so not really narrow-spectrum but one of the few antimicrobials where resistance development is relatively rare |
Moderate-spectrum antimicrobials
Please note that the table below is not a complete list. * These antimicrobials are not authorized veterinary medicinal products and can only be used in accordance with the prescribing cascade.
| Drug name |
Spectrum (good susceptibility) |
| Macrolides or macrolide-related (tylosin, tilmicosin, tulathromycin, clarithromycin*, azithromycin*) |
Primarily Gram-positive organisms:
- Aerobes: Listeria spp., Corynebacterium spp., Bacillus spp. and Rhodococcus equi
- Anaerobes: Actinomyces spp., Bacteroides spp. and some Fusobacterium spp.
Note: the newer generation agents such as azithromycin and clarithromycin have increased Gram-negative and Gram-positive activity (e.g. against mycobacteria)
|
| Lincosamides (lincomycin, clindamycin) |
Primarily Gram-positive aerobic and anaerobic organisms.
Note: clindamycin is particularly effective against anaerobic organisms |
Broad-spectrum antimicrobials
Please note that the table below is not a complete list.
| Drug name |
Spectrum (good susceptibility) |
| Extended spectrum penicillins (amoxicillin ± clavulanate, ampicillin) |
A good range of Gram-positive and Gram-negative aerobic and anaerobic organisms, including: all organisms susceptible to penicillin G and also Borrelia spp., Pasteurella spp., Haemophilus spp., Moraxella spp. and Leptospira spp. |
| Cephalosporins (cefalexin) |
A good range of Gram-positive and Gram-negative aerobic and anaerobic organisms, similar to the extended spectrum penicillins |
Tetracyclines (tetracycline, doxycycline) |
A good range of Gram-positive and Gram-negative organisms. They also have activity against Rickettsia, Chlamydophila, Ehrlichia and Mycoplasma |
| Potentiated sulphonamides |
A good range of Gram-positive and Gram-negative organisms. In vivo activity against anaerobic organisms is limited. Activity against some protozoal organisms is also limited |
| Fluoroquinolones (marbofloxacin, enrofloxacin) |
Many Gram-negative aerobic organisms are highly susceptible. Gram-positive aerobic organisms also susceptible, although minimum inhibitory concentration (MIC) values tend to be higher compared with Gram-negative aerobic organisms. Variable susceptibility of anaerobic organisms and Pseudomonas |