Antibiotic use

About antibiotics


The First antibiotic, Penicillin, was discovered in 1928 by Alexander Fleming. It took another two decades before it was first used in human medicine.

Use of antimicrobials

Antibiotics are being used in the treatment of infectious diseases in humans and animals.

There are several ways in which they are being used:

  • Curative: the use of an antibiotic on an animal that shows signs of a bacterial infection.
  • Metaphylactic: the treatment of group members of an animal that shows signs of a bacterial infection where the group members are at risk of becoming diseased as well.
  • Prophylactic: preventive administration of antibiotics to prevent animals becoming infected without clinical signs of infection, the structural returning treatment of a group of animals.

It has been described by law (Belgian Regulation on Veterinary Practice, chapter 3) that reaching a diagnosis, setting a therapy and prescribing medicine is reserved to veterinarians. He/she has received the appropriate education and has the knowledge to do these things in the most optimal way.

What do antibiotics do

Antibiotics are substances (natural or synthetic) that slow down the growth of bacteria or kill the bacteria. Different antibiotics work through several mechanisms of action or through interference with bacterial metabolism, which is explained in the figure below:

Antibiotic classes




(Benzylpenicillin, Amoxicillin, Ampicillin, Fenoxymethylpenicillin, Cloxacillin, Oxacillin, Nafcillin)



Small spectrum: Benzylpenicillin, Fenoxymethylpenicillin, Cloxacillin, Oxacillin and Nafcillin
Broad spectrum: Aminopenicillins : Amoxicillin, Ampicillin


Small spectrum: GRAM + coccen en staven, zowel aeroob als anaeroob en o.a. ook Bordetella spp. Actinobacillus pleuropneumoniae, Pasteurella multocida, Mannheimia haemolytica
Broad spectrum: GRAM + en GRAM – (minder goede werking tegen GRAM + dan small spectrum)

Mechanism of action

Penicillins are bactericide.

Oral biological availibility

Benzylpenicillin: bad (not stable in contact with acidity of the stomach)
Fenoxymethyl penicillin: good
Amoxicillin: good
less then amoxicillin

Degree of tissue penetration 

Moderate, not intercellular

Elimination path

Through the kidneys (tubular).


Synergetic: Aminosids, Cefalosporins (or combinations)
Antagonistic: Bacteriostatic antibiotics


  • Little toxic (even when far above therapeutic dosing)
  • Hypersensitivity possible (humans and animals)
  • Cannot be used with rabbit, hamster, chinchilla, Guinea pig
  • Not oral in ruminants (dysbacteriosis) and other herbivores
  • Horses are very sensitive to procaine (in some preparations)
  • Incidentally procainepenicillines give cause for abortion in sows
  • Incorrect (too warm) storage conditions give risk to toxicity phenomena in piglets
  • Placenta barrier can be passed to a greater or lesser extent
  • It’s deemed to be safe during gestation
  • Excretion trough the milk takes place (possibly diarrhoea, neonate allergic reaction)

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