Macrolides and Lincosamides
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These are two structurally distinct groups of antibiotics but they share many properties. Macrolides are macrocyclic lactones and ones used in veterinary medicine are; Erythromycin, tylosin, spiramycin, tilmicosin and tulathromycin.
(Tiamulin and Valnemulin and similiar to macrolides but are actually semi-synthetic derivatives of pleuromutilin antiobiotics.)
Lincosamides are monoglycosides, which have an amino acid like side chain. The ones in use are Lincomycin, clindamycin and pirlimycin.
Mechanism of Action
Both groups of antiobiotics work by inhibiting protein synthesis. They do this by effecting translocation performed on the bacterial ribosome.
Spectrum of Activity
Macrolides
- They are active against gram-positive cocci and work very well against Staphs and Streps
- They are active against the hardier of gram-negatives.
- They are active against anaerobes, some mycoplasmas, chlamydophila and rickettsia.
Lincosamides
- They are active against gram-positive bacteria and mycoplasma.
- They are highly active against anaerobes.
- Clindamycin is the most potent and is effective against Toxoplasma gondii.
Pharmacokinetic Considerations
Both sets of drugs are weakly basic and are very lipid soluble, this means that they are well absorbed from the gasrtointestinal tract in mono-gastric animals. They have a very wide volume of distribution and will become ion-trapped in acidic fluid such as milk and prostatic fluid. They don't enter the CSF as they bind to plasma proteins. They are mainly eliminated via hepatic metabolism.
Spiramycin has long withdrawal periods as it concentrates readily in tissues. Tulathromycin has a very long half-life in pigs. Tilmicosin will have effective levels to be active against Pasteurella species in the lung for up to four days.
Side Effects and Contraindications
Macrolides
- There will be irritation on intramuscular and sub-cutaneous injections.
- There are dose-associated effects on the gastrointestinal tract. In the horse they can seriously upset the normal flora of the gut. In dogs they cause smooth muscle stimulation that can result in vomiting.
- Tylosin, tiamulin and tilmocisin should not be used in horses.
- Tilmicosin can be fatal to man if accidentally injected.
- Tiamulin and Valnemulin if given with ionophore growth promoters can be fatal.
- Valnemulin has severe adverse reactions with Landrace pigs and their crosses.
Lincosamides
- Can cause serious and fatal diarrhoea in man, horses, rabbits and other herbivores.
- They musn't be given intravenously as they can cause neuromuscular blockades and cardio-depression.