2. Members
The polyether ionophore class of antibiotics includes:
1. Lasalocid (Avatec)
2. Maduramicin (Cygro)
3. Monensin
4. Narasin (Monteban)
5. Salinomycin
6. Semduramicin.
These drugs are used exclusively in veterinary medicine for
their antibacterial and anticoccidial activities.
3. Description
Ionophore structures involve an alkyl-rich, lipid-soluble
exterior and a cage like interior that is capable of binding and
shielding monovalent metal ions (e.g., sodium, potassium)
and divalent metal ions (e.g., magnesium, calcium)
4. History
1951
The first ionophore to be discovered was lasalocid, a
fermentation product of Streptomyces lasaliensis.
It is a divalent polyether ionophore.
1967
The discovery of monensin, a fermentation product of
Streptomyces cinnamonensis.
It is a monovalent polyether ionophore.
5. Cont. …
1972
The discoveries of salinomycin, a fermentation product of
Streptomyces albus.
It is a monovalent polyether ionophore.
1975
The discoveries of narasin (salinomycin methyl analoge), a
fermentation product of Streptomyces aureofaciens.
It is a monovalent polyether ionophore.
6. Cont. …
1983
The discovery of maduramicin, a fermentation product of
Actinomadura yumaense.
It is a monovalent polyether ionophore.
1988
The discover of semduramicin, a fermentation product of
Actinomadura roseorufa.
It is a monovalent polyether ionophore.
7. Mechanism of Action
Polyether ionophores have a different mode of action from
therapeutic antibiotics.
Ionophores are highly lipophilic and able to transport cations
across cell membranes of susceptible bacteria.
8. Cont. …
1. They exchange intracellular potassium for extracellular
protons, and extracellular sodium for intracellular protons,
disrupts ion gradients.
2. Because the potassium gradient is greater than the sodium
gradient, the net effect of these exchanges is the
accumulation of protons inside the bacterium.
3. The cellular response to this homeostatic disturbance is the
activation of ATP-dependent processes, which in turn,
exhausts cellular energy sources and leads to cell death.
9. Cont. …
The anticoccidial activity of ionophores is thought to alter
membrane integrity and internal osmolality of extracellular
sporozoites and merozoites.
Because coccidia have no osmoregulatory organelles,
perturbances of internal osmotic conditions lead to cell death.
10. Spectrum
They are most effective against Gram-positive bacteria
– Because the peptidoglycan layer is porous, allowing them to pass
through to reach the cytoplasmic membrane, where they rapidly
dissolve into the membrane.
11. Resistance
Ionophore resistance appears to be mediated by extracellular
polysaccharides (glycocalyx) that exclude ionophores from the
cell membrane.
12. Indications
The ionophores are also approved for use as coccidiostats in
poultry, cattle, sheep, goats, and rabbits.