Polyether antibiotics include lasalocid, maduramicin, monensin, narasin, salinomycin, and semduramicin. They are used exclusively in veterinary medicine as antibacterials and to prevent coccidiosis. These ionophores bind and transport metal ions across cell membranes, disrupting ion gradients in bacteria and protozoa and ultimately exhausting their energy, leading to cell death. They were discovered through fermentation of various Streptomyces and Actinomadura bacteria between 1951-1988 and are most effective against gram-positive bacteria and coccidia.

1. Antibiotic Groups
Polyether Antibiotics (Ionophores)

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.