21. Macrolides

Question 1

Macrolides. Drugs

Answer 1

• azithromycin
• clarithromycin*
• tylosin
• tylvalosin
• tilmicosin
• tulathromycin
• erythromycin
• spiramycin
• gamithromycin
• tildipirosin

Question 2

Macrolides. Specificity of chemical structure

Answer 2

• macrocyclic lactone ring attached to sugar
• lipophilicity is not bad but is decreased because of sugar, can’t cross BBB
• broad distribution in tissues
• WEAK BASES -> inside of macrophage pH is acidic. Macrolide (lipophilic) goes inside of macrophage and will be polarised (NH3) -> ion trapping. Can’t leave the cells -> very high IC concentration -> long half-life. Tetracyclines and phenicols also have high intracellular concentration but not as good as macrolides

Question 3

Macrolides. Mode and mechanism of action

Answer 3

Bacteriostatic. Inhibition of protein synthesis - 50S

Question 4

Macrolides. Resistance

Answer 4

• not so common
• decreased permeability
• degrading enzymes
• modified binding site (50S) -> cross resistance (phenicols, lincosamides)

Question 5

Macrolides. Antimicrobial spectrum

Answer 5

• gram+ and few gram— (including anaerobic, fastidious)
• Campylobacter (azithromycin, clarithro, erythro)
• Brachyspira hyodysenteriae (TYLVALOSIN !)
• Lawsonia intracellularis (tylosin, tylvalosin)
• Bordetella bronchiseptica
• Mycoplasma, Chlamydophilia - IC
• Borellia
• Rhodococcus equi (azithro, clarithro, erythro)

Question 6

Macrolides. Can they be given to adult horses?

Answer 6

No. But can be given to foals (haven’t developed proper micro flora yet) in case of Rhodococcus equi infection. Erythromycin - 1st choice in this case. But its important to separate mare from foal because mother will eat foal’s feces and die

Question 7

Usage of erythromycin

Answer 7

SAM: campylobacteriosis (from raw meat)
Horses: Rhodococcus equi (foals)

Question 8

Usage of spiramycin

Answer 8

• frequent usage in oral cavity infections in SAM
• rarely in large animals (tissue irritation and long WP)
• macrolide

Question 9

Tylosin

Answer 9

• old drug, frequent resistance
• Lawsonia intracellularis in pigs (proliferation enteropathy)
• pigs + ruminants + poultry: resp tract infections, necrotic enteritis
• SAM: ARD only (antibiotic responsive diarrhoea)

Question 10

Tilmicosin

Answer 10

• TOXIC! Can be given only orally
• cardiotoxicity -> NOT in horses, goats, humans
• only in ruminants, pigs and poultry - cattle SC, pigs PO
• excellent concentration level in the lungs, good against respiratory complex infections (fastidious gram— and Mycoplasma spp)

Question 11

Tylvalosin

Answer 11

• kinda updated tylosin
• pigs, poultry
• B. hyodysenteriae, L. itracellularis
• respiratory complex (Mycoplasma +++, fastidious gram— +)

Question 12

Tulathromycin, gamithromycin

Answer 12

• injectable (disadvantage, also price)
• ruminants, pigs
• excellent distribution
• fastidious organisms +++, mycoplasma +++
• super high concentration in the lungs -> respiratory tract infections! - main indication

Question 13

Tildipirosin

Answer 13

• kinda same astulathromycin, gamithromycin but duration of action is longer
• respiratory tract infections

Question 14

Azithromycin, clarithromycin

Answer 14

• oral application (small animals, human)
• excellent absorption and distribution (lungs, bones, tonsils)
• outstanding against gram+, fastidious gram—, Borellia, Mycoplasmae, Campylobacter, R. equi