Lecture 36 Polymyxins, Bacitracin, Mupirocin, Fusidic Acid

Question 1

What is bacitracin (MOA)?

Answer 1

polypeptide produced by Bacillus subtilis, 3 subgroups A, B, and C, with A being major component of products available

MOA: inhibits growth of bacterial cell wall by inhibiting transfer of polysaccharides, peptidoglycans and lipopolysaccharides to growing cell wall, interferes with sterol synthesis in humans and is too toxic for systemic use

often formulated with polymyxin B +/- neomycin

Question 2

Spectrum of activity of bacitracin

Answer 2

Gram+: Staphylococci, streptococci, corynebacterium, clostridia

Question 3

What are AEs of bacitracin?

Answer 3

ell tolerated topically, minor skin irritation, rarely contact dermatitis

anaphylaxis may occur rarely with open lesions in intraoperative setting or packing for rhinoplasty

may be cross-sensitivity with polymyxin B allergy

Question 4

What is polymyxin B (MOA)?

Answer 4

isolated from Bacillus polymyxa

MOA: are cationic branched cyclic decapeptides, destroy bacterial membranes with detergent-like action

used for prevention and tx of minor skin infections, often in combo with bacitracin +/- neomycin

Question 5

Spectrum of activity of polymyxin B?

Answer 5

Gram -: bactericidal against many, retained activity against MDR bacilli, like P. aeruginosa, A. baumannii and CRE

activity decreased in presence of divalent cations, resistance rarely develops

Question 6

What are AEs of polymyxin B?

Answer 6

binds to cell membranes with high affinity therefore little systemic absorption, few rxn when applied to open wounds, contact sensitization possible

Question 7

What is colistin (AEs as well)?

Answer 7

is a polymyxin used sometimes due to multidrug resistant organisms ⇒ drug of last resort used IV

AE: dose related nephrotoxicity (30-60% usually reversible) and neurotoxicity

Question 8

What is mupirocin (MOA)?

Answer 8

unique structure, short fatty acid side chain linked to monic acid by ester linkage

MOA: inhibits bacterial isoleucyl tRNA synthetase, inhibits elongation of protein chains

Question 9

Spectrum of activity of mupirocin?

Answer 9

Gram +: S. aureus (MRSA), S. epidermidis, S. pyogenes, S. pneumoniae, S. agalactiae

*long term use can lead to resistance with staph

Question 10

What are AEs of mupirocin?

Answer 10

well tolerated, low affinity for human isoleucyl tRNA synthetase

propylene glycol base may irritate mucous membranes

minimal contact dermatitis, prolonged use may lead to overgrowth of fungi

Question 11

What is fusidic acid (MOA)?

Answer 11

isolated from Fusidium coccineum

carboxylic acid belonging to group of tetracycline terpines

MOA: inhibits bacterial protein synthesis by interfering with elongation factor G

Question 12

Spectrum of activity of fusidic acid?

Answer 12

Gram +: S. aureus, streptococci, Corynebacterium, Clostridia