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Mode of action

The lipid carrier involved in transporting the cell wall building block across the membrane is a C55 isoprenyl phosphate. The lipid acquires an additional phosphate group in the transport process and must be dephosphorylated in order to regenerate the native compound for another round of transfer. Ramoplanin as cyclic peptide antibiotics binds to the C55 lipid carrier. Ramoplanin prevents it from participating in transglycosylation thus disrupting the lipid carrier cycle.

Antimicrobial activity

Ramoplanin displays activity against aerobic and anaerobic Grampositive bacteria by preventing cell wall peptidoglycan formation through binding to a key intermediate moiety, lipid II, and thereby disrupting bacterial cell wall synthesis. The primary use of ramoplanin is in the treatment of Clostridium difficile infections.

Mechanism of action

The mechanism of action of ramoplanin involves sequestration of peptidoglycan biosynthesis lipid intermediates, thus physically occluding these substrates from proper utilization by the latestage peptidoglycan biosynthesis enzymes MurG and the transglycosylases (TGases). Ramoplanin is structurally related to two cell wall-active lipodepsipeptide antibiotics, janiemycin and enduracidin, and is functionally related to members of the lantibiotic class of antimicrobial peptides (mersacidin, actagardine, nisin, and epidermin) and glycopeptide antibiotics. As a consequence of its unique mechanism of action, cross-resistance with existing glycopeptides and beta-lactam antibiotics has not been observed.

Pharmacokinetics

Ramoplanin is not absorbed from the intestinal tract. When ramoplanin (200 and 400 mg) was administered orally to two groups of healthy volunteers over a period of 10 days, no ramoplanin could be detected in plasma and urine. With the 200-mg dose, concentrations in stools varied between 467 and 1043 mg/g, and with the 400-mg dose, concentrations were between 765 and 2032 mg/g. Results from an in vitro gut model and hamster model revealed that ramoplanin may be more effective than vancomycin at killing spores and preventing spore recrudescence.

Toxicology

When administered orally in a double-blind randomized placebocontrolled study, no adverse reactions were observed in patients receiving two daily doses of ramoplanin (100 or 400 mg) in comparison with the placebo. Single and repeated topical application in ten healthy human volunteers revealed very low irritation rates and no sensitization after 21 days.