Pharmacology · Antibacterial Agents

Glycopeptides and Lipopeptides

Vancomycin, second-generation glycopeptides, and daptomycin

Vancomycin binds the D-Ala-D-Ala terminus of peptidoglycan precursors, blocking both transglycosylation and transpeptidation — it remains active against MRSA because its mechanism is entirely independent of penicillin-binding proteins.
AUC-guided TDM has replaced trough-only monitoring for vancomycin — the target AUC/MIC of 400–600 mg·h/L achieves efficacy while avoiding the excess nephrotoxicity caused by high-trough-targeting strategies.
Red man syndrome is a rate-dependent histamine release reaction, not IgE-mediated allergy — it is prevented by slowing the infusion and pretreating with diphenhydramine; it is not a contraindication to vancomycin.
Daptomycin is inactivated by pulmonary surfactant — never use it for pneumonia regardless of in vitro susceptibility; use vancomycin or linezolid for MRSA pulmonary infections.
The see-saw effect: organisms with elevated vancomycin MICs (VISA) typically also have elevated daptomycin MICs — always test daptomycin susceptibility before using it as salvage after vancomycin failure.

Abbreviations: MRSA = methicillin-resistant Staphylococcus aureus · MSSA = methicillin-susceptible S. aureus · VRE = vancomycin-resistant Enterococcus · VISA = vancomycin-intermediate S. aureus · VRSA = vancomycin-resistant S. aureus · TDM = therapeutic drug monitoring · AUC = area under the concentration-time curve · MIC = minimum inhibitory concentration · AKI = acute kidney injury · CPK = creatine phosphokinase · ABSSSI = acute bacterial skin and skin structure infection · OPAT = outpatient parenteral antibiotic therapy

Vancomycin

Mechanism, Spectrum, and Pharmacokinetics

Vancomycin

Mechanism

Binds D-Ala-D-Ala terminus of lipid II (peptidoglycan precursor) — blocks transglycosylation and transpeptidation
Large molecule (1,450 Da) — cannot penetrate gram-negative outer membrane; gram-positive only
Unaffected by PBP mutations → active vs. MRSA
Bactericidal; time-dependent killing

Spectrum

MRSA, MSSA, coagulase-negative staphylococci, streptococci, S. pneumoniae, E. faecalis
Oral vancomycin: local GI action only — C. difficile colitis (no systemic absorption)

Pharmacokinetics and TDM

IV only for systemic infections; ~50% protein bound; renal elimination — dose-adjust in renal impairment
AUC-guided TDM (current standard): target AUC/MIC 400–600 mg·h/L for MRSA; Bayesian software + 2 timed samples preferred over trough-only monitoring
MIC ≥2 mcg/mL — consider alternative agents; efficacy unreliable

Adverse Effects and Resistance

Key Toxicities and VISA/VRSA

Nephrotoxicity

Proximal tubular injury; exposure-dependent
Vancomycin + piperacillin-tazobactam → significantly higher AKI risk than vancomycin + cefepime
Generally reversible; monitor creatinine

Red Man Syndrome

Rate-dependent histamine release — NOT IgE-mediated allergy
Flushing, erythema, pruritus (face, neck, upper torso) — slow infusion ≥60 min + diphenhydramine prevents; not a contraindication to vancomycin

Resistance

VISA: cell wall thickening → more D-Ala-D-Ala decoy targets; arises after prolonged vancomycin exposure
VRSA: vanA gene acquired from VRE via conjugation → D-Ala-D-Ala replaced by D-Ala-D-Lac → eliminates binding; rare; requires linezolid or daptomycin

Second-Generation Glycopeptides

Agent	Half-Life / Dosing	Approved For	Key Feature	Caution
Teicoplanin	70–100 hr / once-daily	Gram-positive infections (not approved in US)	IM or IV; less red man syndrome than vancomycin	TDM required; susceptible to vanA resistance
Dalbavancin	~14–15 days / 1–2 doses total	ABSSSI (MRSA and susceptible organisms)	No TDM required; ultra-long half-life enables OPAT with single or two-dose regimen	Dose-adjust if CrCl <30 mL/min
Oritavancin	~245 hr / single IV dose	ABSSSI	Triple mechanism (D-Ala-D-Ala binding + membrane disruption + transpeptidation inhibition); partial activity vs. vanA	Interferes with coagulation assays (PT, aPTT, anti-Xa) for up to 120 hours after dose
Telavancin	~8 hr / once-daily IV	Hospital-acquired/ventilator-associated bacterial pneumonia; complicated skin infections	D-Ala-D-Ala binding + membrane depolarization (dual mechanism)	Black box: nephrotoxicity; teratogenic (avoid in pregnancy — fetal harm in animal studies)

Daptomycin

Mechanism, Spectrum, and Pharmacokinetics

Daptomycin

Mechanism

Ca²⁺-dependent insertion into bacterial cell membrane → depolarization
Collapses transmembrane potential → arrests DNA, RNA, and protein synthesis simultaneously
Bactericidal; concentration-dependent killing; no cross-resistance with cell wall or ribosomal agents

Spectrum

MRSA, MSSA, VRE, VISA, VRSA — gram-positive only
Key indications: MRSA bacteremia and right-sided endocarditis; VRE bacteremia
No gram-negative activity; inactivated by pulmonary surfactant — never for pneumonia

Pharmacokinetics

IV once daily; ~90% protein bound; low volume of distribution; renal elimination — dose-adjust if CrCl <30 mL/min
Higher doses (8–10 mg/kg/day) used for bacteremia and endocarditis; lower doses (6 mg/kg/day) for skin infections

Adverse Effects and Resistance

Myopathy and the See-Saw Effect

Skeletal Muscle Toxicity

Myopathy and CPK elevation; rarely rhabdomyolysis
Monitor CPK weekly — stop if >5× ULN with symptoms or >10× ULN asymptomatic
Suspend statins during daptomycin therapy (additive myopathy risk)
Eosinophilic pneumonia: rare paradoxical pulmonary toxicity — presents as worsening respiratory status; stop drug immediately

See-Saw Effect (Resistance)

VISA cell wall thickening reduces daptomycin access to the membrane — vancomycin MIC ↑ parallels daptomycin MIC ↑
Always confirm daptomycin susceptibility before using as salvage after vancomycin failure — cross-resistance is common

Critical Rule: Daptomycin and Pneumonia — Surfactant Inactivation

Pulmonary surfactant completely inactivates daptomycin by binding the drug before it can reach bacterial membranes. In vitro susceptibility results are irrelevant for pulmonary infections — a susceptible MIC in the laboratory does not predict clinical activity in the lung. Never use daptomycin for pneumonia regardless of the organism or susceptibility report. For MRSA pneumonia, use vancomycin (with AUC-guided monitoring) or linezolid (ZEPHYR trial data support linezolid superiority for nosocomial MRSA pneumonia).

Red man syndrome is frequently misidentified as penicillin or vancomycin allergy. It is a rate-dependent, IgE-independent histamine release reaction that has nothing to do with immune sensitization. Slowing the infusion to at least 60–90 minutes and premedication with diphenhydramine prevents it in most patients. A history of red man syndrome is not a contraindication to vancomycin and should not prompt selection of an alternative agent.

Suggested References

Author / Source	Title	Publication
Katzung BG, ed.	Basic and Clinical Pharmacology, 15th ed. — Chapter 43: Beta-Lactam Antibiotics and Other Cell Wall- and Membrane-Active Agents	McGraw-Hill, 2021
Brunton LL, Knollmann BC, eds.	Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. — Chapter 50: Penicillins, Cephalosporins, and Other Beta-Lactam Antibiotics	McGraw-Hill, 2023
Breukink E, de Kruijff B	Lipid II as a target for antibiotics	Nat Rev Drug Discov. 2006;5(4):321–332
Fowler VG Jr, Boucher HW, Corey GR, et al.	Daptomycin versus standard therapy for bacteremia and endocarditis caused by Staphylococcus aureus	N Engl J Med. 2006;355(7):653–665
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Navalkele B, Pogue JM, Karino S, et al.	Risk of acute kidney injury in patients on concomitant vancomycin and piperacillin-tazobactam compared to those on vancomycin and cefepime	Clin Infect Dis. 2017;64(2):116–123
Sivagnanam S, Deleu D	Red man syndrome	Crit Care. 2003;7(2):119–120
Hidayat LK, Hsu DI, Quist R, et al.	High-dose vancomycin therapy for methicillin-resistant Staphylococcus aureus infections: efficacy and toxicity	Arch Intern Med. 2006;166(19):2138–2144
Howden BP, Davies JK, Johnson PDR, et al.	Reduced vancomycin susceptibility in Staphylococcus aureus, including vancomycin-intermediate and heterogeneous vancomycin-intermediate strains: resistance mechanisms, laboratory detection, and clinical implications	Clin Microbiol Rev. 2010;23(1):99–139
Zhanel GG, Calic D, Schweizer F, et al.	New lipoglycopeptides: a comparative review of dalbavancin, oritavancin and telavancin	Drugs. 2010;70(7):859–886
Boucher HW, Wilcox M, Talbot GH, et al.	Once-weekly dalbavancin versus daily conventional therapy for skin infection	N Engl J Med. 2014;370(23):2169–2179
Belley A, McKay GA, Arhin FF, et al.	Oritavancin disrupts membrane integrity of Staphylococcus aureus and vancomycin-resistant enterococci to effect rapid bacterial killing	Antimicrob Agents Chemother. 2010;54(12):5369–5371
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Silverman JA, Mortin LI, Vanpraagh AD, et al.	Inhibition of daptomycin by pulmonary surfactant: in vitro modeling and clinical impact	J Infect Dis. 2005;191(12):2149–2152
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