Daptomycin

Daptomycin, from Streptomyces roseosporus, requires physiological calcium to oligomerise and insert its lipid tail into phosphatidylglycerol-rich regions of the bacterial membrane. The resulting aggregates distort membrane curvature, mislocalise the cell division and cell wall synthesis machinery, and collapse the membrane potential. Killing is rapid and concentration-dependent, which is why it is dosed once daily at high peaks. Pulmonary surfactant binds and inactivates the molecule, so daptomycin is clinically useless in pneumonia — a failure demonstrated in its own phase 3 programme rather than inferred. Resistance emerges through mprF and related mutations that alter membrane charge, and it is more likely after prior vancomycin exposure.

Targets: Bacterial cytoplasmic membrane, Phosphatidylglycerol, Membrane potential, Cell division machinery

• · Dose figure here is per kilogram: 4 mg/kg once daily, so about 280-350 mg for a 75 kg adult. Course is typically 7-14 days.
• · 6 mg/kg daily is the approved dose. Courses run 2-6 weeks depending on source control and complications.
• · 8-10 mg/kg is widely used off-label for persistent MRSA bacteraemia, left-sided endocarditis, VRE and bone or prosthetic joint infection. Efficacy data are observational; CPK monitoring becomes mandatory at these doses.

Work out your exact syringe units →

• commonCreatine phosphokinase elevation— The signature toxicity. Usually asymptomatic, but rises steeply above 8 mg/kg and can progress to myopathy or rhabdomyolysis if not caught.
• commonMuscle pain and weakness— New myalgia on daptomycin means checking CPK the same day, not waiting.
• commonGastrointestinal upset— Nausea, diarrhoea and constipation.
• uncommonFalsely prolonged prothrombin time / INR— A laboratory artefact with certain recombinant thromboplastin reagents. Draw the sample at trough to minimise it.
• rareEosinophilic pneumonia— Typically appears after 2-4 weeks of therapy with fever, dyspnoea and new infiltrates. It is a drug reaction, not treatment failure — stopping daptomycin is the treatment.
• rarePeripheral neuropathy— Reported in early studies at high doses; generally reversible.

• Pneumonia of any kind — daptomycin is inactivated by pulmonary surfactant and failed its phase 3 pneumonia trial. Using it here is a genuine treatment error.
• Known hypersensitivity to daptomycin.
• Pre-existing myopathy or unexplained CPK elevation without close monitoring.

• cautionstatins — Additive myopathy risk. Many clinicians hold the statin for the duration of daptomycin therapy; if it is continued, CPK must be watched closely.
• redundantvancomycin — Overlapping MRSA coverage. Combination is reserved for persistent bacteraemia salvage, sometimes with a beta-lactam to enhance daptomycin binding.
• synergyceftaroline — Beta-lactams increase daptomycin binding to the bacterial membrane (the 'seesaw effect'); this combination is used in refractory MRSA bacteraemia.
• cautiontobramycin — Mutual increase in plasma concentrations reported; clinical significance is uncertain but worth watching.

• · CPK at baseline and at least weekly during therapy, and more often at doses above 8 mg/kg or with concurrent statins.
• · Renal function, since dosing interval changes below CrCl 30 mL/min.
• · New cough, fever or dyspnoea after two weeks of therapy should trigger a chest film and eosinophil count to rule out eosinophilic pneumonia.
• · Follow-up blood cultures in bacteraemia to confirm clearance and detect emerging resistance.

Prescription-only injectable medicine, approved in the US, EU and most other markets; generic since 2016.

• Fowler et al. 2006, daptomycin versus standard therapy for S. aureus bacteraemia and endocarditis (trial)
• Cubicin (daptomycin for injection) US prescribing information (label)
• Reviews of high-dose daptomycin for enterococcal and refractory gram-positive infection (review)

A cyclic lipopeptide that inserts its lipid tail into the Gram-positive membrane in a calcium-dependent way, oligomerises, and causes rapid depolarisation without lysing the cell. Killing is concentration-dependent and very fast, which is why it is dosed once daily at a high peak rather than by continuous exposure.

The defining error is using it for pneumonia. Pulmonary surfactant binds and inactivates daptomycin, so it fails in the lung specifically - not because the organism is resistant but because the drug never works there. The second is forgetting statin interaction: both cause myopathy, and the combination compounds it, so statins are usually held during a course.

• Gram-positive cytoplasmic membrane, calcium-dependent insertion — Requires physiological calcium; activity is lost in calcium-free media

  Membrane depolarisation and rapid concentration-dependent killing

Among the fastest bactericidal agents available for Gram-positive infection; blood cultures typically clear faster than on vancomycin.

Preferred over vancomycin in MRSA bacteraemia with high vancomycin MICs or in vancomycin failure. Useless in pneumonia, where vancomycin, linezolid or ceftaroline are the options.

• ?Whether routinely holding statins during therapy is necessary, or only in patients with other myopathy risk factors, is not firmly established.