Polymyxin b and fosfomycin mechanism of actions and side effects

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polymyxin B AND fosfomycin

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Polymyxin B fosfomycin prescribing information adverse reactions mechanism action

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site:dailymed.nlm.nih.gov fosfomycin tromethamine adverse reactions diarrhea nausea label

Drug	Mechanism of action	Important adverse effects
Polymyxin B	A cationic polypeptide antibiotic that binds to lipopolysaccharide and phospholipids in the outer membrane of susceptible Gram-negative bacteria. It acts like a detergent, disrupting membrane integrity, causing leakage of cell contents and rapid bacterial death.	Nephrotoxicity: acute kidney injury, reduced urine output. Neurotoxicity: paresthesia, dizziness, ataxia, weakness; rarely neuromuscular blockade and respiratory paralysis. With topical use: contact dermatitis or hypersensitivity.
Fosfomycin	Enters bacteria through glycerophosphate/glucose-6-phosphate transport systems and irreversibly inhibits MurA (enolpyruvyl transferase). This blocks an early cytoplasmic step in peptidoglycan cell-wall synthesis, producing bactericidal activity.	Usually mild: diarrhea, nausea, headache, abdominal discomfort, vaginitis. Rarely: hypersensitivity reactions and C. difficile-associated diarrhea. IV fosfomycin, where used, may cause electrolyte disturbances such as hypernatremia and hypokalemia.

High-yield distinction

Polymyxin B damages the bacterial cell membrane.
Fosfomycin inhibits bacterial cell-wall synthesis.

Polymyxins act as membrane-disrupting cationic detergents and are limited by renal and neurologic toxicity. Katzung's Basic and Clinical Pharmacology, 16th ed., “Polymyxins” section. Fosfomycin inhibits enolpyruvyl transferase in peptidoglycan synthesis; common effects are diarrhea, vaginitis, nausea, and headache. Lippincott Illustrated Reviews: Pharmacology, “Fosfomycin” section. The DailyMed fosfomycin label provides formulation-specific adverse-effect information.

Both drugs acn we use in polymyxin b and fosfomycin in liver disease and aki on ckd patient?

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polymyxin B acute kidney injury

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polymyxin B renal impairment hepatic impairment dosing prescribing information

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fosfomycin renal impairment hepatic impairment dosing oral prescribing information

Short answer:

Liver disease: Both can usually be used, with no routine hepatic dose adjustment.
AKI on CKD: Avoid IV polymyxin B if an effective safer antibiotic is available. Fosfomycin is generally the safer of the two for kidneys, but the choice and dose depend on formulation, renal function, infection site, and culture susceptibility.

Drug	Liver disease	AKI on CKD
Polymyxin B	Usually no dose adjustment solely for liver dysfunction, but monitor closely in severe illness.	High-risk / generally avoid if alternatives exist. It can cause or worsen AKI and neurotoxicity. Use only for susceptible multidrug-resistant Gram-negative infection when benefits outweigh risks, ideally with infectious-disease input. Avoid concurrent nephrotoxins such as aminoglycosides, NSAIDs, IV contrast when possible, vancomycin if alternatives exist, and other polymyxins.
Fosfomycin	Usually acceptable. It is not significantly metabolized by the liver.	Usually preferable to polymyxin B for renal safety. Oral fosfomycin is primarily for uncomplicated lower UTI/cystitis, not pyelonephritis, bacteremia, or sepsis. In severe renal impairment, drug elimination is prolonged and urinary concentrations may be less reliable. IV fosfomycin, where used, requires renal dose adjustment, typically when CrCl is ≤50 mL/min, and monitoring for sodium load, hypokalemia, and fluid overload.

Important practical points

Do not routinely combine polymyxin B and fosfomycin just because the patient has renal failure. A combination may sometimes be selected for a documented extensively drug-resistant organism, but only based on culture sensitivity, source of infection, and specialist advice.
For a UTI in AKI on CKD:
- Fosfomycin may be an option only for uncomplicated bladder infection if the organism is susceptible.
- It is not appropriate as sole therapy for fever, flank pain, pyelonephritis, obstruction, prostatitis, or bloodstream infection.
For a systemic MDR Gram-negative infection:
- Polymyxin B might be used as salvage therapy, but it is nephrotoxic. In AKI on CKD, seek safer active alternatives first, guided by culture and sensitivity.
- Monitor creatinine, urine output, potassium, magnesium, neurologic symptoms, and concomitant nephrotoxins daily.
Polymyxin B has historical labeling advising dose reduction in renal impairment, while modern pharmacokinetic guidance often does not routinely reduce the maintenance dose because clearance is largely nonrenal. This does not make it safe in AKI. Dosing must be individualized by the treating team, ideally with antimicrobial-stewardship or infectious-disease support. The Polymyxin B prescribing information stresses careful renal assessment and avoidance of other nephrotoxic/neurotoxic drugs.

For fosfomycin, the current IV product information states that renal dose adjustment is required at creatinine clearance ≤50 mL/min, and hepatic impairment does not affect hepatic metabolism because the drug is not metabolized through the liver, per the IV fosfomycin label. In CKD, oral fosfomycin treatment failure has been reported more often for MDR urinary infections, so culture-directed treatment matters. Brenner and Rector’s The Kidney, “Persons with Renal Failure.”

Antibiotics for CKD Nad Cirrhosis patient, which are safe?

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antibiotic dosing renal impairment cirrhosis guideline ceftriaxone linezolid doxycycline

There is no single antibiotic that is universally “safe” in both CKD and cirrhosis. Choice depends on the infection site, culture result, eGFR/AKI severity, Child-Pugh class, allergy, current drugs, and whether the patient is on dialysis.

Often practical options, depending on the infection

Antibiotic	CKD / AKI	Cirrhosis	Key caution
Ceftriaxone	Usually no renal adjustment up to 2 g/day	Usually no hepatic adjustment	Often useful for pneumonia, sepsis, SBP, or UTI when susceptible. Use extra caution in combined severe renal plus hepatic failure; can cause biliary sludge.
Cefotaxime	Requires renal adjustment	Generally usable	Common option for spontaneous bacterial peritonitis (SBP).
Other cephalosporins such as cefepime, ceftazidime, cephalexin	Usually require renal adjustment	Generally safe in liver disease	Cefepime accumulation in CKD can cause encephalopathy, confusion, or seizures.
Penicillins / beta-lactams such as amoxicillin, ampicillin-sulbactam, piperacillin-tazobactam	Usually require renal adjustment	Often usable	Check sodium load with IV preparations, especially in ascites or fluid overload.
Doxycycline	Usually no renal dose adjustment	Usually usable	Consider alternatives or monitor in severe liver failure or prolonged treatment.
Azithromycin	No usual renal adjustment	Use cautiously in severe liver disease	Risk of cholestatic liver injury and QT prolongation.
Linezolid	No routine renal dose adjustment	Usually usable	Monitor CBC closely, especially for thrombocytopenia, which is common in cirrhosis and may be more likely in renal dysfunction.
Clindamycin	No renal adjustment	Dose interval or monitoring may be needed in severe hepatic dysfunction	High risk of C. difficile diarrhea.
Fosfomycin, oral	Generally kidney-safe, but effectiveness may be less reliable in advanced CKD	Usually usable	Only for susceptible uncomplicated lower UTI/cystitis, not pyelonephritis, urosepsis, or bacteremia.

Antibiotics to avoid if possible in AKI on CKD plus cirrhosis

Aminoglycosides: gentamicin, amikacin, tobramycin
High nephrotoxicity risk. Cirrhosis increases susceptibility to aminoglycoside-associated kidney injury.
Polymyxin B and colistin
Reserve for multidrug-resistant infections when no safer effective drug is available. Can worsen AKI and cause neurotoxicity.
Vancomycin
Can be used if clearly needed, but needs renal dosing and drug-level guided monitoring. Risk rises with other nephrotoxins, especially piperacillin-tazobactam in some settings.
Trimethoprim-sulfamethoxazole
Requires renal adjustment and can cause hyperkalemia, increased creatinine, AKI, cytopenias, and liver injury. Use only with close monitoring if necessary.
Nitrofurantoin
Avoid if eGFR is <30 mL/min/1.73 m² and do not use for pyelonephritis or sepsis.
Fluoroquinolones: ciprofloxacin, levofloxacin
Can be used selectively with renal dose adjustment, but avoid unnecessary use because of CNS effects, QT prolongation, tendon injury, dysglycemia, and C. difficile. Moxifloxacin does not need renal adjustment but should be used cautiously in significant hepatic impairment.

In cirrhosis-specific situations

Suspected SBP: cefotaxime or ceftriaxone are standard common choices, with albumin considered when kidney dysfunction is present.
Acute variceal GI bleeding: ceftriaxone is commonly used for infection prophylaxis. The AASLD guidance summary lists ceftriaxone for patients with cirrhosis and GI bleeding.
Hepatic encephalopathy: rifaximin is used to reduce intestinal ammonia-producing bacteria. It is not appropriate for treating systemic infections.

A useful default: If empiric IV therapy is required in a patient with cirrhosis and AKI on CKD, ceftriaxone is often a relatively kidney-friendly option when it covers the suspected organism and infection source. Its label notes that renal or hepatic dysfunction alone usually does not require adjustment up to 2 g/day, but combined severe dysfunction needs caution, per DailyMed ceftriaxone information.

Do not start an antibiotic solely based on organ disease. Obtain cultures first when feasible, calculate current eGFR or creatinine clearance, assess for dialysis, and narrow treatment as soon as sensitivity results return.

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