POLY-MXB

Indications

• Pneumonia caused by multidrug-resistant gram-negative bacteria
• Septicemia caused by gram-negative bacteria
• Urinary tract infections caused by resistant organisms
• Skin infections caused by resistant gram-negative bacteria

Dosage

Children: Refer to BNF for Children for appropriate dosing in paediatric patients.

Adults: Refer to local guidelines or BNF for specific dosing recommendations based on the type and severity of infection.

Mechanism of action

Polymyxin exerts its antibacterial effect by disrupting the integrity of the bacterial cell membrane. It binds to the lipopolysaccharides and phospholipids in the outer membrane of gram-negative bacteria, leading to increased permeability and eventual cell lysis.

Pharmacodynamics

Polymyxin has a bactericidal effect against susceptible gram-negative organisms. Its action is concentration-dependent, with higher concentrations leading to a more significant bactericidal effect. Resistance can occur through modifications in the bacterial cell membrane components that reduce drug binding.

Pharmacokinetics

Polymyxin is poorly absorbed from the gastrointestinal tract and is typically administered parenterally (intravenously or intramuscularly) for systemic infections. It has a volume of distribution that suggests extensive tissue penetration but is primarily eliminated by the kidneys. Half-life varies based on renal function, and dose adjustments may be necessary in patients with renal impairment.

Adverse effects

• Nephrotoxicity
• Neurotoxicity
• Allergic reactions
• Respiratory distress
• Nausea
• Vomiting

Interactions

• Increased nephrotoxicity when used with other nephrotoxic agents such as aminoglycosides or cisplatin
• Potential for respiratory depression with neuromuscular blocking agents

Precautions

• Use with caution in patients with renal impairment
• Monitor renal function during therapy
• Consider the risk of neurotoxicity, especially with prolonged use

Pregnancy

Polymyxin is classified as category C. Its safety during pregnancy has not been established, thus it should only be used if clearly needed.

Breast-feeding

It is not known if polymyxin is excreted in human milk. Caution is advised when administering to nursing mothers.

Storage

Store at room temperature, away from light and moisture. Protect from freezing.

Formulations

• Polymyxin B sulfate injection
• Polymyxin E (colistin) inhalation solution
• Topical formulations

Dosage

Children: Refer to specific drug guidelines as dosing in units varies based on the drug and its clinical application.

Adults: Refer to specific drug guidelines as dosing in units varies based on the drug and its clinical application.

Mechanism of action

The mechanism of action of drugs measured in units depends on the specific substance. For example, insulin (measured in units) facilitates glucose uptake in cells by binding to insulin receptors, activating a signaling pathway that enhances glucose transporter translocation to the cell membrane. This results in a decrease in blood glucose levels. Similarly, other drugs measured in units may exert their effects through receptor binding, enzyme catalysis, or other biochemical interactions.

Pharmacodynamics

Pharmacodynamics describes the effects of the drug on the body and includes the relationship between drug concentration and effect. For substances measured in units, the pharmacodynamic response may be variable and is often dependent on the individual’s sensitivity to the drug, receptor availability, and other pharmacological factors. For instance, the effect of 1 unit of insulin can vary significantly among individuals based on their insulin sensitivity and metabolic state.

Pharmacokinetics

Pharmacokinetics refers to the absorption, distribution, metabolism, and excretion of drugs. For substances measured in units, the pharmacokinetic profile can differ widely. For instance, insulin is rapidly absorbed when administered subcutaneously, distributed throughout the body, metabolized by the liver and kidneys, and its effects can be observed within minutes. Other drugs may have different absorption rates, half-lives, and routes of elimination.

Pregnancy

Consult a healthcare professional. The safety of this drug during pregnancy has not been established.

Breast-feeding

Consult a healthcare professional. The safety of this drug during breastfeeding has not been established.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.