Colistimethate sodium is a surface active agent which penetrates into and disrupts the bacterial cell membrane. It has been shown to have bactericidal activity against Aerobic gram-negative microorganisms e.g. Enterobacter aerogenes, E. coli, Klebsiella pneumoniae and Pseudomonas

Pharmacology

Colistimethate is a surface active agent which penetrates into and disrupts the bacterial cell membrane. Colistimethate is polycationic and has both hydrophobic and lipophilic moieties. It interacts with the bacterial cytoplasmic membrane, changing its permeability. This effect is bactericidal. There is also evidence that polymyxins enter the cell and precipitate cytoplasmic components, primarily ribosomes.

Each vial contains Colistimethate Sodium 1 MIU or 34 mg Colistin.

Each vial contains Colistimethate Sodium 2 MIU or 68 mg Colistin.

Each vial contains Colistimethate Sodium 3 MIU or 102 mg Colistin.

Each vial contains Colistimethate Sodium 4.5 MIU or 150 mg Colistin.

Colistimethate is indicated for the treatment of acute or chronic infections caused by sensitive strains of certain gram-negative bacilli. It is particularly indicated in the infection caused by sensitive strains of Pseudomonas aeruginosa. Colistimethate is not indicated for infections due to Proteus or Neisseria. Colistimethate is very effective in the treatment of infections due to the following gram-negative organisms: Enterobacter aerogenes, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa.

Maintenance dose: 9 MIU/day in 2-3 divided doses. In patients who are critically ill, a loading dose of 9 MIU should be administered.

Renal impairment patients: Dose adjustments in renal impairment patients are necessary. Dose reductions are recommended for patients with creatinine clearance < 50 ml/min. Twice daily dosing is recommended.

• Creatinine clearance <50-30 ml/min: daily dose 5.5-7.5 MIU
• Creatinine clearance <30-10 ml/min: daily dose 4.5-5.5 MIU
• Creatinine clearance <10 ml/min: daily dose 3.5 MIU

Haemodialysis (HD) patients:

• No-HD days: 2.25 MIU/day (2.2-2.3 MIU/day).
• HD days: 3 MIU/day (Should be given after the HD session) Twice daily dosing is recommended.

Pediatric population: The dose should be based on lean body weight.

• Children ≤40 kg: 75,000-150,000 IU/kg/day divided into 3 doses.
• Children >40 kg: >150,000 IU/kg/day has been reported in children with cystic fibrosis.

Hepatic impairment patients: There are no data in patients with hepatic impairment. Caution is advised when administering colistimethate sodium in these patients.

Administration

Direct Intermittent Administration- Slowly inject one-half of the total daily dose over a period of 3 to 5 minutes every 12 hours.

Continuous Infusion- Slowly inject one-half of the total daily dose over 3 to 5 minutes. Add the remaining half of the total daily dose of Colistimethate for injection to one of the following:

• 0.9% NaCl
• 5% dextrose in 0.9% NaCl
• 5% dextrose in water
• 5% dextrose in 0.45% NaCl
• 5% dextrose in 0.225% NaCl
• Lactated Ringer's solution

There are not sufficient data to recommend usage of Colistimethate for injection with other drugs or other than the above listed infusion solutions. Administer the second half of the total daily dose by slow intravenous infusion, starting 1 to 2 hours after the initial dose, over the next 22 to 23 hours. In the presence of impaired renal function, reduce the infusion rate depending on the degree of renal impairment. The choice of intravenous solution and the volume to be employed are dictated by the requirements of fluid and electrolyte management. Any infusion solution containing Colistimethate sodium should be freshly prepared and used for no longer than 24 hours.

Alternative method- As per specialized references for intermittent infusion: Prescribed dose can be diluted in 50-100 ml 0.9% NaCl and administer over 30-60 minutes in IV route.

The use of Colistimethate Sodium Parenteral is contraindicated for patients with a history of sensitivity to the drug or any of its components.

The following adverse reactions have been reported: gastrointestinal upset, tingling of extremities and tongue, slurred speech, dizziness, vertigo and paresthesia, generalized itching, urticaria and rash, fever, increased blood urea nitrogen (BUN), elevated creatinine and decreased creatinine clearance, respiratory distress and apnea, nephrotoxicity and decreased urine output.

Overdose Effects

Overdosage with colistimethate sodium can cause neuromuscular blockade characterized by paresthesia, lethargy, confusion, dizziness, ataxia, nystagmus, disorders of speech and apnea. Respiratory muscle paralysis may lead to apnea, respiratory arrest and death. Overdosage with the drug can also cause acute renal failure, manifested as decreased urine output and increases in serum concentrations of B.U.N and creatinine. As in any case of overdose, Colistimethate Sodium therapy should be discontinued and general supportive measures should be utilized.

Colistimethate should be used with caution in patient with impaired renal function. When actual renal impairment is present, Colistimethate may be used, but the greatest caution should be exercised and the dosage should be reduced in proportion to the extent of the impairment. Colistimethate should be used with caution in neonates, infants and children.

Pregnancy & Lactation

There are no adequate and well-controlled studies about the use of Colistimethate in pregnant women. Since colistimethate is transferred across the placental barrier in humans, it should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. It is not known whether Colistimethate is excreted in human breast milk. Therefore, caution should be exercised when administered to nursing women.