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• It is a broad spectrum antifungal agent. It binds to ergosterol in the fungal cell membrane forming large channels through which cellular contents leak leading to cell death. Toxicity results from the binding of ampho B molecules to cholesterol in the host's cell membrane. The renal epithelial cells are particularly susceptible to this adverse effect.
• Ampho B is used (IV) for the treatment of serious systemic infections (aspergellosis, candidiasis) and fungal meningitis (small doses, <1 mg, are given intrathecally 3 times/wk for 10 wks).
• Candida cystitis is treated via bladder irrigation.
• The oral preparation, which is not absorbed, is used (500 mg bid) for  selective bowel decontamination

Available As

Lyophilized powder for injection (50 mg vial).

Dose

• Before initiating IV therapy a test dose (1 mg over 30 min) may be necessary.
• The initial IV dose may be 0.5 mg/kg qday infused over 4 - 6 hrs. The dose may be increased up to a maximum of 1.5 mg/kg IV qday.
• Ampho B may also be used for bladder irrigation (50 mg/1000 mL of sterile water for injection) infused into the bladder via a 3-way foley at a rate of ~42 mL/hr for 5 days.

Pharmacokinetics

The kinetics of ampho B is complicated and not fully elucidated. It appears to be metabolized in the liver and its metabolites excreted in urine (<5% of the dose is excreted unchanged in the urine). However, liver disease does not appear to affect its serum level. It is not absorbed by the GI, and it is not removed by hemodialysis.

Side Effects

• Infusion-related:   dyspnia, tachycardia, fever and chills are common with the 1st few doses. Typically, this reaction starts within the first 2 hrs of infusion and may last for 2 - 4 hrs. This reaction may be mediated by the release of TNF and IL-1 from macrophages. Anaphylaxis is rare. Premedications include acetaminophen (Tylenol) and diphenhydramine (Benadryl).
• Nephrotoxicity (~ 80% of pts): renal tubular damage, renal tubular acidosis, hypokalemia, hypomagnesemia, and possibly increased intrarenal vascular resistance.

References

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