| Absorption: |
| The polyene macrolide antibiotics are poorly absorbed from the GI tract, although amphotericin B has reached reasonable blood levels in some experimental animals. Amphotericin B is usually administered IV (occasionally intrathecally or intraocularly) or topically. Nystatin and piramycin are mostly applied topically. Nystatin is given PO to treat intestinal candidiasis. Absorption is minimal from sites of local application. |
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| Distribution: |
| Amphotericin B becomes widely distributed in the body after IV infusion. It appears to become associated with cholesterol-containing membranes in many different tissues from which it is slowly released into the circulation. Penetration into the CSF, saliva, aqueous humor, vitreous humor, and hemodialysis solutions is generally poor. Amphotericin B becomes highly bound to plasma lipoproteins (~95%). |
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| Biotransformation and Excretion: |
| About 5% of a total daily dose is excreted unchanged in the urine. Over a 2-wk period, ~20% of the drug may be recovered in the urine. The hepatobiliary system accounts for 20-30% of the excretion process. The fate of the remainder of amphotericin B is unknown. |
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| Pharmacokinetics: |
| Amphotericin B has a biphasic elimination pattern. The initial phase lasts 24 hr, during which levels fall rapidly (70% for plasma and 50% for urine). The second elimination phase has a 15-day half-life, during which plasma concentrations decline very slowly. Amphotericin B is usually infused IV, every 48-72 hr, until the total cumulative dosage has been reached. |
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