Amphotericin B and the kidneys: why kidney function is monitored

Amphotericin B is an antifungal medicine reserved for serious infections. The patient leaflet for a UK liposomal product describes it as an antifungal antibiotic given as a drip into a vein in hospital. It is used for fungal infections of deep organs, for suspected fungal infection in people with a raised temperature and neutropenia (a low number of infection-fighting white blood cells, which can be a side effect of cancer treatment), and for visceral leishmaniasis, a disease caused by a parasite.

Several formulations exist. The prescribing information stresses that different amphotericin products (conventional sodium deoxycholate, liposomal and lipid complex) are not equivalent in how they behave in the body and in dosing, and must not be used interchangeably without accounting for those differences. That difference matters for the kidneys.

The kidneys filter the blood and are exposed to high concentrations of many drugs. The prescribing information states that nephrotoxicity occurs to some degree in most patients who receive conventional amphotericin B intravenously. The liposomal formulation is designed to reduce that harm. In a double-blind study of 687 patients described in the same document, the incidence of nephrotoxicity, measured as a rise in serum creatinine to more than twice baseline, was approximately half that seen with conventional amphotericin B.

The British National Formulary lists renal impairment, renal tubular acidosis and nephrocalcinosis among the side effects of intravenous amphotericin B, and notes that liposomal amphotericin B may be less nephrotoxic than conventional, non-liposomal amphotericin B.

Kidney injury from amphotericin B is most often found by blood tests before the person feels any different. The patient leaflet lists abnormal kidney or liver results in blood or urine tests among common side effects, and kidney failure and kidney problems among side effects of unknown frequency. Low blood potassium, a very common effect, may cause tiredness, confusion and muscle weakness or cramps, and low magnesium and calcium can do the same. High blood potassium is also listed.

Because treatment is given in hospital, the team normally notices a change quickly. Tell the nurse or doctor if you feel more tired than expected, notice you are passing much less urine, develop swelling, or have muscle cramps or weakness during treatment.

According to the patient leaflet, blood is tested for creatinine (a chemical that reflects kidney function) and electrolyte levels, particularly potassium and magnesium, before and during treatment, because both can be abnormal if there are kidney problems. This is particularly important if there is previous kidney damage or other medicines that can harm the kidney are being taken.

The prescribing information says that laboratory evaluation of serum electrolytes, particularly potassium and magnesium, as well as kidney, liver and blood-cell function, should be performed at least once weekly. The BNF gives the same minimum frequency. If clinically significant reduction in kidney function or other worsening occurs, the document says consideration should be given to dose reduction, treatment interruption or discontinuation.

The patient leaflet and prescribing information identify several situations where the kidney is at greater risk: pre-existing kidney disease or previous kidney failure, and use of other medicines that may cause kidney damage. The leaflet names immunosuppressants such as ciclosporin and tacrolimus, and says certain cancer medicines can cause kidney damage, wheezing or trouble breathing and low blood pressure when taken with amphotericin B. If you take any of these, regular blood samples will be taken to check your kidneys.

The prescribing information lists ciclosporin, aminoglycosides, polymyxins, tacrolimus and pentamidine as nephrotoxic agents that may enhance the potential for drug-induced renal toxicity, and recommends regular monitoring of renal function in anyone receiving them together. It also says that people with pre-existing kidney impairment have received liposomal amphotericin B at starting doses of 1 to 3 mg/kg/day in clinical trials without needing a dose adjustment, which shows that kidney disease is not an automatic bar to treatment, but needs close monitoring.

The treating team balances the infection against the kidney effect. Options described in the prescribing information include reducing the dose, pausing treatment or stopping it. Fluids, review of other kidney-toxic drugs and repeat testing are usual parts of the response, and the NHS describes how acute kidney injury is generally managed: stopping or changing any medicine that could be causing damage, and giving fluids. Many people recover kidney function, but those with severe fungal infection are often unwell for other reasons, so follow-up kidney tests after discharge are sensible.

Amphotericin B is a hospital-only treatment, started and supervised by microbiology, infectious diseases or haematology teams. The same monitoring applies whether treatment is NHS or private. If you have questions about the choice of formulation or about kidney tests, ask the team treating you.