AmBisome: Its Uses, Side Effects, and How It Works

AmBisome is a liposomal formulation of amphotericin B, one of the oldest and broadest-spectrum antifungal drugs available. It wraps the active drug inside tiny fat-based spheres called liposomes, which lets doctors deliver higher doses with substantially less kidney damage and fewer infusion reactions than the conventional version of the drug. It is used to treat serious fungal infections, visceral leishmaniasis, and cryptococcal meningitis, and it remains a frontline option in settings where other antifungals fail or are not suitable.

What Makes AmBisome Different From Regular Amphotericin B

Amphotericin B has been a workhorse antifungal since the 1950s, but its conventional form, amphotericin B deoxycholate, earned the nickname “ampho-terrible” among clinicians because of harsh side effects, especially kidney toxicity. AmBisome was developed to solve that problem. It packages amphotericin B inside small, single-layered liposomes made of specialized phospholipids and cholesterol. These liposomes use high-transition-temperature phospholipids, meaning the fat membrane stays rigid and intact at body temperature, keeping the drug locked inside while it circulates through the bloodstream.¹ The result is a stable complex between the drug and the lipid bilayer that maintains low toxicity and stays intact in the blood for extended periods.²

The specific lipid recipe matters. AmBisome’s membrane is composed of hydrogenated soy phosphatidylcholine, distearoylphosphatidylglycerol, and cholesterol in a defined ratio, with amphotericin B intercalated into this bilayer.³ This is not just a cosmetic difference. The liposome can reach fungal cell walls intact, where it then disrupts and releases its drug cargo directly at the site of infection.¹ Because the drug rides inside liposomes rather than floating free in the blood, it is far less likely to damage healthy human cells along the way.

How It Kills Fungi

The active ingredient, amphotericin B, works by punching holes in fungal cell membranes. Fungal cells rely on a molecule called ergosterol to keep their membranes structurally sound, much the way human cells use cholesterol. Amphotericin B binds to ergosterol and forms pores in the membrane, causing the cell to leak its contents and die.⁴ This mechanism is why the drug has such a broad spectrum of activity: virtually all pathogenic fungi depend on ergosterol, so the drug works against yeasts like Candida, molds like Aspergillus, and even rarer organisms like Fusarium and the agents of mucormycosis.

The liposomal packaging does not change this fundamental mechanism. What it changes is how the drug reaches the fungus. The liposome circulates in the blood, preferentially accumulates in infected tissues, and delivers its payload when it encounters fungal cell walls. The net effect is that the antifungal punch stays the same while the collateral damage to human kidneys and other organs drops substantially.⁵

What Happens in the Body After Infusion

One of AmBisome’s distinguishing features is the way it behaves in the bloodstream compared with conventional amphotericin B. When healthy volunteers received both formulations in a head-to-head pharmacokinetic study, peak blood levels after AmBisome were roughly 16 times higher than after conventional amphotericin B. Yet the drug largely stayed within the bloodstream and nearby compartments rather than distributing widely across the body the way the conventional form does.⁶ Total clearance rates were similar between the two drugs, but the amount of unchanged amphotericin B showing up in urine and feces was about ten times lower with AmBisome, suggesting the liposomes sequester the drug and slowly release it within tissues rather than letting it wash through the kidneys.

Animal studies fill in the tissue distribution picture further. In long-term rat studies, AmBisome accumulated heavily in the liver and spleen, with concentrations there far exceeding those in the blood. Kidney and lung levels were closer to plasma levels, and elimination from tissues took one to four weeks.⁷ This pattern of tissue retention helps explain why AmBisome can be effective with less frequent dosing for some conditions.

Approved and Established Uses

AmBisome has accumulated decades of clinical evidence across a surprisingly wide range of infections. Its uses span life-threatening fungal disease, parasitic infection, and preventive treatment in patients with weakened immune systems.

Invasive Fungal Infections and Febrile Neutropenia

For patients whose immune systems are severely compromised, such as those undergoing chemotherapy or bone marrow transplants, invasive fungal infections are a leading cause of death. AmBisome is a first-line option for empirical antifungal therapy when these patients develop persistent fever that does not respond to antibiotics.⁸ In a landmark randomized trial of over 680 neutropenic patients, AmBisome matched conventional amphotericin B in overall treatment success (about half of patients in each group). Where AmBisome pulled ahead was safety: kidney toxicity occurred in about 19% of AmBisome-treated patients versus 34% with the conventional drug, and fewer patients had breakthrough fungal infections on AmBisome.⁹

Beyond empirical therapy, AmBisome is used to treat confirmed infections with Candida species, Aspergillus, and other invasive molds. It also sees use in mucormycosis, a devastating infection often seen in immunocompromised patients or those with uncontrolled diabetes. In a prospective study of 40 mucormycosis patients treated with high-dose AmBisome (10 mg/kg) for one month, the overall response rate was 45% and the 12-week survival rate was 62%.¹⁰ Mucormycosis is notoriously difficult to treat, and even those numbers represent meaningful progress when surgery is not feasible or sufficient on its own.

Visceral Leishmaniasis

Visceral leishmaniasis, also called kala-azar, is a parasitic disease spread by sandflies that can be fatal without treatment. AmBisome is the treatment of choice in many settings, in part because a single intravenous dose can achieve cure rates comparable to multi-week courses of older drugs. In a large Indian trial, a single AmBisome dose cured over 95% of patients at six months, matching the conventional multi-dose amphotericin B regimen.¹¹ A systematic review and meta-analysis of comparative studies confirmed that liposomal amphotericin B was not inferior to the deoxycholate formulation in India, and that a single dose as low as 3.75 mg/kg could achieve cure rates above 89%.¹²

Results from other regions have been strong as well. In Bangladesh, a single-dose AmBisome protocol achieved a 97% final cure rate in primary health-care settings, demonstrating that the approach can work outside of specialized hospitals.¹³ The simplicity of a one-shot treatment is a huge advantage in remote or under-resourced areas where patients may struggle to complete a longer drug course.

Cryptococcal Meningitis

HIV-associated cryptococcal meningitis remains one of the biggest killers of people living with advanced HIV, particularly in sub-Saharan Africa. The AMBITION-cm trial, a large randomized study, tested whether a single high dose of AmBisome could replace more complex multi-drug regimens. Ten-week mortality was about 25% in the AmBisome group compared with about 29% in the control group, meeting the criteria for non-inferiority and, in adjusted analysis, showing superiority. Serious adverse events were also less common in the AmBisome arm, with half of patients experiencing grade 3 or 4 events versus about 62% in the control group.¹⁴ This finding has reshaped treatment guidelines and made AmBisome the backbone of recommended regimens for this disease in low-resource settings.

Side Effects and Toxicity

AmBisome is substantially safer than conventional amphotericin B, but it is not side-effect-free. Understanding where the risks remain helps patients and clinicians prepare.

Kidney Damage

Kidney toxicity is the side effect most closely associated with all forms of amphotericin B. Meta-analyses and systematic reviews put the rate of nephrotoxicity with AmBisome somewhere between 9% and 25%, compared with 12% to 50% for conventional amphotericin B. Severe kidney toxicity is rarer still with AmBisome, estimated at about 2.4%, compared with roughly 11.5% for the conventional drug and 7.2% for another lipid formulation called amphotericin B lipid complex. Very few patients on AmBisome have to stop treatment because of kidney problems, with discontinuation rates around 0.3% versus nearly 5% for conventional amphotericin B.¹⁵ Even so, clinicians still monitor kidney function closely during treatment, because the risk climbs at higher doses and in patients who are already receiving other drugs that stress the kidneys.¹⁶

Electrolyte Disturbances

Amphotericin B, even in its liposomal form, can cause potassium levels to drop. The drug increases the permeability of cells lining the kidney tubules, causing potassium to leak into the urine. In one study tracking adult patients on AmBisome, median potassium levels fell from 3.9 to 3.3 mmol/L over just seven days of treatment. While the liposomal formulation blunts this effect relative to conventional amphotericin B, it remains clinically relevant and often requires supplementation.¹⁷ Magnesium can drop as well, through a related tubular mechanism, so both electrolytes are typically checked regularly during therapy.

Infusion Reactions and Hypersensitivity

Some patients develop fever, chills, or rigors during or shortly after the infusion. These reactions are less frequent with AmBisome than with other lipid formulations or conventional amphotericin B. In a head-to-head study, chills and rigors occurred in fewer than a quarter of AmBisome patients on day one compared with about 80% of patients on amphotericin B lipid complex.¹⁸

Rarer but more alarming are true hypersensitivity-like reactions, including chest tightness, flushing, and difficulty breathing, sometimes occurring even in patients who have never received the drug before. These reactions appear to involve complement activation triggered by the liposomes themselves rather than a classical allergic mechanism. The immune system can recognize the lipid particles as foreign and mount an inflammatory response on first exposure.¹⁹ Slowing the infusion rate and premedicating with antihistamines or hydrocortisone can help prevent or manage these episodes.

Liver Effects and Neonates

In very low birth weight infants treated for systemic Candida infections, AmBisome still produced significantly less kidney and liver toxicity than conventional amphotericin B. Kidney toxicity occurred in about 21% of the AmBisome group versus 55% with the conventional drug, and liver toxicity in 25% versus 65%.²⁰ These are vulnerable patients with immature organs, so the safety advantage of the liposomal formulation is especially meaningful in this population.

How It Compares to Other Lipid Formulations

AmBisome is not the only lipid-based amphotericin B product. Others include amphotericin B lipid complex (Abelcet) and amphotericin B colloidal dispersion (Amphocil). All three are less nephrotoxic than conventional amphotericin B, but they are not interchangeable. They differ in their physical structure, the way they circulate in the blood, how they are cleared, and their side-effect profiles.²¹ AmBisome is the only true liposomal product of the three, consisting of uniform small vesicles, while the others use ribbon-like lipid complexes or disc-shaped particles.

In the clinical trial comparing AmBisome with Abelcet in neutropenic patients, AmBisome had substantially lower rates of kidney toxicity and fewer infusion reactions, with therapeutic outcomes being similar across all groups.¹⁸ This is why, in practice, AmBisome tends to be preferred when the budget allows, though the higher cost pushes some institutions toward other options.

Use in Children

Pediatric patients can receive AmBisome at doses similar to those used in adults. A pharmacokinetic and safety study in immunocompromised children tested doses ranging from 2.5 to 10 mg/kg per day. Drug exposure increased proportionally with dose, and infusion-related side effects occurred in about 11% of infusions overall. Kidney function did decline, with serum creatinine rising from about 0.45 to 0.63 mg/dL across the study population, and the increase was more pronounced at doses of 5 mg/kg and above. At the highest dose of 10 mg/kg, there was a trend toward more potassium drops and vomiting.²² The study concluded that AmBisome is tolerable in children but that kidney monitoring is essential, especially at higher doses.

When Fungi Fight Back

Amphotericin B resistance has historically been rare, partly because the drug targets a fundamental structural component of the fungal membrane rather than a specific enzyme that can be easily mutated. But resistance is not impossible, and a few recent findings have been sobering. In Candida auris, a multidrug-resistant yeast that has become a growing global threat, researchers identified a mutation in a gene called ERG6 that disrupted ergosterol production entirely and caused a more than 32-fold increase in resistance to amphotericin B. Without ergosterol in the membrane, the drug essentially loses its target.²³

A similar story has played out with Candida lusitaniae, where resistant isolates showed altered expression of multiple genes in the ergosterol-making pathway, leading to reduced ergosterol content in their membranes.²⁴ These cases are still uncommon, but they are a reminder that even the most durable antifungals are not invulnerable to evolution. AmBisome’s liposomal packaging does not overcome resistance to the active drug itself; if a fungus no longer has ergosterol in its membrane, no amount of improved delivery will help.

Cost and Access Challenges

For all its clinical advantages, AmBisome has a significant problem: price and availability. The drug is difficult and expensive to manufacture, and most of the global supply comes from a single manufacturer, Gilead Sciences.²⁵ This creates a stark disparity. In wealthy countries, AmBisome is widely available. In low- and middle-income countries, where the burden of fungal infections and leishmaniasis is highest, many hospitals still use conventional amphotericin B deoxycholate, despite its harsher side-effect profile, simply because AmBisome is too expensive or not reliably supplied.

Gilead does offer a no-profit price of $16.25 per vial to 116 countries, but that price is restricted to only two indications (visceral leishmaniasis and cryptococcal meningitis) and comes with complex requirements designed to prevent diversion of the product to other uses. The administrative burden and long delivery times mean the discounted price is not widely used in practice.²⁶ The same source notes that some low-income countries paradoxically pay more per vial than high-income countries because of opaque pricing policies.

Generic competition could change this equation. There are currently no patent barriers preventing generic manufacturers from producing liposomal amphotericin B, and regulatory pathways for doing so have become clearer. But producing a true liposomal product to the required quality standard is technically demanding, and generic manufacturers have naturally prioritized entering more lucrative high-income markets first.²⁷ Expanding production capacity to serve both markets simultaneously remains one of the key obstacles to equitable global access.

Off-Label and Emerging Applications

Beyond its established uses, AmBisome has been tried in some creative ways. It has been used preventively in bone marrow transplant recipients to reduce fungal colonization rates, and it has treated infections caused by uncommon molds like Fusarium and the agents of mucormycosis when other drugs fail or are unavailable.²⁸ In at least one published case, AmBisome was used as a topical preparation, applied directly to a cutaneous Fusarium infection in a critically ill burn patient when the conventional topical form of amphotericin B was unavailable due to drug shortages. The treatment was successful, opening a small window into potential non-intravenous applications.²⁹

The broader trend in AmBisome research has been finding ways to simplify dosing. The single-dose protocols that have proven effective for visceral leishmaniasis and cryptococcal meningitis represent a meaningful shift from multi-week courses. Simpler regimens are easier on patients, reduce the total drug needed per course, and are more practical in settings with limited health infrastructure. Whether similar dosing simplifications can be applied to other fungal infections remains an active area of investigation.