Amphotericin B
Encyclopedia
Amphotericin B is a polyene
Polyene antimycotic
Polyene antimycotics, sometimes referred to as polyene antibiotics, are a class of antimicrobial polyene compounds that target fungi. These polyene antimycotics are typically obtained from some species of Streptomyces bacteria. The polyenes bind to ergosterol in the fungal cell membrane and...

 antifungal drug, often used intravenously for systemic fungal infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

s. It was originally extracted from Streptomyces
Streptomyces
Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high guanine and cytosine content...

 nodosus
, a filamentous
Hypha
A hypha is a long, branching filamentous structure of a fungus, and also of unrelated Actinobacteria. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium; yeasts are unicellular fungi that do not grow as hyphae.-Structure:A hypha consists of one or...

 bacterium, in 1955 at the Squibb Institute for Medical Research from cultures of an undescribed streptomycete isolated from the soil collected in the Orinoco River region of Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...

. Its name originates from the chemical's amphoteric properties. Two amphotericins, amphotericin A and amphotericin B are known, but only B is used clinically, because it is significantly more active in vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...

. Amphotericin A is almost identical to amphotericin B (having a double C=C bond between the 27th and 28th carbon), but has little antifungal activity.
Currently, the drug is available as plain amphotericin B, as a cholesteryl sulfate complex (ABCD), as a lipid complex (ABLC), and as a liposomal
Liposome
Liposomes are artificially prepared vesicles made of lipid bilayer. Liposomes can be filled with drugs, and used to deliver drugs for cancer and other diseases. Liposomes are composite structures made of phospholipids and may contain small amounts of other molecules...

 formulation (LAmB). The latter formulations have been developed to improve tolerability for the patient, but may show considerably different pharmacokinetic characteristics compared to plain amphotericin B.

Antifungal

Oral preparations of amphotericin B are used to treat thrush
Oral candidiasis
Oral candidiasis is an infection of yeast fungi of the genus Candida on the mucous membranes of the mouth. It is frequently caused by Candida albicans, or less commonly by Candida glabrata or Candida tropicalis...

; these are virtually nontoxic, in contrast to typical intravenous therapy
Intravenous therapy
Intravenous therapy or IV therapy is the infusion of liquid substances directly into a vein. The word intravenous simply means "within a vein". Therapies administered intravenously are often called specialty pharmaceuticals...

 (IV) doses.

One of the main intravenous uses is in treating various systemic fungal infections (e.g. in critically ill, comorbidly infected or immunocompromised patients), including cryptococcal meningitis.

Amphotericin B is also commonly used in tissue culture
Tissue culture
Tissue culture is the growth of tissues or cells separate from the organism. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, such as broth or agar...

 to prevent fungi from contaminating cell cultures. It is usually sold in a concentrated solution, either on its own or in combination with the antibiotics penicillin
Penicillin
Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....

 and streptomycin
Streptomycin
Streptomycin is an antibiotic drug, the first of a class of drugs called aminoglycosides to be discovered, and was the first antibiotic remedy for tuberculosis. It is derived from the actinobacterium Streptomyces griseus. Streptomycin is a bactericidal antibiotic. Streptomycin cannot be given...

.

Antiprotozoan

Another IV use is as a drug of last resort in otherwise untreatable parasitic protozoan infections
Protozoan infection
Protozoan infections are parasitic diseases organisms formerly classified in the Kingdom Protozoa. They include organisms classified in Amoebozoa, Excavata, and Chromalveolata....

 such as visceral leishmaniasis
Visceral leishmaniasis
Visceral leishmaniasis , also known as kala-azar, black fever, and Dumdum fever, is the most severe form of leishmaniasis. Leishmaniasis is a disease caused by protozoan parasites of the Leishmania genus. This disease is the second-largest parasitic killer in the world , responsible for an...

 and primary amoebic meningoencephalitis
Primary amoebic meningoencephalitis
Primary amoebic meningoencephalitis is a disease of the central nervous system caused by infection from Naegleria fowleri.-Presentation:...

.

Mechanism of action

As with other polyene antifungals, amphotericin B associates with ergosterol
Ergosterol
Ergosterol is a sterol found in fungi, and named for ergot, a common name for the members of the fungal genus Claviceps from which ergosterol was first isolated. Ergosterol does not occur in plant or animal cells...

, the main component of fungal cell membranes, forming a transmembrane channel that leads to monovalent ion (K+
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

, Na+
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

, H+
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 and Cl
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...

) leakage, which is the primary effect leading to fungal cell death. Recently, however, researchers found evidence that pore formation is not necessarily linked to cell death (i.e. Angewandte Chemie Int. Ed. Engl. 2004). The actual mechanism of action may be more complex and multifaceted.

Mechanism of toxicity

Mammalian and fungal membranes both contain sterols, a primary membrane target for amphotericin B. Because mammalian and fungal membranes are similar in structure and composition, this is one mechanism by which amphotericin B causes cellular toxicity. Amphotericin B molecules can form pores in the host membrane as well as the fungal membrane. This impairment in membrane barrier function can have lethal effects.
Amphotericin administration is limited by infusion-related toxicity. This is thought to result from innate immune production of proinflammatory cytokines.

Side effects

Amphotericin B is well-known for its severe and potentially lethal side effects. Very often, a serious acute reaction after the infusion (1 to 3 hours later) is noted, consisting of high fever, shaking chills, hypotension
Hypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...

, anorexia
Anorexia (symptom)
Anorexia is the decreased sensation of appetite...

, nausea
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...

, vomiting
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...

, headache
Headache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...

, dyspnea
Dyspnea
Dyspnea , shortness of breath , or air hunger, is the subjective symptom of breathlessness.It is a normal symptom of heavy exertion but becomes pathological if it occurs in unexpected situations...

 and tachypnea
Tachypnea
Tachypnea means rapid breathing. Any rate between 12-20 breaths per minute is normal. Tachypnea is a respiration rate greater than 20 breaths per minute. - Distinction from other breathing terms :...

, drowsiness, and generalized weakness. This reaction sometimes subsides with later applications of the drug, and may in part be due to histamine liberation. An increase in prostaglandin
Prostaglandin
A prostaglandin is any member of a group of lipid compounds that are derived enzymatically from fatty acids and have important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring....

 synthesis may also play a role. This nearly universal febrile response necessitates a critical (and diagnostically difficult) professional determination as to whether the onset of high fever is a novel symptom of a fast-progressing disease, or merely the induced effect of the drug. To decrease the likelihood and severity of the symptoms, initial doses should be low, and increased slowly. Acetaminophen, pethidine, diphenhydramine and/or hydrocortisone have all been used to treat or prevent the syndrome, but the prophylactic use of these drugs is often limited by the patient's condition.

Intravenously administered amphotericin B has also been associated with multiple organ damage in therapeutic doses. Nephrotoxicity
Nephrotoxicity
Nephrotoxicity is a poisonous effect of some substances, both toxic chemicals and medication, on the kidneys. There are various forms of toxicity. Nephrotoxicity should not be confused with the fact that some medications have a predominantly renal excretion and need their dose adjusted for the...

 (kidney damage) is a frequently reported side effect, and can be severe and/or irreversible. It is much milder when delivered via liposome
Liposome
Liposomes are artificially prepared vesicles made of lipid bilayer. Liposomes can be filled with drugs, and used to deliver drugs for cancer and other diseases. Liposomes are composite structures made of phospholipids and may contain small amounts of other molecules...

s (AmBisome), and this is, therefore, the preferred method (see below). The integrity of the liposome is disrupted when it binds to the fungal cell wall, but is not affected by the mammalian cell membrane, thus less toxicity is seen. The association with liposomes decreases the exposure of the kidneys to amphotericin B, which explains less nephrotoxic effects. Additionally, electrolyte imbalances (e.g. hypokalemia
Hypokalemia
Hypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...

 and hypomagnesemia
Hypomagnesemia
Hypomagnesemia is an electrolyte disturbance in which there is an abnormally low level of magnesium in the blood. Usually a serum level less than 0.7 mmol/L is used as reference. The prefix hypo- means low . The middle 'magnes' refers to magnesium...

) may also result. In the liver, increased liver enzymes and hepatotoxicity
Hepatotoxicity
Hepatotoxicity implies chemical-driven liver damage.The liver plays a central role in transforming and clearing chemicals and is susceptible to the toxicity from these agents. Certain medicinal agents, when taken in overdoses and sometimes even when introduced within therapeutic ranges, may injure...

 (up to and including fulminant liver failure) are common. In the circulatory system, several forms of anemia and other blood dyscrasias (leukopenia
Leukopenia
Leukopenia is a decrease in the number of white blood cells found in the blood, which places individuals at increased risk of infection....

, thrombopenia), serious cardiac arrhythmias (including ventricular fibrillation
Ventricular fibrillation
Ventricular fibrillation is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly. Ventricular fibrillation is a medical emergency and most commonly identified arrythmia in cardiac arrest...

), and even frank cardiac failure have been reported. Skin reactions, including serious forms, are also possible.

Interactions

  • Flucytosine
    Flucytosine
    Flucytosine, or 5-fluorocytosine, a fluorinated pyrimidine analogue, is a synthetic antimycotic drug.It is structurally related to the cytostatic fluorouracil and to floxuridine. It is available in oral and in some countries also in injectable form. A common brand name is Ancobon. Flucytosine was...

    : Toxicity of flucytosine is increased and allows a lower dose of amphotericin B. Amphotericin B may also facilitate entry of flucystosine into the fungal cell by interfering with the permeability of the fungal cell membrane.
  • Diuretics or cisplatin
    Cisplatin
    Cisplatin, cisplatinum, or cis-diamminedichloroplatinum is a chemotherapy drug. It is used to treat various types of cancers, including sarcomas, some carcinomas , lymphomas, and germ cell tumors...

    : Increased renal toxicity and increased risk of hypokalemia
  • Corticosteroid
    Corticosteroid
    Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex. Corticosteroids are involved in a wide range of physiologic systems such as stress response, immune response and regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte...

    s: Increased risk of hypokalemia
  • Cytostatic drugs: Increased risk of kidney damage, hypotension and bronchospasms
  • Other nephrotoxic drugs : Increased risk of serious renal damage, monitor kidney function closely
  • Foscarnet
    Foscarnet
    Foscarnet is the conjugate base of the chemical compound with the formula HO2CPO3H2.-Uses:This phosphonic acid derivative is an antiviral medication used to treat herpes viruses, including drug resistant cytomegalovirus and herpes simplex viruses types 1 and 2...

    , ganciclovir
    Ganciclovir
    Ganciclovir INN is an antiviral medication used to treat or prevent cytomegalovirus infections.Ganciclovir sodium is marketed under the trade names Cytovene and Cymevene . Ganciclovir for ocular use is marketed under the trade name Vitrasert...

    , tenofovir, adefovir
    Adefovir
    Adefovir dipivoxil, previously called bis-POM PMEA, with trade names Preveon and Hepsera, is an orally-administered nucleotide analog reverse transcriptase inhibitor .-Uses:...

    : Risk of hematological and renal side effects of amphotericin B are increased.
  • Transfusion of leukocytes : Risk of pulmonal (lung) damage occurs. Space the intervals between the application of amphotericin B and the transfusion, and monitor pulmonary function.

Clinical efficacy

Liposomal amphotericin B was effective as empirical therapy or as treatment for confirmed invasive fungal infections in several randomized, double-blind trials (n = 73 − 1095) in adult and pediatric patients.

Liposomal and lipid complex preparations

From studies, it appears that liposomal amphotericin B preparations exhibit fewer side effects, while having similar efficacy. Various preparations have recently been introduced. All of these are more expensive than plain amphotericin B.

AmBisome is a liposomal formulation of amphotericin B for injection
Injection (medicine)
An injection is an infusion method of putting fluid into the body, usually with a hollow needle and a syringe which is pierced through the skin to a sufficient depth for the material to be forced into the body...

, developed by NeXstar Pharmaceuticals (acquired by Gilead Sciences
Gilead Sciences
Gilead Sciences is a biopharmaceutical company that discovers, develops and commercializes therapeutics. For many years since the company was founded, the company concentrated primarily on antiviral drugs to treat patients infected with HIV, hepatitis B or influenza. In 2006, Gilead acquired two...

 in 1999). It is marketed by Gilead in Europe and licensed to Astellas Pharma
Astellas Pharma
is a Japanese pharmaceutical company, formed on 1 April 2005 from the merger of and .Astellas' franchise areas are urology, immunology , dermatology, cardiology, and infectious disease...

 (formerly Fujisawa Pharmaceuticals) for marketing in the USA, and Sumitomo Pharmaceuticals in Japan.

Fungisome is a liposomal complex of amphotericin B, and being the latest and cheapest addition to the lipid formulations of amphotericin B, it has many advantages. It is marketed by Lifecare Innovations of India. Other formulations include Amphotec (Intermune) and Abelcet (Sigma-Tau Pharmaceuticals). Abelcet is not a liposomal preparation but rather a lipid complex preparation. Ampholip is a lipid complex formulation of amphotericin B marketed by Bharat Serums & Vaccines Ltd, Mumbai, India.

Oral preparations

A major barrier to the use of amphotericin in resource-poor settings is that it must be given intravenously (except for topical applications). An oral preparation exists, but is not yet commercially available.

External links

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