Amiloride, sold under the trade name Midamor among others, is a medication typically used with other medications to treat
high blood pressure
Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...
or
swelling due to
heart failure
Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...
or
cirrhosis of the liver
Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue repai ...
.
Amiloride is classified as a
potassium-sparing diuretic
Potassium-sparing diuretics refers to drugs that cause diuresis without causing potassium loss in the urine. They are typically used as an adjunct in management of hypertension, cirrhosis, and congestive heart failure. The steroidal aldostero ...
. Amiloride is often used together with another diuretic, such as a
thiazide
Thiazide () refers to both a class of sulfur-containing organic molecules and a class of diuretics based on the chemical structure of benzothiadiazine. The thiazide drug class was discovered and developed at Merck and Co. in the 1950s. The first ...
or
loop diuretic
Loop diuretics are diuretics that act on the Na-K-Cl cotransporter along the thick ascending limb of the loop of Henle in the kidney. They are primarily used in medicine to treat hypertension and edema often due to congestive heart failure or c ...
.
[ It is taken ]by mouth
Oral administration is a route of administration where a substance is taken through the mouth. Per os abbreviated to P.O. is sometimes used as a direction for medication to be taken orally. Many medications are taken orally because they are i ...
.[ Onset of action is about two hours and it lasts for about a day.][
Common side effects include ]high blood potassium
Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0mmol/L (3.5 and 5.0mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Occasi ...
, vomiting
Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose.
Vomiting can be the result of ailments like Food-poisoning, foo ...
, loss of appetite, rash, and headache.[ The risk of high blood potassium is greater in those with ]kidney problems
Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...
, diabetes
Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...
, and those who are older.[ Amiloride blocks the epithelial sodium channel (ENaC) in the late distal tubule, connecting tubule, and collecting duct of the ]nephron
The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure ca ...
, which both reduces absorption of sodium ion from the lumen of the nephron and reduces excretion of potassium ion into the lumen.[
Amiloride was developed in 1967. It is on the ]World Health Organization's List of Essential Medicines
The WHO Model List of Essential Medicines (aka Essential Medicines List or EML), published by the World Health Organization (WHO), contains the medications considered to be most effective and safe to meet the most important needs in a health ...
.
Medical uses
Amiloride may be used in combination with a thiazide diuretic for treatment of high blood pressure or (less commonly) in combination with a loop diuretic for treatment of heart failure
Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...
. The potassium-sparing effects of amiloride offset the low blood potassium
Hypokalemia is a low level of potassium (K+) in the blood serum. Mild low potassium does not typically cause symptoms. Symptoms may include feeling tired, leg cramps, weakness, and constipation. Low potassium also increases the risk of an abnor ...
(hypokalemia) that is often induced by thiazides or loop diuretics, which is of particular importance in people for whom maintaining a normal level of potassium is critically important. For example, people that are taking ''Digitalis
''Digitalis'' ( or ) is a genus of about 20 species of herbaceous perennial plants, shrubs, and biennials, commonly called foxgloves.
''Digitalis'' is native to Europe, western Asia, and northwestern Africa. The flowers are tubular in sha ...
'' (i.e. digoxin
Digoxin (better known as Digitalis), sold under the brand name Lanoxin among others, is a medication used to treat various heart conditions. Most frequently it is used for atrial fibrillation, atrial flutter, and heart failure. Digoxin is on ...
) are at higher risk for changes in heart rhythm if their potassium levels get too high. The 2017 clinical practice guidelines of the American College of Cardiology
The American College of Cardiology (ACC), based in Washington, D.C., is a nonprofit medical association established in 1949. It bestows credentials upon cardiovascular specialists who meet its qualifications. Education is a core component of the ...
/American Heart Association
The American Heart Association (AHA) is a nonprofit organization in the United States that funds cardiovascular medical research, educates consumers on healthy living and fosters appropriate cardiac care in an effort to reduce disability and death ...
Task Force on Clinical Practice Guidelines list amiloride as a "secondary" oral antihypertensive, with minimal efficacy. For people with resistant hypertension, already taking a thiazide diuretic, an angiotensin converting enzyme inhibitor
Angiotensin-converting-enzyme inhibitors (ACE inhibitors) are a class of medication used primarily for the treatment of high blood pressure and heart failure. They work by causing relaxation of blood vessels as well as a decrease in blood vol ...
(ACE-i) or an angiotensin II receptor blocker
Angiotensin II receptor blockers (ARBs), formally angiotensin II receptor type 1 (AT1) antagonists, also known as angiotensin receptor blockers, angiotensin II receptor antagonists, or AT1 receptor antagonists, are a group of pharmaceuticals tha ...
(ARB), and a calcium channel blocker
Calcium channel blockers (CCB), calcium channel antagonists or calcium antagonists are a group of medications that disrupt the movement of calcium () through calcium channels. Calcium channel blockers are used as antihypertensive drugs, i.e., as ...
, the addition of amiloride (or spironolactone
Spironolactone, sold under the brand name Aldactone among others, is a medication that is primarily used to treat fluid build-up due to heart failure, liver scarring, or kidney disease. It is also used in the treatment of high blood pressure ...
) was better at reducing blood pressure than adding a beta-blocker (bisoprolol
Bisoprolol, sold under the brand name Zebeta among others, is a beta blocker medication used for heart diseases. This includes tachyarrhythmias, high blood pressure, chest pain from not enough blood flow to the heart, and heart failure. It is ...
) or an alpha-1 blocker
Alpha-1 blockers (also called alpha-adrenergic blocking agents or alpha-1 antagonists) constitute a variety of drugs that block the effect of catecholamines on alpha-1-adrenergic receptors. They are mainly used to treat benign prostatic hyperpla ...
(doxazosin
Doxazosin, sold under the brand names Cardura among others, is a medication used to treat symptoms of benign prostatic hyperplasia (enlarged prostate) and hypertension (high blood pressure). For high blood pressure, it is a less preferred option. ...
). When combined with hydrochlorothiazide, the addition of amiloride had positive effects on blood pressure and blood sugar tolerance. Amiloride may therefore be useful for preventing the metabolic side effects of thiazide diuretics, allowing for the use of higher thiazide doses (in line with how they were originally studied).
Amiloride is the treatment of choice for Liddle phenotype, which is characterized by high blood pressure, low blood potassium, and metabolic alkalosis in conjunction with a low plasma renin activity and a low aldosterone. Some people with the Liddle phenotype have Liddle syndrome
Liddle's syndrome, also called Liddle syndrome, is a genetic disorder inherited in an autosomal dominant manner that is characterized by early, and frequently severe, high blood pressure associated with low plasma renin activity, metabolic alkal ...
, which involves a genetic mutation resulting in upregulation of the epithelial sodium channel (ENaC), located in the apical membrane of polarized epithelial cells in the late distal tubule and collecting duct
The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis. The collecting duct system is the last part of nephron and participates in elect ...
of the kidney. Because Liddle phenotype usually involves an upregulation of ENaC channels, leading to retention of sodium and water and to hypokalemia, amiloride is useful as an ENaC channel inhibitor due to its promotion of sodium excretion and its potassium-sparing effects, restoring potassium to normal levels.
Amiloride can be used as a monotherapy (single-drug therapy) or an adjunctive therapy alongside other diuretics (e.g. hydrochlorothiazide
Hydrochlorothiazide is a diuretic medication often used to treat high blood pressure and swelling due to fluid build-up. Other uses include treating diabetes insipidus and renal tubular acidosis and to decrease the risk of kidney stones in tho ...
, furosemide
Furosemide is a loop diuretic medication used to treat fluid build-up due to heart failure, liver scarring, or kidney disease. It may also be used for the treatment of high blood pressure. It can be taken by injection into a vein or by mouth ...
) for the treatment of ascites
Ascites is the abnormal build-up of fluid in the abdomen. Technically, it is more than 25 ml of fluid in the peritoneal cavity, although volumes greater than one liter may occur. Symptoms may include increased abdominal size, increased weight, ab ...
and edema
Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's Tissue (biology), tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels t ...
(swelling) due to cirrhosis of the liver
Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue repai ...
. The 2012 clinical practice guidelines by the American Association for the Study of Liver Diseases The American Association for the Study of Liver Diseases (AASLD) is a leading organization of scientists and health care professionals committed to preventing and curing liver disease. AASLD was founded in 1950 by a group of leading liver specialist ...
(AASLD) states that amiloride can be used to treat ascites in place of spironolactone
Spironolactone, sold under the brand name Aldactone among others, is a medication that is primarily used to treat fluid build-up due to heart failure, liver scarring, or kidney disease. It is also used in the treatment of high blood pressure ...
if it isn't tolerated (e.g. due to the side effect of gynecomastia
Gynecomastia (also spelled gynaecomastia) is the abnormal non-cancerous enlargement of one or both breasts in males due to the growth of breast tissue as a result of a hormone imbalance between estrogens and androgens. Updated by Brent Wisse (1 ...
), though amiloride isn't a preferred drug due to cost and lack of efficacy.
Specific populations
Diabetics
People with diabetes are at higher risk for kidney problems
Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...
, which increases their risk for hyperkalemia (high blood potassium). The use of amiloride in people with diabetes requires careful potassium and kidney function monitoring to prevent toxicity. Amiloride must be discontinued for at least 3 days prior to glucose tolerance testing, due to the risk for fatal hyperkalemia.
Poor kidney function
People with poor kidney function (e.g. blood urea nitrogen >30 mg/dL, or serum creatinine
Creatinine (; ) is a breakdown product of creatine phosphate from muscle and protein metabolism. It is released at a constant rate by the body (depending on muscle mass).
Biological relevance
Serum creatinine (a blood measurement) is an importa ...
>1.5 mg/dL) are at high risk for hyperkalemia.
Lactation
There is no data on the use of amiloride in women that are breastfeeding. While diuretics can make lactation difficult, it is unlikely that amiloride would induce this effect in the absence of other diuretics.
Pregnancy
Data from the use of amiloride in animals suggests that it does not pose a risk to the developing fetus. However, when used in combination with the drug acetazolamide
Acetazolamide, sold under the trade name Diamox among others, is a medication used to treat glaucoma, epilepsy, altitude sickness, periodic paralysis, idiopathic intracranial hypertension (raised brain pressure of unclear cause), urine alkalin ...
during the process of organ formation, amiloride increases the risk for kidney and ureter abnormalities. Limited human data from use during pregnancy suggests an association with a specific congenital penis abnormality if taken during the first trimester, as well as a risk for mild intrauterine growth restriction
Intrauterine growth restriction (IUGR), or fetal growth restriction, refers to poor growth of a fetus while in the womb during pregnancy. IUGR is defined by clinical features of malnutrition and evidence of reduced growth regardless of an infant's ...
if taken throughout pregnancy.
Contraindications
Amiloride is contraindicated in people with kidney problems (e.g. anuria, acute or chronic kidney disease
Chronic kidney disease (CKD) is a type of kidney disease in which a gradual loss of kidney function occurs over a period of months to years. Initially generally no symptoms are seen, but later symptoms may include leg swelling, feeling tired, vo ...
, or diabetic nephropathy
Diabetic nephropathy, also known as diabetic kidney disease, is the chronic loss of kidney function occurring in those with diabetes mellitus. Diabetic nephropathy is the leading causes of chronic kidney disease (CKD) and end-stage renal disease ...
), elevated blood potassium (≥5.5 mEq/L), or people that are hypersensitive to amiloride or any ingredients within the specific formulation. Use is also contraindicated in people that are already taking potassium-sparing drugs (e.g. spironolactone
Spironolactone, sold under the brand name Aldactone among others, is a medication that is primarily used to treat fluid build-up due to heart failure, liver scarring, or kidney disease. It is also used in the treatment of high blood pressure ...
and triamterene
Triamterene (trade name Dyrenium among others) is a potassium-sparing diuretic often used in combination with thiazide diuretics for the treatment of high blood pressure or swelling. The combination with hydrochlorothiazide, is known as hydro ...
) or whom are taking potassium supplements (e.g. potassium chloride) in most circumstances.
Adverse effects
Amiloride is generally well tolerated. Common adverse effects to the use of amiloride include elevated blood potassium, mild skin rashes, headaches, and gastrointestinal side effects (nausea, vomiting, diarrhea, decreased appetite
Anorexia is a medical term for a loss of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a loss of appetite, some of which may be harmless, while others ...
, flatulence
Flatulence, in humans, is the expulsion of gas from the intestines via the anus, commonly referred to as farting. "Flatus" is the medical word for gas generated in the stomach or bowels. A proportion of intestinal gas may be swallowed environm ...
, and abdominal pain). Mild symptoms of high blood potassium concentrations include unusual skin sensations, muscle weakness, or fatigue, but more severe symptoms such as flaccid paralysis
Flaccid paralysis is a neurological condition characterized by weakness or paralysis and reduced muscle tone without other obvious cause (e.g., trauma). This abnormal condition may be caused by disease or by trauma affecting the nerves associ ...
of the limbs, slow heart rate
Bradycardia (also sinus bradycardia) is a slow resting heart rate, commonly under 60 beats per minute (BPM) as determined by an electrocardiogram. It is considered to be a normal heart rate during sleep, in young and healthy or elderly adults, a ...
, and even shock
Shock may refer to:
Common uses Collective noun
*Shock, a historic commercial term for a group of 60, see English numerals#Special names
* Stook, or shock of grain, stacked sheaves
Healthcare
* Shock (circulatory), circulatory medical emergen ...
can occur.
Overdose
There exists no overdose data on amiloride in humans, though it is expected than an overdose would produce effects consistent with its therapeutic effects; e.g. dehydration due to over-diuresis, and electrolyte disturbances related to hyperkalemia. It is unknown if amiloride can be dialyzed off, and no specific antidote against it exists. Treatment is generally supportive, though hyperkalemia can be treated.
Interactions
Amiloride may have important drug-drug interactions when combined with other medications that also increase potassium levels in the blood, leading to hyperkalemia. For example, the combination of amiloride with angiotensin-converting enzyme (ACE) inhibitors
Angiotensin-converting-enzyme inhibitors (ACE inhibitors) are a class of medication used primarily for the treatment of hypertension, high blood pressure and heart failure. They work by causing relaxation of blood vessels as well as a decrease i ...
like lisinopril
Lisinopril is a medication of the angiotensin-converting enzyme (ACE) inhibitor and is used to treat high blood pressure, heart failure, and after heart attacks. For high blood pressure it is usually a first-line treatment. It is also used to ...
, or angiotensin II receptor type 1
Angiotensin II receptor type 1 (AT1) is the best characterized angiotensin receptor. It is encoded in humans by the ''AGTR1'' gene. AT1 has vasopressor effects and regulates aldosterone secretion. It is an important effector controlling blood pre ...
(AT1) antagonists like losartan
Losartan, sold under the brand name Cozaar among others, is a medication used to treat high blood pressure (hypertension). It is in the angiotensin II receptor antagonist, angiotensin receptor blocker (ARB) family of medication, and is consider ...
, may lead to high levels of potassium in the blood, requiring frequent monitoring.
Pharmacology
Mechanism of action
Diuresis
Amiloride works by directly blocking the epithelial sodium channel (ENaC) with an IC50 around 0.1 μM, indicating potent blockade. Antagonism of ENaC thereby inhibits sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
reabsorption in the late distal convoluted tubule
The distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting tubule.
Physiology
It is partly responsible for the regulation of potassium, sodium, calcium, and pH.
On its apical surface (lumen ...
s, connecting tubules, and collecting ducts in the nephron
The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure ca ...
. This promotes the loss of sodium and water from the body, and reduces potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
excretion. The drug is often used in conjunction with a thiazide
Thiazide () refers to both a class of sulfur-containing organic molecules and a class of diuretics based on the chemical structure of benzothiadiazine. The thiazide drug class was discovered and developed at Merck and Co. in the 1950s. The first ...
diuretic to counteract with a potassium-losing effect. Due to its potassium-sparing capacities, hyperkalemia
Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0mmol/L (3.5 and 5.0mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Occasi ...
(elevated potassium concentration in the blood) can occur. The risk of developing hyperkalemia is increased in patients who are also taking ACE inhibitor
Angiotensin-converting-enzyme inhibitors (ACE inhibitors) are a class of medication used primarily for the treatment of hypertension, high blood pressure and heart failure. They work by causing relaxation of blood vessels as well as a decrease i ...
s, angiotensin II receptor antagonist
Angiotensin II receptor blockers (ARBs), formally angiotensin II receptor type 1 (AT1) antagonists, also known as angiotensin receptor blockers, angiotensin II receptor antagonists, or AT1 receptor antagonists, are a group of pharmaceuticals tha ...
s, other potassium-sparing diuretics
Potassium-sparing diuretics refers to drugs that cause diuresis without causing potassium loss in the urine. They are typically used as an adjunct in management of hypertension, cirrhosis, and congestive heart failure. The steroidal aldosterone ...
, or any potassium-containing supplements.
Miscellaneous
A fraction of the effects of amiloride is inhibition of cyclic GMP-gated cation channels in the inner medullary collecting duct
The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis. The collecting duct system is the last part of nephron and participates in elect ...
.[ page 875]
Amiloride has a second action on the heart, blocking Na+/H+ exchangers sodium–hydrogen antiporter 1 or NHE-1.
Amiloride also blocks the Na+/H+ antiporter on the apical surface of the proximal tubule
The proximal tubule is the segment of the nephron in kidneys which begins from the renal pole of the Bowman's capsule to the beginning of loop of Henle. It can be further classified into the proximal convoluted tubule (PCT) and the proximal straig ...
cells in the nephron, abolishing more than 80% of the action of angiotensin II
Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the adre ...
on the secretion of hydrogen ions in proximal tubule cells. Note that amiloride is not an angiotensin II receptor blocker
Angiotensin II receptor blockers (ARBs), formally angiotensin II receptor type 1 (AT1) antagonists, also known as angiotensin receptor blockers, angiotensin II receptor antagonists, or AT1 receptor antagonists, are a group of pharmaceuticals tha ...
(like losartan
Losartan, sold under the brand name Cozaar among others, is a medication used to treat high blood pressure (hypertension). It is in the angiotensin II receptor antagonist, angiotensin receptor blocker (ARB) family of medication, and is consider ...
, for example). The Na-H transporter is also found in the Jejunum of the small intestine, as a result, amiloride also blocks the reabsorption of Na, and thereby water in the intestines.
Amiloride is considered to be a reversible, pan-acid-sensing ion channel
Acid-sensing ion channels (ASICs) are neuronal voltage-insensitive sodium channels activated by extracellular protons permeable to Na+. ASIC1 also shows low Ca2+ permeability. ASIC proteins are a subfamily of the ENaC/Deg superfamily of ion chann ...
(ASIC) inhibitor that prevents the transient flow of ions but not the sustained flow of ions. ASICs are members of the ENaC family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
of protein channels, and are found in the nervous system
In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes th ...
, the cardiovascular system
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
, the gastrointestinal system
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...
, and the skin
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...
. Broadly, ASICs are involved in harm detection, chemosensation (pH changes specifically), and touch
In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), and pain. It is ...
.
Pharmacokinetics
Absorption
Amiloride has an oral bioavailability
In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation.
By definition, when a medication is administered intravenously, its bioavailability is 100%. H ...
of 50%, meaning that about 50% of an oral dose is absorbed into the blood stream. Coadministration with food reduces the amount of amiloride that is absorbed by the body by about 30%, though it does not affect the rate of absorption. However, taking amiloride with food helps to reduce the incidence of its gastrointestinal side effects. After being taken, amiloride's diuretic effect occurs within 2 hours, with peak diuresis within 6–10 hours. The diuretic effects of amiloride persist for about 24 hours after administration.
Distribution
Amiloride cross the placenta and distributes into breast milk ''in vivo''.
Metabolism
Amiloride is not metabolized by the liver. In comparison, the ENaC inhibitor triamterene
Triamterene (trade name Dyrenium among others) is a potassium-sparing diuretic often used in combination with thiazide diuretics for the treatment of high blood pressure or swelling. The combination with hydrochlorothiazide, is known as hydro ...
is metabolized by the liver.
Excretion
About 50% of amiloride is excreted unchanged by the kidneys, while around 40% is excreted in the feces (likely drug that wasn't absorbed). The half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
of amiloride in humans is between 6 and 9 hours, which may be prolonged in people with poor kidney function.
Pharmacogenomics
A single nucleotide polymorphism
In genetics, a single-nucleotide polymorphism (SNP ; plural SNPs ) is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently larg ...
(SNP) in the protein NEDD4L
Neural precursor cell expressed developmentally downregulated gene 4-like (NEDD4L) or NEDD4-2 is an enzyme (ubiquitin ligase) of the NEDD4 family.
In human the protein is encoded by the ''NEDD4L'' gene. In mouse the protein is commonly known as NE ...
may impact how amiloride affects a person's blood pressure in people with high blood pressure
Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...
.
Chemistry
Amiloride is a pyrazinoylguanidine, composed of a substituted pyrazine
Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C4H4N2. It is a symmetrical molecule with point group D2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine. It is a ''"deliquescent crystal or wax-lik ...
ring structure with a carbonylguanidinium substituent. Amiloride's pKa is 8.67, which is due to the guanidinium
Guanidine is the compound with the formula HNC(NH2)2. It is a colourless solid that dissolves in polar solvents. It is a strong base that is used in the production of plastics and explosives. It is found in urine predominantly in patients experie ...
group. In high pH (alkaline, low hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
concentration) environments, the guanidinium group is deprotonated and the compound is rendered neutral, depleting its activity on sodium channels. Amiloride, as a pure substance, is highly fluorescent
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
, with excitation wavelength
Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating f ...
s at 215, 288, and 360 nm, emitting light at 420 nm.
History
Amiloride was first synthesized and discovered by the Merck Sharp and Dohme Research Laboratories in the late 1960s. The drug was discovered as part of a screening process of chemicals that reversed the effects of mineralocorticoids ''in vivo''. Amiloride was the only drug in the screen that was capable of causing the excretion of sodium (natriuresis) without a concomitant urinary excretion of potassium (kaliuresis). Thousands of amiloride analogues have been studied since its initial discovery, which have been used to study the effects of sodium transporters.
Amiloride was approved by the U.S. Food and Drug Administration
The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respon ...
(FDA) on October 5, 1981.
Society and culture
It is on the World Health Organization's List of Essential Medicines
The WHO Model List of Essential Medicines (aka Essential Medicines List or EML), published by the World Health Organization (WHO), contains the medications considered to be most effective and safe to meet the most important needs in a health ...
.
Amiloride is on the World Anti-Doping Agency
The World Anti-Doping Agency (WADA; french: Agence mondiale antidopage, AMA) is a foundation initiated by the International Olympic Committee based in Canada to promote, coordinate, and monitor the fight against drugs in sports. The agency's key ...
's list of banned substances, as it is considered a masking agent
A masking agent is a reagent used in chemical analysis which reacts with chemical species that may interfere in the analysis.
In sports a masking agent is used to hide or prevent detection of a banned substance or illegal drug like anabolic stero ...
. Diuretics like amiloride act as masking agents by reducing the concentration of other doping agents due to promoting diuresis, increasing the total volume of the urine. The list includes other potassium-sparing diuretics, such as triamterene
Triamterene (trade name Dyrenium among others) is a potassium-sparing diuretic often used in combination with thiazide diuretics for the treatment of high blood pressure or swelling. The combination with hydrochlorothiazide, is known as hydro ...
and spironolactone
Spironolactone, sold under the brand name Aldactone among others, is a medication that is primarily used to treat fluid build-up due to heart failure, liver scarring, or kidney disease. It is also used in the treatment of high blood pressure ...
. In 2008, amiloride and the potassium-sparing diuretic triamterene
Triamterene (trade name Dyrenium among others) is a potassium-sparing diuretic often used in combination with thiazide diuretics for the treatment of high blood pressure or swelling. The combination with hydrochlorothiazide, is known as hydro ...
were found in 3% of positive diuretic doping samples.
Formulations and trade names
* Amiloride hydrochloride
In chemistry, a hydrochloride is an acid salt resulting, or regarded as resulting, from the reaction of hydrochloric acid with an organic base (e.g. an amine). An alternative name is chlorhydrate, which comes from French. An archaic alternative na ...
** Midamor (U.S.)
* Co-amilozide
Co-amilozide ( BAN) is a non- proprietary combination of amiloride and hydrochlorothiazide. Co-amilozide is used in the treatment of hypertension and congestive heart failure with the tendency of the thiazide to cause low potassium levels ( hypok ...
(amiloride hydrochloride with hydrochlorothiazide
Hydrochlorothiazide is a diuretic medication often used to treat high blood pressure and swelling due to fluid build-up. Other uses include treating diabetes insipidus and renal tubular acidosis and to decrease the risk of kidney stones in tho ...
)
* Co-amilofruse
Co-amilofruse (BAN) is a nonproprietary name used to denote a combination of amiloride and furosemide, which are both diuretics. Co-amilofruse is a treatment for fluid retention (oedema), either in the legs (peripheral edema) or on the lungs (pulm ...
(amiloride hydrochloride with furosemide
Furosemide is a loop diuretic medication used to treat fluid build-up due to heart failure, liver scarring, or kidney disease. It may also be used for the treatment of high blood pressure. It can be taken by injection into a vein or by mouth ...
)
* Amiloride hydrochloride with cyclopenthiazide
* Amiloride hydrochloride with bumetanide
Bumetanide, sold under the brand name Bumex among others, is a medication used to treat swelling and high blood pressure. This includes swelling as a result of heart failure, liver failure, or kidney problems. It may work for swelling when oth ...
Research
Amiloride is an inhibitor of NHE-1, which helps to maintain normal pH within cells. Cancer cells in leukemia
Leukemia ( also spelled leukaemia and pronounced ) is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ' ...
, a type of blood cancer, have higher pH compared to normal cells. Amiloride affects the splicing and regulation
Regulation is the management of complex systems according to a set of rules and trends. In systems theory, these types of rules exist in various fields of biology and society, but the term has slightly different meanings according to context. For ...
of multiple genes involved in cancer, though they do not appear to be directly related to its effects on pH. Amiloride has been tested ''in vitro
''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...
'' as an adjunct to the anticancer drug imatinib
Imatinib, sold under the brand names Gleevec and Glivec (both marketed worldwide by Novartis) among others, is an oral chemotherapy medication used to treat cancer. Imatinib is a small molecule inhibitor targeting multiple receptor tyrosine kin ...
, which appeared to show a synergistic effect. Modified versions of amiloride, known as 5'-(N,N-dimethyl)-amiloride (DMA), 5-N-ethyl-N-isopropyl amiloride (EIPA), and 5-(N,N-hexamethylene)-amiloride (HMA), are being studied for the treatment of leukemia
Leukemia ( also spelled leukaemia and pronounced ) is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ' ...
.
Cystic fibrosis
Cystic fibrosis (CF) is a rare genetic disorder that affects mostly the lungs, but also the pancreas, liver, kidneys, and intestine. Long-term issues include difficulty breathing and coughing up mucus as a result of frequent lung infections. O ...
is a genetic disorder due to a mutation in the ''CFTR
Cystic fibrosis transmembrane conductance regulator (CFTR) is a membrane protein and anion channel in vertebrates that is encoded by the ''CFTR'' gene.
Geneticist Lap-Chee Tsui and his team identified the CFTR gene in 1989 as the gene linked wi ...
'' gene, which encodes for the CFTR chloride channel. There is evidence that suggests that the molecular target of amiloride, ENaC, is also implicated in cystic fibrosis due to its effects on mucus in the lungs. Aerosolized formulations of amiloride have been tested in clinical trials, though long-term clinical trials have failed to show much utility. Due to its short duration of action, it was thought that longer-acting ENaC inhibitors may prove more effective. However, longer-acting ENaC inhibitors (i.e. benzamil) have also failed clinical trials, despite an improvement in both the solubility and potency of the drugs. A third generation amiloride analogue (N-(3,5-diamino-6-chloropyrazine-2-carbonyl)-N'-4- -(2,3-dihydroxypropoxy)phenylutyl-guanidine methanesulfonate, research name "552-02"), with better pharmacokinetic
Pharmacokinetics (from Ancient Greek ''pharmakon'' "drug" and ''kinetikos'' "moving, putting in motion"; see chemical kinetics), sometimes abbreviated as PK, is a branch of pharmacology dedicated to determining the fate of substances administered ...
properties, is being studied.
Pain induced by exposure to acid is attenuated by amiloride in human trials, which may indicate a role for amiloride in the treatment of pain in the future.
References
External links
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Potassium-sparing diuretics
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