Nephrotoxic injury

Nephrotoxic injury is damage to one or both of the kidneys that results fromexposure to a toxic material, usually something taken by mouth.

The kidneys are the primary organs of the urinary system, which removes wastefrom the blood and excretes them from the body in urine. Every day, the kidneys filter about 45 gal (180 l) of blood, about four times as much as the amount that passes through any other organ. Because of this high volume, the kidneys are more often exposed to toxic substances in the blood and are very vulnerable to injury from those materials.

Each kidney contains more than one million structures called nephrons. Each nephron consists of two parts: the renal corpuscle and the renal tubule. The renal corpuscle is where the blood is filtered. It is made up of a network ofcapillaries (the glomerulus) and the structure that surrounds these capillaries (Bowman's capsule). Blood flows into the glomerulus, where the liquid partof the blood (plasma) passes through the walls of the capillaries and into Bowman's capsule. The plasma, now called filtrate, contains substances that the body needs, such as water, glucose, and other nutrients, as well as wastes,excess salts, and excess water. When the filtrate moves from Bowman's capsule into the renal tubules, the beneficial substances are reabsorbed into the blood stream. The remaining filtrate is then passed to the bladder as urine.

When the kidneys are exposed to a toxic material, damage can occur in a number of ways. Some toxins directly kill cells in the glomerulus or the renal tubules. Other toxins create substances or conditions, such as allergic reactions, that cause cell death. Nephrotoxic injury can lead to acute renal failure,in which the kidneys suddenly lose their ability to function, or chronic renal failure, in which kidney function slowly deteriorates. Untreated, renal failure can result in seizures, coma, and death.

Several different substances can be toxic to the kidneys. These include antibiotics; pain relievers (analgesics); contrast agents used in some diagnostictests, such as sodium iodide; heavy metals, such as lead, mercury, arsenic, and uranium; anti/cancer drugs; solvents and fuels, such as carbon tetrachloride, methanol, and ethylene glycol; herbicides and pesticides; and excess uric acid.

The elderly and people whose kidneys are already weakened by disease are especially susceptible to nephrotoxic injury. So are people who are exposed overlong periods to heavy metals or solvents on the job or at home. Severe dehydration increases the risk of nephrotoxic injury, as do diseases that cause overproduction of uric acid.

Symptoms of nephrotoxic injury include excess urea in the blood (azotemia), anemia, increased acidity of the blood (acidosis), excess fluids in the body (overhydration), and high blood pressure (hypertension). Blood, pus, or uric acid crystals may be present in the urine, and urine output may decrease.

Physicians detect kidney damage through physical examination, blood tests, urine tests, and imaging procedures. To find out whether the damage is due to nephrotoxic injury, the physician will ask about the patient's medical history, current prescriptions and exposure to solvents and other toxins.

Nephrotoxic injury is treated in the hospital. The goal of treatment is to remove the toxin from the patient's system, while maintaining kidney function.The removal method depends on the type of toxin and may include the use of diuretics or chelates to enhance excretion of the toxin in urine, or, in extreme cases, the direct removal of toxins from the blood using an artificial filtering system.

If the damage has not caused acute renal failure, kidney function can be fully restored once the toxin is removed from the body. However, if permanent damage has resulted in chronic renal failure, lifelong dialysis or a kidney transplant may be necessary.

The risk of nephrotoxic injury can be reduced by taking no more than the recommended dosages of antibiotics or analgesics. Elderly patients who take analgesics daily (for heart problems or arthritis, for example) should be closelymonitored to prevent accidental overdose. Patients should alert health care workers to any underlying conditions, such as diabetes or allergies to antibiotics, that may heighten the effect of a potential nephrotoxin. Safety recommendations for using solvents or handling heavy metals should be followed.

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