drugs
Drug Elimination
Drug elimination in the urine
Several factors, including certain characteristics of the drug, affect the kidneys’ ability to excrete drugs. To be extensively excreted in urine, a drug or metabolite must be water soluble and must not be bound too tightly to proteins in the bloodstream. The acidity of urine, which is affected by diet, drugs, and kidney disorders, can affect the rate at which the kidneys excrete some drugs. In the treatment of poisoning with some drugs, the acidity of the urine is changed by giving antacids (such assodium bicarbonate) or acidic substances (such as ammonium chloride) to speed up the excretion of the drug. The kidneys’ ability to excrete drugs also depends on Urine flow Blood flow through the kidneys The condition of the kidneys Kidney function can be impaired by many disorders (especially high blood pressure, diabetes, and recurring kidney infections), by exposure to high levels of toxic chemicals, and by age-related changes. As people age, kidney function slowly declines. For example, the kidneys of an 85-year-old person excrete drugs only about half as efficiently as those of a 35-year-old person. In people whose kidney function has declined, the “normal” dosage of a drug that is eliminated primarily through the kidneys may be too much and may cause side effects. Therefore, health care practitioners sometimes must adjust the drug dosage based on the amount of decline in the person’s kidney function. People with impaired kidney function require lower drug doses than those with normal kidney function. Health care practitioners have several ways to estimate the decline in kidney function. Sometimes they base an estimate solely on the person’s age. However, they can get a more accurate estimate of kidney function by using the results of tests that measure the level of creatinine (a waste product) in the blood and sometimes also the urine. They use these results to calculate how effectively creatinine is removed from the body (called creatinine clearance—see Kidney Function Tests ), which reflects how well the kidneys are functioning. 