Table of Contents
What do excretion rates of drugs depend on?
In kidney, excretion of drugs depends on glomerular filtration, active tubular secretion, and passive tubular absorption. Urine and blood pH and the physical characteristics of the drug molecule are important in determining whether the drug is excreted in the urine or remains in the circulation.
How does the body excrete drugs?
Most drugs, particularly water-soluble drugs and their metabolites, are eliminated largely by the kidneys in urine. Therefore, drug dosing depends largely on kidney function. Some drugs are eliminated by excretion in the bile (a greenish yellow fluid secreted by the liver and stored in the gallbladder).
Why do some drugs excreted unchanged?
Such drugs will therefore be excreted unchanged in the urine because they do not need to undergo biotransformation to increase their water solubility. Active secretion into the renal tubules occurs for some drugs that are not readily filtered in the glomerulus.
What promotes excretion of acidic drugs?
The drug must be excreted rapidly from the body, so one strategy is to alter the urine pH to increase excretion. In aspirin poisoning for example, making the urine more alkaline with sodium bicarbonate increases ionisation of the salicylic acid (aspirin metabolite) therefore increasing its excretion from the body.
What factors affect excretion of a drug?
Factors affecting renal excretion of drugs include: kidney function, protein binding, urine pH and urine flow.
What factors affect drug clearance?
The elimination half-life is calculated by dividing the natural log of 2 by the elimination rate constant. Factors that affect clearance are: body weight, body surface area, cardiac output, drug-drug interactions, genetics, liver and kidney function, and plasma protein binding.
What is an excretion rate?
test of kidney function The clearance of inulin and some other compounds is not altered by raising its plasma concentration, because the amount of urine completely cleared of the agent remains the same. But the excretion rate equals total quantity excreted per millilitre of filtrate per minute,…
What is excretion rate?
Urinary excretion rate = Filtration rate – Reabsorption rate + Secretion rate. Although the strictest sense of the word excretion with respect to the urinary system is urination itself, renal clearance is also conventionally called excretion (for example, in the set term fractional excretion of sodium).
Is drug elimination and excretion the same?
Drug elimination is the removal of an administered drug from the body. It is accomplished in two ways, either by excretion of an unmetabolized drug in its intact form or by metabolic biotransformation followed by excretion.
What does the excretory system excrete?
This is the job of the excretory system. You remove waste as a gas (carbon dioxide), as a liquid (urine and sweat), and as a solid. Excretion is the process of removing wastes and excess water from the body.
What’s the difference between clearance and the rate of drug elimination?
Clearance is defined as ‘the volume of blood cleared of drug per unit time’. Drug elimination rate is defined as ‘the amount of drug cleared from the blood per unit time’ In first order kinetics, elimination rate is proportional to dose, while clearance rate remains independent of the dose.
Where does the majority of drug excretion take place?
As can be seen in the preceding equation, the main contributors to drug excretion are the kidneys and the liver. Water-soluble compounds are excreted primarily by the kidneys, while larger, more hydrophobic compounds are the responsibility of the liver.
Which is more likely to be excreted in bile?
Drugs with a molecular weight (MW) exceeding 300 daltons and with polar and lipophilic groups are more likely to be excreted in bile. Clearance is a measure of the ability of the body to eliminate a drug. The elimination behavior of a drug is described most simply by its half-life, the time needed for the drugs concentration to be halved.
How does body fluid affect drug metabolism and excretion?
Drug metabolism and excretion are profoundly affected by the size of various body fluid compartments. Fluid distribution among these compartments is significantly different in infancy and childhood, which in turn alters the action of certain drugs in this age group. A brief review of body fluid nomenclature may be helpful at this point.
Which is the most common route of drug elimination?
Renal excretion is the most common route of drug elimination. However, many drugs are excreted into bile via the liver and some volatile substances (primarily gaseous anesthetics) can be excreted via the lungs.