Drugs and behaviour
Elimination
The Kidneys
Primary function of the kidneys is to maintain correct balance of electrolytes in body fluids (water and salt)
Filters 1 liter of plasma per min; produces 1 cobic cm of urine per min
Filters everything out of the blood then selectively reabsorbs
Blood passes into a nephron (a long tube)
Bowman’s capsule which contains a clump of capillaries (glomerulus)
Nephron connects with collecting tubes that empty into the bladder
The nephron is the functional unit of the kidney. There are millions of nephrons.
Filtration
Everything other that protein, red, and white cells, drug bound to proteins passes through pores in capillaries into the nephron
Distal Reabsorption
Non-ionized drug molecules (lipid soluble) are reabsorbed into capillaries
Ionized molecules required by body (glucose) actively transported back into capillaries
Ionized drug molecules (non-lipid soluble) pass into the bladder pH influences reabsorption pH of urine: around 6 , ranges 4.4 to 8 pH manipulated more acidic or basic to facilitate excretion of drugs
Kidney makes urine basic to up secretion of barbiturates (weak acid) or give bicarbonate to overdose patient
Cocaine – give NH4CI
Rate of elimination
There are sufficient liver enzymes to metabolize high concentration of drugs
But, lower levels of drug leads to slower metabolism
Therefore, rate of excretion described by half-life
Half-life (T ½) = Time to reduce [ ] of drug in blood plasma by one half
First Order Kinetics
Rate of metabolism is proportional to the [ ] of the drug; half-life does not vary with the dose; 97% eliminated in 5 half lives
Zero Order Kinetics
Drug cleared at a constant rate (independent of dose)
Alcohol – removed from the body at approximately 15 mg/100ml of blood per hour
Not described in terms of half-life
Factors Affecting Metabolism
Stimulation of enzyme systems
Depression of enzymes systems
Age
Species
Stimulation of enzymes activity
Enzyme induction: drug
The Kidneys
Primary function of the kidneys is to maintain correct balance of electrolytes in body fluids (water and salt)
Filters 1 liter of plasma per min; produces 1 cobic cm of urine per min
Filters everything out of the blood then selectively reabsorbs
Blood passes into a nephron (a long tube)
Bowman’s capsule which contains a clump of capillaries (glomerulus)
Nephron connects with collecting tubes that empty into the bladder
The nephron is the functional unit of the kidney. There are millions of nephrons.
Filtration
Everything other that protein, red, and white cells, drug bound to proteins passes through pores in capillaries into the nephron
Distal Reabsorption
Non-ionized drug molecules (lipid soluble) are reabsorbed into capillaries
Ionized molecules required by body (glucose) actively transported back into capillaries
Ionized drug molecules (non-lipid soluble) pass into the bladder pH influences reabsorption pH of urine: around 6 , ranges 4.4 to 8 pH manipulated more acidic or basic to facilitate excretion of drugs
Kidney makes urine basic to up secretion of barbiturates (weak acid) or give bicarbonate to overdose patient
Cocaine – give NH4CI
Rate of elimination
There are sufficient liver enzymes to metabolize high concentration of drugs
But, lower levels of drug leads to slower metabolism
Therefore, rate of excretion described by half-life
Half-life (T ½) = Time to reduce [ ] of drug in blood plasma by one half
First Order Kinetics
Rate of metabolism is proportional to the [ ] of the drug; half-life does not vary with the dose; 97% eliminated in 5 half lives
Zero Order Kinetics
Drug cleared at a constant rate (independent of dose)
Alcohol – removed from the body at approximately 15 mg/100ml of blood per hour
Not described in terms of half-life
Factors Affecting Metabolism
Stimulation of enzyme systems
Depression of enzymes systems
Age
Species
Stimulation of enzymes activity
Enzyme induction: drug