Pharmacology and Therapeutics Flashcards
what is drug absorption?
movement of drug from site of administration in the body to site of measurement
what is drug distribution?
reversible transfer of absorbed drug into and out of various tissues in the body from the bloodstream
what is drug metabolism?
conversion of drug to a usually more water soluble compound
what is drug excretion?
loss of unchanged drug from the body in the urine or faeces
what is elimination?
drug metabolism + drug excretion
what is disposition?
drug distribution +drug elimination
what are the factors affecting the amount of drug appearing in systemic circulation after oral dosage?
chemical properties
- chemical stability to acids/bases and enzymes
- solubility in water or lipid (polarity)
- molecular weight (size)
physiological variables
- food, gastric pH
- gut mobility
- cut blood flow
what is the effect of pH on ionisation?
H+ + X- <—> HX
(ions) (compound)
if acid is added, the equilibrium moves to the right
more H+ ions, equilibrium shifts to decrease H+ ion concentration, favours the forward reaction and shifts to the right.
which types of drug cross the lipid biological barrier better, ionised or unionised?
unionised
what factors effect drug distribution?
distribution
- reversible transfer of drug form blood to tissues
- the steady state process attained is called ‘distribution equilibrium’
physiochemical properties
- small, non polar, lipid soluble etc.
some drugs bind to circulating plasma proteins
- acidic drugs to albumin
- basic drugs to alpha1- acid glycoprotein
only free drugs can distribute to tissues and exert pharmacological action.
what is a free drug?
an active drug
formula for drug concentration?
drug concentration = drug dose/ volume of distribution
how many phases does metabolism have?
