absorption and distribution of drugs
TRANSCRIPT
Absorption and drug
distribution Dr.S.VASANTH
Route with high bio availability ……….?
Transport across biological membrane ….?
Absorption of drug …….?
Distribution of drug ….?
Plasma proteins ……….?
Pre session
What is pharmacokinetics ?
ADME
What is pharmacokinetics ?
Transport across biological memberane
Lipid
Biological membrane
passive transport
Active transport
Facilitated diffusion
Symport
Antiport
Primary active transport
Secondary active transport
Biological membrane
pH of medium = pKa then drug is 50 % unionised and 50 % ionized
pH more than Pka medium is alkaline Acidic drugs ,ionization form increases and
nonionized decreases Basic drugs, unionized form increases and
ionized form decreases
Absorption is movement of the drug from its site of administration into the circulation
Different routes of drug absorption ?
Factors affecting drug absorption ?
Absorption
Lipid solublity /aqueous solublity
pH/pKA value
Gastric emptying /gut motility
Particle size and formulation
Food and presence of other substance /drug
Gastrointestinal disease
First pass metabolism
What is first pass metabolism ?
What is bioavailablity ?
Nitrates
Hydrocortisone
Lignocaine
Propanolol
Salbutamol
morphine
Drugs with high first pass metabolism
Rate and extent of a drug form the dosage form in unchanged form in the systemic circulation
Fraction of drug or percentage of drug reaches systemic circulation in unchanged form
Lipid solublity /ionization /pH Area of absorbing surface Blood circulation Gastric motility Presence of food Disease state of git
Factors affecting bioavailablity
First pass metabolism
Pharmaceutical factors
disintegration time
dissolution rate/time
Genetic influence's
Bioequvalance?
Phenytoin a(dilantin)
Phenytoin b (eptoin)
Apparent volume of distribution Volume in which drug appears to be
distributed ( apparent )if concentration throughout the body was same to that of the plasma
aVd= dose administered I.V /plasma concentration achieved
Distribution
Factors which affects the drug distributions
1). tissue permeability of drug a. physicochemical property – i) molecular
size ii) pKa iii) o/w partion
coefficient b. physiological barriers 2). Organ tissue size and perfusion rate 3). Binding of drug to tissue components a. with blood components b.with extravascular tissue proteins 4). Miscellaneous factors a. age b.Pregnancy d.Obesity e.Diet f.Disease states
g.Drug interaction
Redistribution ?
Plasma protein binding
Albumin
Alpha1 acid glycoproteins
Binding
Maintance of plasma concentration
Free and bound form measurement
Low vd- highly bound form
Long acting – highly bound
Not removed by hemodialysis
Displacement reaction
Hypoalbuminemia ,chirosis
Diazepam
Midazolam
Warfarin
Imipramine
cyclosporine
Drugs with high plasma protein binding
Bioavailablity 100% ……… ?
Bioequvalence ?.............
Volume of distribution ?
Significance of plasma protein binding ??
Post session