Pharmacokinetics;-
Important points;- 1. Definition
2. Stages of pharmacokinetics
3. Example
Defination;- Pharmacokinetics is the quantitative study of drug movement in, through and out of the body.
- Pharmacokinetic consideration, therefore determine the route of the drug administration ,dose, maximum action of the drug,duration of action and frequency of drug administration
stages of pharmacokinetics;- Mainly pharmacokinetics have 4 steps-
1. Absorption
2. Distribution
3. Metabolism
4. Excretion
1. Absorption;- Absorption is movement of the drug from its site of administration into the systemic circulation.
-Absorption of drug depend upon some factors- a. Lipid solubility
b. Nature of drug
c. PH of medium
Note- 1. Lipid soluble drug can cross plasma membrane easily.
2. Acidic drug can easily absorbe in acidic medium and same as basic drug.
Bioavailability;- It is the fraction of the given dosewhich reaches systemic circulation
-Oral route given drugs which shows variety of the bioavailability from 5-100%.
- IV route given drugs shows 100% bioavailability.
2. Distribution;- Once a drug reaches to blood stream now it gets distributated to tissue
Distribution of the drug depends upon;- 1. Lipid solubility
2. Plasma protein binding(PPB)
3. Barrier
Plasma protein binding;- Acidic drug bind with - Albumin
Basic drug bind with - alpha-1 acid glycoprotein
Importance of PPB;- 1. Distribution of drug is decrease
2. Duration of drug is increase
3. Displacement intraction
3. Metabolism(Biotransformation);- Biotransformation means chemical alteration of the drug and drug makes chemically inactive . Mostly metabolic reaction(catabolic & anabolic) occurs by microsomal enzymes. and main aim of the metabolism is - drug change in water souble nature. microsomal enzyme depends on enzyme inducer and enzyme inhibitor
Mostly metabolism occurs by only two microsomal enzymes likes CYP3A4 and CYP2D6
4. Excretion;- After the metabolism ,drug gets functionally inactive and now filter , excrete out the body via- kidney(mainly), sweat, tear, faeces, and breast milk(may be)
Renal excretion;- The kidney is responsible for excreting water soluble drug . amount of drug and its metabolites are present in urine .
3 main steps of urine formation is- 1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion
1. Glomerular filtration;- Lipid soluble drug can cross the membrane easily and water soluble drug also crosses because glomerular capsule have small pore these are responsible for it.
2. Tubular reabsorption;- Lipid soluble drug can be reabsorbe from membrane of PCT but water soluble drug can't cross the membrane and it excrete out by urine.
This concept used in acidic and basic drug poisoning
3. Tubular secretion;- Tubular secretion take place via pumps or transporters. These transporter are small in size so only one substance can enter in onetime ,so this concept used in increase the duration of action
example;-penicillin is short acting drug this given with probenaceid then penicilin act as long acting drug