What are the factors affecting drug absorption?
- Factors related to the drug
- Factors related to the absorbing surface
What are the factors related to the drug that affects drug absorption?
Molecular size: Small molecules are absorbed > large molecules.
Drug formulations: Sustained-release (SR) tablets→ slow absorption.
Drug combination: Vit C →↑ iron absorption.
Lipid solubility: The pKa and drug ionization
What are the factors related to the absorbing surface that affect drug absorption?
Route: The IV route is the fastest, while the rectal is the slowest.
The integrity of the absorbing surface: may ↑ or ↓ absorption.
Total surface area: absorption across the intestine more
efficient (intestine has a large surface area).
Rate of the circulation: at the site of absorption (blood flow).
How is loading dose calculated? And what does it depend on?
Ld = Vd * Cp
Vd (volume of distribution)
How to calculate maintanence dose? And what does it depend on?
{MD= CL X Cp}
Cl (clearance rate)
What is the definition of clearance?
The volume of fluid (usually plasma or blood) from which drug is removed per unit time (ml usually per minute).
What is the definition of elimination?
The processes involved in the removal of drugs from the body (and/or plasma)
What is elimination half-life? And what is it used for?
- It is the time taken for the concentration of a drug in the blood to fall half its original value.
- Used in determination of inter dosage interval.
What are the patterns of elimination?
- First-order elimination
- Zero-order elimination
What is the definition of first-order elimination? And what dugs show this type of elimination?
- A constant fraction (PERCENTAGE) of the drug is eliminated per unit time (t1/2 is constant).
- Most drugs follow first order
What is the definition of zero-order elimination?
- A constant AMOUNT of drug is eliminated per unit time (t1/2 is variable), Drug cumulation and interactions are common.
- Aspirin & phenytoin (zero-order in high doses)
What is steady-state concentration?
- Steady level of drug in the plasma is achieved when the rate of administration equals the rate of elimination.
- Steady-state plasma concentration abbreviated → Cpss.
What is the concept of the role of 5?
The rule of 5 :
- Cpss is reached after 4-5 t 1/2.
- If a dose is changed, new Cpss after 4-5 t 1/2
- Complete drug elimination after 4-5 t 1/2. (if the drug given once or stoped after continuous administration)
How to achieve Cpss. After first t 1/2?
To achieve Cpss after first t 1/2 → give double the dose (loading dose) in the first time only then give the usual dose (maintenance dose)
Percentage of the drug in body after one-time administration or stopping after continuous administration.
50 25 12.5 6.25 3.125
Percentage of the drug in blood in cases of Continous administration
50 75 87.5 93.75 96.875
What are the types of receptors?
Ligand-gated ion channel:
- Nicotinic & GABAA receptor.
G protein-coupled:
- Muscarinic receptors.
- Adrenergic receptors.
- Histamine 1&2 receptors.
Tyrosine kinase linked:
- Insulin receptor.
Intracellular:
- Glucocorticoid receptors.
What are adverse drug reactions?
An ADR is any response to a drug which is noxious, unintended and occurs at doses used in man for prophylaxis, or therapy.
What are types of clinical defect of the drug?
- Desirable
- Undesirable
What are type types of adverse drug reactions?
Type A - Augmented Type B - Bizzare Type C - Continous Type D - Delayed Type E - End of use
Type A - Augmented
Related to the pharmacological action
E.g: bleeding with anticoagulants
Type B - Bizzare
Unrelated to the pharmacological action
example: plastic anemia from carbimazole
Type C - Continous
Chronic affects - dose and time related
Example: Analgesic nephropathy
Type D - Delayed
Unmmon, time-related delay in Onset
Example: Tetratogenesis
