Pharmacology Part-2

1. Bioavailabity:-  Presence of  drug in its active form in tissue or body fluid for its pharmacological action is termed as Bioavailability of the Drug.

2. Plasma Concentration:- The amount of the drugs into unit volume of the plasma of the body either in the active or inactive form is termed as Plasma Concentration of drug. The Plasma concentration of drug is depended on the route of administration of the drug. (See Fig.1)


3. Peak Concentration:- The maximum limit of concentration of  drug in the blood is known as peak concentration of the drug. It is generally denoted by C-max ( Maximum concentration of drug).
Peak Time- The Maximum time taken to attain the maximum concentration is termed as Peak Time. It is denoted by T- max.(See Fig.1)

Fig.1

4. Half Life- The time taken in which a drug reduces its concentration to 50%  of the peak concentration is known as half life of Drug. It is denoted as T-1/2. It is very helpful to determine the dose and frequency of any drug. If a drugs half life is more then the drug will be longer available in the plasma and frequency of drug administration is less. Eg. If the half life of a drug is 10 Hrs and the Peak plasma concentration is 20 mg/dl that means that the drug reduce to 10 mg/dl, the time taken is 10 hrs.

5. Onset of action- The time required to have visible effect of the drug after its administration.

6. Duration of Action- The time for which action of drug persist.

Therapeutic Index

7. Therapeutic Index- The Therapeutic index is a ratio between LD-50 and ED-50. Lethal dose (LD50) is the amount of an ingested substance that kills 50 percent of the Experimental Animal. Effective Dose (ED50) is the amount of of a drug needed to cure 50% of the Patients. drugs have larger therapeutic index is more safer. Drug with 1 therapeutic index is Unsafe for use.

Calculation of T.I.

8. Protein Binding- Post absorption the drug involve

Protein Binding

into the circulation process. Some of the Drug binds with the protein available in the blood circulation which are globulin and albumin. This bonding of Drug with the protein is an reversible process. All the drugs have capacity to bound with the proteins and according to this ability drugs are classified into Highly Protein Bound & Less Protein Bound. The Drug which is bound with the protein does not show any pharmaceutical action or not eliminated. This Protein bound drug is stored in the blood stream and when the free drug concentration is lowered in to the circulation, this stored drug is released. Now we can say that, Drug with higher protein binding exhibits longer duration of action and slower onset of action whereas, Drug with lower protein binding exhibits Shorter duration of action but quicker onset of action.

Enterohepatic Circulation

9. Enterohepatic Circulation- After absorption of the drug it reaches into the liver through portal vein where it is metabolized then again comes into systemic circulation. Some drugs after reaching liver may be secreted with bile and stored in the gall bladder and eventually are excreted into duodenum through bile duct.
From intestine it will be again absorbed and sent back to liver, which again released through bile in intestine again which shows a cyclic movement from Liver-intestine and intestine to liver. This Process is known as Enterohepatic Circulation. Drugs which enters in Enterohepatic circulation not easily available for excretion.

10. Placebo- Placebo is a pharmacologically inert substance with no known effect, which match with drug (under study), in its color, taste, smell & shape. It is generally used in clinical trials to avoid the pshychological effect produced by drug.

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Thanks & Regards.

Pankaj Pathak

Pharma Traino

www.pharmatraino.in

pharmatraino@gmail.com

+91- 7379163991