*Definition of POSOLOGY ?

It is branch of medical science which deal with the study of doses of drugs required to produce a specific pharmacological action.

*Meaning of POSOLOGY ?

Posology are made with two words combination.

1.Posos:- Means 'how much,

2.Logus:- Means 'Science,

*What is DOSE ?

The dose is defined as a quantity of drug which is enough but not too much to produce specific pharmacological action.

*The various factors affecting the dose of drug?

1.Age 

Generally old people and children are required small doses of drugs as compair to adults.

Age are determined the capacity of metabolism and excreting the drugs from body.

2. Sex 

Generally female adults required smaller doses as compair to males due to presence of more body fat .

3.Route of administration

Rate of absorption depends upon route of administration thus dose differs according to route.

For example

Intravenous dose

^ 

Intramuscular dose

^

Subcutaneous dose

^

Oral dose

4. Body Weight

According to Weight, the dose of drug varies .

Heavy weight person required larger dose as compared to normal weight person.

Generally 70kg is considered as a normal weight of adults for calculating doses.

5.Time of administration.

If the drugs are taken after meals(full stomach) absorption is lesser but no GIT(gastro intestinal tract) irritation.

If the drugs are taken on empty stomach or before meals then absorption of drug is greater but GIT(Gastro intestinal tract) irritation may be occur.

6.presence of Disease

In diarrhoea condition absorption of some drug are lesser.

7.Genetic Factor 

Deficiency of certain enzymes may be produce hereditory disorders .for example diabetes mellitus.

Drug allergies are also heritable for example sulpha allergy and penicillin allergy.

8.Environmental factors

The dose required to produce the action during day and night may be different due to some physiological changes in body functions.for example dose of phenobarbitone (barbiturates) required to produce a sleep during day time is higher than dose required to produce sleep at night.

9.Acquired Tolerance

It means a large quantity of a drug is required in order to obtain a desired effect on a drug. For example morphine,heroin produce Toler.

10.Idiosyncrasy 

It is ane abnormal or unusual response given by a drug. For example in some persons morphine causes asthma.

11.Rate of Elimination (cumulation)

Cumulation means accumulation of drug in the body due to slow excretion causing toxicity for example digitalis, chloramphenicol.

12.Synergism 

When administration of two or more drugs may result in incease of action . This phenomenon is known as synergism . For example aspirin phenacetin and caffeine as analgesic.

13.Antagonism

The opposite action of two drugs on the same physiological system is called antagonist.for example morphine and naloxone.

14. Tachyphylaxsis

Repeated administration of drug within short intervals of time decreases pharmacological response progressively. This is known as tachyphylaxis.for example ephedrine in treatment of bronchial asthma.