Posology Factors affecting posology Pharmaceutics-1

Posology |Factors affecting posology |Pharmaceutics-1| B.Pharmacy 1st year |Semester-1 notes 

Posology b.pharmacy pharmaceutics-1 notes

Definition: 

Posology is a branch of medical science which deals with dose or quantity of drugs which can be administered to a patient to get the desired pharmacological action.

Factors Affecting Posology:-

1. Age: People can be divided into age groups:

1. Newborn: From birth to 30 days.

2. Infant: Up to 1 year old

3. A child between the ages of 1 and 4 years

4. A child between the ages of 5 and 12.

5. Adult

6. Geriatric patients (adults).

In children the enzyme systems in the liver and kidney system remain undeveloped. So the total dose should be less than that of an adult. In older patients kidney function decreases. The rate of metabolism in the liver also decreases. Intake of the drug in the gut is slower in older patients. So in older patients the dose is small and should be given tactfully.

2. Sex: Special care should be taken when giving any medicine to a woman during menstruation, pregnancy and breastfeeding. Vigorous vomiting should not be given during pregnancy and pregnancy. Antimalarials, ergot alkaloids should not be taken during pregnancy to prevent fetal deterioration. Antimicrobials and sedatives are not taken during breastfeeding because these are extracted from the milk and the baby may eat.

3) Body size: It affects the fullness of the drug in the body. The average dose is calculated for a person who weighs 70kg (BW). In a patient who is overweight (obese) or thin (thin) the dose can be calculated on the basis of body weight.

4. Management route

In the case of intravenous injection the amount of the drug quickly reaches the circulatory system which is why the dose becomes smaller in i.v. injection than oral route or any other route.

5. Management time

Medications are absorbed very quickly on an empty stomach. The presence of food in the stomach slows down the absorption of the drug. Therefore a strong medicine is given before meals. An irritating drug is given after meals so that the medicine is purified with food and thus produces less irritation.

6. Natural features

The restorative drugs are taken during the day and the narcotic forms are taken at night. Therefore the required sedative dose during the day will be much higher than at night.

Alcohol is better tolerated in winter than in summer.

7. Attitude

Psychological attitudes can affect a drug response, e.g. a nervous and anxious patient needs normal sensations. A placebo is an inactive substance that does not contain any medication. The placebo is widely used for lactose intolerant and fortified water injections. Sometimes patients often experience certain psychological effects on this placebo. Placebos are widely used in clinical trials for drugs.

8. Pathological Conditions (i.e. Presence of Diseases)

Many diseases can affect the dose of the drug:

In intestinal infections such as achlorhydria (decreased production of HCl acid in the stomach) aspirin absorption decreases.

In liver disease (such as cirrhosis of the liver) the metabolism of other drugs (such as morphine, pentobarbitone etc.) decreases.

In kidney disease the release of drugs (such as aminoglycosides, digoxin, phenobarbitone) is reduced, so a small dose of the drug should be given.

9. Collection

Any drug will accumulate in the body if the absorption rate exceeds the level of elimination. Slowly digested drugs often accumulate in the body and often cause toxicity e.g. prolonged use of chloroquin causes damage to the retina.

10. Drug interactions

Simultaneous administration of two drugs may cause similar effects or increase or decrease.

11. Idiosyncrasy

This is an unusual reaction to medication in a few patients. For example, in some patients, aspirin can cause asthma, penicillin can cause irritating rash on the skin, and so on.

12. Genetic diseases

Some patients may have genetic defects. They have no enzymes. In those cases some drugs are contraindicated.

e.g. Patients who do not have Glucose-6-phosphate dehydrogenase enzyme should not be given primaquin (an anti-malarial drug) as it will cause bleeding.

13. Tolerance

In some cases a higher dose of the drug is required to produce the given response (previously a smaller dose was required).