Dose and dosage of drugs, factors influencing dose, calculation of dose on the basis of age, sex, surface area, veterinary dose

1. POSOLOGY
Parag Jain
Assistant Professor
Chhattrapati Shivaji Institute
of Pharmacy
Durg, Chhattisgarh
Presented by

2. INTRODUCTION
• The word posology is came from the Greek words.
• The meaning of “Posos” is How Much and “Logos”
means Science.
• Posology is a branch of medical science.
• We can not fixed the dose of drug, because there are many
types of factors, which may influence the doses.
• The official dose of any medicines are given in pharmacopoeia,
which is show the actual average dose of medicines for adults
to be taken within 24 hrs.
• Hence it is a duty of doctors prescribe accurate dose and
mention frequency of medicines in prescription.

3. DEFINITION OF POSOLOGY
• Posology: It is a science which teach how to calculate
dose and quantity of drug , which is need to prescribe
to patient in order to get desire pharmaceutical action.

4. FACTORS INFLUENCING DOSE
• The ideal dose of medicines only produce desired
pharmacological action but may this action varies from person to
person.
• due to this reason, the dose of official medicines are given in the
form of range, which give the pharmacological action and the
given range of dose depend on the adult requirement.
• There are some factors, which may affect the dose of drugs:
• Age
• Sex
• Body weight
• Route of administration

5. • Time of administration
• Environmental factor
• Emotional factor
• Presence of disease
• Accumulation
• Additive effect
• Synergism
• Antagonism
• Idiosyncrasy
• Tolerance
• Tachyphylaxis
• Metabolic disturbances

6. 1.Age
• The pharmacokinetic of drugs to be altered with age.
• Hence age plays an important role when
prescribing the medicines.
• Adult need high amount of dose than children or old
people , because they are not able to excrete the
drugs as adult can.
• Eg: paracetamol- 500 mg is adult dose not for children
Pharmacokinetic: It means ADME of drug

7. 2.Sex
• Women do not always respond to the action of drug
in same manner as it is done in men.
• In women, morphine produce excitement before
sedation but not happen same in men.
• Eg: Antihistamine, morphine and tetracycline not
given to the lactation mother, because these drugs
are excreted in milk.

8. 3. Body weight
• The dose is refer as dose for adults body weight
between 50- 100 kg.
• But in case of children or obese patient, the
dose of drug calculated according to body weight.
• If adult dose prescribed to children or obese
patient may chance of Causing undesirable effect

9. 4.Route of administration
• In oral route need high dose than
intravenous ,because IV administration of drug directly
goes to blood stream.
• Hence, the effectiveness can control by route
of administration.

10. 5.Time of administration
• Absorption of drug may decrease in presence of
food in stomach.
• Therefore, effect of drug become more if taken before
meal.
• Eg: Antacid should be taken before 1 hr of meal for
getting better effect.

11. 6.Environmental factor
• In day time the effect of stimulant drugs are more.
• Whereas sedative drugs are more effective at night.
• Eg: hypnotic has less effective at day and more
effective at night.

12. 7.Emotional factor
• Personality and behavior of doctor may affect
the effect of drug if he prescribe drug for
psychosomatic disorder.
• Female some time need less dose, because
female are more emotional than men.

13. 8.Presence of disease
• If patient have liver cirrhosis, then chloropromazine
produce prolong effect
• In case of fever patient can better tolerated antipyretic
drugs than normal one.

14. 9.Accumulation
• If drugs are repeatedly taken at short time drug
become accumulate into body, it will slowly excrete
out and may cause toxic effect.

15. 10.Additive effect
• When two or more drugs taken together, the total
action of drugs become more than their sum of
individual action.

16. 11.Synergism
• When drug taken in combination, their action
become increase.
• Synergism help to get desire action not achieve in
single dose. Eg:
Paracetamol+Aceclofenac+Seratopeptidase

17. 12.Antagonism
• Action of one drugs opposed by another drug if
administrated together .
• This kind of effect to be useful in poisoning cases.
• Eg: Milk of magnesia given in acid poisoning, because
milk of magnesia (alkaline) neutralize the effect of acid.

18. 13.Idiosyncrasy
• It is an extra effect of drug, which is different from its
actual effect.
• The idiosyncrasy word now replaced by allergy. Eg:
Small dose of quinine may cause ringing in ears.

19. 14.Tolerance
• Large dose of drug is need to obtain an effect produced by
normal dose of drug are called as drug tolerance.
• Types:
• True tolerance: Produced by administration of oral
route or parental route of drug.
• Pseudo tolerance: Produced by oral route of administration.
Eg: Alcoholic person may tolerate large quantity of alcohol.

20. 15.Tachyphylaxis
• If drug administered repeatedly at short interval then
the action of drug decrease due to blocking of cell
receptor and this decreased response can not
reversed by increasing dose.
• Eg: If ephedrine given in repeated dose in short
interval may produce very less effect for bronchial
asthma.

21. 16.Metabolic disturbances
• In which the effect of drug changed due to
change in body temperature, electrolyte balance,
acid-base balance
• Eg: Salicylic acid work on patient having fever,
not work on normal patient.

22. CALCULATIONS OF DOSES
• The administration of average dose for adult within 24
hrs by oral route are represent in official book.
• Whenever other route is used then the dose is
adjusted accordingly.
• Actually , the doses are calculate in proportion
to Age, Body weight and Surface area of patient.

23. A. Doses proportion to age
In which, child dose calculated from adult
dose following formula.
1. Young’s Formula: For under 12 years age child.
Age in year
Dose for child= ----------------------- X Adult dose Age
in year+12

24. 2. Dilling’s Formula: For children between 4 to 20 years old.
Age in year
Dose for child= ——————————— X Adult dose
20
B. Dose proportionate to body weight:
Calculating dose for child by using body weight.
Child’s weight in Kg
Dose for child = ------------------------------ X Adult dose
70

25. S.A of child
Percentage of adult dose = -----------------------X 100
S.A of adult
C. Doses proportionate to Surface Area (S.A):
Child dose can calculate according to surface
area, Its more satisfactory and complicated than method
based on age

26. VETERINARY DOSES
• Pharmacist having a compounding or dispensing knowledge of all
medicines whether it is for human beings or animal.
• The dose required for animal are higher side than for human
beings, because of this the dose for animals are calculate on the
basis of their surface area or body weight.
• Factors influencing dose of drug in animal:
• Age
• Sex
• Body weight and size
• Time of administration
• Route of administration

27. • Environmental conditions
• Habit
• Rate of elimination
• The effect of drug 10.Purpose of medication
• Species
• Character of drug

28. 1. Age:
• Young animal required less dose than adult one,
because susceptibility reason of young animal.
• Susceptibility: lack of ability to resist something.
2. Sex:
• Always female animal required less dose than male
animal, because many drugs are contra-indicated to
pregnant animal and may cause abortion.

29. 3. Body weight and size:
• The dose for animal is depend on their body weight and size.
• The size of animals are varies according to their breeds.
• Eg: In case of dogs. Heavy breed can tolerate some drugs but
lighter breeds can not.
4. Time of administration:
• Little dose of drug is more effective if taken in an empty
stomach than food stomach.
• Hence, time of administration of drug consider to achieve
desire effect.
• Eg: Purgative is more effective in an empty stomach.

30. 5. Route of administration:
• The dose of drugs changes with its route of
administration. Parenteral preparation given in small
dose than oral preparation.
• Oral >S/C>I/M>I/V
6. Environmental condition:
• Environmental moisture and temperature may affect
to animals tissue.
• In rainy season, when the climate little humid
and hot, less dose needed than in winter when
climate is dry and cold.

31. 7. Habit:
• Habit affect the dose and may develop tolerance for
drug.
• Hence, normal dose fail to produce desire effect, then
need to increase the dose.
8. Rate of elimination:
• This factor affect the dose of drug.
• Those drug are excrete at faster rate , need
large dose to produce effect.

32. 9. The effect of drug:
• When two drugs has similar action , given in combination
their action will increases than their individual dose.
• Otherwise they oppose to another drug. Will not
get actual effect.
10.Purpose of medicine:
• The dose of drug changes with it use
• Eg: Mg sulphate: act as purgative in large dose whereas
act like antacid or laxative in small dose.
• Laxative: same as purgative but less effective Antacid:
remove gases from GIT or anti-flatulent

33. 11. Species:
• The dose of drugs are not similar for all species.
• The dose for cow is different from horse, sheep, cat,
etc.
• Eg: opium produce excitement in horse but narcosis in
dog.
12. Character of the drugs:
• Large dose of Crude drug need to produce effect in
animal than its active constituents.
• Eg: Nux-vomica given in large dose than strychnine
alkaloid given in small dose.

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