Posology is the science of dosage, which encompasses the study of the amount of a medication that should be given to a patient, the frequency of administration, and the duration of treatment. It is a crucial aspect of pharmacology and therapeutics, as determining the correct dosage is essential for ensuring the safety and efficacy of a medication. Here are some of the key factors that are considered when determining posology: The patient's age, weight, and medical condition: These factors can all affect how a medication is metabolized and excreted from the body. For example, children and older adults may require different dosages than adults, and people with certain medical conditions may need to avoid certain medications or take them at lower doses. The severity of the condition being treated: The severity of the condition will often determine the dosage of medication that is needed. For example, someone with a mild infection may only need a low dose of antibiotics, while someone with a severe infection may need a higher dose. The form of the medication: Different forms of the same medication (e.g., tablets, capsules, injectables) can be absorbed into the body at different rates. This needs to be taken into account when determining the dosage. The route of administration: The route of administration (e.g., oral, intravenous, topical) can also affect how a medication is absorbed into the body. This needs to be taken into account when determining the dosage. Posology is a complex field, and there are many different factors that need to be considered when determining the correct dosage for a particular patient. It is important to consult with a healthcare professional to get advice on the appropriate dosage for any medication you are taking. Here are some additional details about posology: Posology is often expressed in terms of the following: Dose: The amount of medication that is given at one time. Frequency: How often the medication is given. Duration: How long the medication is taken for. There are a number of different ways to express posology, including: Milligrams (mg): This is a unit of mass that is commonly used to measure the amount of medication in tablets, capsules, and liquids. Micrograms (mcg): This is a unit of mass that is used to measure very small amounts of medication. International units (IU): This is a unit of activity that is used to measure some medications, such as insulin. Units: This is a unit that is used to measure some medications, such as heparin. The specific way that posology is expressed will vary depending on the medication and the condition being treated.

1. Unit 1.
Akanksha Patel
Asst prof.
Posology
The word posology is Derived from the Greek word ‘Posos-how much’, and ‘logos- science’.
“ It is the branch of medical science dealing with dose Or quantity of drugs which can be
administered to a patient to get the desired pharmacological actions”.
1. Age
2. Body weight
3. Sex/ gender
4. Route of Administration
5. Time of administration
6. Presence of disease/ pathological condition.
7. Environmental factors
8. Rate of elimination
9. Idiosyncrasy
10. Tachyphylaxis
11. Synergism
12. Antagonism
13. Psychological factors.

2. Unit 1.
Akanksha Patel
Asst prof.
1. Age: In determining the dose of a drug, the age of the patient is of great importance, especially
in the case of children and the elderly. The lower age group patients such as infants and chil-
dren have striking physiological differences from adults. This is because the organs liver and
kidney, which are responsible for biotransformation and excretion, are immature and still in the
generative stage.
In the case of geriatrics (elderly patients), the liver and kidney functions progressively decline
and the organs exhibit impaired ability to inactivate or excrete drugs.
2. Body weight: The recommended adult dose is based on the normal body weight of 70 kg but a
dose will be very less for a muscular person weighing about 100 kg and will be very high for
lean patient weighing about 40 kg. Child doses are usually calculated on the basis of body
weight.
3. Sex/Gender: In general, women require lesser dose than men because of their smaller body size
and also because they are more responsive and sensitive to certain drugs. Many drugs should
be avoided or monitored carefully during menstruation, pregnancy, and lactation.
4. Route of administration: The route of administration influences the efficacy of a drug in terms
of drug response, Absorption of drugs is more rapid and complete by parenteral administration
than by oral route. Drugs that are administered by parenteral route require lesser dose when
compared to oral doses.
A Single drug may exhibit varied uses through different routes. For example, magnesium
sulfate on oral administration results in purgative action, whereas it produces CNS depression
and hypotension when given intravenously.
5. Time of administration: Drugs that are absorbed rapidly should be given on empty stomach
whereas drugs that are irritant to the gastrointestinal tract should be given after meals. For
example,
-fatty meals enhance the absorption of griseofulvin, whereas food interferes with the absorption of
ampicillin.
-Antihistaminic drugs are more effective with empty stomach.

3. Unit 1.
Akanksha Patel
Asst prof.
6. Presence of disease/Pathological conditions: It is not only drugs that modify disease pr cesses,
but the presence of diseases can also influence drug disposition and drug action, For example,
gastrointestinal diseases can alter the absorption of orally administered drugs.
7. Environmental factors: Alcohol is better tolerated in a cold environment than in hot summer
The dose of sedative required to induce sleep during the day is more than that required in the
night. Hypnotics taken at night and in quiet, familiar surroundings may work more easily.
8. Rate of elimination: If age or disease impairs liver function, the breakdown of drugs may be
delayed, whereas if the kidney activity is reduced, the excretion of drugs will be incomplete.
Both the situations cause greater and prolonged activity of medicaments with a risk of toxic
reactions.
9. Idiosyncrasy: This is a genetically determined abnormal reactivity to a chemical. This term is
used to indicate exceptional and individual intolerance towards certain drugs. The drug interacts
with some unique feature of the individual, not found in majority of subjects, and produces the
uncharacteristic reaction.
10. Tachyphylaxis: This is defined as the rapid development of tolerance on repeated doses of a
drug in quick succession with a marked reduction in clinical response.(Tolerance refers to the
requirement of a higher dose of a drug to produce a given response.)
Examples of such drugs are ephedrine and nicotine.
11. Synergism: When the action of one drug is promoted or enhanced by the other, the drugs are
termed as synergistic in nature and the phenomenon as synergism. In a synergistic pair, both
the drugs can show action in the same direction or one may be inactive but still enhance the
action of the other when given together. The following are some examples of synergism:
(a) Aspirin + paracetemol is used as an analgesic/antipyretic
(b) Amlodipine + atenolol is used as an antihypertensive.
(c) Glibenclamide + metformin is used as a hypoglycemic.

4. Unit 1.
Akanksha Patel
Asst prof.
12. Antagonism: Antagonism is a phenomenon in which one drug decreases or blocks the action of
another. In an antagonistic pair, one drug is inactive as such but antagonizes the effect of the
other. The following are some examples of antagonism: a) Charcoal adsorbs alkaloids and can
prevent their absorption-used in alkaloidal poisoning.
(b) Potassium permanganate oxidizes alkaloids-used for gastric lavage in poisoning.
(c) Tannins + alkaloids-insoluble alkaloidal tannate is formed.
(d) Chelating agents (calcium disodium edetate) form complexes with toxic metals such as lead and
arsenic.
(d) Chelating agents (calcium disodium edetate) form complexes with toxic metals such as lead and
arsenic.
13. Psychological factors: Patient's beliefs, attitudes, and expectations remarkably affect the
efficacy of the drug, especially in the case of centrally acting drugs. For example, a nervous
and anxious patient needs more general anesthetic.
Formulas based on age, body weight, body surface area-

5. Unit 1.
Akanksha Patel
Asst prof.