What is pharmacokinetics? | Types of dose

Types of Dose


Pharmacokinetics is the study of how the body processes a drug, including how it is absorbed, distributed, metabolized, and eliminated. It is concerned with understanding the movement of drugs within the body, from the point of administration to the point of elimination.

General principles of pharmacokinetics:


Most drugs are administered orally and the gastrointestinal absorption of drugs is a function of its physio-chemical properties (PKa, lipophilicity, molecular weight) and the Physiology of the gastrointestinal tract (pH, gastric emptying).


Distribution is a function of

affinity of drug for tissues and plasma blood flow rates to organs.

physiochemical properties of drug.


The drug may be bio transformed by metabolism mainly in the liver or other tissues.


Is a function of biotransformation in delivered to metabolites , excretion of the drug by the kidney.

What is dose?


It is a specific amount of a drug given to produce a desired effect.

Types of dose

Types of Dose:

Therapeutic dose / effective dose (ED50):

The average dose required to produce therapeutic effect in 50% of population treated is called therapeutic or effective dose (ED 50).

Maximal tolerated dose:

The substantial dose of a drug that can be taken securely is called maximal tolerated dose.

Initial dose:

Those of a drug given at the start of the treatment is called initial dose.

Maintenance dose:

Dose administered to replenish the amount of the drug which is eliminated in intervals between two doses, so that our steady concentration of drug is maintained in the plasma.

Loading dose:

The dose of a drug administered to rapidly achieve the desired concentration of drug in the body. In loading those, the amount of drugs should be increased but not the rate of administration.

Loading dose = Vd×Tc

Where VD = volume of distribution and Tc = target concentration.

Important note:

Drugs which is initiated with a initial loading dose include digoxin, teicoplanin, variconazole and procainamide. Phenytoin is for acute status epilepticus is given with a initial loading dose, and Co-administered with benzodiazepine.

Toxic dose (LD50):

Dose above the effective dose produced death in 50% of population treated is called toxic dose or lethal dose (LD50).

What is therapeutic index?

Therapeutic index:

Therapeutic index is the ratio between toxic dose (LD50) an effective dose (ED50).

Therapeutic index = LD50 / ED50

The therapeutic index is a measure of the drug safety because a large value indicates that there is a wide margin between doses that are effective and doses that are toxic.


Warfarin (anticoagulant) Is a drug with a small therapeutic index.

Penicillin (antibacterial) is a drug with a large therapeutic index.

Some other drugs with low therapeutic index include  Theophylline, lithium, digitalis, anti arrhythmic agents and antiepileptic drugs.

What is therapeutic window?

Therapeutic window:

It is a well defined range of a drugs serum concentration at which a desired effect occurs, below which there is a little effect and above which toxicity occur. it is the safe range between the minimum therapeutic concentration to minimum toxic concentration of a drug.

Learn more

What is pharmacokinetics?

What is the general principles of pharmacokinetics?

What is absorption In pharmacokinetics?

What is distribution in pharmacokinetics?

What is metabolism in pharmacokinetics?

What is elimination in pharmacokinetics?

What is dose?

Types of dose

Therapeutic dose or effective dose

What is therapeutic dose?

What is effective dose?

What id ED50?

What is maximal tolerated dose?

What is initial dose?

What is maintenance dose?

What is loading dose?

Formula for loading dose

What is toxic dose?

What is LD50?

What is therapeutic index?

Formula for therapeutic index

Examples of therapeutic index

Examples of drugs in therapeutic index

What is therapeutic window?

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