What are the four phases of drug action?

The four phases of drug action are absorption, distribution, metabolism, and excretion. Understanding these phases is crucial in pharmacology because they describe how a drug interacts with the body once it is administered.

• Absorption refers to the process by which a drug enters the bloodstream from the site of administration. This phase can be influenced by factors such as the route of administration (oral, intravenous, etc.), the drug's formulation, and the patient’s physiological condition.

• Distribution involves the dispersion of the drug throughout the body tissues and fluids. Once a drug is in the bloodstream, it binds to proteins within the plasma and then travels to various organs and sites of action. Factors such as blood flow, tissue permeability, and the drug's lipid solubility can affect distribution.

• Metabolism is the phase where the body chemically modifies the drug, primarily in the liver. This process transforms the drug into more water-soluble compounds for easier excretion. The rate and extent of metabolism can influence how long the drug remains active in the body, as well as its potential toxic effects.

• Excretion is the final phase whereby the drug or its metabolites are eliminated from the body, mainly through the kidneys in urine, but also through bile, sweat, saliva,