Pharmacokinetics: Drug Movement & Body Processes

Pharmacokinetics: Drug Movement in the Body

Pharmacokinetics is the study of all processes that occur from the moment a drug is administered until it is excreted, and how it exercises its effect at a determined concentration during an established time at its site of action.

Key Pharmacokinetic Processes (LADME)

Liberation

Liberation is the process by which the active ingredient of a medication is released from its dosage form. This involves disintegration and dissolution, making it available for absorption into the bloodstream. Some formulations prevent the disaggregation of the drug in the stomach lining to protect the active ingredient from stomach acid, which can also cause a delay in its release.

Absorption

Absorption is the process by which the active ingredient of an administered drug reaches the bloodstream from outside the organism. This absorption and its velocity determine the drug's bioavailability. To enter the body, the drug must pass through specific absorption pathways:

• Indirect Pathways: The drug penetrates the skin or mucous membranes.
  • Gastrointestinal Mucosa: Mouth, stomach, intestines.
  • Genito-urinary: Bladder, urethra, vagina.
  • Respiratory: Nose, trachea, bronchi, lungs.
  • Conjunctival.
• Direct Pathways: Offer a fast absorption rate, where the drug directly reaches the absorption site. The fastest way for drugs is via parenteral routes, which are absorbed through capillaries to reach general circulation.

Distribution

Distribution is the process where drugs, after reaching the blood plasma, distribute to other body areas. These areas may include sites of action, storage, or excretion. The volume of distribution (Vd) depends on the amount of drug given and its concentration in the plasma.

Metabolism

Metabolism is a set of enzyme reactions that drugs undergo in the body, resulting in a series of chemical substances. These reactions primarily occur in organs like the kidneys and liver, allowing for the elimination of the drug and reducing its toxicity once its therapeutic effect has been exerted.

Elimination

Elimination is the process by which drugs are removed from the circulation and expelled from the body once their effect has ceased. Pathways of excretion include:

• Kidneys
• Lungs
• Liver
• Salivary Glands
• Mammary Glands
• Intestinal Tract
• Sweat Glands
• Tear Glands

Depending on the drug concentration in the blood, it will be concentrated in these elimination pathways. Elimination primarily depends on renal excretion, pulmonary excretion, and hepatic excretion.

Therapeutic Drug Groups

Drugs are categorized into various therapeutic groups based on their primary action and target systems:

• Digestive System and Metabolism: Antacids, Antidiarrheals.
• Blood and Blood-Forming Organs: Anticoagulants, Antianemics.
• Cardiovascular System: Cardiac drugs, Anti-angina medications.
• Dermatology: Antiviral, Anti-psoriatic.
• Genito-urinary Therapy.
• Antineoplastic Agents.
• Musculoskeletal System.
• Nervous System: Anxiolytics, Anesthetics.