Pharmacology: Components of Medicines

Inert Constituents

• Medicines often contain other substances besides the active drug, such as excipients, stabilizers, and solvents, to make them more convenient to use.

Toxicology

• Branch of pharmacology that deals with the undesirable effects of chemicals on living systems, from individual cells to humans to complex ecosystems.

Pharmacogenetics

• Study of genetic influences on responses to drugs.
• Focuses on familial idiosyncratic drug reactions, where affected individuals show an abnormal response to a class of drug.
• Also covers broader variations in drug response, where the genetic basis is more complex.

Pharmacogenomics

• Overlaps with pharmacogenetics, describing the use of genetic information to guide the choice of drug therapy on an individual basis.
• The underlying principle is that differences between individuals in their response to therapeutic drugs can be predicted from their genetic makeup.

The Nature of Drugs

• Drug molecules interact with specific molecules in the biologic system that play a regulatory role.

Pharmacology

• Study of substances that interact with living systems through chemical processes, especially by binding to regulatory molecules (receptors) and activating or inhibiting normal body processes.

Drug

• Defined as a chemical substance of known structure, which, when administered to a living organism, produces a biological effect.

Medicine

• A chemical preparation, which usually but not necessarily contains one or more drugs, administered with the intention of producing a therapeutic effect.

Sources of Drugs

• Plants (e.g., alkaloids)
• Animals (e.g., insulin, heparin)
• Minerals (e.g., magnesium sulfate)
• Microorganisms (e.g., penicillin)
• Semisynthetic (e.g., hydromorphone, hydrocodone)
• Synthetic (e.g., aspirin, paracetamol)
• Genetic engineering (e.g., human insulin, hepatitis B vaccine)

Drug Nomenclature

• Chemical name
• Non-proprietary name (generic name)
• Proprietary name (brand name)

Drug Reactivity and Drug-Receptor Bonds

• Drugs interact with receptors by means of chemical forces or bonds, including covalent, electrostatic, and hydrophobic bonds.

Interactions between a Drug and the Body

• Divided into two classes: pharmacodynamics and pharmacokinetics.

Pharmacodynamics

• The actions of the drug on the body, determining the group in which the drug is classified and playing a major role in deciding whether that group is appropriate therapy for a particular symptom or disease.

Pharmacokinetics

• The actions of the body on the drug, governing the absorption, distribution, metabolism, and elimination of drugs and being of great practical importance in the choice and administration of a particular drug for a particular patient.

Protein Targets for Drug Action

• Receptors
• Ion channels
• Enzymes
• Carrier molecules (transporters)

Receptors

• Sensing elements in the system of chemical communications that coordinate the function of all the different cells in the body.

Ion Channels

• Some ion channels incorporate a receptor and open only when the receptor is occupied by an agonist; others are gated by different mechanisms.

Enzymes

• Many drugs are targeted on enzymes, for example, captopril acts on angiotensin-converting enzyme (ACE) and inhibits it.

Carrier Molecules

• Transport of ions and small organic molecules across cell membranes generally requires a carrier protein.

Coupling

• The transduction process that links drug occupancy of receptors and pharmacologic response.

Affinity

• The ability of the drug to bind to the receptor.

Intrinsic Efficacy

• The ability of the drug to produce a response.

Constitutive Activity

• The effect occurring in the absence of agonist, referring to the inherent or spontaneous activity of a receptor in the absence of any ligand.

Agonists

• Molecules that, upon binding, cause a change in the activity of their targets by producing a conformational change.

Full Agonists

• Produce a maximal response upon binding to their targets, having high affinity and full intrinsic efficacy.

Partial Agonists

• Produce a submaximal response upon binding to their targets, having high affinity but low intrinsic efficacy.

Inverse Agonists

• Reduce any constitutive activity, resulting in effects that are opposite to the effects produced by conventional agonists at that receptor.