Pharmacology Overview and Drug Interactions

Study Notes

Pharmacology studies substances that interact with living systems via chemical processes, especially through binding to regulatory molecules.
These substances may produce therapeutic effects or toxic effects on parasites within a patient.
A drug is defined as any substance that induces a change in biological function via its chemical actions.

Drug molecules primarily interact with specific regulatory molecules in biological systems known as receptors.
Toxicology, a branch of pharmacology, addresses unwanted chemical effects on living systems from individual cells to ecosystems.

Effective drug molecules require appropriate size, electrical charge, shape, and atomic composition for successful receptor interaction.
Drugs may be administered far from their intended action site (e.g., oral pills for headaches).
Useful drugs must effectively reach and be retained at their site of action while also being inactivated or excreted at appropriate rates.

Placebos lack specific biological activity for the condition being treated.
Agonists, antagonists, and partial agonists are ligands that bind to the receptor activation sites.

Pharmacokinetics covers drug concentration time course, absorption, distribution, metabolism, and elimination.
Dosage schedules are critical for effective drug administration.
Variability may arise from genetic, environmental, and host factors affecting drug responses.

Drugs act on cell membranes by:
- Targeting specific receptors (e.g., adrenoceptors, histamine receptors).
- Modulating ion passage through cell membranes (e.g., calcium channel blockers).
- Inhibiting membrane-bound enzymes (e.g., cardiac glycosides blocking ATPase).

Drugs influence metabolic processes within cells through:
- Enzyme inhibition (e.g., aspirin inhibiting platelet cyclo-oxygenase).
- Blocking transport processes (e.g., probenecid affecting renal anion transport).
- Incorporation into larger molecules (e.g., 5-fluorouracil in RNA).

Successful antimicrobial agents alter unique metabolic processes in microorganisms (e.g., penicillin inhibiting bacterial cell wall formation).

Drugs can exert effects through:
- Direct chemical interaction (e.g., chelating agents).
- Osmotic effects (e.g., magnesium sulfate as a purgative).

Four main regulatory proteins serve as primary drug targets:
- Receptors
- Enzymes
- Carrier molecules (transporters)
- Ion channels

Most receptors are protein macromolecules; their activation leads to conformational changes that elicit cellular responses.
Receptors mediate chemical communication coordinating various body functions through hormones and transmitters.

Ligand-Gated Ion Channels
- Regulate ion flow across membranes; responses are rapid and last milliseconds.
- Examples include nicotinic and GABA receptors.
G Protein-Coupled Receptors (GPCRs)
- Consist of a single peptide with seven membrane-spanning regions linked to a G protein.
- Activation leads to changes in second messenger concentrations; responses last seconds to minutes.
Enzyme-Linked Receptors
- Enzymatic activity is part of receptor structure; binding can activate or inhibit these enzymes.
- Responses duration spans minutes to hours and often involve growth factor receptors or insulin receptors.

Insulin binds to its receptor, leading to autophosphorylation and the activation of downstream signaling pathways that affect cellular metabolism and function.