These are the simple concepts that are important to know and understand with medications:
Pharmacokinetics: the time of course of what the body does to the drug. Kinetics is about movement (the drugs transporting to and from the receptors) – mnemonic “ADME”
- Absorption: the movement of a drug from the bloodstream to the tissues. Most lipid-soluble drugs are absorbed through passive diffusion (directly penetrate membrane or dissolve in lipid layer)
- Distribution: when drugs are carried throughout the body and delivered to targets of action. Consider albumin levels: decrease protein = decrease distribution (older adults) or protein-bound drugs.
- Metabolism: the action of enzymes to activate meds. Drugs must become more hydrophilic (water-soluble for excretion).
- Excretion: the process of medications eliminated from the body unchanged or as metabolites.
Pharmacodynamics: What the drug does to the body -mnemonic 3D “dynamic drug – does to the body”. The relationships between drug concentrations & responses. Drug activity at receptors:
- Help a process happen: agonist
- Block a process from happening: antagonist
- Receptors: Drugs must bind to for effect
- Know that: All drugs have an effect
- A drug’s ability to cause a response is called its efficacy i.e. Morphine
- If you give a bigger dose you will get a bigger effect up to a point, most drugs have a ceiling.
Drug’s Potency & Selectivity: a potent drug is strong, but not necessarily better (2 nickels equals one dime, i.e. same) and can cause more side effects.
- Potency is not an important drug quality as you can give more of another drug to reach the same potency i.e. the opioid equivalent chart.
- Selectivity: the intended effects of a drug.
Adverse Drug Reactions (ADR): Unfavorable or unintended response to a drug that is given in normal dosages. Different from side-effects (SE) which is usually an undesirable or desirable additional effect that is known. ADR may be:
- Inherent pharmacologic effect (hypoglycemia/insulin)
- An allergic reaction: typical immunological response
- A local irritant effect: inflammation
- Often r/t P450 enzyme system and biotransformation alteration
- Interaction awareness; must be aware of and consult resources for possible interactions of new drugs with the current meds ->Report serious ADRs to FDA Medwatch Reporting Program
Properties of an Ideal Drug:
- Effectiveness: elicits responses for which it is given – most important
- Safety: Cannot produce harmful effects even at very high dosages and for a long time
- Selectivity: Only elicits a response for which it is given, no side effects
- Reversible action: most drugs should be reversible
- Predictability: Know with certainty exactly how an individual patient will respond – impossible, must individualize
- Ease of administration: simple, convenient route – enhances compliance and decreases errors
- Freedom from drug interactions: few drugs are without drug interaction
- Low cost: easy to afford; a significant factor in adherence, esp. with elderly
- Chemical stability: drugs’ ability to be stored for a long time without loss of effectiveness – variable between drugs
- Possession of a simple generic name: easier to remember and less confusion amongst drugs
