Pharmacodynamics Core Concepts Flashcards

Flashcards summarizing core pharmacodynamic concepts including dose-response parameters, receptor theory, drug side effects and ADRs, tolerance vs. tachyphylaxis, placebo pathways, PK/PD interactions, drug-nutrient/lab interactions, and drug-induced photosensitivity.

How is Pharmacodynamics defined in nursing?

Pharmacodynamics tells us what the drug does to the body, or the biological response.

What is Maximal Efficacy ($E_{max}$)?

The largest biological effect a drug can produce. Giving more drug after reaching this ceiling will not increase therapeutic effect, only the risk of toxicity.

How is drug Potency defined?

The amount of drug needed to produce a specific biological response (e.g., Fentanyl requires a much smaller dose than Morphine to produce an effect).

What is the Onset of Action?

The time it takes for a drug to reach the Minimum Effective Concentration (MEC) after administration, initiating a therapeutic response.

What is Peak Action?

The point at which a drug reaches its highest concentration in the blood plasma, resulting in the maximum therapeutic response.

What is Duration of Action?

The length of time the drug maintains its therapeutic effect (the time plasma levels remain above the MEC until they drop below it via clearance).

What defines the Therapeutic Range?

The safe plasma zone between the Minimum Effective Concentration (MEC) and the Minimum Toxic Concentration (MTC).

When should a nurse draw a drug's trough level?

Immediately before (usually 15–30 minutes) administering the next scheduled dose.

How does a receptor agonist function?

It binds to a receptor and activates it to produce a full biological response (100% effect).

How does a partial agonist function?

It binds to a receptor but produces only a moderate, submaximal response due to lower intrinsic activity than a full agonist.

How does a receptor antagonist function?

It binds to a receptor with high affinity but zero activation intensity (0% effect), blocking endogenous chemicals or agonist drugs from activating it.

What is a nonspecific drug effect?

An effect occurring when a drug targets one exact type of receptor, but that specific receptor is located in multiple different anatomical sites throughout the body.

How does Bethanechol (Urecholine) exhibit nonspecific drug effects?

It specifically targets cholinergic receptors, causing urination in the bladder (intended effect) while lowering heart rate, causing diarrhea, and constricting pupils in non-target sites.

What is a nonselective drug effect?

An effect occurring when a drug acts on entirely different types of receptors across various tissue layers.

Which three receptor profiles does Epinephrine bind to?

$\alpha_1$ receptors (constricts blood vessels), $\beta_1$ receptors (increases heart rate), and $\beta_2$ receptors (dilates bronchioles).

What is the key difference between Side Effects and Adverse Drug Reactions (ADRs)?

Side effects are secondary, predictable effects at therapeutic doses that do not typically require stopping the drug; ADRs are unintended, unpredictable, noxious effects at therapeutic doses that always require clinical intervention.

What is an Idiosyncratic Response to a drug?

A completely unexpected, highly unusual, and individualized reaction to a drug that is not related to its known pharmacological properties or allergies.

What is the difference between Drug Tolerance and Tachyphylaxis?

Tolerance is a gradual decrease in drug responsiveness over a prolonged period of exposure; Tachyphylaxis is an acute, rapid decrease in responsiveness occurring almost immediately after administration.

Why must nitroglycerin transdermal patches have a drug-free interval of 10–12 hours at night?

To prevent tachyphylaxis, which occurs when the body rapidly exhausts the cofactors needed to convert nitroglycerin into its active vasodilator form.

How does Naloxone prove that the placebo effect in pain management is biological?

Injecting Naloxone instantly abolishes placebo analgesia because Naloxone physically blocks the mu-opioid receptors targeted by the brain's endogenous endorphins.

What is the distinction between Pharmacokinetic (PK) and Pharmacodynamic (PD) interactions regarding drug blood levels?

PK interactions directly change drug concentrations in the blood/tissue; PD interactions alter the overall biological effect while blood concentrations remain unchanged.

What occurs in a Pharmacodynamic Synergistic Effect ($1 + 1 > 2$)?

The combined effect of two drugs is significantly greater than the sum of their individual effects (e.g., mixing alcohol and benzodiazepines enhancing GABA activity).

Why does consuming Vitamin K reduce the effectiveness of Warfarin?

Warfarin inhibits Vitamin K Epoxide Reductase (VKORC1); excess Vitamin K bypasses this block, allowing the body to produce clotting factors and counteracting the drug's effect.

What severe reaction can occur when taking MAOIs alongside Tyramine-rich foods?

A hypertensive crisis caused by a massive accumulation of norepinephrine triggering severe vasoconstriction.

How does Amiodarone alter thyroid laboratory panel results?

It is rich in iodine and blocks the conversion of $T_4$ to active $T_3$, changing serum TSH, $T_3$, and $T_4$ values.

What causes the cell damage in a phototoxic drug reaction?

The drug absorbs UV light and transfers energy to oxygen molecules upon returning to ground state, producing reactive oxygen species (ROS) and free radicals that damage cell membranes and DNA.

What immunological mechanism causes a photoallergic drug reaction?

UV light converts drug molecules in the skin into haptens that bind to skin proteins to form a novel antigen, triggering a delayed T-cell-mediated hypersensitivity reaction (24–72 hours onset).