Introduction: Pharmacology
Basics of Pharmacology
Pharmacokinetics
What the body does to the drug
Think: ADME = Absorption -> Distribution -> Metabolism -> Excretion
A - Absorption
How does the medication get into the bloodstream?
Ex.
PO/oral: absorbed through GI tract
IV: directly into bloodstream -> essentially immediate systemic availability
IM: absorbed from muscle
Subcutaneous: absorbed from tissue
Sublingual: absorbed under tongue
Inhaled: absorbed through lungs
Topical: primary local effect depending on medication
Things can affect absorption: food, GI motility, blood flow, pH, other meds, & route of administration
D - Distribution
Once the med reaches bloodstream, where does it go?
It distributes throughout body tissues and fluids.
Things can influence distribution: blood flow, body composition, protein binding, ability to cross the BBB (blood brain barrier), lipid vs water solubility
A medication doesn’t necessarily distribute equally throughout the body.
M - Metabolism
The body chemically changes the medication, often making it easier to eliminate.
The liver is the major organ involved.
This is why liver function matters when administering meds
You may hear about: First pass metabolism
Oral medications travel through the GI tract and then through the liver before reaching systemic circulation, so some of the medication can be metabolized before reaching the bloodstream
E - Excretion
How does the medication leave the body?
The kidneys are extremely important.
Medications may be eliminated through: urine, feces/bile, lungs, sweat, breast milk
This is why kidney function is a huge nursing consideration.
If a patient has impaired renal function, a medication that is normally eliminated by the kidneys may accumulate.
Half-life
The time it takes for the amount of medication in the body to decrease by 50%
Ex.
100 mg -> 50 mg -> 25 mg -> 12.5 mg
N/N^0 = (1/2)^n
Understand the concept.
Short half-life
Leaves the body relatively quickly
May require more frequent dosing
Long half-life
Stays in the body longer
May require less frequent dosing
Can take longer to clear
*** Half-life influences how long a medication stays in the body and how long it may take to reach steady state or clear.
Pharmacodynamics
What the drug does to the body
This is different from pharmacokinetics
Pharmacokinetics: What the body does to the drug
Pharmacodynamics: What the drug does to the body
Pharmacodynamics include things like: receptors, drug effects, dose-response relationships, therapeutic effects, adverse effects
Receptors
Many medications work by interacting with receptors.
Think of a receptor as a lock and a drug as something that interacts with that lock.
Different drugs can interact with the same receptor in different ways.
Agonist
An agonist activates a receptor.
Think: agonist = activates
Antagonist
An antagonist blocks a receptor or prevents activation
Think: antagonist = against/blocking
This becomes REALLY important when you learn medications!
Therapeutic effect vs side effect vs adverse effect vs toxicity
Therapeutic effect
The desired effect
Ex.
A PT receives an antihypertensive
Desired effect: Blood pressure decreases
Side effect
An expected, secondary effect that isn't necessarily the intended therapeutic effect.
Ex.
A medication causes drowsiness even through its primary purpose isn't sedation.
Adverse effect
An undesirable and potentially harmful reaction.
Some adverse effects are mild; others can be serious
Toxicity
Too much drug effect / excessive drug accumulation resulting in harmful effects.
This can happen because of: excessive dose, accumulation, impaired metabolism, impaired excretion, drug interactions
A useful hierarchy:
Therapeutic - desired
Side effect - unwanted but often expected
Adverse effect - harmful/unwanted reaction
Toxicity - harmful effects from excessive drug exposure
Therapeutic index
Conceptually describes the margin between an effective dose and a toxic dose.
A medication with a narrow therapeutic window requires particularly careful monitoring because the effective dose and toxic dose are relatively close together.
Ex.
Warfarin, digoxin, certain anticonvulsants
For now just understand
Narrow therapeutic window = less room for dosing error.
Drug classes you should recognize
Class -> general action -> why it's given -> major things to monitor
ACE inhibitors
Ex.
Lisinopril, Enalapril, Ramipril
Generally these decrease BP
They interfere with the renin-angiotensin-aldosterone system.
Important concepts: lower BP, can cause cough, hyperkalemia, hypotension, and angioedema can occur and can be serious.
Kidney function matters
Beta blockers
Ex.
Metoprolol, Atenolol, Propranolol
Generally these decrease HR & BP
Beta blocker -> blocks sympathetic effects -> slower heart / lower BP
Major nursing considerations: HR, BP, dizziness, bradycardia
Always pay attention to PT's HR before administration.
Calcium-channel blockers
Ex.
Amlodipine, Diltiazem, Verapamil
Generally these relax blood vessels and/or decrease cardiac activity
Depending on the drug, you may see: lower BP, lower HR, vasodilation.
Potential concerns: Hypotension, dizziness, bradycardia with some agents, peripheral edema
Diuretics
"Water pills" ; they make you piss
They increase sodium/water excretion through the kidneys
Ex.
Loop: Furosemide (Lasix)
Thiazide: Hydrochlorothiazide
Potassium-sparing: Spironolactone
Generally these decrease fluid volume -> lowers BP / lowers edema
But here's the important nursing connection: If you're making the PT pee more, you need to think about fluid balance, BP, electrolytes, kidney function
For example, some diuretics can cause hypokalemia, while potassium-sparing medications can cause hyperkalemia.
Anticoagulants
Ex.
Heparin, Enoxaparin, Warfarin, Apixaban
Decrease clot formation
Think: Anticoagulant = affects the clotting process
Major nursing concern: BLEEDING, watch for things such as unusual bruising, bleeding, hematuria, GI bleeding, Changes in neurological status that could suggest intracranial bleeding
Different anticoagulants have different monitoring requirements.
Antiplatelets
Ex.
Aspirin, Clopidogrel
They interfere with platelet aggregation, also decrease clot formation. But they aren’t the same as anticoagulants.
Antiplatelet
Platelets
Anticoagulant
Coagulation / clotting factors
Insulin
Lowers blood glucose
Hypoglycemia: symptoms include shaking, sweating, confusion, weakness, tachycardia, irritability, and severe hypoglycemia can lead to seizures and unconsciousness.
Insulin lowers blood glucose -> you need to monitor glucose levels -> watch for hypoglycemia
Opioids
Ex.
Morphine, Oxycodone, Hydromorphone, Fentanyl
Generally used for pain management
Major concerns: respiratory depression, but also sedation, hypotension, constipation, nausea/vomiting, dependency/addiction
One HUGE nursing principle:
With opioids, respiratory status matters.
** Naloxone: an opioid antagonist used to reverse opioid effects.
NSAIDs
Ex.
Ibuprofen, Naproxen, Ketorolac
Generally decrease pain, inflammation, and fever
Major concerns: GI irritation/bleeding, kidney injury, fluid retention, cardiovascular risks in certain PT's
NSAIDs -> stomach + kidneys + bleeding
Antibiotics
Antibiotics treat bacterial infections (NOT viruses)
Major concepts: broad vs narrow spectrum, culture and sensitivity, resistance, allergies, adverse effects, completing prescribed therapy, timing, renal/hepatic considerations.
Culture -> identify organism -> determine susceptibility -> choose appropriate antibiotic
Corticosteroids
Ex.
Prednisone, Methylprednisolone, Dexamethasone
Generally these decrease inflammation and suppress immune responses
Important potential effects: increased blood glucose, increased infection risk, fluid retention, mood changes, GI effects, long-term effects on bone health, adrenal function, etc.
Some corticosteroids should not by abruptly stopped after prolonged use.
Benzodiazepines
Ex.
Lorazepam, Diazepam, Midazolam, Alprazolam
Generally these are CNS depressants -> sedation/anxiolysis
Potential effects: drowsiness, decreased anxiety, impaired coordination, respiratory depression, particularly with other CNS depressants, dependence
Benzodiazepines + opioids = potentially dangerous CNS/respiratory depression
Antidepressants
Major categories include SSRIs & SNRIs
SSRIs
Ex.
Sertraline, Fluoxetine, Escitalopram
Generally increase serotonergic signaling
SNRIs
Ex.
Venlafaxine, Duloxetine
A major thing to understand before school:
These medications don't necessarily produce immediate therapeutic effects.
Many antidepressants take weeks for their full therapeutic effects to develop.
Medication Routes
PO
By mouth
IV
Intravenous
IM
Intramuscular
SQ / SubQ
Subcutaneous
SL
Sublingual
PR
Rectal
Topical
Applied to skin
Inhalation
Breathed into lungs
Transdermal
Through skin into systemic circulation
Medication safety
*** Prioritize this
Right Patient - Is this the correct Pt?
Right medication - Is this the correct drug?
Right dose - Is the dose correct?
Right route - PO? IV? IM? Etc.
Right time - Is it due now?
And depending the framework/program: right documentation, reason, response, education, refusal…
The larger principle is verify before you administer.
Medication Reconciliation
What medications is the Pt actually taking?
This includes: prescription medications, OTC medications, vitamins, supplements, herbal products
Because Pts can have interactions that aren’t obvious if you only look at their prescriptions.
Drug Interactions
Medication A affects medication B
Ex.
Two CNS depressants together -> increased sedation / respiratory depression
Drug-food interaction
Food affects a medication.
Some meds have specific food restrictions or timing considerations.
Medication doesn't exist in isolation.
Pharmacological vs non-pharmacological treatment
Nursing isn't "Pt has problem -> give medication."
You also consider: positioning, oxygen when indicated, hydration, nutrition, rest, mobility, ice/heat when appropriate, wound care, pt education, environmental changes, emotional support.
Medication is only one intervention.
Medication Assessment
Before giving medication, you should be thinking about why the Pt is getting this medication
Ex.
Pt is prescribed metoprolol
Don't just think "give metoprolol"
Think:
Why?
Hypertension? Arrhythmia? Heart failure? Other indication?
What does it do?
Decreases sympathetic cardiac effects.
What should I assess?
HR/BP & relevant pt status
What could go wrong?
Bradycardia, hypotension, etc.
What should I teach?
Depends on the medication and indication
That is nursing pharmacology thinking.
Lab Values
Electrolytes
Na+ - Sodium
K+ - Potassium
Ca2+ - Calcium
Mg2+ - Magnesium
Kidney
BUN
Creatinine
eGFR
Liver
AST
ALT
Blood
Hgb
Hct
Platelets
Glucose
Blood glucose
A1C
You'll repeatedly connect medications to these.
Ex.
Diuretic -> electrolytes + kidney function + BP
Vital Signs + Medications
Whatever the medication affects, assess that.
Ex.
Medication lowers BP -> check BP
Medication lowers HR -> check HR
Medications affects fluid balance -> I&O + weight + edema + electrolytes
Weight-based medications
You'll see mg/kg, meaning the dose depends on the pts weight
Ex.
Medication ordered: 5 mg/kg
Pt's weight: 20 kg
Dose: 100 mg
*** that is a perfect dosage calc problem!
Concentration
If you have 250 mg / 5 mL, there are 250 mg of medication in every 5 mL
You then use that concentration to determine how many mL the pt should receive.
***This connects directly to D/H x W dosage calculations.
IV Medications
IV medication enter the bloodstream directly, so errors can become serious very quickly.
You'll encounter: IV push, IV piggyback (IVPB), continuous infusion, intermittent infusion
Calculations will involve: mL/hr, drops/min, units/hr, mgc/min, mcg/kg/min
High-alert medications
Some medications have a particularly high risk of causing significant harm if administered incorrectly.
Ex.
Insulin, Anticoagulants, Opioids, certain IV meds
Hospitals often have additional safety procedures for these medications.
***The more dangerous the medication, the more carefully you verify it.