PN Pharmacology: Oral Medications, Calculations, Common Drug Classes, Side Effects

PN Pharmacology: Oral Medications, Calculations, Common Drug Classes, Side Effects

A practical guide for practical nurses (PNs) to administer, calculate, and monitor oral medications safely.

What Is This?

Oral pharmacology is the study of medications given by mouth (tablets, capsules, liquids, sublingual, buccal). PNs use this knowledge to: - Calculate safe doses based on patient weight, age, and renal/hepatic function. - Administer drugs correctly (e.g., with/without food, crushed vs. whole). - Monitor for side effects and drug interactions. - Educate patients on proper use and risks.

Why it matters today: Oral medications are the most common route of administration. Errors in dosing, timing, or patient education can cause harm, legal liability, or treatment failure.

Why It Matters

1. Patient Safety: 1 in 5 medication errors involve oral drugs (ISMP). Miscalculations or improper administration can lead to overdose, underdose, or adverse reactions.
2. Efficiency: Correct dosing and administration reduce hospital readmissions and improve outcomes (e.g., antibiotics, antihypertensives).
3. Legal Compliance: PNs must document doses, times, and patient responses per state nursing boards and facility policies.
4. Patient Trust: Clear education on side effects and administration builds compliance (e.g., "Take this with food to avoid nausea").

Core Concepts

1. Drug Forms & Routes

2. The 6 Rights of Medication Administration

Verify every time before giving a drug:
1. Right Patient (2 identifiers: name + DOB/MRN).
2. Right Drug (check label 3x: when pulling, preparing, and administering).
3. Right Dose (calculate and double-check; use drug guide for safe ranges).
4. Right Route (oral, sublingual, etc.—never assume).
5. Right Time (e.g., "bid" = twice daily; "q6h" = every 6 hours).
6. Right Documentation (time, dose, route, patient response, and any refusals).

Pro Tip: Add the "7th Right"—Right to Refuse. Document if a patient declines and notify the provider.

3. Drug Calculations: Key Formulas

Basic Dose Calculation

Formula: Desired Dose (mg) / Available Dose (mg) × Quantity (mL/tablet) = Amount to Administer

Example: Order: Amoxicillin 500 mg PO q8h Available: 250 mg/5 mL suspension Calculation: 500 mg / 250 mg × 5 mL = 10 mL

Weight-Based Dosing

Formula: Patient Weight (kg) × Dose (mg/kg) = Total Dose (mg)

Example: Order: Gentamicin 2 mg/kg IV q8h Patient weight: 68 kg Calculation: 68 kg × 2 mg/kg = 136 mg

Critical Note: - Always convert pounds (lbs) to kilograms (kg): Weight (lbs) ÷ 2.2 = Weight (kg) - Check safe dose ranges in a drug guide (e.g., Lexicomp, Davis’s Drug Guide).

IV to PO Conversion

Some drugs have equivalent oral doses (e.g., levothyroxine, furosemide). Use a conversion table or consult pharmacy.

4. Common Drug Classes & Side Effects

Red-Flag Side Effects (Report Immediately): - Anaphylaxis (hives, swelling, stridor). - Stevens-Johnson Syndrome (rash + blisters; e.g., with sulfa drugs). - Neuroleptic Malignant Syndrome (fever, rigidity; e.g., antipsychotics). - Serotonin Syndrome (agitation, tachycardia; e.g., SSRIs + tramadol).

How It Works: The Journey of an Oral Medication

1. Administration:
2. Patient swallows drug (or dissolves sublingual/buccal).

3. First-pass effect: Some drugs (e.g., morphine, propranolol) are metabolized by the liver before reaching systemic circulation.

4. Absorption:

5. Stomach: Acidic drugs (e.g., aspirin) absorb here.
6. Small Intestine: Most drugs absorb here (pH 6–7.4).

7. Factors affecting absorption:

   • Food (e.g., levothyroxine on empty stomach; ibuprofen with food).
   • GI motility (e.g., diarrhea speeds up transit; constipation slows it).
   • Drug form (e.g., liquid > tablet absorption).

8. Distribution:

9. Drug binds to proteins (e.g., albumin) or travels freely in blood.

10. Key sites: Brain (BBB), fat (lipophilic drugs like diazepam), muscle.

11. Metabolism:

12. Liver (CYP450 enzymes): Breaks down drugs (e.g., warfarin, statins).

13. Genetics: Some patients are "poor metabolizers" (e.g., codeine-morphine conversion).

14. Excretion:

15. Kidneys: Filter water-soluble drugs (e.g., penicillin, lithium).
16. Liver/Bile: Fat-soluble drugs (e.g., digoxin) excreted in feces.
17. Half-life (t½): Time for drug concentration to drop by 50%. Determines dosing frequency (e.g., q6h vs. q24h).

Hands-On: Getting Started

Prerequisites

• Knowledge: Basic math (fractions, decimals), metric conversions (mg-g, mL-L).
• Tools:
• Drug guide (e.g., Davis’s Drug Guide, Lexicomp).
• Calculator (or phone app like MedCalc).
• Measuring devices (oral syringes, medicine cups).
• Skills: Ability to read orders, verify allergies, and document.

Step-by-Step: Administering an Oral Medication

Scenario: Patient is ordered acetaminophen 650 mg PO q6h PRN for pain >4/10.

1. Verify the Order:

2. Check MAR (Medication Administration Record) for:

   • Drug name, dose, route, frequency, PRN reason.
   • Allergies (e.g., "NKDA" = no known drug allergies).

3. Calculate the Dose:

4. Available: 325 mg tablets.

5. Calculation: 650 mg / 325 mg = 2 tablets.

6. Prepare the Medication:

7. Wash hands.
8. Pour 2 tablets into a medicine cup.

9. Do not touch tablets (use gloves if needed).

10. Perform the 6 Rights:

11. Patient: Scan ID band + ask name/DOB.
12. Drug: Check label 3x (acetaminophen 325 mg).
13. Dose: 2 tablets = 650 mg.
14. Route: PO (oral).
15. Time: Check last dose (q6h = every 6 hours).

16. Documentation: Leave blank until after administration.

17. Administer:

18. Assist patient to sit up.
19. Offer water (unless NPO).

20. Stay until patient swallows pills (prevent "cheeking").

21. Document:

22. Time, dose, route, pain score (e.g., "650 mg PO given for pain 5/10. Pain now 2/10").

23. PRN meds: Always document why it was given (e.g., "PRN for headache").

24. Monitor:

25. Reassess pain in 30–60 minutes.
26. Watch for side effects (e.g., rash, nausea).

Common Pitfalls & Mistakes

Best Practices

1. Double-Check Calculations:
2. Have a second nurse verify high-alert drugs (e.g., insulin, opioids, heparin).

3. Use the "5-second rule": Pause and recheck your math before administering.

4. Teach Patients Effectively:

5. Teach-back method: "Can you show me how you’ll take this at home?"
6. Side effects: "This may cause dizziness—stand up slowly."

7. Missed doses: "If you miss a dose, take it as soon as you remember, unless it’s almost time for the next dose."

8. Document Thoroughly:

9. PRN meds: Always note why it was given (e.g., "PRN for nausea").

10. Refusals: Document reason (e.g., "Patient refused—stated ‘I don’t need it’").

11. Monitor for Adverse Reactions:

12. Allergic reactions: Stop drug, assess ABCs (airway, breathing, circulation), notify provider.

13. Toxicity: Know antidotes (e.g., naloxone for opioids, vitamin K for warfarin).

14. Stay Updated:

15. Attend pharmacology updates (e.g., new black-box warnings for NSAIDs).
16. Use drug interaction checkers (e.g., Epocrates, Micromedex).

Tools & Frameworks

Real-World Use Cases

1. Post-Op Pain Management

Scenario: A patient s/p knee replacement is ordered oxycodone 5 mg PO q4h PRN for pain >5/10. - PN Actions: - Assess pain scale (e.g., 7/10). - Check last dose (q4h = 4 hours since last dose). - Administer 5 mg with water. - Document: "0900: Oxycodone 5 mg PO given for pain 7/10. Pain now 3/10. RR 16, no sedation." - Monitor for respiratory depression (RR <12).

2. Hypertension Management

Scenario: A patient with BP 160/90 is ordered lisinopril 10 mg PO daily. - PN Actions: - Check BP (hold if SBP <90). - Teach: "This may cause a dry cough—let us know if it’s bothersome." - Monitor for angioedema (swelling of face/lips—emergency). - Document: "1000: Lisinopril 10 mg PO given. BP 158/88. No cough or swelling."

3. Antibiotic Stewardship

Scenario: A patient with a UTI is ordered ciprofloxacin 500