Key Takeaways
- Anaphylaxis is a medical emergency—stop medication and call for help immediately
- Opioid + benzodiazepine combination significantly increases respiratory depression risk
- Vitamin K foods (leafy greens) decrease warfarin effectiveness
- Elderly patients are at increased risk due to polypharmacy and altered drug metabolism
- Report adverse effects promptly and document patient responses to medications
Last updated: January 2026
Adverse Effects and Drug Interactions
Recognizing adverse drug effects and understanding drug interactions is critical for patient safety. LPN/VNs must monitor for expected and unexpected medication responses and report concerns promptly.
Terminology
| Term | Definition |
|---|---|
| Side Effect | Expected, often unavoidable effect secondary to therapeutic action |
| Adverse Effect | Harmful, unintended response to medication |
| Adverse Drug Reaction (ADR) | Serious adverse effect requiring intervention |
| Toxic Effect | Result of excessive dosing or accumulation |
| Allergic Reaction | Immune-mediated hypersensitivity response |
| Idiosyncratic Reaction | Unusual, unpredictable response in a particular patient |
| Anaphylaxis | Severe, life-threatening allergic reaction |
Signs of Anaphylaxis
Anaphylaxis is a medical emergency. Recognize and act immediately:
| System | Manifestations |
|---|---|
| Respiratory | Stridor, wheezing, dyspnea, throat tightness |
| Cardiovascular | Hypotension, tachycardia, weak pulse, shock |
| Skin | Hives, flushing, pruritus, angioedema |
| GI | Nausea, vomiting, abdominal cramps, diarrhea |
| Neurological | Dizziness, syncope, confusion |
Anaphylaxis Response:
- STOP the medication immediately
- Call for help (code/rapid response)
- Maintain airway, give oxygen
- Prepare for epinephrine administration (IM, anterolateral thigh)
- Establish IV access for fluids
- Monitor vital signs continuously
- Document event thoroughly
Drug-Drug Interactions
| Interaction Type | Description | Example |
|---|---|---|
| Synergism | Combined effect greater than sum | Opioid + benzodiazepine → increased sedation/respiratory depression |
| Antagonism | One drug reduces effect of another | Naloxone reverses opioid effects |
| Potentiation | One drug enhances another's effect | Probenecid prolongs penicillin effects |
| Additive | Combined effect equals sum | ASA + ibuprofen → increased bleeding risk |
High-Risk Interaction Categories:
| Category | Drugs | Concern |
|---|---|---|
| Bleeding risk | Warfarin + ASA/NSAIDs | Increased hemorrhage risk |
| Serotonin syndrome | SSRIs + MAOIs, tramadol | Fever, agitation, tremor, can be fatal |
| QT prolongation | Multiple QT-prolonging drugs | Arrhythmias, torsades de pointes |
| CNS depression | Opioids + benzodiazepines + alcohol | Respiratory depression, death |
| Hyperkalemia | ACE inhibitors + potassium supplements | Cardiac arrhythmias |
Drug-Food Interactions
| Drug | Food/Nutrient | Interaction |
|---|---|---|
| Warfarin | Vitamin K foods (leafy greens) | Decreased anticoagulation |
| MAOIs | Tyramine-rich foods (aged cheese, wine) | Hypertensive crisis |
| Tetracycline | Dairy products | Decreased absorption |
| Levothyroxine | Calcium, iron supplements | Decreased absorption |
| Grapefruit juice | Many drugs (statins, CCBs) | Increased drug levels, toxicity |
| Metformin | Alcohol | Increased lactic acidosis risk |
Drug-Disease Interactions
| Drug | Condition | Concern |
|---|---|---|
| NSAIDs | Renal disease | Worsens kidney function |
| Beta blockers | Asthma/COPD | May worsen bronchoconstriction |
| Anticholinergics | Glaucoma | Increases intraocular pressure |
| Decongestants | Hypertension | Increases blood pressure |
| Metformin | Liver disease | Increased lactic acidosis risk |
| Opioids | Respiratory conditions | Respiratory depression |
Age-Related Considerations
Pediatric Patients:
- Immature liver and kidney function affects metabolism
- Weight-based dosing essential
- Different volume of distribution
- Cannot verbalize side effects
- Higher risk of medication errors
Geriatric Patients:
- Decreased liver and kidney function
- Altered body composition (more fat, less water)
- Multiple medications (polypharmacy)
- Increased sensitivity to many drugs
- Higher fall risk with sedating medications
- Beers Criteria lists potentially inappropriate medications for elderly
Monitoring and Reporting
LPN/VN Responsibilities:
-
Before Administration:
- Review allergies
- Check for contraindications
- Assess for potential interactions
- Verify appropriate dose for patient factors
-
During/After Administration:
- Monitor for expected therapeutic effects
- Watch for adverse effects
- Assess vital signs as indicated
- Document patient response
-
When Adverse Effects Occur:
- Hold subsequent doses
- Notify RN and/or prescriber
- Document findings
- Implement supportive measures as ordered
- Complete adverse event/incident reports
High-Alert Monitoring
| Drug Class | Key Monitoring Parameters |
|---|---|
| Anticoagulants | Bleeding signs, labs (PT/INR, aPTT), stool for occult blood |
| Insulins | Blood glucose, hypoglycemia symptoms |
| Opioids | Respiratory rate, sedation level, pain relief |
| Antibiotics | Allergic reactions, C. diff symptoms, superinfection |
| Digoxin | Apical pulse, toxicity symptoms, drug levels |
| Diuretics | Electrolytes, I&O, weight, BP |
| Antihypertensives | Blood pressure, orthostatic changes, HR |
Test Your Knowledge
A patient on warfarin reports eating large amounts of spinach and kale over the past week. What effect might this have on therapy?
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Test Your Knowledge
Which combination of medications poses the highest risk for respiratory depression?
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C
D
Test Your Knowledge
What are the early signs of serotonin syndrome?
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B
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D