What are the key factors to consider before administering medication to a patient, especially those with impaired renal function, pregnancy, or a history of adverse reactions?

Key Factors to Consider Before Administering Medication

Renal Function Assessment

Before prescribing any medication, obtain an estimated glomerular filtration rate (eGFR) and assess renal function, as impaired kidney function is the single most critical factor affecting drug safety and dosing. 1

Specific Renal Considerations:

• Assess eGFR before initiating any renally-cleared medication, as patients with chronic kidney disease (CKD) are more susceptible to nephrotoxic effects and medication accumulation 1
• For medications with narrow therapeutic windows (e.g., vancomycin, digoxin, aminoglycosides), use validated eGFR equations combining creatinine and cystatin C, or measured GFR for greater accuracy 1
• In patients with extremes of body weight, use eGFR non-indexed for body surface area, especially for medications requiring minimum effective concentrations 1
• Monitor eGFR at least annually in all patients on renally-cleared medications, and more frequently in elderly patients at risk for declining renal function 1
• For metformin specifically: contraindicated if eGFR <30 mL/min/1.73 m²; initiation not recommended if eGFR 30-45 mL/min/1.73 m²; discontinue if eGFR falls below 30 during therapy 2

Opioid Selection in Renal Impairment:

• Fentanyl is the preferred opioid for any degree of renal dysfunction, including dialysis patients, due to minimal renal clearance and lack of active metabolites 3
• Morphine and codeine are contraindicated in renal impairment due to accumulation of toxic metabolites 3
• Hydromorphone requires significant dose reduction and extended intervals due to active metabolite accumulation 3
• Buprenorphine is equally safe in CKD stages 4-5 with no dose reduction necessary 3

Pregnancy and Teratogenicity

When prescribing to patients of childbearing potential, always review teratogenicity potential and provide regular reproductive counseling. 1

• Assess pregnancy status before initiating any medication with known teratogenic effects 1
• Doxycycline is pregnancy category D and should be avoided in pregnant women 4
• Metformin considerations: while not explicitly contraindicated, requires careful risk-benefit assessment in pregnancy 2

Hepatic Function

Avoid medications in patients with clinical or laboratory evidence of hepatic disease when hepatic clearance is significant. 2

Specific Hepatic Considerations:

• For metformin: avoid use in patients with hepatic impairment, as impaired lactate clearance increases lactic acidosis risk 2
• For opioids: fentanyl remains safest with unaffected pharmacokinetics in hepatic disease; all opioids can precipitate hepatic encephalopathy requiring cautious use 3
• Assess hepatic function before initiating medications with significant hepatic metabolism 1

Drug Interactions and Polypharmacy

Review all medications—prescription, over-the-counter, herbal, and supplements—to identify potential drug-drug interactions and unnecessary duplications. 1

• Assess for medications that impair renal function, result in hemodynamic changes, interfere with acid-base balance, or increase drug accumulation 2
• For metformin: concomitant use with drugs affecting renal function increases lactic acidosis risk; requires more frequent monitoring 2
• Review and limit over-the-counter medicines and herbal remedies that may be harmful, particularly in CKD patients 1
• Establish collaborative relationships with pharmacists to ensure comprehensive medication management and drug stewardship 1

Age-Related Considerations

Elderly patients (≥65 years) require special attention due to increased risk of adverse effects from age-related physiologic changes. 1, 2

• Assess renal function more frequently in elderly patients, as they have greater likelihood of hepatic, renal, or cardiac impairment 1, 2
• For metformin: risk of lactic acidosis increases with age; assess renal function more frequently in elderly patients 2
• Consider low-dose regimens for elderly patients, as most substances are prescribed in inappropriately high doses 1
• Evaluate for declining function comprehensively, including cognitive impairment, which predicts drug-related hospital admissions 1

Contraindications and Absolute Restrictions

Identify absolute contraindications before prescribing any medication. 2

Metformin-Specific Contraindications:

• eGFR <30 mL/min/1.73 m² 2
• Clinical or laboratory evidence of hepatic disease 2
• Acute conditions with hypoxemia risk: acute congestive heart failure with hypoperfusion, cardiovascular collapse, acute myocardial infarction, sepsis 2
• During iodinated contrast procedures: discontinue in patients with eGFR 30-60 mL/min/1.73 m², history of liver disease, alcoholism, heart failure, or intra-arterial contrast administration 2

Monitoring Requirements

Monitor eGFR, electrolytes, and therapeutic medication levels when indicated, particularly for medications with narrow therapeutic windows or nephrotoxicity potential. 1

• For medications with narrow therapeutic windows: monitor therapeutic levels, renal function, and electrolytes in both outpatient and hospital settings 1
• For metformin: obtain eGFR at least annually; monitor vitamin B12 at 2-3 year intervals 2
• For opioids: respiratory monitoring every 15 minutes after each dose, including respiratory rate, oxygen saturation, and sedation level 3

Special Clinical Situations

Surgical Procedures and NPO Status:

• Temporarily discontinue metformin during surgical procedures with restricted food/fluid intake due to volume depletion and hypotension risk 2

Alcohol Use:

• Warn against excessive alcohol intake with metformin, as alcohol potentiates effects on lactate metabolism 2

Comorbidities:

• Consider GFR when dosing renally-cleared medications 1
• Assess benefit versus risk when prescribing nephrotoxic medications to CKD patients 1
• For patients with ≥3 comorbid conditions: initiate direct communication with primary care provider about treatment plan 1

Patient Education and Involvement

Educate patients regarding expected benefits and possible risks so they can identify and report adverse events. 1

• Provide explicit written instructions for appointments, medications, and treatments, particularly for patients with cognitive impairment 1
• For metformin: educate patients about lactic acidosis symptoms (malaise, myalgias, abdominal pain, respiratory distress, somnolence) and instruct immediate discontinuation if symptoms occur 2
• Include patients in medication safety through self-monitoring and reporting 1

Common Pitfalls to Avoid

• Never use standard dosing protocols for organ failure—always start with lower doses and titrate carefully 3
• Do not assume all medications within a class are equally safe—recognize differences in metabolite accumulation and risk profiles 3
• Avoid reflexive prescribing without assessing renal function, particularly for renally-cleared medications 1
• Do not ignore over-the-counter medications and supplements when assessing drug interactions 1