For a patient with moderate renal impairment (creatinine clearance 30–50 mL/min) undergoing a standard 12‑week varenicline (Chantix) smoking‑cessation regimen, how many 0.5 mg tablets are required and which pack sizes (53, 56, or 60 tablets) should be used?

Varenicline Pack Sizes for Moderate Renal Impairment: 12-Week Regimen

For a patient with moderate renal impairment (CrCl 30–50 mL/min) undergoing a standard 12-week varenicline regimen, you need a total of 137 tablets of 0.5 mg, requiring one 53-tablet starter pack plus two 56-tablet continuation packs (or alternative combinations totaling ≥137 tablets). 1

Renal Dosing Requirement

• Patients with moderate renal impairment (creatinine clearance 30–50 mL/min) require dose reduction to 0.5 mg twice daily (maximum 1 mg/day total) throughout the entire 12-week treatment course. 2, 3
• This differs fundamentally from the standard regimen used in patients with normal renal function, which escalates to 1 mg twice daily after the first week. 1
• Varenicline is almost exclusively excreted unchanged in urine (approximately 90%), making renal function the most clinically important factor affecting drug exposure and necessitating dose adjustment. 3

Tablet Count Calculation

The modified dosing schedule for moderate renal impairment requires:

• Days 1–3: 0.5 mg once daily = 3 tablets
• Days 4–7: 0.5 mg twice daily = 8 tablets
• Weeks 2–12 (77 days): 0.5 mg twice daily = 154 tablets

Total: 165 tablets of 0.5 mg for the complete 12-week course 1

Pack Size Selection Strategy

Option 1 (Most Practical):

• One 53-tablet starter pack (covers titration week plus initial maintenance)
• Two 56-tablet continuation packs (112 tablets for remaining weeks)
• Total: 221 tablets (provides adequate supply with buffer for missed doses) 1

Option 2 (Minimal Waste):

• Three 56-tablet packs = 168 tablets (closest to the 165 required) 1

Option 3:

• One 53-tablet pack + one 56-tablet pack + one 60-tablet pack = 169 tablets 1

Critical Prescribing Considerations

• The standard "starter pack" containing 53 tablets is designed for the titration schedule (0.5 mg once daily × 3 days, then 0.5 mg twice daily × 4 days, then 1 mg twice daily), but in moderate renal impairment, patients never escalate to 1 mg twice daily. 1
• Ensure the prescription explicitly states "0.5 mg twice daily for entire 12 weeks" to prevent pharmacy or patient confusion with standard dosing protocols. 2, 1
• Renal function should be monitored upon initiation, especially given rare case reports of varenicline-associated acute renal failure in patients with preexisting renal insufficiency. 4

Mandatory Behavioral Counseling Integration

• Varenicline must always be combined with behavioral counseling—pharmacotherapy alone is insufficient for optimal outcomes. 1
• Schedule at least four counseling sessions during the 12-week period, with the first session within 2–3 weeks of starting medication; sessions lasting 10–30+ minutes are associated with higher quit rates. 1
• First follow-up visit at 2–3 weeks is mandatory to assess medication tolerability (particularly nausea, which occurs in 28–40% of patients) and smoking status. 1

Safety Monitoring in Renal Impairment

• The 29% increase in systemic varenicline exposure seen with cimetidine co-administration (which inhibits renal tubular secretion via hOCT2) demonstrates the importance of renal clearance; moderate renal impairment produces similar increases in drug exposure, justifying the dose reduction. 5
• Monitor for neuropsychiatric symptoms (depression, suicidal ideation, agitation) throughout treatment, though large-scale trials found no significant increase in these events with varenicline versus placebo. 1
• Nausea management is particularly important in this population; the reduced dose (0.5 mg twice daily) may actually improve tolerability compared to standard dosing. 1

Contraindications Specific to This Population

• Varenicline is contraindicated if creatinine clearance falls below 30 mL/min during treatment (would require further dose reduction to 0.5 mg once daily). 2
• Absolute contraindication in patients with brain metastases or active seizure disorders due to seizure risk. 1