I was prescribed nortriptyline 25 mg nightly, but the CVS pharmacy gave me oral solution (10 mg/5 mL) with instructions to take 1 mL each evening; what volume should I take to receive the correct 25 mg dose?

Nortriptyline Oral Solution Dosing Error: Correct Volume Calculation

You need to take 12.5 mL of the oral solution each evening to receive your prescribed 25 mg dose of nortriptyline, not 1 mL as the pharmacy label incorrectly states. 1

Understanding the Dispensing Error

The pharmacy dispensed nortriptyline oral solution at a concentration of 10 mg/5 mL, which means:

• Every 5 mL contains 10 mg of nortriptyline 1
• To receive 25 mg, you need 12.5 mL (calculated as: 25 mg ÷ 10 mg × 5 mL = 12.5 mL)

The label instruction stating "take 1 mL" would only deliver 2 mg of nortriptyline—a potentially dangerous underdose that is only 8% of your prescribed amount.

Immediate Action Required

Contact the pharmacy immediately to correct this error before taking any medication. This represents a significant medication error that could result in:

• Treatment failure for your condition (whether depression, neuropathic pain, or other indication) 1
• Delayed therapeutic benefit as nortriptyline requires consistent dosing to achieve therapeutic plasma levels of 50-150 ng/mL 1
• Potential worsening of symptoms due to inadequate medication levels

Proper Dosing Instructions

Once the pharmacy corrects the label, your instructions should read:

• "Take 12.5 mL by mouth once daily in the evening" 1, 2
• Use an oral syringe marked in milliliters (mL) for accurate measurement—never use household teaspoons 2
• The pharmacy should provide you with an appropriately calibrated oral dosing syringe 2

Why This Error Matters Clinically

Nortriptyline has a narrow therapeutic window with optimal plasma concentrations between 50-150 ng/mL 1. Taking only 1 mL (2 mg) instead of 12.5 mL (25 mg) would result in:

• Subtherapeutic drug levels that provide no clinical benefit 1
• Failure to achieve the intended therapeutic effect for your condition 1
• Potential need to restart titration if the error continues for multiple days

Verification Steps

When the pharmacy provides corrected instructions:

• Confirm the concentration is 10 mg/5 mL 1
• Verify the volume calculation: 25 mg ÷ 2 mg/mL = 12.5 mL
• Request an oral syringe calibrated to at least 15 mL with 0.5 mL markings 2
• Have the pharmacist demonstrate proper measurement technique before leaving

Common Pitfalls to Avoid

• Never use household spoons for measuring liquid medications, as they vary significantly in volume and lead to dosing errors 2
• Do not estimate volumes by eye—always use calibrated measuring devices 2
• Avoid confusion between "mL" and "mg"—these are different units (volume vs. weight) 2
• Check that your dosing device markings match the prescribed volume to prevent measurement errors 2

Monitoring for Therapeutic Effect

Once you begin taking the correct 12.5 mL (25 mg) dose:

• Initial effects may take 1-2 weeks to become apparent 1
• Full therapeutic benefit typically requires 4-6 weeks of consistent dosing 1
• Report any side effects to your prescriber, particularly dry mouth, constipation, dizziness, or drowsiness 1
• Your prescriber may adjust the dose based on clinical response and tolerability, with plasma level monitoring if doses exceed 100 mg daily 1