Drug Dilution Calculator
Calculate drug dilutions precisely and safely using the fundamental equation C1×V1=C2×V2.
Ex: mg/mL, %, g/L
mL
desired
What is Drug Dilution?
Dilution is the process of reducing the concentration of a substance by adding solvent (diluent). In pharmacy, it is essential for preparing medications at appropriate concentrations for safe administration. The formula C1×V1=C2×V2 allows calculating how much diluent to add to achieve the desired concentration, where C1 and V1 are the initial concentration and volume, and C2 and V2 are the final concentration and volume.
Dilution Formula
C1 = Initial concentration | V1 = Initial volume | C2 = Final concentration (less than C1) | V2 = Final volume (greater than V1). Concentration units must be the same for C1 and C2. Volume units must be the same for V1 and V2.
Practical Dilution Examples
You have 10 mL of gentamicin 40 mg/mL and need 5 mg/mL concentration. C1=40, V1=10, C2=5. Calculating: V2 = (40×10)/5 = 80 mL. Add 70 mL of diluent.
Dilute 5 mL of 20% NaCl to 0.9% NaCl. C1=20, V1=5, C2=0.9. Calculating: V2 = (20×5)/0.9 = 111 mL. Add 106 mL of distilled water.
Dilute 2 mL of morphine 10 mg/mL to final volume of 10 mL. C1=10, V1=2, V2=10. Calculating: C2 = (10×2)/10 = 2 mg/mL. Add 8 mL of normal saline.
Safety Considerations in Dilutions
ALWAYS use diluent compatible with the medication (check package insert). Maintain aseptic technique for injectable preparations. Label immediately after preparation including: medication, final concentration, date/time, expiration, preparer. Check stability - some dilutions have short shelf life. Never mix incompatible medications. Use filters when indicated. Store appropriately (temperature, light). For high-alert medications (insulin, heparin, chemotherapy), perform double-check. Dispose properly of leftovers. When in doubt, consult a pharmacist.
Frequently Asked Questions about Dilution
Which diluent should I use?
The diluent depends on the medication. Most common: 0.9% saline (NaCl), water for injection, 5% dextrose, distilled water (oral use). ALWAYS consult the medication's package insert for compatible diluent. Some medications are incompatible with certain diluents and may precipitate or lose activity.
Do concentration units need to be the same?
Yes, C1 and C2 must be in the same unit (both in mg/mL, or both in %, etc). V1 and V2 must also be in the same unit (both in mL). If units differ, convert first before using the formula.
How long does a dilution last?
Stability varies greatly by medication. Some dilutions must be used immediately (e.g., ceftriaxone after reconstitution), others last 24-48h refrigerated, some are stable for weeks. ALWAYS consult specialized literature or pharmacist. When in doubt, use immediately.
Can I dilute any medication?
No. Some medications cannot be diluted (e.g., suspensions, specific emulsions, modified-release formulations). Others have minimum or maximum concentrations. Vein-irritating medications (e.g., vancomycin, chemotherapy) require specific dilutions. Always check the package insert.
What to do if I make a dilution error?
NEVER administer a dilution if there's doubt about its preparation. Discard and prepare again. If already administered and error suspected, immediately notify physician and nursing, monitor patient, document incident. Dilution errors can cause toxicity (high concentration) or inefficacy (low concentration).