Alligation Alternate Calculator (Two-Strength Mixing)
Calculates exact volumes/weights of a higher-strength (CH) and lower-strength (CL) preparation needed to compound a desired intermediate strength (CD).
⚠️ Educational Calculation & Clinical Safety Safeguard: Desired concentration CD must lie strictly between CL and CH (CL < CD < CH). Educational calculations do not replace clinician assessment, patient-specific laboratory monitoring, or institutional prescribing protocols.
Interactive Calculator
Allowed physiological/compounding range: 0.1 to 100 %
Allowed physiological/compounding range: 0 to 99.9 %
Allowed physiological/compounding range: 0.05 to 99.95 %
Allowed physiological/compounding range: 1 to 50000 mL or g
Calculated Output (mL of CH & mL of CL)
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Step-by-Step Mathematical Derivation & Explanation:
Validated Formula & Conversion Rules
Parts of CH = CD − CL; Parts of CL = CH − CD; Total Parts = CH − CL; Volume(CH) = Final Volume × [Parts(CH) / Total Parts]Worked Clinical Example
Prepare 450 mL of Dextrose 10% (D10W) from D50W (50%) and D5W (5%): Parts D50W = 10 − 5 = 5; Parts D5W = 50 − 10 = 40 (Total 45 parts). Volume D50W = 450 × (5/45) = 50 mL; Volume D5W = 450 × (40/45) = 400 mL.
Rounding Rules, Clinical Interpretation, Assumptions & Known Limitations
- 1. Purpose: Calculates exact volumes/weights of a higher-strength (CH) and lower-strength (CL) preparation needed to compound a desired intermediate strength (CD).
- 2. Required Inputs & Validated Units: Higher Concentration (CH) (%, range 0.1–100), Lower Concentration (CL, use 0 for water) (%, range 0–99.9), Desired Intermediate Concentration (CD) (%, range 0.05–99.95), Total Final Volume / Weight (mL or g, range 1–50000)
- 3. Output Unit:
mL of CH & mL of CL - 4. Result Interpretation Notes: Uses Alligation Alternate to determine proportional parts and volumes of higher (CH) and lower (CL) strength stocks.
- 5. Rounding Guidance: Round compounded volumes to 0.1 mL.
- 6. Mathematical & Clinical Assumptions: Assumes additive volumes and identical concentration units (% w/v or % v/v) across CH, CL, and CD.
- 7. Known Limitations & Contraindications to Formula Use: Desired concentration (CD) must lie strictly between CL and CH; use 0% when mixing with pure solvent/vehicle.
- 8. Supporting Compendial & Clinical References: Indian Pharmacopoeia (IP 2022), National Formulary of India (NFI), British National Formulary (BNF), and NCBI Bookshelf Clinical Pharmacology Compendia.