Pharmaceutics

Cumulative Drug Release Calculator

Corrected cumulative amount and % drug release from a dissolution or release study, with the sample-withdrawal correction worked out at every time point.

Study set-up

Drug / formulation (optional)

Printed on the lab record.

Dissolution / release medium volume (V)

Sample withdrawal volume (Vs)

Default for every time point; override a row in the table.

Label claim / theoretical drug amount

Dilution factor

1 if the sample was read undiluted. 5 mL made up to 25 mL → 5.

Assumption

Each withdrawn sample is replaced with an equal volume of fresh medium, so the vessel volume V stays constant.

Calibration curve

Y = a + bX, where Y is absorbance and X is concentration.

Intercept (a)

Slope (b)

AU/(µg/mL)

Concentration unit (X)

Y = a + bX(Y = absorbance, X = conc. in µg/mL)

Open calibration tool

Time points

Time | Absorbance readings B1…Bn | Sample volume withdrawn. Leave a sample volume blank to use the default Vs.

Absorbance readings per time point

1–6 readings. Every visible reading is required.

Sampling times, absorbance readings and sample volumes
#	Time(min)	B1(AU)	B2(AU)	B3(AU)	B4(AU)	Average(AU)	Sample withdrawn(mL)	Remove
T1						—
T2						—
T3						—
T4						—
T5						—
T6						—
T7						—

Load an example data set (you can edit every value)

Correction method

Laboratory calculation card

Enter the set-up, the calibration line and every absorbance reading to calculate the release profile.

Average absorbance Ȳ = (B1 + B2 + … + Bn) / n

C = (Ȳ − a) / b → actual C = C × dilution factor

Method A — Practical-sheet method (previous corrected concentration)

Correction CFₙ = (Vsₙ₋₁ / V) × Ccorrₙ₋₁ (CF₀ = 0, Ccorr₀ = C₀)

Corrected concentration Ccorrₙ = Cₙ + CFₙ

Cumulative amount = Ccorrₙ × V

% Release = (Cumulative amount / label claim) × 100

C is converted to mg/mL before any amount is calculated (µg/mL × 0.001). Vs is the volume withdrawn at each time point; the correction at a time point uses the samples withdrawn before it. The formulas of the other method appear here when you switch to it.

Dissolution CalculatorThe same absorbance → concentration → % release workflow for a dissolution run.Calibration Curve CalculatorFits the least-squares line this calculator reads concentrations from.

References

United States Pharmacopeia–National Formulary. General Chapter <711> Dissolution. Rockville (MD): USP.
Harris DC, Lucy CA. Quantitative Chemical Analysis. 10th ed. New York: W. H. Freeman (Macmillan Learning); 2019.

Common questions

Because every earlier sample took drug out of the vessel. C × V counts only the drug still in the medium, so the release would be underestimated, and the error grows with every sample withdrawn.

The one your practical sheet or monograph specifies. Method A adds a fraction Vs/V of the previous corrected concentration; Method B adds back the milligrams removed by every earlier sample. With small samples in a large vessel they differ only slightly — switch on "Compare both methods" to see by how much.

The drug removed at a time point leaves the vessel after that reading, so it only affects later time points. The volume withdrawn at the last time point therefore does not change any result.

Usually an input is: check the label claim, the dilution factor, and that the calibration unit (µg/mL vs mg/mL) matches the line. A tablet can also genuinely contain slightly more than its label claim.

Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy