Intrinsic Dissolution Rate Calculation

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Intrinsic Dissolution Rate (IDR) Calculator

Intrinsic Dissolution Rate:

(mg / min / cm²)

function calculateIDR() { var mass = parseFloat(document.getElementById('idr_mass').value); var time = parseFloat(document.getElementById('idr_time').value); var area = parseFloat(document.getElementById('idr_area').value); var resultDiv = document.getElementById('idr_result_container'); var resultValue = document.getElementById('idr_result_value'); if (isNaN(mass) || isNaN(time) || isNaN(area) || mass <= 0 || time <= 0 || area <= 0) { alert("Please enter valid positive numeric values for all fields."); resultDiv.style.display = "none"; return; } // IDR = (dm / dt) * (1 / A) // dm = mass change, dt = time change, A = constant surface area var idr = mass / (time * area); resultValue.innerText = idr.toFixed(4); resultDiv.style.display = "block"; }

Understanding Intrinsic Dissolution Rate (IDR)

In pharmaceutical development, the Intrinsic Dissolution Rate (IDR) is a critical physical property of a drug substance. It defines the dissolution rate of a pure drug substance under conditions of constant surface area, temperature, pH, and stirring speed.

The Importance of IDR

Unlike standard dissolution testing of tablets or capsules, IDR focuses solely on the raw API (Active Pharmaceutical Ingredient). This value is essential for:

  • Predicting Bioavailability: Identifying if a drug will likely have absorption issues in the GI tract.
  • Formulation Strategy: Determining if salt formation, particle size reduction, or complexation is necessary to improve solubility.
  • Quality Control: Ensuring batch-to-batch consistency of the solid-state form (polymorphs).

The Calculation Formula

The calculation is based on the slope of the cumulative amount of drug dissolved over time, normalized by the surface area of the compressed drug disk:

IDR = (m / t) / A

Where:

  • m: Cumulative amount of drug dissolved (mg).
  • t: Time interval (min).
  • A: Surface area of the drug disk (cm²).

Example Calculation

Suppose you are testing a new API using a Wood's Apparatus. You compress the powder into a disk with a surface area of 0.5 cm². After 20 minutes, you measure that 2.4 mg of the drug has dissolved into the medium.

Calculation:

  • IDR = (2.4 mg / 20 min) / 0.5 cm²
  • IDR = 0.12 mg/min / 0.5 cm²
  • IDR = 0.24 mg/min/cm²

Interpreting Results

Generally, drug substances with an IDR greater than 1.0 mg/min/cm² are considered to have high solubility and are unlikely to have dissolution-limited absorption. Substances with an IDR lower than 0.1 mg/min/cm² are typically considered poorly soluble and often require specialized formulation techniques to ensure clinical efficacy.

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