Medication Expiration Potency Calculator

Formula: How potency loss is modeled

Many drug degradation processes are approximated as first‑order kinetics, meaning the rate of loss is proportional to how much active ingredient remains. Temperature effects are often described by the Arrhenius equation; for a practical approximation this calculator uses a Q₁₀ model (how much the degradation rate changes per 10 °C).

Step 1: Convert “base monthly potency loss at 25°C” into a rate constant

If the base monthly loss at 25°C is L%, the fractional loss per month is L/100. Under a first‑order assumption, the monthly rate constant at 25°C is:

How to use: Step 2: Adjust the rate for temperature using Q 10

For a storage temperature T (°C), the model uses:

k_T = k₂₅ × Q₁₀^(T−25)/10

Step 3: Compute remaining potency after t months

For t months past expiration, remaining potency is:

P(%) = 100 × e^{−k_T × t}

Worked example

Suppose a solid oral tablet is stored at 30°C for 12 months past expiration. You choose a base monthly loss of 0.5% at 25°C and Q₁₀=2.

1. Convert loss to rate: k₂₅ = −ln(1−0.005) ≈ 0.0050125
2. Temperature adjustment: (30−25)/10 = 0.5, so k_T = 0.0050125 × 2^0.5 ≈ 0.00709
3. Potency after 12 months: P = 100 × e^{−0.00709×12} ≈ 91.8%

This suggests roughly ~92% potency under these assumptions. Real-world results can be meaningfully different depending on humidity, formulation, container integrity, and whether the product was opened.

Typical illustrative parameter choices (not recommendations)

The inputs “Base monthly potency loss” and Q₁₀ vary widely by product. Use these only as rough starting points when you do not have manufacturer-specific stability data.

Q₁₀ values are commonly assumed around 2 for rule‑of‑thumb temperature sensitivity, but real values can differ.

Limitations & assumptions (read before using)

• Not medical advice. This is an educational model; it cannot tell you whether to take any expired medication.
• Safety/sterility not assessed. The calculator estimates potency only. It does not account for microbial growth, loss of sterility, particulate contamination, container failure, or toxic degradation products.
• First-order + Q₁₀ simplification. Many products do not follow a single exponential decay or have temperature behavior well captured by one Q₁₀.
• Storage conditions are more than temperature. Humidity, light, oxygen, freeze/thaw cycling, and whether the package was opened can dominate outcomes.
• High-risk categories where you should not rely on this estimate: sterile ophthalmic drops, injectables, reconstituted antibiotics, insulin/biologics, nitroglycerin, epinephrine autoinjectors, and medications with narrow therapeutic windows.
• Expiration dates are conservative but product-specific. Manufacturer stability testing and label storage instructions are the authoritative source.

Interpreting the result

• Potency (%) is an estimate of how much active ingredient remains relative to the labeled amount at time 0.
• A lower potency estimate generally implies reduced effectiveness, but it does not quantify clinical effect for any individual.
• Safety is not implied by higher potency. A product can retain potency yet still be unsafe (e.g., contamination, sterility loss, unstable formulations).

What to do next

• Check the label for required storage (refrigeration, light protection, moisture control).
• If the medication is critical or high-risk, or if it is a sterile product, contact a pharmacist rather than relying on an estimate.
• Dispose of unused/expired medicines using local take-back programs when available.