Formula Used
Peak to trough ratio: Ratio = Peak concentration / Trough concentration.
Absolute difference: Difference = Peak concentration - Trough concentration.
Percent decline: Percent decline = ((Peak - Trough) / Peak) × 100.
Time gap: Time gap = Trough time - Peak time. If timing crosses the next dose, the interval is used to wrap the time.
Elimination rate: k = ln(Peak / Trough) / Time gap. This requires peak to be greater than trough.
Estimated half-life: Half-life = 0.693 / k.
Segment exposure: AUC segment = (Peak - Trough) / k, using an exponential decline assumption.
Dose normalized values: Normalized concentration = Concentration / Daily dose.
These formulas are mathematical summaries. They are not treatment orders.
How to Use This Calculator
Enter the measured peak and trough levels in the same unit.
Add the collection times as hours after the dose.
Enter the dosing interval, such as 24 hours for once daily dosing.
Add dose details when available. They help normalize values.
Use the optional ratio flag for your local review threshold.
Press calculate. The result appears above the form.
Download CSV for spreadsheets or PDF for a simple report.
Do not use this page to start, stop, split, or change methadone.
Understanding Peak and Trough Review
Methadone levels can vary across one dosing interval. A peak level usually reflects the higher concentration after a dose. A trough level reflects the lower concentration before the next dose. This calculator organizes both values with dose timing. It does not decide treatment. It supports structured review.
Why Timing Matters
Timing is central for useful interpretation. A common review compares a post dose peak with a late interval trough. The calculator asks for hours after dose, dosing interval, and daily dose. It then reports the peak to trough ratio. It also estimates decline and apparent half life when valid times are entered. These values can show whether the measured pattern is steep, moderate, or flat.
What The Ratio Shows
The peak to trough ratio is simple. It divides the peak concentration by the trough concentration. A higher ratio means a larger swing between the two samples. Some clinical discussions use a ratio above two as a possible marker of faster clearance. This is not a diagnosis. Symptoms, adherence, interacting medicines, pregnancy status, liver function, and sample timing can change meaning.
Using Results Responsibly
The calculator includes caution messages. They are not dosing instructions. Methadone has serious safety risks, including sedation and breathing problems. Any dose change, split dosing decision, or repeat test should be handled by a licensed clinician. Results should be checked against the laboratory report, collection time, and patient history.
Documentation Benefits
A structured calculator can reduce transcription errors. It can also create a record for chart notes. The CSV export stores inputs and outputs in a spreadsheet friendly format. The PDF export creates a brief summary for review. Keep patient identifiers out of shared files unless your workflow protects privacy.
Practical Workflow
First, enter the measured peak and trough levels in the same unit. Next, add the collection times after the dose. Then enter the dosing interval and daily dose if known. Submit the form. Review the ratio, difference, percent decline, estimated elimination rate, half life, average estimate, and dose normalized values. Use the example table to compare typical scenarios. Repeat calculations when corrected lab times become available. Always treat the output as a calculation aid, not as independent medical guidance only.
FAQs
What is a methadone peak level?
A peak level is a measured concentration after dosing, often when the blood level is expected to be higher. Exact timing must follow the ordering clinician or lab instructions.
What is a methadone trough level?
A trough level is usually measured near the end of a dosing interval, before the next dose. It helps show the lower measured concentration.
Does this calculator recommend a methadone dose?
No. It only performs math on entered values. Methadone decisions require licensed clinical review because safety risks can be serious.
Why is the peak to trough ratio important?
The ratio shows the concentration swing between two samples. A larger ratio may prompt review of timing, symptoms, adherence, interactions, or metabolism.
Can I enter mg/L instead of ng/mL?
Yes. Select the matching unit before calculating. Both peak and trough values must use the same unit for valid comparison.
What if the peak is lower than the trough?
The tool will flag that pattern. Check sample labels, collection times, lab units, missed doses, and data entry before interpreting the result.
Why does half-life show as N/A?
Half-life needs peak greater than trough and a valid time gap. If either condition is missing, the estimate is not calculated.
Are CSV and PDF exports secure?
Exports are created in the browser from displayed results. Avoid including patient identifiers unless your storage and sharing process protects privacy.