Immunosuppressant Dosing Calculator
Drug levels and dose adjustments for transplant patients.
About this calculator
Transplant recipients take immunosuppressant drugs to prevent organ rejection, and several of the most common ones -- tacrolimus, cyclosporine, sirolimus, and everolimus in particular -- have a narrow therapeutic window: too little risks rejection, too much risks toxicity. Clinicians manage this with therapeutic drug monitoring, measuring a trough level (the drug concentration right before the next dose) and comparing it to a target range. When a measured trough falls outside the target, this calculator applies a simple linear proportion -- new dose = current dose x (target midpoint / measured trough) -- to estimate an adjusted dose that should bring the trough toward the middle of the target range.
This proportional approach is a common starting heuristic in clinical pharmacology; it assumes a roughly linear dose-to-trough relationship, which holds reasonably well for small adjustments but becomes less reliable for drugs with non-linear absorption or when other medications interact with metabolism, so actual dose changes are always confirmed by a transplant pharmacist or physician. Target trough ranges vary by drug, by how long ago the transplant occurred (targets are typically set higher in the early post-transplant period and tapered over time), and by institutional protocol -- the ranges built into this calculator are representative figures drawn from transplant pharmacology references, not a single universal guideline. Because the dose-adjustment formula only activates when a current trough level and current dose are both entered, patient weight does not change the recommended dose in that scenario -- weight is used only as a fallback starting-dose estimate when no current trough or dose has been entered yet.
Medical Disclaimer
This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.
This tool estimates a starting point only and is not a validated clinical decision-support system. It does not account for every patient-specific factor (organ function, drug interactions, allergies, comorbidities, or current clinical status). Any dose, rate, or setting must be independently verified by the treating clinician and pharmacist or respiratory therapist against current institutional protocols, product labeling, and the patient's full clinical picture before being administered or applied.
Inputs
Results
Recommended dose (mg/day)
187.5
How to Use This Calculator
- Enter Patient weight (kg) and select the Drug (Tacrolimus, Cyclosporine, Mycophenolate, Sirolimus, or Everolimus).
- Enter the Current trough level (ng/mL) and Current total daily dose (mg).
- Review the Recommended dose (mg/day) result.
- Use Dose change (%), Trough in range (0/1), Status (1-3), and Toxicity risk (0-100) to inform your decision.
How the result changes with Current trough level (ng/mL)
| Current trough level (ng/mL) | Recommended dose (mg/day) |
|---|---|
| 4 | 375 |
| 6 | 250 |
| 12 | 125 |
| 20 | 75 |
What each input means
- Patient weight
- Patient body weight in kilograms.
- Drug
- Select immunosuppressant drug.
- Current trough level (ng/mL)
- Most recent trough drug level (units vary by drug).
- Current total daily dose (mg)
- Current total daily dose in mg (sum of all daily doses).
What each result means
- Recommended dose (mg/day)
- Adjusted total daily dose to achieve target trough.
- Dose change (%)
- Percentage change from current dose.
- Trough in range (0/1)
- 1 = current trough is within therapeutic range.
- Status (1-3)
- 1 = subtherapeutic, 2 = therapeutic, 3 = supratherapeutic.
- Toxicity risk (0-100)
- Relative toxicity risk based on trough elevation above range.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersPatient weight (kg) = 70, Drug = 1, Current trough level (ng/mL) = 8, Current total daily dose (mg) = 150 = 4 input(s) provided
- Calculate Recommended dose187.5 = 187.5
- Calculate Dose changeDose change25 = 25
- Calculate Trough in rangeTrough in range1 = 1
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does a higher measured trough level lead to a lower recommended dose?
The adjustment is an inverse proportion: recommended dose = current dose x (target midpoint / measured trough). If the measured trough is already above the target midpoint, that ratio is less than 1, so the calculator recommends reducing the dose toward the target; if the trough is below the midpoint, the ratio exceeds 1 and the dose is scaled up. A higher trough at a fixed dose signals the drug is accumulating more than expected, which is exactly the situation that calls for a downward dose adjustment.
Does patient weight change the recommended dose once a trough level is entered?
No, and this can be counterintuitive. Once a current trough level AND current dose are both entered, the calculator switches to the proportional trough-adjustment formula, which depends only on those two values and the drug's target range -- patient weight drops out of the calculation entirely at that point. Weight only drives the recommended dose when no current trough or dose has been entered, in which case the calculator falls back to a weight-based starting-dose estimate instead.
Are the target trough ranges the same for every immunosuppressant?
No -- each drug has its own range because they work through different mechanisms and have different toxicity profiles. Tacrolimus and sirolimus/everolimus target ranges are commonly cited in single-digit to low-teens ng/mL, while cyclosporine's target range is measured in the hundreds of ng/mL -- roughly an order of magnitude higher, reflecting how each drug's assay and dosing convention differ, not that one drug is inherently "stronger."
Why do target trough ranges vary between clinical sources?
Target ranges are influenced by the type of organ transplanted, how many months or years have passed since transplant (targets are usually set higher early on and lowered for long-term maintenance), and institutional protocol. The ranges in this calculator are representative reference figures, not a single fixed guideline -- a patient's actual target should always come from their transplant team, not from a generic calculator.
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