Therapeutic Drug Monitoring
Every therapeutic drug monitoring calculator on CalcEngines — unit converters, derived indices and interpretive tools, each with its formula, a worked example and the reference intervals it is judged against.
30 calculators in this section
- Adjusted Body Weight CalculatorAdjusted body weight is ideal body weight plus 40% of the excess — the dosing weight for aminoglycosides in obesity. This works it out, says whether the usual trigger (actual weight more than 20% above ideal) is met, and declines to adjust when actual weight is below ideal.
- Aminoglycoside Half-Life CalculatorCalculate an aminoglycoside elimination half-life from a paired peak and trough, and check the dosing interval against it.
- Carbamazepine Unit ConverterConvert carbamazepine between µg/mL, mg/L and µmol/L, with the autoinduction that makes an early level unreliable and the epoxide metabolite the routine assay does not see.
- Ciclosporin Unit ConverterConvert whole-blood ciclosporin between ng/mL and nmol/L, with the C0 versus C2 sampling question and the toxicities that distinguish it from tacrolimus.
- Clozapine Unit ConverterConvert clozapine trough levels between ng/mL and nmol/L, with the response and seizure thresholds and why stopping smoking is the interaction to watch for.
- Corrected Phenytoin Calculator (Sheiner-Tozer)Correct a total phenytoin level for hypoalbuminaemia using the Sheiner-Tozer equation, so a low albumin does not mask a therapeutic free level.
- Corrected Phenytoin in Renal FailureCorrect a total phenytoin level in patients with a creatinine clearance below 20 mL/min, where uraemia displaces phenytoin from albumin more than hypoalbuminaemia alone.
- Digitoxin Unit ConverterConvert digitoxin between ng/mL, µg/L and nmol/L — and start from the fact the page exists for: digitoxin is not digoxin. Different molecule, half-life measured in days, hepatic rather than renal clearance, and a therapeutic range more than ten times higher.
- Digoxin Unit ConverterConvert digoxin between ng/mL, µg/L and nmol/L, with the separate heart-failure and atrial fibrillation targets and the six-hour sampling rule that makes a level interpretable.
- Dosing Weight Calculator: Actual, Ideal, Adjusted or Lean?Which body weight to dose on — actual, ideal, adjusted or lean — for aminoglycosides, vancomycin, Cockcroft-Gault creatinine clearance and unfractionated heparin, with the number and the source for each. Where published guidance disagrees, as it does for Cockcroft-Gault and heparin in obesity, the page prints the disagreement instead of choosing silently.
- Drug Half-Life and Steady State CalculatorCalculate a drug's elimination half-life from two timed levels, and the time to reach steady state on the current regimen.
- Gentamicin Unit ConverterConvert gentamicin between mg/L, µg/mL and µmol/L, with the trough and peak targets separated by regimen — because a gentamicin level without a documented dose time and sampling time cannot be interpreted at all.
- Hartford Nomogram Checker: Can This Gentamicin Level Be Used?The Hartford nomogram turns one gentamicin or tobramycin level, 6 to 14 hours after a 7 mg/kg dose, into a q24h, q36h or q48h interval — but only for the patients it was built on. This checks the published exclusions, the dose, the weight and the timing, and tells you whether the chart can be used at all. It does not read the level off the chart, because the paper publishes the lines only as a picture.
- Ideal Body Weight Calculator (IBW)Ideal body weight by the Devine formula, from sex and height in centimetres or inches. It is worth knowing what this number is: Devine published it in 1974 as a way to size gentamicin doses, not as a statement of what anyone ought to weigh — and it is the weight most often fed into Cockcroft-Gault.
- Lamotrigine Unit ConverterConvert lamotrigine between µg/mL and µmol/L, with the valproate and enzyme-inducer interactions and the pregnancy-related clearance changes that drive most requests for a level.
- Lean Body Weight Calculator (Janmahasatian)Lean body weight by the Janmahasatian 2005 equation, from sex, weight and height. Unlike ideal body weight it responds to actual weight — but it climbs towards a ceiling rather than rising without limit, which is what makes it a better size descriptor than total weight for some drugs in obesity.
- Levetiracetam Unit ConverterConvert levetiracetam between µg/mL and µmol/L, and see why this renally cleared antiepileptic rarely needs routine monitoring outside pregnancy, renal impairment and dialysis.
- Lidocaine Unit ConverterConvert lidocaine — lignocaine in British usage — between µg/mL, mg/L and µmol/L, with the antiarrhythmic infusion range and the two facts that matter about it: toxicity is neurological before it is cardiac, and levels rise disproportionately in heart failure and liver disease.
- Lithium Unit ConverterConvert lithium between mmol/L, mEq/L and mg/L — mmol/L and mEq/L are the same number because lithium is monovalent — and read the result against the rule that makes it interpretable: the sample must be taken 12 hours after the dose.
- Loading Dose CalculatorCalculate a loading dose from volume of distribution, weight and target concentration — and see why it does not change in renal or hepatic impairment even though the maintenance dose does.
- Maintenance Dose CalculatorCalculate the maintenance dose per interval from clearance, target steady-state concentration and dosing interval — the dose that must fall in renal or hepatic impairment.
- Methotrexate Unit ConverterConvert high-dose methotrexate levels between µg/mL and µmol/L, with the time-based thresholds that decide when leucovorin rescue can stop.
- Phenobarbital Unit ConverterConvert phenobarbital between µg/mL, mg/L and µmol/L — and read the result knowing that the half-life is measured in days, so a level taken before steady state says almost nothing, and that tolerance means the quoted range guides rather than dictates.
- Phenytoin Unit ConverterConvert phenytoin between µg/mL, mg/L and µmol/L, with the 40–79 µmol/L guide range, the saturable kinetics that make small dose changes dangerous, and why the total level misleads when albumin is low.
- Tacrolimus Unit ConverterConvert whole-blood tacrolimus trough levels between ng/mL and nmol/L, with target ranges by time since transplant and the CYP3A4 interactions that move levels fastest.
- Theophylline Unit ConverterConvert theophylline between µg/mL, mg/L and µmol/L, with a narrow window that overlaps toxicity and the clearance changes — smoking cessation above all — that move a stable patient into it.
- Tobramycin Unit ConverterConvert tobramycin between mg/L, µg/mL and µmol/L, with trough and peak targets separated by regimen — and with the timing rule that decides whether a level means anything at all.
- Valproate Unit ConverterConvert valproate between µg/mL, mg/L and µmol/L, and see why saturable protein binding means the total level understates exposure — and when a free valproate level is the right test.
- Vancomycin AUC24 CalculatorEstimate AUC24 for vancomycin dosing from total daily dose and creatinine clearance, in line with the AUC-guided 2020 consensus guideline.
- Vancomycin Dose Adjustment CalculatorAdjust a vancomycin dose proportionally from a measured level, using linear pharmacokinetics to reach a target AUC24 or trough.