Therapeutic Drug Monitoring

Calculate an aminoglycoside elimination half-life from a paired peak and trough, and check the dosing interval against it.

Convert 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.

Convert whole-blood ciclosporin between ng/mL and nmol/L, with the C0 versus C2 sampling question and the toxicities that distinguish it from tacrolimus.

Convert 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.

Correct a total phenytoin level for hypoalbuminaemia using the Sheiner-Tozer equation, so a low albumin does not mask a therapeutic free level.

Correct a total phenytoin level in patients with a creatinine clearance below 20 mL/min, where uraemia displaces phenytoin from albumin more than hypoalbuminaemia alone.

Convert 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.

Calculate a drug’s elimination half-life from two timed levels, and the time to reach steady state on the current regimen.

Convert 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.

Convert levetiracetam between µg/mL and µmol/L, and see why this renally cleared antiepileptic rarely needs routine monitoring outside pregnancy, renal impairment and dialysis.

Calculate 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.

Calculate the maintenance dose per interval from clearance, target steady-state concentration and dosing interval — the dose that must fall in renal or hepatic impairment.

Convert high-dose methotrexate levels between µg/mL and µmol/L, with the time-based thresholds that decide when leucovorin rescue can stop.

Convert 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.

Convert 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.

Convert 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.

Convert 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.

Estimate AUC24 for vancomycin dosing from total daily dose and creatinine clearance, in line with the AUC-guided 2020 consensus guideline.

Adjust a vancomycin dose proportionally from a measured level, using linear pharmacokinetics to reach a target AUC24 or trough.