Maintenance Dose Calculator (Pharmacokinetics)
Calculate the maintenance dose that keeps an average steady-state concentration from clearance, target Css, dosing interval, bioavailability and salt factor — per dose, per day and as an infusion rate.
How it works
dosing rate (mg/h) = CL (L/h) × Css (mg/L) ÷ (F × S) · maintenance dose (mg) = dosing rate × dosing interval τ (h) · daily dose = dosing rate × 24
At steady state the amount of drug eliminated in each dosing interval equals the amount given, so the dosing rate must equal clearance multiplied by the desired average concentration. Clearance can come from population equations (for example a fraction of creatinine clearance for renally cleared drugs) or, better, from the patient’s own levels. This gives the average steady-state concentration; peaks and troughs swing around it more when the interval is long compared with the half-life — use the time-to-steady-state calculator to see the fluctuation.
Worked example
With a clearance of 2.8 L/h and a target average concentration of 10 mg/L, the dosing rate is 2.8 × 10 = 28.0 mg/h. Given every 12 hours IV (F = 1, S = 1), the maintenance dose is 28 × 12 = 336 mg, a total daily dose of 672 mg/24 h.
Sources: StatPearls — Drug Clearance · StatPearls — Pharmacokinetics
Frequently asked questions
What is the difference between a loading and a maintenance dose?
The loading dose (Vd × concentration) fills the body to the target level once. The maintenance dose (CL × concentration × interval) replaces what is eliminated each interval to keep it there.
How does kidney function change the maintenance dose?
For a renally cleared drug, clearance falls in proportion to creatinine clearance, so the maintenance dose (or the dosing frequency) is reduced; the loading dose usually stays the same.
Why use an average steady-state concentration?
It is what clearance determines. For drugs with long half-lives compared with the interval, peaks and troughs stay close to the average; for short half-lives, use peak and trough equations instead.
How long until the maintenance dose reaches steady state?
About 4–5 half-lives, independent of the dose. A loading dose gets there sooner.
Related calculators
Educational pharmacokinetic estimate for health professionals only — not medical advice or a prescription. Population parameters vary widely between patients; base real dosing on the product label, measured drug levels, local protocols and a clinical pharmacist.