What is a maintenance dose?

A maintenance dose is the amount of a drug given at regular intervals to keep the plasma concentration at a therapeutic steady-state level, replacing the amount eliminated between doses.

How is clearance measured?

Clearance (CL) represents the volume of plasma cleared of drug per unit time (L/h or mL/min). It can be estimated from creatinine clearance for renally cleared drugs or from population pharmacokinetic studies.

What is steady-state concentration (Css)?

Css is the plasma concentration achieved when drug input equals drug elimination. At steady state the average concentration remains constant over each dosing interval.

Why does bioavailability (F) matter?

Oral drugs are not fully absorbed. Bioavailability (F, 0–1) corrects for this: Maintenance Dose = (CL × Css × Interval) / F. For IV drugs F = 1.

Is this calculator for IV maintenance fluids?

No. This tool calculates steady-state maintenance doses for pharmacological drugs based on clearance and target plasma concentration. For IV maintenance fluid volume, clinicians use the Holliday-Segar formula or 4-2-1 rule based on body weight.

Is this tool a substitute for clinical judgment?

No. This calculator is for educational and reference use only. Actual patient dosing requires clinical assessment, patient-specific parameters, and the judgment of a licensed healthcare professional.

How many doses until steady state is reached?

Steady state is reached after approximately 4–5 half-lives regardless of dose or dosing interval. This calculator shows the dose needed to maintain Css once it is achieved.

Drug Maintenance Dose Calculator

Calculate the required maintenance dose to achieve and sustain a target steady-state drug concentration.

Drug & Patient Parameters

Clinical Scope: Calculates pharmacological drug maintenance dosing (CL × C_ss × τ / F). For IV hydration fluid rates, refer to a Holliday-Segar (4-2-1) maintenance fluid tool.

Total Body Clearance (CL)

L/h

Volume of plasma cleared per hour

Target Steady-State Concentration (Css)

mg/L

Desired average plasma concentration at steady state

Dosing Interval (τ)

Bioavailability (F)

0–1

Use 1.0 for IV; for oral drugs enter fraction absorbed (e.g. 0.85)

Enter parameters on the left and click Calculate to see your results.

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Summary

The Maintenance Dose Calculator uses core pharmacokinetic principles to determine how much drug must be administered at each dosing interval to maintain a desired steady-state plasma concentration. It applies the formula: Maintenance Dose = Clearance × Target Css × Dosing Interval, optionally adjusted for bioavailability. This tool is intended for educational and reference purposes only; always consult a licensed clinician before making any dosing decisions.

How it works

Enter the drug's total body clearance (L/h).
Set the target steady-state plasma concentration (Css) in mg/L.
Choose or type the dosing interval (hours between doses).
Enter bioavailability (F) — defaults to 1.0 for IV administration.
Click Calculate to see the maintenance dose per interval and the daily dose.
Review the full pharmacokinetic breakdown in the results panel.

Use cases

Pharmacy students learning clinical pharmacokinetics.
Healthcare educators demonstrating steady-state dosing concepts.
Pharmacists double-checking maintenance dose calculations.
Researchers comparing dosing regimens across different clearance values.
Medical professionals reviewing drug dosing for patients with altered clearance.
Software developers building clinical decision-support tools.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu