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Maintenance Dose Calculator (MD = Css · CL · τ / F)

· Last updated：2026-08-04

This tool is for informational purposes only and does not constitute medical, financial, or legal advice; consult a qualified professional for advice.

Calculate the maintenance dose that holds the average steady-state concentration at a target value: MD = Css,avg · CL · τ / F, where Css,avg is the target average concentration, CL is clearance, τ is the dosing interval, and F is bioavailability (1 for IV, <1 for oral). Derived from steady-state mass balance (rate in = rate out): the dose per interval equals the amount cleared over one interval, corrected for bioavailability. Targets the AVERAGE Css,avg — the peak Cmax,ss and trough Cmin,ss fluctuate around it depending on t½ and τ. Valid only for linear pharmacokinetics with fixed dose and interval — NOT for Michaelis-Menten drugs (phenytoin). Optional body-weight input converts the result to mg/kg. Not medical advice.

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Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category
Health
Input types
number
Output type
json
Sample coverage
4
API ready
Yes

Overview

The Maintenance Dose Calculator estimates the dose per interval needed to maintain a target average steady-state concentration using MD = Css,avg × CL × τ / F. Enter the target concentration, clearance, dosing interval, and bioavailability; optionally add body weight for an mg/kg result. This calculator is for linear pharmacokinetics with a fixed dose and interval and is not medical advice.

When to use

  • Estimate a maintenance dose from a target average steady-state concentration, clearance, dosing interval, and bioavailability.
  • Compare maintenance doses for IV administration and oral dosing with a specified bioavailability.
  • Convert the calculated maintenance dose to mg/kg when body weight is available.

How it works

  1. 1Enter the target average steady-state concentration Css,avg in mg/L.
  2. 2Enter clearance in L/h, the dosing interval τ in hours, and bioavailability F between greater than 0 and 1.
  3. 3The calculator applies MD = Css,avg × CL × τ / F to calculate the maintenance dose in mg.
  4. 4Optionally enter body weight to report the dose in mg/kg and choose the number of decimal places.

Use cases

  • Pharmacokinetic teaching: demonstrate how clearance, dosing interval, and bioavailability affect maintenance dose.
  • Route comparison: compare an IV maintenance dose with an oral dose when oral bioavailability is below 1.
  • Weight-based reporting: add body weight to express the calculated dose in both mg and mg/kg.

Examples

1. Oral theophylline maintenance dose

Pharmacokinetics student

Background

A learner is reviewing how oral bioavailability changes the maintenance dose needed to maintain an average target concentration.

Problem

Calculate the dose for Css,avg = 10 mg/L, clearance = 2.8 L/h, a 12-hour interval, bioavailability of 0.9, and body weight of 70 kg.

How to use

Enter 10 for target Css,avg, 2.8 for clearance, 12 for the dosing interval, 0.9 for bioavailability, and 70 kg for body weight.

Decimal places: 4

Outcome

The calculator returns 373.3333 mg every 12 hours, equivalent to 5.3333 mg/kg, using MD = Css,avg × CL × τ / F.

2. IV maintenance dose

Clinical pharmacology learner

Background

A learner wants to calculate an IV maintenance dose using complete bioavailability and an 8-hour dosing interval.

Problem

Calculate the dose for Css,avg = 10 mg/L, clearance = 2.8 L/h, dosing interval = 8 hours, and F = 1.

How to use

Enter 10 for target Css,avg, 2.8 for clearance, 8 for the dosing interval, and 1 for bioavailability. Leave body weight blank.

FAQ

What formula does the calculator use?

It uses MD = Css,avg × CL × τ / F, where Css,avg is the target average concentration, CL is clearance, τ is the dosing interval, and F is bioavailability.

What bioavailability should I enter for IV dosing?

Enter F = 1 for IV dosing. For oral dosing, enter the applicable fraction between greater than 0 and 1.

Does the result represent the peak or trough concentration?

No. The calculation targets the average steady-state concentration. Peak and trough concentrations can fluctuate around that average.

Can I calculate a dose per kilogram?

Yes. Enter body weight in kilograms to receive the maintenance dose in mg/kg in addition to the total dose in mg.

When should this calculator not be used?

It is not intended for nonlinear or Michaelis-Menten pharmacokinetics, such as the dose-concentration relationship associated with phenytoin. It is not medical advice.

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Decimal places: 4

Outcome

The calculator returns 224 mg every 8 hours. No mg/kg value is reported because body weight was not entered.