What does Css,avg mean?

Css,avg is the average plasma concentration at steady state during repeated fixed-interval dosing.

Which inputs are required?

Dose, bioavailability, clearance, and dosing interval are required.

Do I need half-life and Vd?

No. They are optional for Css,avg, but both are needed for the peak, trough, and accumulation estimates.

What model does this calculator use?

It uses linear pharmacokinetics with a fixed dose and interval. Peak and trough estimates use a one-compartment IV-bolus model.

Can it be used for nonlinear drugs?

No. It is not valid for Michaelis-Menten or other nonlinear pharmacokinetics.

Steady-State Concentration Calculator (Css = F·Dose / CL·τ) | Online Free Tool

Execution

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2 examples

Theophylline 200 mg q8h PO, F=0.9, CL=2.8: Css,avg ≈ 8.0357 mg/L

Css,avg = 0.9 × 200 / (2.8 × 8) = 8.0357 mg/L. Theophylline therapeutic range 5–15 µg/mL ≈ mg/L.

{"result":"Css,avg = 8.0357 mg/L (no peak/trough without t½ and Vd).","metadata":{"input":{"dose":200,"bioavailability":0.9,"clearance":2.8,"interval":8},"result":{"cssAvg":8.0357,"accumulationIndex":null,"cmaxSS":null,"cminSS":null,"model":"Linear pharmacokinetics, fixed dose/interval. Css,avg only; peak/trough need t½ and Vd. Not medical advice."}}}

IV 100 mg q12h, CL=5, Vd=50, t½=6.93: Rac≈2, Cmax,ss=4, Cmin,ss=2

Css,avg = 100/(5×12) = 1.6667 mg/L. With t½=6.93 and Vd=50: k=0.1, e^(-0.1·12)=0.301, Rac=1/(1-0.301)=1.43, Cmax,ss=100/50×1.43=2.8586, Cmin,ss=2.8586×0.301=0.8604.

{"result":"Css,avg = 1.6667 mg/L; Rac = 1.4292, Cmax,ss = 2.8584 mg/L, Cmin,ss = 0.8604 mg/L.","metadata":{"input":{"dose":100,"bioavailability":1,"clearance":5,"interval":12,"halfLife":6.93,"vd":50},"result":{"cssAvg":1.6667,"accumulationIndex":1.4292,"cmaxSS":2.8584,"cminSS":0.8604,"k":0.1,"timeTo94PctHalfLives":4,"timeTo97PctHalfLives":5,"model":"Linear PK, fixed dose/interval, one-compartment IV bolus peak/trough. Not medical advice."}}}

Inputs

Set the required fields, then run the tool.

7 options

SettingsAdjust formats, ranges, numbers, and modes.7

Dose per interval (mg)numberRequiredDose administered at each interval. Must be positive.Bioavailability FnumberRequiredFraction of dose reaching systemic circulation. IV=1, oral<1. Range (0, 1].Clearance CL (L/h)numberRequiredDrug clearance in L/h. Must be positive.Dosing interval τ (h)numberRequiredTime between consecutive doses in hours. Must be positive.Half-life t½ (h, optional)numberOptionalOptional elimination half-life. Required for accumulation index and peak/trough.Volume of distribution Vd (L, optional)numberOptionalOptional Vd. Required with t½ for one-compartment peak/trough estimation.Decimal PlacesnumberOptional

Result

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Prepared example runs

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2 examples

Theophylline 200 mg q8h PO, F=0.9, CL=2.8: Css,avg ≈ 8.0357 mg/L

Css,avg = 0.9 × 200 / (2.8 × 8) = 8.0357 mg/L. Theophylline therapeutic range 5–15 µg/mL ≈ mg/L.

IV 100 mg q12h, CL=5, Vd=50, t½=6.93: Rac≈2, Cmax,ss=4, Cmin,ss=2

Css,avg = 100/(5×12) = 1.6667 mg/L. With t½=6.93 and Vd=50: k=0.1, e^(-0.1·12)=0.301, Rac=1/(1-0.301)=1.43, Cmax,ss=100/50×1.43=2.8586, Cmin,ss=2.8586×0.301=0.8604.

Inputs

Set the required fields, then run the tool.

7 options

SettingsAdjust formats, ranges, numbers, and modes.7

Result

Ready for a run

Run the tool to preview files, text, structured data, or streamed output here.

Examples

1. Estimate average theophylline concentration

Clinical pharmacology student

Background

A repeated oral theophylline regimen uses a 200 mg dose every 8 hours, with bioavailability of 0.9 and clearance of 2.8 L/h.

Problem

Calculate the average steady-state concentration without estimating peak or trough values.

How to use

Enter dose 200 mg, bioavailability 0.9, clearance 2.8 L/h, and interval 8 h. Leave half-life and Vd blank.

Dose: 200 mg; F: 0.9; CL: 2.8 L/h; τ: 8 h; decimal places: 4

Outcome

The calculator returns Css,avg = 8.0357 mg/L and indicates that peak and trough values were not calculated because half-life and Vd were not provided.

2. Calculate IV steady-state peak and trough

Pharmacokinetics learner

Background

An IV regimen gives 100 mg every 12 hours. Clearance is 5 L/h, volume of distribution is 50 L, and half-life is 6.93 hours.

Problem

Estimate average concentration, accumulation, steady-state peak, and steady-state trough.

How to use

Enter dose 100 mg, bioavailability 1, clearance 5 L/h, interval 12 h, half-life 6.93 h, and Vd 50 L.

Dose: 100 mg; F: 1; CL: 5 L/h; τ: 12 h; t½: 6.93 h; Vd: 50 L; decimal places: 4

Steady-State Concentration Calculator (Css = F·Dose / CL·τ) | Online Free Tool | Elysia Tools

Steady-State Concentration Calculator (Css = F·Dose / CL·τ)

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Examples

1. Estimate average theophylline concentration

2. Calculate IV steady-state peak and trough

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