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Workflow Playbook

Pharmacokinetic Teaching and Dose-Model Checks

Explore pharmacokinetic formulas, model assumptions, and result consistency for teaching or QA without giving medication dosing or clinical advice.

Start here

New to this workflow? Follow the steps in order, starting with the first tool below. Already know what you need? Jump straight to the matching step — every tool in this workflow is listed in the comparison table.

First tool: Bioavailability Calculator (F = AUC_po · Dose_iv / AUC_iv · Dose_po)

Hubs

Tools in this workflow, compared

ToolWhat it doesCategory
Bioavailability Calculator (F = AUC_po · Dose_iv / AUC_iv · Dose_po)Calculate the absolute bioavailability F of an extravascular (typically oral) dose: F = (AUC_po · Dose_iv) / (AUC_iv · Dose_po), where AUC_po and AUC_iv are the areas under the concentration-time curve after oral and IV dosing, and the doses correct for any difference in amount administered. F is dimensionless and lies in [0, 1]; IV bioavailability is by definition 1, while oral F < 1 reflects incomplete absorption and/or first-pass metabolism. AUC can be in any consistent unit (e.g. mg·h/L) since it cancels out of the ratio. Valid only for linear pharmacokinetics, the same drug molecule, and doses within the linear range. Not medical advice.Health
Dose by Body Surface Area Calculator (BSA = √(H·W/3600))Calculate an individualized drug dose from body surface area using the Mosteller formula: BSA (m²) = √(Height(cm) · Weight(kg) / 3600), then Dose = Drug_dose_per_m² × BSA. BSA is the recommended normalization for many cytotoxic and pediatric regimens because drug clearance scales more linearly with BSA than with body weight across patients of different sizes. Also reports the standard adult dose at the reference adult BSA of 1.73 m² for comparison. Valid only for linear drug clearance — BSA dosing does not apply to saturable (Michaelis-Menten) pathways. Not medical advice.

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Continue with adjacent topic clusters

Health
Dosing Interval Designer (Peak/Trough Ratio)Design the dosing interval τ from the steady-state peak/trough concentration ratio. For one-compartment linear kinetics at steady state, the peak-to-trough ratio over one interval is P = Cmax,ss / Cmin,ss = e^(kτ) where k = ln2 / t½. Mode A: given a target peak/trough ratio, solve for the dosing interval τ = ln(P) · t½ / ln2. Mode B: given a chosen interval τ, compute the resulting peak/trough ratio P = e^(kτ). Note: P reflects fluctuation WITHIN one interval and is NOT the accumulation index (R = 1/(1-e^(-kτ))). Valid only for linear one-compartment kinetics, steady state, fixed dose and interval. Not medical advice.Health
Drug Accumulation Index Calculator (R = 1/(1-e^(-kτ)))Calculate the drug accumulation index R under repeated fixed-interval dosing with linear first-order elimination: R = 1 / (1 - e^(-kτ)), where k = ln2 / t½ and τ is the dosing interval. R is the ratio of the steady-state peak concentration to the peak concentration after the first dose — it quantifies how much the body burden rises at steady state versus a single dose. For example, dosing once per half-life (τ = t½) gives R = 2. The term e^(-kτ) is the fraction of peak concentration remaining at the end of one interval. Valid only for linear first-order elimination with fixed dose and interval — NOT for Michaelis-Menten drugs (phenytoin) or non-linear kinetics. Not medical advice.Health
Drug Clearance Calculator (CL)Calculate drug clearance CL in two modes. (A) Definition: CL = elimination rate / concentration, valid for any pharmacokinetic model. (B) Linear first-order: CL = k · Vd (or derive k from t½ via k = ln2 / t½). Also reports the relationship t½ = 0.693 · Vd / CL. CL is a definitional parameter independent of Vd. Linear mode applies only to first-order elimination — NOT to Michaelis-Menten drugs (phenytoin, high-dose ethanol). Reference: theophylline CL ≈ 2.8 L/h in a 70 kg non-smoking adult. Not medical advice.Health
Drug Half-Life Concentration CalculatorEstimate plasma drug concentration at a chosen time after an IV bolus using a one-compartment model with first-order elimination: C(t) = (Dose / Vd) · e^(-k·t), where k = ln2 / t½. Includes initial concentration C0, elimination rate constant k, percent remaining, and number of half-lives elapsed. Valid only for linear pharmacokinetics — NOT for Michaelis-Menten drugs (phenytoin, high-dose ethanol) or multi-compartment distribution. Reference: theophylline Vd ≈ 0.45 L/kg, t½ ≈ 8 h. Not medical advice.Health
Elimination Rate Constant Calculator (k = ln2 / t½)Convert an elimination half-life to the first-order elimination rate constant: k = ln2 / t½ = 0.693 / t½. Also reports the fraction of drug remaining after 1/2/3/4/5 half-lives (50%, 25%, 12.5%, 6.25%, 3.125%), the number of half-lives required to reach steady state (≈4 for 94%, ≈5 for 97%), and the time to ~99% elimination (≈6.64 half-lives). Valid only for first-order (linear) elimination — NOT for zero-order or Michaelis-Menten kinetics (phenytoin, high-dose ethanol, high-dose aspirin). Not medical advice.Health
Half-Life CalculatorExponential decay for radioactive isotopes and drugs: remaining amount, derived half-life, time to target, or steady-state accumulation. Uses N(t) = N0·e^(-λt).Math & Numbers
IV Infusion Rate Calculator (R₀ = Css · CL)Calculate the continuous IV infusion rate that maintains a target steady-state plasma concentration: R₀ = Css · CL, where Css is the target concentration and CL is clearance. At steady state, the infusion rate equals the elimination rate. If the IV solution concentration (mg/mL) is provided, the tool additionally derives the infusion-pump delivery rate in mL/h, which is what the pump is actually set to in clinical practice. This is an IV-only tool — bioavailability F is not applicable. Reaching steady state requires approximately 4–5 half-lives. Not medical advice.Health
Loading Dose Calculator (LD = Css · Vd / F)Calculate the loading dose required to rapidly reach a target plasma concentration: LD = Css · Vd / F, where Css is the target concentration, Vd is the volume of distribution, and F is bioavailability (1 for IV, <1 for oral). A loading dose achieves Css essentially immediately (one-compartment IV bolus) instead of waiting 4–5 half-lives for accumulation. For oral loading, divide by F. Maintenance dosing (MD = Css·CL·τ/F) must follow to sustain the concentration. Loading doses are hazardous for narrow-therapeutic-index drugs (digoxin, theophylline, antiarrhythmics) — clinical judgement required. Optional body-weight input converts the result to mg/kg. Not medical advice.Health
Maintenance Dose Calculator (MD = Css · CL · τ / F)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.Health
Pediatric Dose Calculator (Young / Clark / mg·kg⁻¹ / BSA)Estimate a pediatric drug dose using one of four methods: (1) Young's rule (age-based) — Child dose = Adult dose × age / (age + 12); (2) Clark's rule (weight in pounds) — Child dose = Adult dose × weight(lb) / 150; (3) mg/kg per-weight regimen (the modern first-line method) — Child dose = dosePerKg × weight(kg); (4) BSA method (Mosteller) — Child dose = Adult dose × BSA_child / 1.73, with BSA = √(height·weight/3600). These are empirical approximations; modern practice prefers drug-specific mg/kg or mg/m² regimens derived from pediatric trials and verified against pediatric references and the approved labeling. Not medical advice.Health
Steady-State Concentration Calculator (Css = F·Dose / CL·τ)Estimate the average steady-state plasma concentration under repeated fixed-interval dosing: Css,avg = (F · Dose) / (CL · τ), where F is bioavailability (1 for IV, <1 for oral), CL is clearance, and τ is the dosing interval. If t½ and Vd are also provided, computes the one-compartment IV-bolus accumulation index Rac = 1/(1-e^(-kτ)), peak Cmax,ss, trough Cmin,ss, and time to ~94%/~97% of steady state (4/5 half-lives). Valid only for linear pharmacokinetics with fixed dose and interval — NOT for Michaelis-Menten drugs or non-linear kinetics. Not medical advice.Health
Trough Level Estimator (Cmin = Cmax · e^(-kτ))Predict the trough concentration Cmin from a measured peak concentration Cmax during therapeutic drug monitoring (TDM): Cmin = Cmax · e^(-kτ), where k = ln2 / t½ and τ is the time from the peak to the next dose. Inputs are the measured peak, the elimination half-life, and the dosing interval. Also reports the fraction of the peak remaining at the trough and the peak-to-trough drop. This tool takes a measured Cmax (the TDM workflow), unlike drug-half-life-dose (which derives C0 from Dose/Vd) and dosing-interval-designer (which outputs a dimensionless peak/trough ratio, not an absolute concentration). Valid for one-compartment first-order elimination with the peak measured post-distribution. Not medical advice.Health
Volume of Distribution Calculator (Vd)Calculate the apparent volume of distribution Vd in two modes. (A) One-compartment IV bolus: Vd = Dose / C0 (C0 = concentration extrapolated to t=0). (B) From clearance and half-life (linear kinetics): Vd = CL · t½ / 0.693. Vd is an APPARENT (theoretical) volume, not an anatomical one — highly tissue-bound drugs (digoxin ≈ 7 L/kg, amiodarone ≈ 66 L/kg) can exceed total body water, while highly plasma-protein-bound drugs (warfarin ≈ 0.14 L/kg) fall far below it. Optional body-weight input converts the result to L/kg. Note: Vd = Dose/C0 gives Vc (initial); Vss (steady state) and Vz (terminal) differ for multi-compartment models, and oral dosing returns Vd/F. Not medical advice.Health

Keep the boundary educational

This workflow is for pharmacokinetic learning, simulation, and QA review. It can show how bioavailability, clearance, half-life, distribution volume, intervals, accumulation, infusion, and steady-state concentration relate under stated assumptions. It must not be used to decide a real patient's medication dose, diagnose a condition, or replace clinical judgment.

Build the model from assumptions

Start by naming the fictional route, exposure assumption, body-size context, and interval question. Then use the clearance, half-life, elimination-rate, and single-dose decay tools to verify that the core parameters point in the same direction. This step is often where unit errors and unrealistic assumptions become visible.

Review results instead of prescribing

The loading, maintenance, infusion, and pediatric tools can support classroom examples, but the output should be labeled as scenario math. Finish by comparing steady-state, accumulation, trough, and volume-of-distribution results. A useful final note says which assumptions were used, which outputs agreed, which values need rechecking, and that no clinical recommendation was made.

Before you start

  • Use only a fictional, classroom, simulation, or QA fixture scenario, not a real patient treatment decision.
  • Record units, route, bioavailability assumption, compartment model, sampling times, and whether the example uses first-order elimination.
  • Have a qualified clinical source review any real-world medication question outside this workflow.

Workflow playbook

Pharmacokinetic modeling workflow: estimate, model, compare, verify

  1. 1

    Frame the teaching scenario

    Define the fictional route, exposure assumption, body-size context, and interval question so later calculations stay inside an educational model.

  2. 2

    Derive elimination parameters

    Compare clearance, half-life, elimination-rate, and single-dose decay outputs to catch unit mismatches before any dose-model example is interpreted.

  3. 3

    Model theoretical regimen examples

    Run loading, maintenance, infusion, and pediatric teaching calculators only as scenario math, then mark the results as non-prescriptive examples.

  4. 4

    Check concentration consistency

    Use steady-state, trough, and distribution calculations to verify whether the simulated outputs agree with the stated model and sampling timeline.

Choose the right path

Is this a teaching model or a real care decision?

Continue only for education, simulation, or result QA. Stop and use qualified clinical review if the output could change a patient's medication.

Are the assumptions internally consistent?

Check route, bioavailability, clearance, volume, half-life, interval, and sampling-time assumptions before comparing concentration outputs.

Done when

  • Every result is labeled as educational or simulated, with no patient-specific dosing instruction or diagnosis.
  • Units, route, model assumption, and source parameters are visible beside each derived value.
  • Final review compares exposure, elimination, interval, accumulation, and trough outputs for consistency rather than selecting a clinical dose.
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Health

Bioavailability Calculator (F = AUC_po · Dose_iv / AUC_iv · Dose_po)

Calculate the absolute bioavailability F of an extravascular (typically oral) dose: F = (AUC_po · Dose_iv) / (AUC_iv · Dose_po), where AUC_po and AUC_iv are the areas under the concentration-time curve after oral and IV dosing, and the doses correct for any difference in amount administered. F is dimensionless and lies in [0, 1]; IV bioavailability is by definition 1, while oral F < 1 reflects incomplete absorption and/or first-pass metabolism. AUC can be in any consistent unit (e.g. mg·h/L) since it cancels out of the ratio. Valid only for linear pharmacokinetics, the same drug molecule, and doses within the linear range. Not medical advice.

Health

Dose by Body Surface Area Calculator (BSA = √(H·W/3600))

Calculate an individualized drug dose from body surface area using the Mosteller formula: BSA (m²) = √(Height(cm) · Weight(kg) / 3600), then Dose = Drug_dose_per_m² × BSA. BSA is the recommended normalization for many cytotoxic and pediatric regimens because drug clearance scales more linearly with BSA than with body weight across patients of different sizes. Also reports the standard adult dose at the reference adult BSA of 1.73 m² for comparison. Valid only for linear drug clearance — BSA dosing does not apply to saturable (Michaelis-Menten) pathways. Not medical advice.

Health

Dosing Interval Designer (Peak/Trough Ratio)

Design the dosing interval τ from the steady-state peak/trough concentration ratio. For one-compartment linear kinetics at steady state, the peak-to-trough ratio over one interval is P = Cmax,ss / Cmin,ss = e^(kτ) where k = ln2 / t½. Mode A: given a target peak/trough ratio, solve for the dosing interval τ = ln(P) · t½ / ln2. Mode B: given a chosen interval τ, compute the resulting peak/trough ratio P = e^(kτ). Note: P reflects fluctuation WITHIN one interval and is NOT the accumulation index (R = 1/(1-e^(-kτ))). Valid only for linear one-compartment kinetics, steady state, fixed dose and interval. Not medical advice.

Health

Drug Accumulation Index Calculator (R = 1/(1-e^(-kτ)))

Calculate the drug accumulation index R under repeated fixed-interval dosing with linear first-order elimination: R = 1 / (1 - e^(-kτ)), where k = ln2 / t½ and τ is the dosing interval. R is the ratio of the steady-state peak concentration to the peak concentration after the first dose — it quantifies how much the body burden rises at steady state versus a single dose. For example, dosing once per half-life (τ = t½) gives R = 2. The term e^(-kτ) is the fraction of peak concentration remaining at the end of one interval. Valid only for linear first-order elimination with fixed dose and interval — NOT for Michaelis-Menten drugs (phenytoin) or non-linear kinetics. Not medical advice.

Health

Drug Clearance Calculator (CL)

Calculate drug clearance CL in two modes. (A) Definition: CL = elimination rate / concentration, valid for any pharmacokinetic model. (B) Linear first-order: CL = k · Vd (or derive k from t½ via k = ln2 / t½). Also reports the relationship t½ = 0.693 · Vd / CL. CL is a definitional parameter independent of Vd. Linear mode applies only to first-order elimination — NOT to Michaelis-Menten drugs (phenytoin, high-dose ethanol). Reference: theophylline CL ≈ 2.8 L/h in a 70 kg non-smoking adult. Not medical advice.

Health

Drug Half-Life Concentration Calculator

Estimate plasma drug concentration at a chosen time after an IV bolus using a one-compartment model with first-order elimination: C(t) = (Dose / Vd) · e^(-k·t), where k = ln2 / t½. Includes initial concentration C0, elimination rate constant k, percent remaining, and number of half-lives elapsed. Valid only for linear pharmacokinetics — NOT for Michaelis-Menten drugs (phenytoin, high-dose ethanol) or multi-compartment distribution. Reference: theophylline Vd ≈ 0.45 L/kg, t½ ≈ 8 h. Not medical advice.

Health

Elimination Rate Constant Calculator (k = ln2 / t½)

Convert an elimination half-life to the first-order elimination rate constant: k = ln2 / t½ = 0.693 / t½. Also reports the fraction of drug remaining after 1/2/3/4/5 half-lives (50%, 25%, 12.5%, 6.25%, 3.125%), the number of half-lives required to reach steady state (≈4 for 94%, ≈5 for 97%), and the time to ~99% elimination (≈6.64 half-lives). Valid only for first-order (linear) elimination — NOT for zero-order or Michaelis-Menten kinetics (phenytoin, high-dose ethanol, high-dose aspirin). Not medical advice.

Math & Numbers

Half-Life Calculator

Exponential decay for radioactive isotopes and drugs: remaining amount, derived half-life, time to target, or steady-state accumulation. Uses N(t) = N0·e^(-λt).

Health

IV Infusion Rate Calculator (R₀ = Css · CL)

Calculate the continuous IV infusion rate that maintains a target steady-state plasma concentration: R₀ = Css · CL, where Css is the target concentration and CL is clearance. At steady state, the infusion rate equals the elimination rate. If the IV solution concentration (mg/mL) is provided, the tool additionally derives the infusion-pump delivery rate in mL/h, which is what the pump is actually set to in clinical practice. This is an IV-only tool — bioavailability F is not applicable. Reaching steady state requires approximately 4–5 half-lives. Not medical advice.

Health

Loading Dose Calculator (LD = Css · Vd / F)

Calculate the loading dose required to rapidly reach a target plasma concentration: LD = Css · Vd / F, where Css is the target concentration, Vd is the volume of distribution, and F is bioavailability (1 for IV, <1 for oral). A loading dose achieves Css essentially immediately (one-compartment IV bolus) instead of waiting 4–5 half-lives for accumulation. For oral loading, divide by F. Maintenance dosing (MD = Css·CL·τ/F) must follow to sustain the concentration. Loading doses are hazardous for narrow-therapeutic-index drugs (digoxin, theophylline, antiarrhythmics) — clinical judgement required. Optional body-weight input converts the result to mg/kg. Not medical advice.

Health

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

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.

Health

Pediatric Dose Calculator (Young / Clark / mg·kg⁻¹ / BSA)

Estimate a pediatric drug dose using one of four methods: (1) Young's rule (age-based) — Child dose = Adult dose × age / (age + 12); (2) Clark's rule (weight in pounds) — Child dose = Adult dose × weight(lb) / 150; (3) mg/kg per-weight regimen (the modern first-line method) — Child dose = dosePerKg × weight(kg); (4) BSA method (Mosteller) — Child dose = Adult dose × BSA_child / 1.73, with BSA = √(height·weight/3600). These are empirical approximations; modern practice prefers drug-specific mg/kg or mg/m² regimens derived from pediatric trials and verified against pediatric references and the approved labeling. Not medical advice.

Health

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

Estimate the average steady-state plasma concentration under repeated fixed-interval dosing: Css,avg = (F · Dose) / (CL · τ), where F is bioavailability (1 for IV, <1 for oral), CL is clearance, and τ is the dosing interval. If t½ and Vd are also provided, computes the one-compartment IV-bolus accumulation index Rac = 1/(1-e^(-kτ)), peak Cmax,ss, trough Cmin,ss, and time to ~94%/~97% of steady state (4/5 half-lives). Valid only for linear pharmacokinetics with fixed dose and interval — NOT for Michaelis-Menten drugs or non-linear kinetics. Not medical advice.

Health

Trough Level Estimator (Cmin = Cmax · e^(-kτ))

Predict the trough concentration Cmin from a measured peak concentration Cmax during therapeutic drug monitoring (TDM): Cmin = Cmax · e^(-kτ), where k = ln2 / t½ and τ is the time from the peak to the next dose. Inputs are the measured peak, the elimination half-life, and the dosing interval. Also reports the fraction of the peak remaining at the trough and the peak-to-trough drop. This tool takes a measured Cmax (the TDM workflow), unlike drug-half-life-dose (which derives C0 from Dose/Vd) and dosing-interval-designer (which outputs a dimensionless peak/trough ratio, not an absolute concentration). Valid for one-compartment first-order elimination with the peak measured post-distribution. Not medical advice.

Health

Volume of Distribution Calculator (Vd)

Calculate the apparent volume of distribution Vd in two modes. (A) One-compartment IV bolus: Vd = Dose / C0 (C0 = concentration extrapolated to t=0). (B) From clearance and half-life (linear kinetics): Vd = CL · t½ / 0.693. Vd is an APPARENT (theoretical) volume, not an anatomical one — highly tissue-bound drugs (digoxin ≈ 7 L/kg, amiodarone ≈ 66 L/kg) can exceed total body water, while highly plasma-protein-bound drugs (warfarin ≈ 0.14 L/kg) fall far below it. Optional body-weight input converts the result to L/kg. Note: Vd = Dose/C0 gives Vc (initial); Vss (steady state) and Vz (terminal) differ for multi-compartment models, and oral dosing returns Vd/F. Not medical advice.