Concept Architecture
Concept
Theoretically, Pharmacokinetics is the quantitative study of the absorption, distribution, metabolism and excretion (ADME) of drugs over time. It describes how the body influences drug concentrations following administration and provides the mathematical framework for predicting drug exposure under different dosing regimens. Pharmacokinetics exists to characterise the time course of drug concentrations and support safe, effective and economically efficient use of medicines.
Mathematically, pharmacokinetics is represented using compartmental and non-compartmental models based on differential equations describing drug movement between compartments and elimination from the body. The mathematical framework estimates parameters such as clearance, volume of distribution, elimination rate constant, half-life and area under the concentration-time curve. Depending on the drug and model complexity, first-order, zero-order or nonlinear kinetics may be applied.
In practice, pharmacokinetic parameters are estimated from plasma or serum concentration-time data collected during clinical pharmacology studies using nonlinear regression, maximum likelihood estimation or population pharmacokinetic modelling. In health economics, pharmacokinetic models inform assumptions regarding dosing frequency, treatment adherence, therapeutic effectiveness, adverse events, treatment persistence and resource utilisation within decision-analytic and pharmacoeconomic evaluations.
Purpose
Used to quantify drug exposure over time, estimate pharmacokinetic parameters, optimise dosing regimens and support clinical, regulatory and health economic evaluations of pharmaceutical interventions.
Mathematical Formulae
Primary Formula
For first-order elimination:
C(t) = C?e???
Supporting Formulae
Elimination half-life:
t� = ln(2) / k
Clearance:
CL = Dose / AUC
Volume of distribution:
Vd = Dose / C?
Relationship between clearance and elimination rate:
k = CL / Vd
Area under the concentration-time curve:
AUC = ??^� C(t) dt
Related Mathematical Methods
- Compartmental Analysis
- Non-Compartmental Analysis
- Population Pharmacokinetic Modelling
- Nonlinear Mixed-Effects Modelling
- First-Order Kinetics
- Maximum Likelihood Estimation
- Nonlinear Regression
Example
A medicine is administered intravenously with an initial plasma concentration of 100 mg/L and an elimination rate constant of 0.20 h??.
Drug concentration after 6 hours:
C(6) = 100 ? e^(?0.20 ? 6)
C(6) = 30.1 mg/L
The elimination half-life is:
t� = 0.693 � 0.20 = 3.47 hours
These estimates are subsequently incorporated into a health economic model to determine dosing frequency, adherence assumptions and treatment costs.
Excel Implementation
| Function | Example Formula | Health Economics Application |
|---|---|---|
| EXP | =C0*EXP(-k*Time) | Calculates drug concentration over time. |
| LN | =LN(2)/k | Calculates elimination half-life. |
| SUMPRODUCT | =SUMPRODUCT(ConcentrationRange,TimeWeights) | Approximates exposure calculations. |
| LINEST | =LINEST(LN(ConcentrationRange),TimeRange) | Estimates the elimination rate constant from concentration-time data. |
| LOGEST | =LOGEST(ConcentrationRange,TimeRange) | Fits exponential pharmacokinetic models. |
VBA (Optional)
VBA can automate estimation of pharmacokinetic parameters, generate concentration-time profiles and perform batch analyses for large pharmacokinetic datasets.
Sources
- Rowland M, Tozer TN. Clinical Pharmacokinetics and Pharmacodynamics: Concepts and Applications.
- Gibaldi M, Perrier D. Pharmacokinetics.
- Gabrielsson J, Weiner D. Pharmacokinetic and Pharmacodynamic Data Analysis: Concepts and Applications.
- Ette EI, Williams PJ. Pharmacokinetics in Drug Development.
- Briggs A, Claxton K, Sculpher M. Decision Modelling for Health Economic Evaluation.
- Drummond MF, Sculpher MJ, Claxton K, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes.
Related Concepts (2)
Frequently Asked Questions (6)
What is pharmacokinetics?
The study of how the body absorbs, distributes, metabolises, and eliminates a drug over time, covering bioavailability, clearance, and half-life.
Source: Rowland & Tozer 2010
What journey of a drug does pharmacokinetics describe?
Pharmacokinetics describes the journey of a drug through the body over time: how it is absorbed into the blood, distributed to the tissues, metabolised into other forms, and finally eliminated. It captures this journey in parameters such as bioavailability, clearance, and half-life, which together determine how much drug reaches its target and for how long. This is distinct from pharmacodynamics, which concerns the effect the drug then has. What the body does to the drug is what it examines. Rowland and Tozer (2010) describe this.
Source: Rowland & Tozer 2010
What processes does pharmacokinetics cover?
Pharmacokinetics covers the processes of absorption, how the drug enters the circulation; distribution, how it spreads through the body; metabolism, how it is chemically altered, chiefly by the liver; and elimination, how it is removed, chiefly by metabolism and kidney excretion, often summarised as absorption, distribution, metabolism, and excretion. So pharmacokinetics covers the drug's journey through the body from entry to removal, which is why it addresses these processes, since together they determine how the drug's concentration changes over time, and understanding them is central to predicting drug levels and designing dosing regimens.
Source: Rowland & Tozer 2010
What are key pharmacokinetic parameters?
Key pharmacokinetic parameters include bioavailability, the fraction of a dose reaching the circulation; volume of distribution, reflecting how widely the drug spreads; clearance, the rate of elimination; and half-life, the time for the concentration to halve. So pharmacokinetics is characterised by these parameters, which is why they are central to dosing, since bioavailability and volume of distribution relate to how much drug reaches and spreads through the body, and clearance and half-life relate to how it is eliminated, together determining the doses and dosing intervals needed to achieve and maintain therapeutic concentrations.
Source: Rowland & Tozer 2010
How does pharmacokinetics differ from pharmacodynamics?
Pharmacokinetics differs from pharmacodynamics in that pharmacokinetics concerns what the body does to the drug, its absorption, distribution, metabolism, and elimination, while pharmacodynamics concerns what the drug does to the body, its effects and mechanisms. So the two are complementary, with pharmacokinetics describing how the drug's concentration changes over time and pharmacodynamics describing how that concentration produces an effect, which is why both are needed to understand drug action, since the drug's effect depends on both the concentration achieved, governed by pharmacokinetics, and the response to that concentration, governed by pharmacodynamics.
Source: Rowland & Tozer 2010
Why is pharmacokinetics important?
Pharmacokinetics is important because understanding how a drug's concentration changes over time is fundamental to determining the right dose and dosing interval to achieve and maintain effective levels while avoiding toxicity, and it explains variability between patients. So pharmacokinetics matters for dosing and for individualising therapy, which is why it is central to pharmacology and drug development, since it determines the doses needed and how factors such as organ function affect drug levels, and together with pharmacodynamics it provides the basis for using drugs effectively and safely by linking dose to concentration and effect.
Source: Rowland & Tozer 2010
Trust Record
Verified by Dr Darrin Baines
British health economist
Professional identity: darrinbaines.org
Verification date: 17 Apr 2026
Content version: 1.0.0
Canonical Identity
- Persistent URI
- https://healtheconomics.wiki/concept/pharmacokinetics
- Term code
- HE-PE-CP-013
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