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Overview of Pharmacokinetics: Four Stages in a Drug Traveling Within the Body

Updated: Mar 20, 2023

Pharmacokinetics is a factor that determines the efficacy of therapeutic drugs. Pharmacokinetics is the study of the movement of drugs within the body upon insertion and excretion.

Pharmacokinetics is a drug’s journey through the body, which is broken down into four different stages abbreviated as ADME: absorption, distribution, metabolism, and excretion.

  • Absorption: observes how a drug travels from the site of administration to the site of action.

  • Distribution: observes the passage of a drug through the bloodstream to different tissues in the body.

  • Metabolism: observes the activity that breaks down a drug.

  • Excretion: observes the elimination of a drug from the body.

4 stages of pharmacokinetics

These stages can be viewed in more detail:


Absorption is the travel of a drug from the site of administration to the bloodstream. The frequency and expansion of drug absorption rely on multiple factors like:

  • Route of administration

  • Drug-food interactions

  • Formulation and chemical properties of a drug

Administration of a drug, via oral, intravenous, and inhalation, influences bioavailability, the portion of the active form of a drug that goes through the bloodstream and arrives at the target site.

In instances where a drug is given intravenously, absorption is not required, and bioavailability is complete since the active form of the medication is circulating in the bloodstream immediately. Despite this, oral administration of medicine has deficient absorption and yields less circulation of the drug being delivered to the site of action.

An example of reduced drug absorption is first-pass metabolism, where many orally administered drugs are metabolized by the liver or gut wall prior to arrival in the bloodstream.

drug distribution within the body


Drug distribution is pertinent since it can affect how much the drug arrives at the active sites, thus influencing drug toxicity and efficacy. Drugs travel from the absorption site to various tissues around the body, like fat, muscle, and even brain tissue. Numerous elements can affect this, like lipophilicity, blood flow, molecular size, and how the drug interacts with aspects of blood, like plasma proteins.

An instance of this is the drug warfarin, which is greatly protein-bound, resulting in a minuscule percentage of the drug being available in the bloodstream to apply its therapeutic effects. Whenever a highly protein-bound drug is provided in tandem with warfarin, it may derail the warfarin from the protein-binding site and boost the amount that enters the bloodstream.

Moreso, anatomical impediments observed in specific organs like the blood-brain barrier, prevent some drugs from getting into brain tissue. Drugs with specific aspects, like high lipophilicity, small size, and molecular weight are more capable to bypass the blood-brain barrier.


Metabolism is the breakdown of compounds as soon as they enter the body. Most of the biotransformation, or metabolism, of all drugs in clinical use is executed through cytochrome P450 (CYP450). The components that affect drug metabolism are:

  • Genetics influence whether a person can metabolize drugs at a quicker or slower rate.

  • Age can affect the performance of the liver; the elderly have a lesser liver function and may metabolize drugs more slowly, increasing the risk of intolerability. Newborns or infants have immature liver performance and may necessitate unique dosing consideration.

  • Drug interactions can result in decreased drug metabolism via enzyme inhibition or increased metabolism by enzyme induction.

decorative picture of drug metabolism

Many drugs metabolized through CYP450 enzymes result in inactive metabolites, which no longer have original drug pharmacologic activity. However, some medications, like codeine, are inactive and become pharmacologically active drugs in the body, or prodrugs.


Elimination of the substance or the product of its metabolism involves both the metabolic process and the excretion of the drug through the kidneys, and to a degree, into the bile.

Expulsion into the urine via the kidneys is one of the more pertinent mechanisms of drug removal. The facts that influence excretion include:

  • Direct renal dysfunction, may extend the half-life of specific drugs and require dose adjustments.

  • Age may contribute to various rates of excretion and affect medication dosages.

  • Pathologies that impact renal blood flow, like congestive heart failure and liver disease can make drug excretion less efficient.

An individual's characteristics influence these four different phases, which inevitably affect medication selection.


Pharmacokinetics is expansive in its field but comprehending simple mechanisms that direct the pharmacokinetics of a drug is pertinent to creating unique 3D pharmaceutical solutions for patients.

Laxxon Medical utilizes its exclusive patented 3D screen printing process to tailor pharmacokinetics for the improvement and benefit of patients.


Laxxon Medical is dedicated to engineering patented 3D pharmaceutical solutions which optimize products and benefit patients. Our goal is to establish SPID®-Technology as a manufacturing process that has the individual and the pharmaceutical partner in mind.

To keep up to date with SPID®-Technology and Laxxon Medical news and announcements, follow us on Twitter and LinkedIn.

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