Latest Pharmacokinetics - StatPearls - NCBI Bookshelf
NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.
StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-.
Pharmacokinetics
Authors
Sean Grogan1; Charles V. Preuss2.
Affiliations
1 University of New England
2 University of South Florida
Last Update: July 30, 2023.
Definition/Introduction
Pharmacokinetics (PK) is the study of how the body interacts with administered substances for the entire duration of
exposure (medications for the sake of this article). This is closely related to but distinctly different from
pharmacodynamics, which examines the drug’s effect on the body more closely. This field generally examines these
four main parameters: absorption, distribution, metabolism, and excretion (ADME).
Possessing an understanding of these processes allows practitioners the flexibility to prescribe and administer
medications that will provide the greatest benefit at the lowest risk and allow them to make adjustments as necessary,
4/16/2026, 1:43:23 PM
, Latest Pharmacokinetics - StatPearls - NCBI Bookshelf
given the varied physiology and lifestyles of patients.
Issues of Concern
Absorption
Absorption is the process that brings a drug from the administration, eg, tablet or capsule, into the systemic
circulation. Absorption affects the speed and concentration at which a drug may arrive at its desired location of effect,
eg, plasma. There are many possible methods of drug administration, including but not limited to oral, intravenous,
intramuscular, intrathecal, subcutaneous, buccal, rectal, vaginal, ocular, otic, inhaled, nebulized, and transdermal.
Each administration method has its own absorption characteristics, advantages, and disadvantages.
The absorption process also often includes liberation or the process by which the drug is released from its
pharmaceutical dosage form. This is especially important in the case of oral medications. For instance, an oral
medication may be delayed in the throat or esophagus for hours after being taken, delaying the onset of effects or even
causing mucosal damage. Once in the stomach, the low pH may begin to chemically react with these drugs before
they even arrive in the systemic circulation.[1]
Bioavailability
Bioavailability is the fraction of the originally administered drug that arrives in systemic circulation and depends on
the properties of the substance and the mode of administration. Bioavailability can be a direct reflection of medication
absorption. For example, when administering medication intravenously, 100% of the drug arrives in circulation
4/16/2026, 1:43:23 PM
NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.
StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-.
Pharmacokinetics
Authors
Sean Grogan1; Charles V. Preuss2.
Affiliations
1 University of New England
2 University of South Florida
Last Update: July 30, 2023.
Definition/Introduction
Pharmacokinetics (PK) is the study of how the body interacts with administered substances for the entire duration of
exposure (medications for the sake of this article). This is closely related to but distinctly different from
pharmacodynamics, which examines the drug’s effect on the body more closely. This field generally examines these
four main parameters: absorption, distribution, metabolism, and excretion (ADME).
Possessing an understanding of these processes allows practitioners the flexibility to prescribe and administer
medications that will provide the greatest benefit at the lowest risk and allow them to make adjustments as necessary,
4/16/2026, 1:43:23 PM
, Latest Pharmacokinetics - StatPearls - NCBI Bookshelf
given the varied physiology and lifestyles of patients.
Issues of Concern
Absorption
Absorption is the process that brings a drug from the administration, eg, tablet or capsule, into the systemic
circulation. Absorption affects the speed and concentration at which a drug may arrive at its desired location of effect,
eg, plasma. There are many possible methods of drug administration, including but not limited to oral, intravenous,
intramuscular, intrathecal, subcutaneous, buccal, rectal, vaginal, ocular, otic, inhaled, nebulized, and transdermal.
Each administration method has its own absorption characteristics, advantages, and disadvantages.
The absorption process also often includes liberation or the process by which the drug is released from its
pharmaceutical dosage form. This is especially important in the case of oral medications. For instance, an oral
medication may be delayed in the throat or esophagus for hours after being taken, delaying the onset of effects or even
causing mucosal damage. Once in the stomach, the low pH may begin to chemically react with these drugs before
they even arrive in the systemic circulation.[1]
Bioavailability
Bioavailability is the fraction of the originally administered drug that arrives in systemic circulation and depends on
the properties of the substance and the mode of administration. Bioavailability can be a direct reflection of medication
absorption. For example, when administering medication intravenously, 100% of the drug arrives in circulation
4/16/2026, 1:43:23 PM
