Journal of Applied Pharmacy
Open Access

Pharmacokinetics: The Science behind Drug Absorption, Distribution, Metabolism and Excretion

Jemmi Neskhome^{* *}Correspondence: Jemmi Neskhome, Department of Medicine, University of California, California, USA, Email:

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Description

Pharmacokinetics, a foundation of pharmacology, searches into the dynamic processes that govern the fate of drugs within the body. It encompasses absorption, distribution, metabolism and excretion collectively dictating how drugs interact with biological systems. This field not only shapes drug dosing regimens but also influences therapeutic efficacy and safety profiles.

Absorption

Absorption marks the initial step as a drug traverses into systemic circulation. The route of administration significantly impacts absorption kinetics. Oral ingestion subjects drugs to Gastrointestinal (GI) barriers such as pH variations, enzymatic degradation, and efflux transporters. In contrast, parenteral routes bypass GI hurdles, offering rapid and predictable drug absorption.

Factors influencing absorption include drug physicochemical properties (e.g., lipophilicity), formulation characteristics (e.g., solubility), and physiological conditions (e.g., gastric emptying rate). Pharmacokinetic models, like the Biopharmaceutical Classification System (BCS), aid in predicting drug absorption based on these parameters.

Distribution

Upon entering systemic circulation, drugs encounter various physiological compartments. Distribution entails drug movement from the bloodstream to target tissues and organs, governed by tissue perfusion, plasma protein binding, and tissue affinity. Highly protein-bound drugs exhibit limited distribution due to their inability to traverse cell membranes.

Factors influencing drug distribution include tissue vascularity, lipid solubility, and pH gradients. The Volume of Distribution (Vd) quantifies the apparent space in which a drug distributes within the body, guiding dosing strategies and predicting drug accumulation.

Metabolism

Metabolism, predominantly occurring in the liver, involves enzymatic biotransformation to facilitate drug elimination. Cytochrome P450 (CYP) enzymes, constituting a major metabolic pathway, catalyze phase I reactions such as oxidation, reduction, and hydrolysis. Phase II conjugation reactions conjugate drug metabolites with endogenous substrates to enhance renal excretion.

Genetic polymorphisms in CYP enzymes influence individual drug metabolism, leading to interpatient variability in drug response and toxicity. Drug-drug interactions further modulate metabolic pathways, affecting drug efficacy and safety profiles. Pharmacogenomic studies elucidate the genetic basis of drug metabolism, guiding personalized medicine approaches.

Excretion

Excretion marks the final stage as drugs undergo elimination from the body, predominantly via renal and hepatic routes. Renal excretion involves glomerular filtration, tubular secretion, and reabsorption processes. Lipophilic drugs undergo hepatic biotransformation into hydrophilic metabolites for renal elimination.

Renal impairment significantly alters drug excretion kinetics, necessitating dose adjustments to prevent drug accumulation and toxicity. Non-renal routes, including biliary and pulmonary excretion, contribute to drug elimination, albeit to a lesser extent. Pharmacokinetic principles underpin dosage adjustments in patients with renal or hepatic dysfunction to optimize therapeutic outcomes.

Clinical applications

Pharmacokinetic principles underpin rational drug dosing strategies across diverse patient populations. Therapeutic Drug Monitoring (TDM) utilizes pharmacokinetic parameters to individualize drug regimens, ensuring therapeutic efficacy while minimizing adverse effects. TDM proves indispensable for drugs with narrow therapeutic indices or significant interpatient variability.

Population pharmacokinetics employs mathematical models to characterize drug disposition in heterogeneous patient cohorts, guiding dosing recommendations. Pharmaco Kinetic-Pharmaco Dynamic (PK-PD) modeling elucidates the relationship between drug concentration and pharmacological response, facilitating drug development and dose optimization.

Conclusion

In conclusion, hospital pharmacy plays a vital role in the delivery of safe, effective, and patient-centered care within healthcare institutions. Through medication dispensing, clinical expertise, and quality improvement initiatives, hospital pharmacists contribute significantly to optimizing medication therapy and enhancing patient outcomes. Despite facing challenges such as medication shortages and workforce shortages, hospital pharmacy remains committed to its mission of promoting medication safety and improving the overall quality of care. As healthcare continues to evolve, the role of hospital pharmacy will remain indispensable in meeting the diverse needs of patients and ensuring excellence in medication management.