Pharmacokinetic studies evaluate drug movement through the body and give crucial information about drug systemic exposure over time. On the other hand, pharmacodynamics describes the effect a drug has on the body. Pharmacokinetic and pharmacodynamic data describe the efficacy and safety profile by correlating dose, exposure, and response.
Each drug product is unique and behaves differently in patients due to inherited biological activity. Patient-specific factors such as age, sex, weight, and genetics influence the way drug products are processed in the body. Hence, an optimal dosing program based on pharmacokinetic and pharmacodynamic data is vital to ensure patients attain optimal therapeutic exposure without intolerable side effects. This goal can be achieved by examining pharmacokinetic properties through drug absorption, distribution, metabolism, and excretion data. The current article dives into this pharmacokinetic process and PK samples in clinical trials.
The ADME process
Absorption, distribution, metabolism, and excretion are internal systems that show drug movement through the body. Pharmacokinetic CRO assesses drug products through PK clinical trials and preclinical assessment to understand the effect of ADME processes on any given drug product. Advanced tools and assessments such as ADME studies and qPCR expression analysis are often dependent on robust method development. So, let us dive deep and understand the ADME properties of a drug product.
Absorption
Absorption is the assessment of drug products traveling from the site of administration to systemic circulation. Bioavailability is the extent of absorption of the drug into the bloodstream. It is the amount of drug product available at the site of action. For example, oral drugs pass through the GI tract and small intestine. This movement reduces its bioavailability. On the other hand, intravenous drugs are injected directly into the bloodstream, and hence, they have 100% bioavailability. Factors affecting drug absorption include the chemical properties of the compound, drug formulation interaction with food and other drugs, and route of administration.
Distribution
Once absorbed, a drug is distributed in the body. Distribution comprises the drug’s movement into different tissues and organs depending on several factors, such as the chemical characteristics of the compound, blood flow, and fluid status. The unit of distribution is called the volume of distribution, which is the quantity of drug available in tissues versus the amount present in the blood.
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Metabolism
The metabolism process alters the drug product, creating new metabolites and compounds. Drug metabolism takes place in multiple areas, such as kidneys, plasma, and gastrointestinal tract. The liver is the primary organ that conducts the majority of metabolism. In two phases, phase 1 and phase 2 metabolism, liver enzymes transform reactive compounds into metabolites. Phase 1 metabolic pathways are pharmacologically active methods, while phase 2 reaction focuses on making the compound more water soluble for excretion.
Excretion
Excretion is eliminating the drug products and their metabolites via excretion. Drug compounds can be excreted through the lungs, gastrointestinal tract, liver, and skin, but the most common route is through the kidney. Some factors that may affect excretion include intrinsic drug properties, age, genetic variation, and health conditions impacting renal blood flow.
