Drug Concentrations: Measurements

Drug concentration represents the drug amount present in a biological sample. It helps assess the initial drug pharmacokinetics in the body.

The samples can be obtained either invasively or non-invasively. Invasive approaches involve parenteral or surgical interventions to collect blood, cerebrospinal fluid, or tissue biopsy. Non-invasive techniques provide samples such as urine, feces, and saliva.

Plasma, a blood component, is frequently used in drug pharmacokinetics studies. Unbound or protein-bound drugs in the circulation account for total plasma concentration. The unbound drug concentration in filtered plasma represents the concentration at the target site.

Tissue biopsies verify whether a drug reaches the target tissue at the desired concentration.

Urine analysis indirectly confirms the drug's bioavailability, reflecting systemic absorption rate, while fecal measurements indicate unabsorbed oral doses or drugs expelled via the bile.

Examining drug levels in autopsy tissues or bodily fluids provides potential causes of death, such as overdose, poisoning, or drug abuse.