Introduction to Pharmacokinetics

Pharmacokinetics are crucial in finding the correct dosage for a disease and a patient. Find out how PK affects you.

What is Pharmacokinetics?

Pharmacokinetics focuses on how drugs are ingested and move throughout the body. Understanding how drugs metabolize helps scientists understand how long a substance stays in the blood and what bodily functions are impacted.¹

What Defines Pharmacokinetics?

Pharmacokinetics focuses on ingestion, distribution, dissolving, excretion, and leftover metabolites from drugs. Essentially, this study focuses on the entire cycle of drug use.

History of PK?

Pharmacokinetics, or PK, was originally studied by pediatrician Friedrich Hartmut Dost in 1953. However, the core concepts behind PK have been studied across various medical fields and cultures for several years before Dost’s medical publications. The study of pharmacokinetics dates as far back as 1847 where it helped define the properties of anesthesia.²

Pharmacokinetics vs. Pharmacodynamics

Unlike pharmacokinetics, pharmacodynamics medical trials focus on how drugs affect the body both in terms of the effects it produces and which brain receptors they bind to. Much like PK, pharmacodynamics is widely attributed to one person, in this case, Oswald Schmiedeberg, but it has a long and varied past across several specializations. Typically, both PK and PD go hand in hand to help shed light on the use and risks of drugs.

Pharmacokinetic Metrics

Pharmacokinetics primarily uses two metrics to gain information about drug cycles for medical trials. First, PK reviews the time it takes for drugs to be entirely processed. Second is the concentration of the drug found in plasma cells. These metrics monitor the long-term applications of pharmaceutical drugs as well as the impact of illicit substances. Another significant metric is the steady-rate concentration which refers to how potent the drug is throughout its life cycle.

Pharmacokinetic Models

PK models are used to estimate the drug time and concentration metrics before the drug is administered. Common PK models include:

Linear PK Model: Linear models suggest that the half-life (the point at which a property’s effectiveness is halved) is consistent despite the amount of the drug ingested. For example, taking double the amount of the drug then increases the drug’s plasma concentration two-fold. Imagine a linear PK model as 2+2=4.
Non-Linear PK Model: Non-linear PK models state that the potency of the drug does not correlate with the dosage. For example, taking double the drug amount may result in having more than double the drug concentration in the body. Imagine a non-linear PK model as 2+2=7. Drugs that follow a non-linear model do so because of the high accumulation of the drug, how its metabolized, and other factors. Non-linear drugs require careful administration and are often classified as prescription.

How Can Pharmacokinetics Aid in Addiction?

Understanding pharmacokinetics helps doctors better combat addiction, specifically withdrawal symptoms. People in active addiction may have multiple chemicals in their symptoms coupled with underlying health issues. These factors can make it challenging to administer the proper dosage of anti-withdrawal drugs.

PK also plays a role in prescribing drugs for mental illness in patients with addictions. People with addictive tendencies may abuse their prescribed drugs unless dosage, potency, and other PK metrics are considered. For example, prescribing a drug that has a short half-life and low dosage may be more beneficial for those in recovery.

Studies on PK and Addiction

Many of the clinical trials on PK and addiction focus on applications of the PK models to treat drug overdose and severe withdrawal symptoms. Several factors are standing in the way of the more widespread use of PK models in addiction.

First, unlike other anti-addiction drugs, I.E., methadone, PK models do little to reduce cravings. Additionally, the testing equipment is expensive and requires additional training that may not always be available to more rural or understaffed clinics. However, the long-term implication of PK far outweighs the negative.

PK helps medical professionals gauge the intensity of the addiction and the brain changes that have occurred. Cocaine, for example, taken frequently in large amounts, will make more drastic changes than sporadic, low doses of marijuana. Using PK models, professionals can chart the time it takes for those changes to take effect and how the patient will respond to various forms of treatment.³

Other Studies on the use of PK

Studies on PK and HIV?

HIV affects millions worldwide. Much like addiction, being able to administer proper dosage levels is paramount to overcoming the disease. Moreover, like addiction, patients with HIV undergo multiple clinical trials, medications and have underlying health issues. Many studies show PK models being used to evaluate the effectiveness of HIV medication.

Currently, PK strategies for HIV patients include peripheral blockers. Peripheral blockers are used to lower drug concentrations by interfering with the binding process causing less of the drug to be absorbed. The other method is enhanced drug metabolism. Enhanced metabolism shortens the amount of time the drug is active in the body. By shortening a drug’s life cycle, the chance of dangerous overlap between medications lowers.

New clinical trials into antiretroviral medication, the kind prescribed for HIV patients, have been unable to report consistent statistics. A big reason why is due to the varied nature of bodily metrics within HIV patients. Some patients may have more activated platelets; others may have underlying health issues unrelated to HIV. Numerous clinical trials have not accounted for these variances. PK allows a medical professional to better tailor treatment to an individual as opposed to just the disease. In this way, patients can receive a higher quality of care.⁴

What to Know About PK and TDM

Therapeutic Drug Monitoring, also known as TDM, aims to maximize the overall efficiency of drug dosage and prescription. Much like PK, TDM monitors the potency of the drug, how much of it is absorbed into the body, and how much of it is needed to be effective while minimizing side effects.

Medical trials show that correct dosage is a combination of knowing the drug, the patient history, and the likelihood of additional chemicals. For broad strokes, PK works well. However, in specialized cases where the patient may metabolize drugs differently or suffer from irregular drug reactions, TDM is superior at establishing acceptable drug levels for a specific patient.⁵