Drugs can be administered a number of different ways: Intravenous, oral, subcutaneous, transdermal, and many more. It is important to understand what happens to these medications once administered to gain insight into not only their therapeutic effect, but also potential adverse effects. The fancy word for this is called pharmacokinetics, or what the "body does to the drug".

Over the next few blog posts, we will detail the four major principles, starting today with absorption.

Absorption- The first thing that occurs upon administration is absorption which lead to availability of the drug to exert its effect (bioavailability). Depending on the route of administration, this can be very high, low, or variable.

For example, intravenous (IV) antibiotics are often given in patients who are critically ill to ensure 100% absorption of the complete dose.

Oral drugs can vary significantly from product to product. Many oral drugs have great absorption which allows for administration instead of IV drugs which can have complications. However a number of factors can decrease oral drug absorption, such as lack of stomach acid due to PPI administration (iron products), or chelation drug interactions where one drug, such as magnesium which is positively charged, can bind to a negatively charged drug, such as ciprofloxacin, in the gastrointestinal tract and therefore decrease its overall absorption. This could lead to clinical failure in the patient.

Subcutaneous administration can typically lead to good overall absorption with certain products. Some commonly administered subcutaneous products include insulin, most GLP-1 agonists used for diabetes and weight loss (e.g. Wegovy), and even anticoagulants such as enoxaparin (Lovenox). A high number of monoclonal antibodies used for a number of diseases states are also administered subcutaneously.

Intramuscular (IM) administration can be highly variable depending on muscle mass and is not administered too often. One exception to this is IM ceftriaxone which is often given in the clinic setting for pediatrics.

Intrathecal administration can be given into the spinal canal and is sometimes used for chemotherapy agents for patients with metastatic disease (e.g. methotrexate).

These are some of the main principles. At TeachMePharm.com, we provide videos that highlight these important principles within the specific drug discussed. Come check us out!

Next post we will go over the second important pharmacokinetic principle: Distribution.

Happy New Year!

Chris