Skip to Content
Search Site Menu


By Richard L. Allen, Jr.

We recently wrote an HPS Legal Alert that discussed the challenges and frequency of medication errors, and the impact this has on patients who are victims of medical malpractice. Knowledge of the common types of medication errors greatly assists in the process of trying to determine if a patient’s injury is related to a medication. As a reminder, the most common errors usually occur at one of these points:

  • Ordering/prescribing
  • Documenting
  • Transcribing
  • Dispensing
  • Administering
  • Monitoring

In addition, when trying to decide whether a medication error was a potential cause of patient injury, it is essential to have a thorough understanding of why the medication was given to the patient and the chemical properties of the medication.

Pharmacodynamics and Pharmacokinetics

Pharmacodynamics is the study of what a drug does to a patient’s body. For example, aspirin will prevent blood clots, insulin lowers the level of glucose in the blood and antihypertensives lower blood pressure.  Pharmacokinetics, on the other hand, studies what the patient’s body does to the drug. For example, enzymes will chemically change the drug to an inert form, or the body will eliminate the drug through the kidneys, liver, lungs or intestines.   

The Half-Life of a Drug and the Therapeutic Index

An estimate of how long it takes for a drug to be removed from your body is called the drug’s “half-life” (time it takes to eliminate one-half (50%) of the drug from the body). Depending on the drug, the half-life can vary from minutes to months. Some variables that may affect the half-life are:

  • Age
  • Blood circulation
  • Gender
  • Organ functions
  • Drug formulation
  • Drug administration

If the half-life of a medication is increased, for example, by decreased kidney function, and the dose of the drug is not lowered, then the drug may reach levels that are harmful to the patient. The range of doses at which a drug is effective without unacceptable adverse events is referred to as the therapeutic index. If a drug has a narrow therapeutic index, it means the drug has a narrow window between an effective dose and one that causes toxic effects.

Pharmacodynamics and Pharmacokinetics When Investigating a Medical Malpractice Case

When a patient experiences an unexpected and unexplained injury, the principals of pharmacodynamics and pharmacokinetics should be used in evaluating whether medical malpractice occurred. For example, Gentamycin is an excellent antibiotic, but it has a fairly narrow therapeutic index, meaning that the difference between a dose that kills bacteria and the dose that harms the body is narrow. Gentamycin is cleared from the body by the kidneys. Patients who have even minor impaired kidney function can suffer permanent hearing loss because of increased levels of Gentamycin. Therefore, a normal dose of this drug, when coupled with minor kidney problems, can cause patient injury.

Key Takeaways

No matter how well-trained the health care professional may be, he or she cannot know every drug, how it interacts with the body, or how the body interacts with it. Consulting with an attorney with a pharmaceutical background, who is well-versed in the study of pharmacodynamics, can assist in determining whether this particular type of medical malpractice case has occurred. If you are dealing with a medical malpractice case (medication error-related or otherwise) and would like to discuss your options, please contact Rick Allen, or any other member of our Haliczer Pettis & Schwamm legal team.