Last week, I talked about how to read drug product information (PI). This week I’ll discuss the parts of the PI that I didn’t cover last week in Medication: Reading the Fine Print. This includes the more complicated concepts, which I will try to put in to simpler terms.
Let’s begin with the description, generally found about half way through the PI. This tells us the drug’s scientific name, classification and gives information about the chemicals in the drug. The additives, weight and forms of the drug are listed. The different strengths (dosages) are listed. A diagram of the drug’s chemical make-up is included here.
Listed next is the mechanism of action, or how the drug works. The clinical pharmacology is next, which includes pharmacodynamics and pharmacokinetics. Pharmacodynamics is about what a drug does to the body. Pharmacokinetics is what the body does to the drug.
Pharmacokinetics (PK), how drugs behave once they are in the body, has four parts:
- Absorption – The process of how the drug is absorbed in the body.
- Distribution – Where the drug is distributed after it enters the body.
- Metabolism – How the drug is broken down by the body.
- Elimination – How the drug leaves the body.
PK information is hard to read. To the untrained, the terms are complicated and abbreviations are used. If you do not have a good working knowledge of science, the information has no frame of reference. However, there are some basic concepts that are useful to know and you can ask your medical provider. These are:
- How long will it take before the drug starts to work?
- When will it be at its peak?
- How long does it take the drug to leave the body?
- Should I take this drug with or without food?
A few more terms may be helpful:
- Half-life or terminal half-life (t ½) Length of time for one-half of a substance to be eliminated from the system. A short half-life is 4 to 8 hours and a long half-life is over 24 hours.
- Peak When the drug is at its highest in the blood.
- Trough – When the drug is at its lowest in the blood.
- Bioavailability – What percentage of the drug is available to be used after it enters the body.
- Clearance – The elimination of a substance from the body.
- Steady state – When the drug stays at a constant level in the body.
- Therapeutic Index (TI) This is a ratio between the average effective dose and the average toxic dose. The closer the ratio is to one, the greater the risk a drug can be toxic (potentially poisonous).
The PK section is where you’ll find information about how the drug works in specific populations, such as those with kidney disease, the elderly, or children. You will also find drug interaction information here.
For the intensely curious, the PI also includes microbiology and drug resistance information. This is followed with nonclinical toxicology. If you are wondering if the drug causes cancer in lab animals, or what it may due to a fetus, look in this section.
If you keep reading, you will come to the clinical study information. This is very interesting, especially if you want to know what your chances are of responding to the drug.
Congratulations if you made it to the end of this article. Hopefully you learned something new. In time, technical information such as this will start to make more sense.