What is Bioavailability & Why Does it Matter?
Medications are typically the main form of treatment for most people with bipolar disorder. The vast majority of people with bipolar disorder also take more than one medication to help keep relapse and symptoms at bay. However, patients may not know much more about their medication than the directions on the bottle. For example, how often and what time to take the medications and whether or not they need to be taken with food. One such detail that may get overlooked when talking to patients about their medication is bioavailability.
I only recently learned the term bioavailability when a person I know began taking an antipsychotic drug called Latuda, which is used to treat bipolar depression. This person said their doctor had told them to take the drug with food due to increased bioavailability. But what does that mean?
Bioavailability is how much of a drug enters circulation and is available at the site of action once administered. Basically, it’s how much of the drug makes it to its intended use. Intravenous drugs, for example, have 100% bioavailability. Some medications for bipolar disorder are administered this way, but the majority of us take our medications in pill form. At this point, bioavailability decreases and may vary from person to person.
There are many factors that may affect bioavailability:
- Physical activity
- How the drug is manufactured
- Gastric emptying rate
- Whether or not the drug is taken with food
- Interactions with food
- Interactions with other medications
- Gastrointestinal health
- System functionality (kidneys, liver, etc.)
Bioavailability is one of the factors in why a medication may or may not work for an individual or whether or not that individual experiences any side effects from the drug. Bioavailability can even change in the same person over time.
So, when instructions are given on how to take medication, it may be related to bioavailability. Some drugs like lurasidone and ziprasidone are affected by food intake, which is why my friend was instructed to take Latuda with food. For these drugs, bioavailability increases when taken with a meal of 350-500 calories. However, food has little effect on the bioavailability of quetiapine.
Other drugs may be affected by the type of food eaten. For example, grapefruit juice can change the bioavailability of many drugs, including psychiatric drugs, by increasing the absorption rate. This can cause a dangerous interaction.
Always talk to your doctor and pharmacist about any medications you may be taking. They can provide essential information on topics like bioavailability, titration and side effects as well as any special instructions for a given medication. They are there to answer any other questions you may have.
Image credit: Abhijit Bhaduri
LaBouff, L. (2018). What is Bioavailability & Why Does it Matter?. Psych Central. Retrieved on January 23, 2018, from https://blogs.psychcentral.com/bipolar-laid-bare/2017/12/what-is-bioavailability-why-does-it-matter/