When taken as directed, Suboxone has about 30% bioavailability.
Suboxone is a combination of buprenorphine and naloxone. Buprenorphine is a partial opioid agonist that eases withdrawal symptoms, while naloxone is an opioid antagonist that is only absorbed if the medication is injected and serves to prevent overdose if the medication is misused.
Buprenorphine lasts for a long time in the body. If needed, naloxone acts quickly but metabolizes out very fast as well.
Metabolites for buprenorphine can last in the body for up to three days, while naloxone only lasts for a few hours.
Suboxone is absorbed through mucous membranes in the mouth, either under the tongue (sublingually) or in the cheek (buccally). It is one of the safest and most effective Medications for Addiction Treatment (MAT), as buprenorphine remains active in the body for a full day.
What Does Bioavailability Mean?
The term bioavailability refers to how much of a drug that is ingested actually becomes active in the body. Different medications are metabolized at different rates, depending on how they are processed by the body, which affects their bioavailability. Moreover, a medication can be more “bioavailable” when it is ingested in a certain way. For example, suboxone has a higher bioavailability when it is absorbed under the tongue as opposed to swallowed orally like most other medications.
Drugs are purposefully designed to have lower or higher bioavailability depending on how we want them to act in the body. For example, prescription painkillers like OxyContin are designed to relieve pain for about 12 hours, and they become fully bioavailable after about 30 minutes. MATs like Suboxone become bioavailable faster, within about 15 minutes, but they last for at least as long as opioids, if not longer, to reduce the risk of relapse.
The Bioavailability of Buprenorphine
Suboxone consists of 2 medications: Buprenorphine and Naloxone. They have different bioavailabilities depending on the way in which they are administered.
Buprenorphine, like all opioids, is most bioavailable when injected. However, this mirrors addictive behaviors and can cause overdose. When dissolved under the tongue (“sublingual administration”), buprenorphine is still effective but is not as bioavailable as if it were injected, so it can be used safely with much lower risk of overdose.
The Bioavailability of Naloxone
Naloxone in Suboxone has the highest availability if administered intravenously (injected). The drug’s half-life is about 2 hours intranasally, about 1.4 hours intramuscularly, and 1.2 hours intravenously. About 25–40% of naloxone metabolites are eliminated in the urine in about 6 hours, 50% in 24 hours, and 60–70% in 72 hours. In contrast, it has a very low bioavailability if taken sublingually, as in the case of Suboxone.
The Bioavailability of Suboxone
Suboxone is a combination of two drugs — buprenorphine and naloxone. They have different bioavailabilities.
The primary drug, buprenorphine, is a partial opioid agonist that binds to opioid receptors in the brain for approximately 24 hours, easing withdrawal symptoms and cravings. When taken sublingually as directed, the buprenorphine in suboxone has about 30% bioavailability, meaning about 30% of the total buprenorphine in the medication is active in the bloodstream. This is enough to keep the body stable for up to 24 hours which is why is is often used only once a day (although some patients do require more frequent dosing, sometimes up to 3 times a day). If injected, buprenorphine has a higher bioavailability and thus could cause an overdose. This is where the Naloxone component of the Suboxone comes in:
Naloxone, which is an opioid antagonist, is included in suboxone to prevent overdose if the medication is injected. When taken sublingually along with buprenorphine in the Suboxone film, it has a very low bioavailability, which means it is not absorbed and therefore does NOT block the action of the primary medication, the buprenorphine, in the body. However, if Suboxone is injected inappropriately, the naloxone has a high bioavailability, and will bind preferentially to opioid receptors in the brain and prevent an overdose on the buprenorphine component.
Suboxone should rest under the tongue for about 15 minutes for the film to dissolve. However, much of the dose begins to enter the bloodstream in about 5 minutes. Do not chew or swallow the film strip as this will decrease the bioavailability of the Suboxone.
How Does Suboxone Compare to Other Medications for OUD?
Suboxone has less potential for abuse than other medications for OUD, including methadone. The reason for this is partially because of the Naloxone component, which prevents an individual from “getting high” if they inject the medication for the reasons described above.
Understanding the concept of a medication’s bioavailability can help us understand why the addition of naloxone to buprenorphine in Suboxone provides a safety mechanism to prevent overdose if the medication is injected.
While buprenorphine and methadone have similar half-lives, which makes them both effective addiction treatments, methadone is a full opioid agonist which has more abuse potential and more risk of accidental overdose, which is why each daily dose has to be supervised at a methadone clinic.
Buprenorphine, especially in the form of Suboxone, causes minimal intoxication and risk for overdose, so it can be prescribed for outpatient use. Suboxone therefore greatly expands the ease and availability of opioid addiction treatment.
- Drug Bioavailability. Merck MSD Manuals. https://www.msdmanuals.com/en-au/professional/clinical-pharmacology/pharmacokinetics/drug-bioavailability. October 2020. Accessed February 2022.
- Buprenorphine. Substance Abuse and Mental Health Services Administration (SAMHSA). https://www.samhsa.gov/medication-assisted-treatment/medications-counseling-related-conditions/buprenorphine. January 2022. Accessed February 2022.
- Naloxone. Centre for Addiction and Mental Health (CAMH). https://www.camh.ca/en/health-info/mental-illness-and-addiction-index/naloxone. Accessed February 2022.
- Bioavailability of Sublingual Buprenorphine. Journal of Clinical Pharmacology. https://pubmed.ncbi.nlm.nih.gov/9048270/#:~:text=Study%20results%20indicate%20that%20bioavailability,almost%20twofold%20overestimation%20of%20bioavailability. January 1997. Accessed February 2022.
- Buprenorphine. DrugBank. https://go.drugbank.com/drugs/DB00921. February 2022. Accessed February 2022.
- Naloxone. DrugBank. https://go.drugbank.com/drugs/DB01183. February 2022. Accessed February 2022.
By Elena Hill, MD, MPH
Elena Hill, MD; MPH received her MD and Masters of Public Health degrees at Tufts Medical School and completed her family medicine residency at Boston Medical Center. She is currently an attending physician at Bronxcare Health Systems in the Bronx, NY where ... Read More
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