Cobicistat is a drug that is used to raise the concentration of certain other drugs in the body. Cobicistat is co-formulated with the following drugs all in one pill called Stribild:
- tenofovir + FTC
The purpose of cobicistat is to raise and maintain levels of elvitegravir so that once-daily dosing of Stribild is effective.
For more detailed information about Stribild, see the following CATIE resources:
Opiate substitution therapy using methadone plays an important role in helping stabilize the lives of people addicted to heroin, morphine and related substances. Another form of opiate substitution uses a co-formulation of two drugs in one pill—buprenorphine and naloxone. This co-formulation is sold under the brand name Suboxone.
All of the above-mentioned drugs are broken down by enzymes in the liver, and because cobicistat can interfere with some of these enzymes, it is possible that it could alter levels of opiates or opiate substitutes, reducing them and causing symptoms of withdrawal or raising them and causing side effects. To investigate this possibility, researchers recruited 22 men and seven women who received elvitegravir and cobicistat (tenofovir and FTC are not expected to interact with opiates and so they were not tested in this experiment) and gave them these drugs at different time points:
- methadone at doses between 80 and 120 mg/day
- buprenorphine 16 mg and naloxone 4 mg, up to buprenorphine 24 mg and naloxone 6 mg
- 150 mg of elvitegravir and 150 mg of cobicistat
These drugs were taken in the morning with a light meal and 240 ml of water for 11 days; participants were monitored during that time and for a further seven days.
Common side effects reported when elvitegravir-cobicistat were taken with methadone or buprenorphine-naloxone included nausea and headache, both experienced by 18% of participants. However, these side effects were generally mild or, at worst, of moderate intensity.
No participant experienced symptoms suggestive of withdrawal or overdose.
According to the research team, “No clinically relevant [interactions] were observed” between the study drugs. Therefore, the researchers concluded that no dose adjustments with methadone or Suboxone are needed when these drugs are taken with Stribild.
—Sean R. Hosein
Bruce R, Winkle P, Custidio J, et al. Pharmacokinetics of cobicistat-boosted elvitegravir administered in combination with methadone or buprenorphine-naloxone. In: Program and abstracts of the 52nd Interscience Conference on Antimicrobial Agents and Chemotherapy, 9-12 September 2012. San Francisco, California. Abstract A-1205.