Standard DoseUsed as a boosting agent (or PK enhancer) at a dose of 150 mg once a day with food taken at the same time with either Prezista 800 mg (co-formulated as Prezcobix), Reyataz 300 mg (co-formulated as Evotaz), or co-formulated in the single-tablet regimens Stribild, Genvoya, and Symtuza.
For adults and children weighing at least 77 pounds (if taken with atazanavir, brand name Reyataz) or at least 88 pounds (if taken with darunavir, brand name Prezista or in the single-tablet regimen Symtuza; darunavir patients must be at least three years old). Tybost is not an HIV drug; it is a pharmacokinetic enhancer or a “booster” used to increase the levels of Prezista 800 mg once daily, Reyataz 300 mg once daily, or elvitegravir 150 mg in Stribild and Genvoya. Tybost is not interchangeable with Norvir when used to increase the levels of other HIV medications.
Take missed dose as soon as possible (at the same time as any separate medication prescribed) unless it’s closer to the time of your next dose. Tybost is not recommended for people with CrCl less than 70 mL/min when co-administered with a regimen containing TDF or for people with severe liver problems.
- See package insert for more complete information on potential side effects and interactions.
ManufacturerGilead Sciences, Inc.
(800) GILEAD-5 (445–3235)
Potential Side Effects and Toxicity
Side effects observed in clinical studies (greater than 2% of patients) include rash, jaundice, and yellowing of the eyes. However, it was studied with Reyataz so the jaundice and yellowing of eyes were most likely due to the Reyataz component. Before taking Tybost, kidney function testing should be conducted, including serum creatinine (SCr), serum phosphorus, urine glucose, and urine protein. These measurements should continue to be monitored while taking Tybost. Cobicistat can cause a small, reversible increase in serum creatinine within the first few weeks of treatment without affecting actual kidney function. The SCr increase occurred within weeks of starting cobicistat and was reversible within a few days after stopping it. The co-administration of Tybost and Viread (tenofovir DF or TDF, also found in Cimduo, Complera, Delstrigo, Symfi/Symfi Lo, Stribild, Truvada, and Temixys) is not recommended if the CrCl is less than 70 mL/min.
Potential Drug Interactions
Tybost interacts with many drugs. Do not take with alfuzosin, colchicine, dihydroergotamine, dronedarone, ergotamine, irinotecan, simvastatin, lovastatin, lurasidone, methyl-ergonovine, ranolazine, rifampin, pimozide, triazolam, oral midazolam, Revatio, or St. John’s wort. Tybost may increase levels of nasal or inhaled fluticasone (Flonase, Advair, Breo Ellipta, Arnuity Ellipta, and Flovent). Use an alternative corticosteroid and monitor for signs of Cushing’s syndrome (increased abdominal fat, fatty hump between the shoulders, rounded face, red/purple stretch marks, increased appetite, bone loss, possible high blood pressure, and sometimes diabetes). No significant interactions with beclomethasone. Tybost may increase levels of certain calcium channel blockers, beta blockers, HMG-CoA reductase inhibitors (statins or cholesterol medicines), anticoagulants, antiplatelets, antiarrhythmics, antidepressants, sedative-hypnotics, rifabutin, bosentan, erectile dysfunction agents, inhaled corticosteroids, and norgestimate. Caution should be taken, with possible dose adjustments of these medications, when used with Tybost. Sporonox (antifungal) and Biaxin (antibiotic) may increase Tybost concentrations. Tybost may also increase Biaxin levels. Rifabutin and some anti-seizure medications, such as carbamazepine (Tegretol), phenobarbital, and phenytoin (Dilantin) may decrease Tybost drug levels. Start metformin at lowest dose and titrate based on tolerability and clinical effect. Do not take with Olysio, Viekira Pak, or Zepatier. Avoid Harvoni if tenofovir disoproxil fumarate (TDF) is part of the HIV regimen.
Tybost has similar drug interactions as Norvir, but they are not interchangeable and there may be some drug interactions with Tybost that are not observed with Norvir. Tybost may increase levels of methamphetamines. Tell your provider or pharmacist about all medications, herbals, and supplements you are taking or thinking of taking, prescribed or not, as there are other drug interactions which are not listed here.
Tybost is not an HIV medication. It is used to boost blood levels of Prezista and Reyataz and is available in fixed-dose tablets with those medications (see Evotaz and Prezcobix, also the single-tablet regimen Symtuza). Cobicistat is also part of the single-tablet regimens Genvoya and Stribild to boost the elvitegravir component. All of these aforementioned regimens are recommended in the DHHS treatment guidelines for use in certain clinical situations. Tybost shares some of the same side effects of increased cholesterol and increased triglycerides as Norvir; however, in clinical trials they were less pronounced. Tybost co-administered with elvitegravir, darunavir, or atazanavir should not be initiated in pregnant individuals and is not recommended during pregnancy. Inadequate levels of ART (antiretroviral therapy) in second and third trimesters as well as viral breakthroughs have been reported. Tybost is not recommended during pregnancy.
Dr. Melanie Thompson:
Cobicistat is now the most commonly used booster, and because it can be coformulated, it is rarely used as a separate pill. Unlike ritonavir, cobicistat has no activity against HIV.
Cobicistat has many drug interactions, but it has a slightly different drug interaction profile compared with ritonavir, and these interactions must be managed carefully. Because cobicistat and ritonavir are not exactly interchangeable, it is important to be very careful when changing from one to the other. Consult an expert if there are any doubts about drug interactions!
Activist Bridgette Picou:
Think of Tybost as just what the name implies, a booster. It is not an antiretroviral itself, but it works with other HIV drugs to increase effectiveness. As a pharmacokinetic enhancer, the mechanism of action is in the liver, which means monitoring for drug-drug reactions. You should also monitor your lipids and triglycerides. Watching your diet and food intake may help with this.