Tybost

Side effects observed in clinical studies (greater than 2% of people) 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. While cobicistat does not affect actual kidney function, its effect on SCr can make monitoring of impaired kidney function more difficult or less accurate.

Tybost is not interchangeable with Norvir. Tybost interacts with many drugs. Do not take with alfuzosin, colchicine, dihydroergotamine, dronedarone, ergotamine, irinotecan, simvastatin, lovastatin, lurasidone, methylergonovine, 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 drug interactions similar to 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 care 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, such as 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. Pregnant individuals can voluntarily enroll in the Antiretroviral Pregnancy Registry through their provider; go to apregistry.com.

Dr. Melanie Thompson:

Cobicistat, a pharmacokinetic (PK) booster with no activity against HIV, is generally coformulated with the protease inhibitors atazanavir and darunavir or the integrase inhibitor elvitegravir. Like the other PK booster, ritonavir, there are a boatload of drug interactions, some dangerous. COBI, however, is not interchangeable with ritonavir in all circumstances. COBI has most of the drug interactions of ritonavir and some that are different. For example, COBI should not be used twice daily with darunavir 600 mg, but is paired with darunavir 800 mg once daily. You should be sure your HIV care provider knows all of the drugs you are taking, including over the counter medications and supplements, and be sure that anyone who prescribes drugs for you knows that you are on cobicistat. You can look up drug interactions at hiv-druginteractions.org but managing them is tricky, so be sure to discuss with an HIV care provider.

Cobicistat-containing regimens should not be taken during pregnancy due to inadequate drug levels of COBI and boosted drugs in the second and third trimester. If you are on a cobicistat-containing regimen and are pregnant or contemplating pregnancy, discuss with your HIV care provider.

COBI will raise your blood creatinine level by about 0.4 mg/dL or less. This occurs soon after starting the drug and is due to changes in creatinine secretion by the kidneys and not because of kidney toxicity. However, when COBI is used with TDF, kidney side effects may be seen, so kidney function should be watched closely.

The COVID-19 treatment Paxlovid includes ritonavir, but it can be taken in addition to a cobicistat-containing regimen, with attention to possible side effects. (See “Norvir.”)

Activist Joey Wynn:

Tybost is a booster, with the same side effect problems as the other booster. Simply say, “What other options are available for me?” and keep moving.