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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Brand Name
Prezcobix
Generic Name
Darunavir Ethanolate And Cobicistat
Active Ingredient
CobicistatCategory
Cytochrome P450 3A Inhibitor [EPC]
Variants
3
References used for this content
This page is for informational purposes only and does not replace medical advice. Before using any prescription or over-the-counter medication for Prezcobix, you must consult a qualified healthcare professional.
Detailed information about Prezcobix
Cobicistat is a cytochrome P450 3A (CYP3A) inhibitor used as a pharmacokinetic enhancer (a 'booster') to increase the blood levels of certain HIV-1 medications, such as atazanavir or darunavir.
The standard adult dosage for Cobicistat (Tybost) is 150 mg taken orally once daily. It is crucial to understand that this dose is not flexible; it is specifically calibrated to provide the optimal level of CYP3A inhibition to boost co-administered drugs.
In both scenarios, the medications must be part of a larger antiretroviral regimen that usually includes two other 'backbone' medications (typically nucleoside reverse transcriptase inhibitors).
Cobicistat is approved for use in pediatric patients weighing at least 35 kg (approximately 77 lbs). The dosage for these pediatric patients is the same as the adult dose: 150 mg once daily. It is generally administered as part of a fixed-dose combination tablet (like Genvoya or Symtuza) or alongside standalone atazanavir or darunavir. Cobicistat has not been established as safe or effective in children weighing less than 35 kg, as the pharmacokinetics in smaller children may differ significantly, potentially leading to sub-therapeutic levels of the boosted drug or increased toxicity.
Cobicistat is known to cause a modest increase in serum creatinine levels. This is not due to a decrease in the glomerular filtration rate (GFR), which is the actual filtering capacity of the kidney. Instead, Cobicistat inhibits the tubular secretion of creatinine.
Clinical trials of Cobicistat did not include sufficient numbers of patients aged 65 and over to determine if they respond differently than younger patients. In general, caution should be exercised when prescribing for elderly patients, reflecting the greater frequency of decreased hepatic, renal, or cardiac function and concomitant diseases or other drug therapies.
For Cobicistat to work effectively, it must be taken exactly as prescribed.
If you miss a dose of Cobicistat, take it as soon as you remember, provided it is within 12 hours of the scheduled time. You must take it with food. If more than 12 hours have passed since the scheduled time, skip the missed dose and return to your regular dosing schedule. Do not 'double up' or take two doses at once to make up for a missed one.
In the event of an overdose, contact your local poison control center or seek emergency medical attention immediately. While there is no specific antidote for Cobicistat, treatment typically involves supportive care, including monitoring of vital signs and observation of the clinical status of the patient. Because Cobicistat is highly protein-bound, it is unlikely to be significantly removed by hemodialysis or peritoneal dialysis.
> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or stop taking the medication without medical guidance, as this can lead to drug resistance.
Because Cobicistat is almost always administered with other medications, it can be difficult to distinguish its side effects from those of the co-administered drugs. However, the following are frequently reported by patients taking Cobicistat-boosted regimens:
Cobicistat is a powerful 'booster' that significantly alters how your body processes other medications. The most critical safety concern with Cobicistat is the high potential for drug-drug interactions. Because it shuts down the CYP3A4 enzyme, taking it with certain other drugs can cause those drugs to build up to toxic, potentially fatal levels. Conversely, taking Cobicistat with drugs that 'induce' or speed up these enzymes can make Cobicistat ineffective, leading to the failure of your HIV treatment and the development of drug resistance.
As noted, while Tybost (standalone Cobicistat) does not have a Black Box Warning, the combination products it is part of often do. Specifically, products like Stribild, Genvoya, and Symtuza carry warnings regarding:
Cobicistat has one of the most extensive lists of drug interactions in modern medicine. The following medications must NEVER be used with Cobicistat because the interaction can cause life-threatening toxicity:
Cobicistat is strictly contraindicated in the following circumstances:
Data from clinical registries and studies indicate that Cobicistat-boosted regimens result in significantly lower exposures of the boosted drugs (like darunavir or atazanavir) during the second and third trimesters of pregnancy. This reduction in drug levels increases the risk of 'virologic failure' (the virus becoming detectable again) and the risk of mother-to-child transmission of HIV.
In the United States and other regions where clean water and infant formula are accessible, the CDC and health authorities recommend that HIV-infected mothers do not breastfeed their infants. This is to avoid the risk of postnatal transmission of HIV-1. It is not known if Cobicistat is excreted in human milk, though it is present in the milk of lactating rats. Because of the potential for HIV transmission and the potential for serious adverse reactions in nursing infants, breastfeeding should be avoided.
Cobicistat is a mechanism-based, 'suicide' inhibitor of the cytochrome P450 3A (CYP3A) family of enzymes. Unlike reversible inhibitors that simply sit in the enzyme's active site, Cobicistat undergoes a partial metabolic cycle by the enzyme, which results in the formation of a reactive intermediate. This intermediate then forms a covalent, irreversible bond with the heme prosthetic group of the CYP3A enzyme. This permanently 'kills' the enzyme molecule. To regain CYP3A activity, the body must synthesize new enzyme proteins. By effectively reducing the population of functional CYP3A4 enzymes in the liver and intestines, Cobicistat slows the oxidative metabolism of co-administered drugs like darunavir, atazanavir, and elvitegravir, thereby increasing their systemic exposure (AUC) and peak concentrations (Cmax).
The primary pharmacodynamic effect of Cobicistat is the inhibition of CYP3A. This effect is dose-dependent but reaches a plateau at the 150 mg dose. Cobicistat also inhibits the tubular secretion of creatinine by inhibiting transporters like MATE1 (Multidrug and Toxin Extrusion transporter 1). This results in a 10-15% increase in serum creatinine, which occurs within the first week of dosing and remains stable. Cobicistat does not have any effect on the QT interval or other cardiac electrophysiological parameters at therapeutic doses.
Common questions about Prezcobix
Cobicistat is used as a 'pharmacokinetic enhancer' or booster for certain medications used to treat Human Immunodeficiency Virus (HIV-1). It is not an antiviral medication itself and does not treat the virus directly. Instead, it works by blocking an enzyme in the liver called CYP3A4 that breaks down other HIV drugs, such as atazanavir or darunavir. By slowing this breakdown, Cobicistat allows the other medications to stay in the body at higher, more effective levels. This often allows for once-daily dosing and reduces the number of pills a patient needs to take.
The most common side effects associated with Cobicistat-boosted regimens include nausea, diarrhea, headache, and fatigue. Many patients also experience a slight increase in serum creatinine levels, which is a known effect of the drug's action on the kidneys and usually does not indicate actual damage. If Cobicistat is taken with atazanavir, yellowing of the skin or eyes (jaundice) is also frequently reported. Most of these side effects are mild and tend to improve as the body adjusts to the medication over several weeks. However, any persistent or severe symptoms should be discussed with a healthcare provider.
There is no known direct interaction between Cobicistat and alcohol that makes it strictly forbidden. However, healthcare providers generally recommend moderation, as both alcohol and some HIV medications can affect liver function. Heavy alcohol consumption can increase the risk of liver inflammation and may worsen gastrointestinal side effects like nausea or diarrhea. Furthermore, alcohol can sometimes interfere with a patient's ability to take their medication consistently at the same time every day. It is best to discuss your alcohol consumption habits with your doctor to ensure your treatment remains safe and effective.
Cobicistat is generally not recommended for use during the second and third trimesters of pregnancy. Clinical studies have shown that the levels of Cobicistat and the drugs it boosts can drop significantly during pregnancy, which may lead to the HIV virus becoming detectable again and increase the risk of passing the virus to the baby. If you are taking Cobicistat and plan to become pregnant or find out you are pregnant, you should contact your doctor immediately. They will likely switch you to a different 'booster' medication, such as ritonavir, which has a more established safety and efficacy profile in pregnant women.
Cobicistat begins to inhibit the CYP3A4 enzyme shortly after the first dose is absorbed, usually within 2 to 5 hours. However, it takes about 7 to 10 days of consistent daily dosing to reach 'steady-state' levels, where the inhibition is constant and the levels of the boosted HIV medication are fully optimized. Because Cobicistat is only one part of a multi-drug regimen, the time it takes to see a decrease in your 'viral load' (the amount of HIV in your blood) depends on the entire combination of drugs. Most patients see a significant drop in viral load within a few weeks of starting treatment.
No, you should never stop taking Cobicistat or any of your HIV medications suddenly without consulting your healthcare provider. HIV treatment requires strict adherence to be successful. If you stop taking the booster, the levels of your other HIV medications will drop rapidly below the range needed to suppress the virus. This gives the HIV virus an opportunity to replicate and mutate, which can lead to drug resistance. Once the virus becomes resistant to a drug, that medication (and often similar drugs) will no longer work for you in the future.
If you miss a dose of Cobicistat, take it as soon as you remember, as long as it is within 12 hours of your regular scheduled time. You must take it with food. If more than 12 hours have passed, skip the missed dose entirely and take your next dose at the regular time. Do not take two doses at once to make up for the missed one. Consistency is vital for HIV treatment, so if you find yourself frequently missing doses, talk to your doctor or pharmacist about tools like pillboxes or phone alarms to help you stay on track.
Weight gain has been observed in some patients starting modern HIV treatment regimens, including those containing Cobicistat. This is often referred to as 'return to health' weight gain, as the body recovers from the effects of the virus. However, some recent studies suggest that certain newer antiretroviral combinations may be more associated with weight gain than older ones. It is not entirely clear if Cobicistat itself causes weight gain, or if it is the result of the overall improvement in health or the other drugs in the combination. If you are concerned about weight changes, discuss a nutrition and exercise plan with your healthcare team.
Cobicistat has a very high potential for drug interactions, and many common medications cannot be taken with it. It blocks the enzyme that clears many drugs from your system, which can cause those drugs to reach dangerous or even fatal levels. This includes certain cholesterol medications (statins), blood thinners, steroids, and medications for erectile dysfunction. Conversely, some drugs can make Cobicistat less effective. You must provide your doctor and pharmacist with a complete list of every medication, supplement, and herbal product (like St. John's Wort) you take before starting Cobicistat.
As of 2024, Cobicistat (Tybost) is still protected by patents in many regions, including the United States, and a standalone generic version is not widely available. However, because it is a component of many different combination tablets, the availability of generic versions of those combinations depends on the patent status of all the drugs involved. Some older combination products may have generic versions available in certain international markets. You should check with your insurance provider or pharmacist for the most current information on generic availability and cost-saving programs.
Other drugs with the same active ingredient (Cobicistat)
> Warning: Stop taking Cobicistat and call your doctor immediately if you experience any of these serious symptoms.
No FDA black box warnings exist for Cobicistat (Tybost) as a standalone agent. However, many of the fixed-dose combination tablets that contain Cobicistat (such as Stribild and Genvoya) carry Black Box Warnings regarding the risk of post-treatment acute exacerbation of Hepatitis B. If a patient has both HIV and HBV and stops taking their Cobicistat-containing combination pill, their Hepatitis B may suddenly become much worse. Always check the specific label of the combination product you are taking.
Report any unusual symptoms to your healthcare provider immediately. Regular blood tests are necessary to monitor for these side effects.
Before starting Cobicistat and throughout your treatment, your healthcare provider will require regular laboratory monitoring:
Cobicistat is not generally known to cause significant impairment of driving or the ability to operate machinery. However, some patients report dizziness or fatigue. You should observe how you react to the medication before engaging in activities that require mental alertness.
There is no direct contraindication between alcohol and Cobicistat. However, chronic heavy alcohol use can damage the liver, which may complicate HIV treatment and increase the risk of hepatotoxicity. Furthermore, alcohol can sometimes worsen the gastrointestinal side effects of the medication.
Never stop taking Cobicistat without consulting your doctor. HIV treatment requires 100% adherence to prevent the virus from mutating and becoming resistant to drugs. If you stop the booster, the levels of your other HIV medications will drop rapidly, allowing the virus to replicate. There is no 'withdrawal syndrome' like that seen with antidepressants, but the risk of treatment failure is high.
> Important: Discuss all your medical conditions, especially kidney or liver disease, with your healthcare provider before starting Cobicistat.
For each major interaction, the mechanism is usually CYP3A inhibition, which leads to increased toxicity of the 'victim' drug. Management strategies involve either avoiding the combination, reducing the dose of the other drug, or switching to a non-CYP3A metabolized alternative.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking. Do not start any new over-the-counter medication without checking with your pharmacist.
These conditions require a careful risk-benefit analysis by a specialist:
There is no known cross-sensitivity between Cobicistat and other classes of antiretrovirals (like NRTIs or NNRTIs). However, because Cobicistat is almost always taken with a protease inhibitor, patients should be screened for allergies to the partner drug (e.g., atazanavir or darunavir). Patients with a history of severe 'sulfa' allergy should be cautious with darunavir/cobicistat combinations, although Cobicistat itself is not a sulfonamide.
> Important: Your healthcare provider will evaluate your complete medical history and current medication list before prescribing Cobicistat to ensure it is safe for you.
Cobicistat is approved for use in pediatric patients with HIV-1 infection who weigh at least 35 kg. The safety and efficacy in children weighing less than 35 kg have not been established. In the 35 kg+ population, the pharmacokinetic profile and side effect profile are generally similar to those seen in adults. Long-term effects on growth and development are still being monitored in ongoing pediatric registries.
There is limited data on the use of Cobicistat in patients aged 65 and older. Clinical considerations for this group include:
Cobicistat is not recommended for initiation in patients with a CrCl < 70 mL/min when part of a TDF-containing regimen. For standalone Tybost, no dose adjustment is required for the booster itself, but the partner drug (atazanavir or darunavir) may have its own renal restrictions. Cobicistat is not significantly removed by dialysis.
No dose adjustment is needed for patients with mild (Child-Pugh Class A) or moderate (Child-Pugh Class B) hepatic impairment. It has not been studied in severe impairment (Class C), and use in such patients is generally avoided unless the benefits clearly outweigh the unknown risks.
> Important: Special populations require individualized medical assessment and frequent monitoring by an HIV specialist.
| Parameter | Value |
|---|---|
| Bioavailability | High (when taken with food) |
| Protein Binding | 97% - 98% |
| Half-life | ~3 to 4 hours |
| Tmax | 2 to 5 hours |
| Metabolism | Primarily CYP3A, minor CYP2D6 |
| Excretion | Fecal 86.2%, Renal 8.2% |
Cobicistat is classified as a Cytochrome P450 3A Inhibitor [EPC] and a Pharmacokinetic Enhancer. It is the first drug in this class designed specifically for boosting without having its own antiviral properties. It is often grouped with 'Antiretroviral Adjunctive Agents.'