Darunavir and cobicistat

Uses

Cobicistat is a CYP3A inhibitor used to increase the systemic exposure of atazanavir or darunavir in combination with other antiretroviral agents in the treatment of HIV-1 infection.

Cobicistat is a CYP3A inhibitor indicated to increase systemic exposure of atazanavir or darunavir (once daily dosing regimen) in combination with other antiretroviral agents in the treatment of HIV-1 infection. It is not interchangeable with ritonavir to increase systemic exposure of darunavir 600 mg twice daily, fosamprenavir, saquinavir, or tipranavir due to lack of exposure data. The use of cobicistat is not recommended with darunavir 600 mg twice daily, fosamprenavir, saquinavir or tipranavir. Complex or unknown mechanisms of drug interactions preclude extrapolation of ritonavir drug interactions to certain cobicistat interactions. Cobicistat and ritonavir when administered with either atazanavir or darunavir may result in different drug interactions when used with concomitant medications.

Darunavir is a HIV protease inhibitor used in the treatment of human immunodeficiency virus (HIV) infection in patients with history of prior antiretroviral therapies.

Darunavir, co-administered with ritonavir, and with other antiretroviral agents, is indicated for the treatment of human immunodeficiency virus (HIV) in children age 3 or above and adults with HIV-1 infection.

Darunavir and cobicistat is also used to associated treatment for these conditions: Human Immunodeficiency Virus (HIV) Infections, Human Immunodeficiency Virus Type 1 (HIV-1) InfectionHuman Immunodeficiency Virus Type 1 (HIV-1) Infection

How Darunavir and cobicistat works

Cobicistat is a mechanism-based inhibitor of cytochrome P450 3A (CYP3A) isoforms. Inhibition of CYP3A-mediated metabolism by cobicistat increases the systemic exposure of CYP3A substrates atazanavir and darunavir and therefore enables increased anti-viral activity at a lower dosage. Cobicistat does not have any anti-HIV activity on its own.

The HIV-1 protease enzyme is necessary for viral precursor protein processing and viral maturation in preparation for infection, and is therefore a target for antiretroviral therapy for HIV. Protease inhibitors are used as a part of highly active antiretroviral therapy (HAART) in patients diagnosed with HIV infection. It has been shown to effectively suppress the virus, leading to significantly decreased morbidity and mortality rates.

Darunavir, a HIV protease inhibitor, prevents HIV replication through binding to the enzyme, stopping the dimerization and the catalytic activity of HIV-1 protease. In particular, it inhibits the cleavage of HIV encoded Gag-Pol proteins in cells that have been infected with the virus, halting the formation of mature virus particles, which spread the infection. The close contact that darunavir makes with the primary chains of the active site amino acids (Asp-29 and Asp-30) on the protease likely contributes to its potency and efficacy against resistant variants of HIV-1.

Darunavir is known to bind to different sites on the enzyme: the active site cavity and the surface of one of the flexible flaps in the protease dimer. Darunavir can adapt to changes in the shape of a protease enzyme due to its molecular flexibility.

Toxicity

The most common adverse reactions reported during clinical trials were jaundice (13%), ocular icterus (15%), and nausea (12%).

LD50 information for darunavir is not readily available in the literature. One-time doses of up to 3,200 mg of darunavir in an oral solution and up to 1,600 mg of the tablet formulation of darunavir with ritonavir have been given volunteers without significant symptoms.

Information about an overdose with darunavir with ritonavir is limited. No specific antidote exists for this drug. Treatment of In the case of an overdose, employ general supportive measures. Monitor vital signs and clinical status. It is unlikely that darunavir not amenable to removal by dialysis due to its high level of protein binding.

Volume of Distribution

The volume of distribution of darunavir in one pharmacokinetic study in conjunction with ritonavir was 206.5 L (with a range of 161.0–264.9) in healthy young adult volunteers. Another pharmacokinetic study revealed a volume of distribution of 220 L.

Elimination Route

Median peak plasma concentrations were observed at 3.5 hours post-dose.

The absolute oral bioavailability of one single 600 mg dose of darunavir alone and with 100 mg of ritonavir twice a day was 37% and 82%, respectively. Exposure to darunavir in boosted patients has been found to be 11 times higher than in unboosted patients. Tmax is achieved approximately 2.4 to 4 hours after oral administration.

When darunavir is taken with food, the Cmax and AUC of darunavir given with ritonavir increase by 30% when compared to the fasted state.

Half Life

The terminal plasma half-life of cobicistat is approximately 3 to 4 hours.

The terminal elimination half-life of darunavir is approximately 15 hours when it is combined with ritonavir.

Clearance

Darunavir has a low renal clearance. After intravenous administration, the clearance darunavir administered alone and with 100 mg ritonavir twice daily, was 32.8 L/h and 5.9 L/h, respectively.

Elimination Route

With single dose administration of [14C] cobicistat after multiple dosing of cobicistat for six days, the mean percent of the administered dose excreted in feces and urine was 86.2% and 8.2%, respectively.

A mass balance study in healthy volunteers demonstrated that after single dose administration of 400 mg 14C-darunavir, given with 100 mg ritonavir, approximately 79.5% and 13.9% of the administered dose of radiolabeled darunavir was obtained in the feces and urine, respectively. Excretion of unchanged drug accounted for 8.0% of the darunavir dose in volunteers who were unboosted.

In boosted darunavir administration, unchanged darunavir made up 48.8% of the excreted dose in boosted subjects due to inhibition of darunavir metabolism by ritonavir. Unchanged drug in the urine made up 1.2% of the administered dose in volunteers who where unboosted, and 7.7% in boosted volunteers.

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