Cobicistat is a potent and selective inhibitor of human cytochrome P450 3A (CYP3A) isoforms:
- CYP3A4: IC₅₀ = 0.11 ± 0.03 μM (recombinant enzyme assay)
- CYP3A5: IC₅₀ = 0.05 ± 0.01 μM (recombinant enzyme assay)
It shows >200-fold selectivity over other CYP isoforms (CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6) with IC₅₀ >25 μM [1].

In both antiviral cellular tests and HIV-1 protease enzymatic assays, cobicistat is inactive against HIV-1 protease (IC50>30 μM). Cobicistat did not reduce HIV replication in a multi-cycle, five-day MT-2 HIV infection experiment (EC50>30 μM). Cobicistat demonstrated no cytotoxicity in tests on MT-2 cells, with CC50 values greater than 80 μM [1]. Ritonavir and Cobicistat inhibit CYP3A via the same mechanism. It implies that the heme group of the CYP3A enzyme may be directly involved in its inhibitory action on CYP3A [1]. In experiments measuring lipid accumulation in human adipocytes, ritonavir demonstrated noteworthy effects, with an EC50 of 16 μM. At doses as high as 30 μM, however, Cobicistat had no effect [1]. When tested at a concentration of 10 μM, ritonavir significantly affected mouse adipocyte glucose absorption assays. Conversely, Cobicistat (10 μM) has a much smaller impact on the absorption of glucose [1].

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Cobicistat inhibits midazolam 1'-hydroxylation in human liver microsomes with IC₅₀ = 0.20 ± 0.08 μM, demonstrating potent CYP3A inhibition in physiologically relevant systems [1]. Time-dependent inhibition studies show cobicistat exhibits mechanism-based inhibition of CYP3A4, with KI = 0.67 μM and kinact = 0.017 min⁻¹ [1]. In Caco-2 cell monolayers, cobicistat is a substrate for P-glycoprotein (efflux ratio = 1.9) but does not significantly inhibit P-gp-mediated digoxin transport at concentrations ≤10 μM [1].

Cobicistat is a novel cytochrome P450 3A4 (CYP3A4) inhibitor in advanced clinical evaluation for use as a pharmacoenhancer of antiretroviral drugs. It lacks significant anti-HIV activity and is more selective than ritonavir in its enzyme inhibition. In addition, its water solubility may lend itself to coformulation with other drugs. Renal adverse effects and a considerable drug interaction potential limit its clinical utility and caution is required when using it. A fixed-dose combination product containing cobicistat in addition to elvitegravir, tenofovir and emtricitabine, and providing a one-pill, once-a-day, antiretroviral regimen was recently approved [2].

Recombinant CYP Inhibition Assay: Recombinant human CYP isoforms were incubated with cobicistat (0.001-30 μM) and CYP-specific fluorescent substrates in phosphate buffer. After NADPH-initiated reaction, fluorescence was measured to calculate enzyme activity and IC₅₀ values [1].
Human Liver Microsome Assay: Human liver microsomes were preincubated with cobicistat (0.003-10 μM) and NADPH. Midazolam was added as substrate, and 1'-hydroxymidazolam formation was quantified by LC-MS/MS to determine IC₅₀ [1].
Mechanism-Based Inhibition Assay: Human liver microsomes were preincubated with varying concentrations of cobicistat (0.1-10 μM) and NADPH for 0-30 min. Residual CYP3A4 activity was measured after dilution using testosterone 6β-hydroxylation assay to determine KI and kinact [1].

Caco-2 Permeability Assay: Caco-2 cell monolayers were incubated with cobicistat (10 μM) in transport buffer. Samples from apical and basolateral compartments were collected at 0-120 min and analyzed by LC-MS/MS to calculate apparent permeability (Papp) and efflux ratio [1]. P-gp Inhibition Assay: Caco-2 cells were incubated with digoxin (P-gp substrate) and cobicistat (0.1-30 μM). Digoxin transport was measured to assess P-gp inhibition potential [1].

Rat Pharmacokinetic Study: Sprague-Dawley rats received single oral doses of cobicistat (10 mg/kg) suspended in 0.5% methylcellulose/0.2% Tween 80. Serial blood samples were collected over 24 hours for PK analysis [1]. Drug Interaction Study in Rats: Rats were pretreated with oral cobicistat (10 mg/kg) or vehicle. After 30 min, midazolam (2 mg/kg) was administered orally. Blood samples were collected for midazolam PK assessment [1].

Absorption, Distribution and Excretion
Median peak plasma concentrations were observed at 3.5 hours post-dose.
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.

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Metabolism / Metabolites
Cobicistat is metabolized by CYP3A and to a minor extent by CYP2D6 enzymes and does not undergo glucuronidation.

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

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Absorption: Oral bioavailability in rats is 39% [1].
Distribution: Volume of distribution at steady state (Vss) is 1.2 L/kg in rats [1].
Metabolism: Primarily metabolized by CYP3A4 and CYP2D6, with oxidative metabolism as major clearance pathway [1].
Excretion: Biliary excretion is significant (≤80% of dose in bile-duct cannulated rats) [1].
Human PK Parameters: At 150 mg dose in humans: Cmax ≈ 1.0 μg/mL, AUC0-24 ≈ 8.0 μg·h/mL, t₁/₂ ≈ 3-4 hr [2].

Protein Binding
97-98% bound to human plasma proteins.

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Cobicistat increases serum creatinine by ~0.1-0.2 mg/dL through inhibition of renal tubular secretion without affecting actual glomerular filtration rate [2]. Clinical trials show common adverse effects: nausea (11-14%), diarrhea (9-12%), and headache (5-8%) [2]. No significant hepatotoxicity observed at therapeutic doses [2].

[1]. Cobicistat (GS-9350): A Potent and Selective Inhibitor of Human CYP3A as a Novel Pharmacoenhancer. ACS Med. Chem. Lett., 2010, 1 (5), pp 209–213.

[2]. Cobicistat, a pharmacoenhancer for HIV treatments. Drugs Today (Barc). 2013 Apr;49(4):233-7.

Cobicistat is a monocarboxylic acid amide obtained by formal condensation of the carboxy group of (2S)-2-({[(2-isopropyl-1,3-thiazol-4-yl)methyl](methyl)carbamoyl}amino)-4-(morpholin-4-yl)butanoic acid with the amino group of 1,3-thiazol-5-ylmethyl [(2R,5R)-5-amino-1,6-diphenylhexan-2-yl]carbamate. Acts as a pharmacoenhancer in treatment of HIV-1 by inhibiting P450 enzymes that metabolise other medications.. It has a role as a P450 inhibitor. It is a member of 1,3-thiazoles, a member of morpholines, a member of ureas, a carbamate ester and a monocarboxylic acid amide.
Cobicistat (brand name: Tybost) is a prescription medicine approved by the U.S. Food and Drug Administration (FDA) for use in adults and children along with the HIV medicines atazanavir (brand name Reyataz) or darunavir (brand name Prezista). Cobicistat is not active against HIV and is only used as a pharmacokinetic enhancer to boost the activity of other HIV medicines.
When taken with atazanavir, cobicistat is approved for use in adults and children who weigh at least 77 lb (35 kg).  (A fixed-dose combination tablet containing atazanavir and cobicistat [brand name: Evotaz] is also available.)
When taken with darunavir, cobicistat is approved for use in adults and children who weigh at least 88 lb (40 kg). (A fixed-dose combination tablet containing darunavir and cobicistat [brand name: Prezcobix] is also available.)
Cobicistat, marketed under the name Tybost (formerly GS-9350), indicated for treating infection with human immunodeficiency virus (HIV). Although it does not have any anti-HIV activity, cobicistat acts as a pharmacokinetic enhancer by inhibiting cytochrome P450 3A isoforms (CYP3A) and therefore increases the systemic exposure of coadministered agents that are metabolized by CYP3A enzymes. More specifically, cobicistat is 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. Increasing systemic exposure of anti-retrovirals (ARVs) without increasing dosage allows for better treatment outcomes and a decreased side effect profile.
Cobicistat is a Cytochrome P450 3A Inhibitor. The mechanism of action of cobicistat is as a Cytochrome P450 3A Inhibitor, and P-Glycoprotein Inhibitor, and Cytochrome P450 2D6 Inhibitor, and Organic Anion Transporting Polypeptide 1B1 Inhibitor, and Organic Anion Transporting Polypeptide 1B3 Inhibitor, and Breast Cancer Resistance Protein Inhibitor, and Multidrug and Toxin Extrusion Transporter 1 Inhibitor.
Cobicistat is a cytochrome P450 3A (CYP3A) inhibitor that can be used to enhance the pharmacokinetic profile of certain anti-HIV-1 agents. Upon administration, cobicistat inhibits the liver enzyme CYP3A4 and limits the breakdown of co-administered agents that are metabolized by CYP3A4, and increases the concentration, systemic exposure and efficacy of the co-administered agent.
A carbamate and thiazole derivative that functions as a CYTOCHROME P450 CYP3A INHIBITOR to enhance the concentration of ANTI-HIV AGENTS, with which it is used in combination, for the treatment of HIV INFECTIONS.
See also: Cobicistat; darunavir (component of); Atazanavir sulfate; cobicistat (component of); Cobicistat; darunavir ethanolate (component of) ... View More ...

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Drug Indication
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.
FDA Label
Tybost is indicated as a pharmacokinetic enhancer of atazanavir 300 mg once daily or darunavir 800 mg once daily as part of antiretroviral combination therapy in human immunodeficiency virus-1 (HIV-1) infected adults and adolescents aged 12 years and older: weighing at least 35 kg co‑administered with atazanavir orweighing at least 40 kg co‑administered with darunavir.
Treatment of human immunodeficiency virus (HIV-1) infection

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Mechanism of Action
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.

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Cobicistat is a mechanism-based CYP3A inhibitor designed as a pharmacoenhancer to boost pharmacokinetics of HIV protease inhibitors [1]. FDA-approved as part of combination regimens (e.g., with elvitegravir) for HIV-1 infection treatment [2]. Unlike ritonavir, it lacks anti-HIV activity and shows improved selectivity for CYP3A over other CYP isoforms [1][2].

C40H53N7O5S2

776.02

775.354

C, 61.91; H, 6.88; N, 12.63; O, 10.31; S, 8.26

1004316-88-4

25151504

White to yellow solid powder

1.2±0.1 g/cm3

974.5±65.0 °C at 760 mmHg

543.2±34.3 °C

0.0±0.3 mmHg at 25°C

1.595

4.77

3

10

20

54

1120

3

CC(C)C1=NC(=CS1)CN(C)C(=O)N[C@@H](CCN2CCOCC2)C(=O)N[C@H](CC[C@H](CC3=CC=CC=C3)NC(=O)OCC4=CN=CS4)CC5=CC=CC=C5

ZCIGNRJZKPOIKD-CQXVEOKZSA-N

InChI=1S/C40H53N7O5S2/c1-29(2)38-43-34(27-53-38)25-46(3)39(49)45-36(16-17-47-18-20-51-21-19-47)37(48)42-32(22-30-10-6-4-7-11-30)14-15-33(23-31-12-8-5-9-13-31)44-40(50)52-26-35-24-41-28-54-35/h4-13,24,27-29,32-33,36H,14-23,25-26H2,1-3H3,(H,42,48)(H,44,50)(H,45,49)/t32-,33-,36+/m1/s1

thiazol-5-ylmethyl ((2R,5R)-5-((S)-2-(3-((2-isopropylthiazol-4-yl)methyl)-3-methylureido)-4-morpholinobutanamido)-1,6-diphenylhexan-2-yl)carbamate

Cobicistat; 1004316-88-4; cobicistatum; CHEBI:72291; LW2E03M5PG; COBICISTAT, (R,R,S)-; GS9350; trade name: Tybost; Genvoya; GS-9350; GS 9350;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 2.08 mg/mL (2.68 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.08 mg/mL (2.68 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.08 mg/mL (2.68 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 5% DMSO+40% PEG 300+ddH2O: 30mg/mL

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 (Please use freshly prepared in vivo formulations for optimal results.)