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 concentration was observed 3.5 hours after administration. Following multiple administrations of cobicistat over 6 consecutive days, the average percentage of the administered dose excreted in feces and urine after a single dose of [14C]cobicistat was 86.2% and 8.2%, respectively. Metabolism/Metabolites Cobicistat is primarily metabolized via CYP3A and a small amount via CYP2D6 enzymes, and is not glucuronidated. Biological Half-Life The terminal plasma half-life of cobicistat is approximately 3 to 4 hours. Absorption: The oral bioavailability in rats is 39% [1]. Distribution: The steady-state volume of distribution (Vss) in rats is 1.2 L/kg [1]. Metabolism: It is primarily metabolized via CYP3A4 and CYP2D6, with oxidative metabolism being the main clearance pathway [1].
Excretion: Bile excretion was significant (≤80% of the dose in cannulated rats)[1].
Pharmacokinetic parameters in humans: At a human dose of 150 mg: Cmax ≈ 1.0 μg/mL, AUC0-24 ≈ 8.0 μg·h/mL, t₁/₂ ≈ 3-4 hours[2].

Protein Binding
97-98% binds to human plasma proteins. Cobicistat increases serum creatinine by approximately 0.1-0.2 mg/dL by inhibiting renal tubular secretion, but does not affect actual glomerular filtration rate [2]. Common adverse reactions observed in clinical trials include nausea (11-14%), diarrhea (9-12%), and headache (5-8%) [2]. No significant hepatotoxicity was 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 formed by the condensation of the carboxyl group of (2S)-2-({[(2-isopropyl-1,3-thiazolyl-4-yl)methyl](methyl)carbamoyl}amino)-4-(morpholin-4-yl)butyric acid with the amino group of 1,3-thiazolyl-5-ylmethyl[(2R,5R)-5-amino-1,6-diphenylhex-2-yl]carbamate. It acts as a pharmacodynamic enhancer in HIV-1 treatment by inhibiting P450 enzymes that metabolize other drugs. It is also a P450 inhibitor itself. It belongs to the 1,3-thiazolides, morpholinides, ureas, carbamates, and monocarboxylic acid amides.
Cobicistat (brand name: Tebostat) is a prescription drug approved by the U.S. Food and Drug Administration (FDA) for use in adults and children in combination with the HIV drugs atazanavir (brand name: Ritaz) or darunavir (brand name: Prezista). Cobicistat itself is ineffective against HIV and is used only as a pharmacokinetic enhancer to improve the efficacy of other HIV drugs.
When used in combination with atazanavir, cobicistat is approved for use in adults and children weighing at least 35 kg (77 lbs). (A fixed-dose combination tablet containing atazanavir and cobicistat [brand name: Evotaz] is also available.)
When used in combination with darunavir, cobicistat is approved for use in adults and children weighing at least 40 kg (88 lbs). (A fixed-dose combination tablet containing darunavir and cobicistat [brand name: Prezcobix] is also available.)
Cobicistat, marketed under the brand name Tybost (formerly GS-9350), is used to treat human immunodeficiency virus (HIV) infection. Although cobicistat itself does not have anti-HIV activity, it acts as a pharmacokinetic enhancer by inhibiting the cytochrome P450 3A isoenzyme (CYP3A), thereby increasing the systemic exposure of combination therapies metabolized by CYP3A. More specifically, cobicistat is indicated for increasing the systemic exposure of atazanavir or darunavir (once-daily dosing) in combination with other antiretroviral drugs for the treatment of HIV-1 infection. Increasing the systemic exposure of antiretroviral drugs (ARVs) without increasing the dose can improve treatment efficacy and reduce side effects. Cobicistat is a cytochrome P450 3A inhibitor. Cobicistat's mechanism of action involves its role as an inhibitor of cytochrome P450 3A, P-glycoprotein, cytochrome P450 2D6, organic anion transporter 1B1, organic anion transporter 1B3, breast cancer resistance protein, and multidrug and toxin efflux transporter 1. Cobicistat is a cytochrome P450 3A (CYP3A) inhibitor that can enhance the pharmacokinetic properties of certain anti-HIV-1 drugs. After administration, cobicistat inhibits the liver enzyme CYP3A4, limiting the breakdown of co-administered drugs metabolized by CYP3A4, thereby increasing the concentration, systemic exposure, and efficacy of the co-administered drugs. Cobicistat is a carbamate and thiazole derivative that, as a cytochrome P450 CYP3A inhibitor, can increase the concentration of anti-HIV drugs used in combination with it for the treatment of HIV infection. See also: Cobicistat; Darunavir (component); Atazanavir Sulfate; Cobicistat (component); Cobicistat; Darunavir Glycolate (component)...See more...

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Drug Indications
Cobicistat is a CYP3A inhibitor used to increase systemic exposure to atazanavir or darunavir (once-daily dosing) in combination with other antiretroviral agents for the treatment of HIV-1 infection. Due to a lack of exposure data, cobicistat cannot be used interchangeably with ritonavir to increase systemic exposure to darunavir (600 mg twice daily), fosanavir, saquinavir, or tepranavir. Cobicistat is not recommended for use in combination with darunavir (600 mg twice daily), fosanavir, saquinavir, or tepranavir. Drug interaction mechanisms are complex or unknown, therefore drug interactions with ritonavir cannot be extrapolated to certain cobicistat interactions. When cobbilstat is used in combination with ritonavir and atazanavir or darunavir, different drug interactions may occur with other medications.
FDA Label
Tybost is indicated as a pharmacokinetic enhancer of atazanavir 300 mg once daily or darunavir 800 mg once daily for the treatment of adults and adolescents aged 12 years and older with human immunodeficiency virus-1 (HIV-1): weighing at least 35 kg when used in combination with atazanavir, or weighing at least 40 kg when used in combination with darunavir.
Treatment of Human Immunodeficiency Virus (HIV-1) Infection
Mechanism of Action

Cobbilstat is a mechanism-based cytochrome P450 3A (CYP3A) isoenzyme inhibitor. Cobbilstat enhances antiviral activity at lower doses by inhibiting CYP3A-mediated metabolism, increasing systemic exposure to CYP3A substrates atazanavir and darunavir. Cobbilstat itself does not have anti-HIV activity.

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Cobicistat is a mechanism-based CYP3A inhibitor designed to act as a pharmacokinetic enhancer to improve the pharmacokinetics of HIV protease inhibitors[1]. It has been approved by the FDA as part of combination therapy regimens (e.g., in combination with elvigravir) for the treatment of HIV-1 infection[2]. Unlike ritonavir, it does not have anti-HIV activity and is more selective for CYP3A than other CYP isoenzymes[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.)