1.1 Indications

1.2 Limitations of Use

• TYBOST 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 TYBOST is not recommended with darunavir 600 mg twice daily, fosamprenavir, saquinavir, or tipranavir [see Warnings and Precautions (5.4)].
• Complex or unknown mechanisms of drug interactions preclude extrapolation of ritonavir drug interactions to certain TYBOST interactions. TYBOST and ritonavir when administered with either atazanavir or darunavir may result in different drug interactions when used with concomitant medications [see Warnings and Precautions (5.3), Drug Interactions (7), and Clinical Pharmacology (12.3)].

2.1 Recommended Dosage in Adults

Administer TYBOST in conjunction with atazanavir or darunavir and other antiretroviral agents in the treatment of adults with HIV-1 infection. The recommended dosages of TYBOST and atazanavir or darunavir given with food are presented in Table 1. TYBOST must be coadministered at the same time as atazanavir or darunavir [see Drug Interactions (7)]. Consult the prescribing information for atazanavir or darunavir.

2.2 Recommended Dosage in Pediatric Patients

Administer TYBOST in conjunction with atazanavir or darunavir and other antiretroviral agents in the treatment of pediatric patients with HIV-1 infection. The recommended dosages of TYBOST and atazanavir or darunavir given with food are based on weight and presented in Table 2. TYBOST must be coadministered at the same time as atazanavir or darunavir [see Drug Interactions (7)]. Consult the prescribing information for atazanavir or darunavir.

2.3 Testing Prior to Initiation of TYBOST

Prior to or when initiating TYBOST and during treatment with TYBOST, on a clinically appropriate schedule, assess estimated creatinine clearance because TYBOST decreases estimated creatinine clearance due to inhibition of tubular secretion of creatinine without affecting actual renal glomerular function [see Warnings and Precautions (5.1)]. When coadministering TYBOST with TDF, assess estimated creatinine clearance, urine glucose, and urine protein at baseline. In patients with chronic kidney disease, also assess serum phosphorus [see Warnings and Precautions (5.2)].

2.4 Renal Impairment

TYBOST coadministered with TDF is not recommended in patients who have an estimated creatinine clearance below 70 mL/min because dose adjustment of TDF is required below 50 mL/min and such dose adjustments have not been established for coadministration with TYBOST [see Warnings and Precautions (5.2) and Adverse Reactions (6.1)].

2.5 Not Recommended During Pregnancy

TYBOST coadministered with darunavir is not recommended for use during pregnancy because of substantially lower exposures of darunavir and cobicistat during the second and third trimesters [see Use in Specific Populations (8.1) and Clinical Pharmacology (12.3)].

TYBOST coadministered with atazanavir is not recommended for use during pregnancy because of substantially lower exposures of cobicistat during the second and third trimesters [see Use in Specific Populations (8.1) and Clinical Pharmacology (12.3)].

TYBOST coadministered with darunavir or atazanavir should not be initiated in pregnant individuals. An alternative regimen is recommended for individuals who become pregnant during therapy with TYBOST coadministered with darunavir or atazanavir.

5.1 Effects on Serum Creatinine

TYBOST decreases estimated creatinine clearance due to inhibition of tubular secretion of creatinine without affecting actual renal glomerular function. This effect should be considered when interpreting changes in estimated creatinine clearance in patients initiating TYBOST, particularly in patients with medical conditions or receiving drugs needing monitoring with estimated creatinine clearance.

Prior to initiating therapy with TYBOST, assess estimated creatinine clearance [see Dosage and Administration (2.3)]. Dosage recommendations are not available for drugs that require dosage adjustments in TYBOST-treated patients with renal impairment [see Adverse Reactions (6.1), Drug Interactions (7.3), and Clinical Pharmacology (12.2)]. Consider alternative medications that do not require dosage adjustments in patients with renal impairment.

Although TYBOST may cause modest increases in serum creatinine and modest declines in estimated creatinine clearance without affecting renal glomerular function, patients who experience a confirmed increase in serum creatinine of greater than 0.4 mg/dL from baseline should be closely monitored for renal safety.

5.2 New Onset or Worsening Renal Impairment When Used with Tenofovir Disoproxil Fumarate

Renal impairment, including cases of acute renal failure and Fanconi syndrome, has been reported when TYBOST was used in an antiretroviral regimen that contained TDF.

• Coadministration of TYBOST and TDF is not recommended in patients who have an estimated creatinine clearance below 70 mL/min because dose adjustment of TDF is required below 50 mL/min and such dose adjustments have not been established for coadministration with TYBOST [see Dosage and Administration (2.3, 2.4)].
• Document urine glucose and urine protein at baseline [see Dosage and Administration (2.3)] and perform routine monitoring of estimated creatinine clearance, urine glucose, and urine protein during treatment when TYBOST is used with TDF. Measure serum phosphorus in patients with or at risk for renal impairment when used with TDF.
• Coadministration of TYBOST and TDF in combination with concomitant or recent use of a nephrotoxic agent is not recommended.

In a clinical trial of TYBOST over 144 weeks (N=692), 10 (2.9%) subjects treated with TYBOST coadministered with atazanavir and TRUVADA® and 11 (3.2%) subjects treated with ritonavir coadministered with atazanavir and TRUVADA discontinued study drug due to a renal adverse event. Seven of the 10 subjects (2.0% overall) in the TYBOST group had laboratory findings consistent with proximal renal tubulopathy leading to study drug discontinuation compared to 7 of 11 subjects (2.0% overall) in the ritonavir group. One subject in the TYBOST group had renal impairment at baseline (i.e., estimated creatinine clearance less than 70 mL/min). The laboratory findings in these 7 subjects with evidence of proximal tubulopathy improved but did not completely resolve in all subjects upon discontinuation of TYBOST coadministered with atazanavir and TRUVADA. Renal replacement therapy was not required in any subject.

5.3 Risk of Serious Adverse Reactions or Loss of Virologic Response Due to Drug Interactions

Initiation of TYBOST, a CYP3A inhibitor, in patients receiving medications metabolized by CYP3A, or initiation of medications metabolized by CYP3A in patients already receiving TYBOST, may increase plasma concentrations of medications metabolized by CYP3A and reduce plasma concentrations of active metabolite(s) formed by CYP3A. Initiation of medications that inhibit or induce CYP3A may respectively increase or decrease concentrations of TYBOST with atazanavir or darunavir.

These interactions may lead to:

• clinically significant adverse reactions, potentially leading to severe, life-threatening, or fatal events from higher exposures of concomitant medications.
• clinically significant adverse reactions from higher exposures of TYBOST and atazanavir or darunavir.

These interactions may lead to:

• loss of therapeutic effect of TYBOST with atazanavir or darunavir and possible development of resistance.
• loss of therapeutic effect of the concomitant medications from lower exposures of active metabolite(s).

See Table 6 for steps to prevent or manage these possible and known significant drug interactions, including dosing recommendations [see Drug Interactions (7)]. Consider the potential for drug interactions prior to and during TYBOST with atazanavir or darunavir therapy; review concomitant medications during TYBOST with atazanavir or darunavir therapy; and monitor for the adverse reactions associated with concomitant medications [see Contraindications (4) and Drug Interactions (7)].

TYBOST or ritonavir when administered with either atazanavir or darunavir may result in different drug interactions when used with concomitant medications. Complex or unknown mechanisms of drug interactions preclude extrapolation of ritonavir drug interactions to certain TYBOST interactions [see Drug Interactions (7) and Clinical Pharmacology (12.3)].

5.4 Antiretrovirals that are Not Recommended in Combination with TYBOST

The following antiretrovirals are not recommended in combination with TYBOST because dosing recommendations for such combinations have not been established and coadministration may result in decreased plasma concentrations of the antiretroviral agents, leading to loss of therapeutic effect and development of resistance:

• More than one antiretroviral that requires pharmacokinetic enhancement (i.e., two protease inhibitors or a protease inhibitor in combination with elvitegravir)
• Darunavir in combination with efavirenz, nevirapine, or etravirine
• Atazanavir in combination with etravirine
• Atazanavir in combination with efavirenz in treatment-experienced patients
• Darunavir 600 mg twice daily
• Other HIV-1 protease inhibitors including fosamprenavir, saquinavir, or tipranavir

TYBOST in combination with fixed-dose combination tablets that contain cobicistat is not recommended.

TYBOST in combination with lopinavir/ritonavir or regimens containing ritonavir is not recommended due to similar effects of TYBOST and ritonavir on CYP3A.

6.1 Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

7.1 Potential Effect of Cobicistat (Coadministered with Atazanavir or Darunavir) on the Pharmacokinetics of Concomitant Drugs

Cobicistat is an inhibitor of CYP3A and CYP2D6. The transporters that cobicistat inhibits include p-glycoprotein (P-gp), BCRP, OATP1B1, and OATP1B3. The plasma concentration of drugs that are primarily metabolized by CYP3A or CYP2D6, or are substrates of P-gp, BCRP, OATP1B1, or OATP1B3 may be increased if those drugs are coadministered with TYBOST.

Based on in vitro data, cobicistat is not expected to induce CYP1A2 or CYP2B6 and based on in vivo data, cobicistat is not expected to induce MDR1 or, in general, CYP3A to a clinically significant extent. The induction effect of cobicistat on CYP2C9, CYP2C19, or UGT1A1 is unknown, but is expected to be low based on CYP3A in vitro induction data.

Coadministration of TYBOST with atazanavir or darunavir with drugs highly dependent on CYP3A for clearance and for which elevated plasma concentrations are associated with serious and/or life-threatening events is contraindicated. Coadministration with drugs that have active metabolite(s) formed by CYP3A may result in reduced plasma concentrations of these active metabolite(s). Coadministration with other CYP3A substrates may require a dose adjustment or additional monitoring as shown in Table 6.

7.2 Potential Effect of Concomitant Drugs on the Pharmacokinetics of Cobicistat (Coadministered with Atazanavir or Darunavir)

Cobicistat is metabolized by CYP3A, and to a minor extent, by CYP2D6. Atazanavir and darunavir are also metabolized by CYP3A.

Coadministration of TYBOST with atazanavir or darunavir in combination with drugs that induce CYP3A activity have the potential to decrease plasma concentrations of cobicistat, atazanavir, and darunavir, which may lead to loss of therapeutic effect and development of resistance (see Table 6).

Coadministration of TYBOST with atazanavir or darunavir in combination with other drugs that inhibit CYP3A may further increase the plasma concentrations of cobicistat, atazanavir, and darunavir (see Table 6).

7.3 Established and Other Potentially Significant Interactions

Coadministration of TYBOST with fosamprenavir, saquinavir, or tipranavir is not recommended because pharmacokinetic data are not available to provide appropriate dosing recommendations. Use of TYBOST with lopinavir is not recommended because lopinavir is co-formulated with ritonavir.

Table 6 provides dosing recommendations as a result of drug interactions with TYBOST coadministered with atazanavir or darunavir. These recommendations are based on either drug interaction trials or predicted interactions due to the expected magnitude of the interaction and potential for serious adverse events or loss of therapeutic effect [see Contraindications (4), Warnings and Precautions (5.3, 5.4), and Clinical Pharmacology (12.3)].

In Table 6, if not specifically stated, the drug interaction information applies to both coadministered agents: TYBOST coadministered with atazanavir or darunavir [see Clinical Pharmacology (12.3)].

In addition to the drug interactions noted in Table 6, TYBOST is not recommended for use in combination with fixed-dose combination tablets that contain cobicistat, lopinavir/ritonavir or regimens containing ritonavir, or in combination with more than one antiretroviral agent that requires pharmacokinetic enhancement [see Warnings and Precautions (5.4)].

Evaluate whether dosing adjustments of concomitant medications or coadministered antiretroviral drugs are necessary in:

• Patients on a stable concomitant medication who initiate or switch to a TYBOST-containing regimen
• Patients on a TYBOST-containing regimen who initiate a new concomitant medication
• Patients initiating a TYBOST-containing regimen and a new concomitant medication simultaneously

Under these circumstances, also monitor for adverse events and/or monitor concentrations of concomitant medications if appropriate.

No dose adjustment is required when TDF or rilpivirine are coadministered with TYBOST and atazanavir or darunavir.

8.1 Pregnancy

8.2 Lactation

8.3 Females and Males of Reproductive Potential

8.4 Pediatric Use

The safety and effectiveness of TYBOST coadministered with atazanavir or darunavir and two nucleoside reverse transcriptase inhibitors for the treatment of HIV-1 infection have been established in virologically suppressed pediatric patients [see Indications and Usage (1.1) and Dosage and Administration (2.2)]:

• weighing at least 35 kg for TYBOST coadministered with atazanavir or
• weighing at least 40 kg for TYBOST coadministered with darunavir.

Use of TYBOST for this indication is supported by evidence from adequate and well-controlled studies in adults, and by pharmacokinetic, safety, and virologic data from an open-label trial (Trial 128) in virologically suppressed, HIV-1 infected pediatric subjects aged 12 years and older. The safety in these subjects through 48 weeks was similar to that in antiretroviral treatment-naïve adults [see Adverse Reactions (6.1), Clinical Pharmacology (12.3), and Clinical Studies (14.2)].

Safety and effectiveness of TYBOST in combination with atazanavir in pediatric patients weighing less than 35 kg have not been established. Safety and effectiveness of TYBOST in combination with darunavir in pediatric patients weighing less than 40 kg have not been established.

8.5 Geriatric Use

Clinical trials of TYBOST did not include sufficient numbers of subjects aged 65 and older to determine whether they respond differently from younger subjects.

8.6 Renal Impairment

No dosage adjustment of TYBOST is required in patients with renal impairment, including those with severe renal impairment. No clinically relevant differences in cobicistat pharmacokinetics were observed between subjects with severe renal impairment and healthy subjects. TYBOST is coadministered with atazanavir or darunavir; therefore, refer to the prescribing information for atazanavir or darunavir for information regarding dosing recommendations of these drugs in patients with renal impairment [see Clinical Pharmacology (12.3)].

TYBOST has been shown to decrease estimated creatinine clearance without affecting actual renal glomerular function. Dosing recommendations are not available for drugs that require dosing adjustment for renal impairment when used in combination with TYBOST [see Dosage and Administration (2), Warnings and Precautions (5.1), Adverse Reactions (6.1), and Clinical Pharmacology (12.2)].

8.7 Hepatic Impairment

No dosing adjustment of TYBOST is necessary for patients with mild-to-moderate hepatic impairment. No data are available in patients with severe hepatic impairment. TYBOST is coadministered with atazanavir or darunavir and other antiretroviral drugs; therefore, refer to the prescribing information of these other drugs for information regarding dosing recommendations in patients with hepatic impairment [see Clinical Pharmacology (12.3)].

12.1 Mechanism of Action

Cobicistat is a mechanism-based inhibitor of cytochrome P450 3A (CYP3A). Inhibition of CYP3A-mediated metabolism by cobicistat increases the systemic exposure of CYP3A substrates atazanavir and darunavir.

12.2 Pharmacodynamics

12.3 Pharmacokinetics

12.4 Microbiology

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

14.1 Clinical Trial Results in HIV-1 Infected Treatment-Naïve Adult Subjects – Trial 114

The activity of TYBOST as a CYP3A inhibitor to increase the systemic exposures of atazanavir or darunavir has been demonstrated in pharmacokinetic trials. In these trials, the exposure of atazanavir or darunavir coadministered with TYBOST 150 mg was consistent with those observed with ritonavir 100 mg [see Clinical Pharmacology (12.2)]. For clinical efficacy of darunavir/ritonavir 800/100 mg once daily, refer to the prescribing information for darunavir.

The safety and efficacy of TYBOST coadministered with atazanavir were evaluated in a randomized, double-blind, active-controlled trial (Trial 114) in HIV-1 infected treatment-naïve subjects with baseline estimated creatinine clearance above 70 mL/min (N=692). In Trial 114, subjects were randomized in a 1:1 ratio to receive either atazanavir 300 mg + TYBOST 150 mg once daily or atazanavir 300 mg + ritonavir 100 mg once daily. All subjects received concomitant treatment with 300 mg of TDF and 200 mg of emtricitabine once a day administered as single tablet TRUVADA. Randomization was stratified by screening HIV-1 RNA level (≤100,000 copies/mL or >100,000 copies/mL).

The mean age of subjects was 37 years (range 19–70); 83% were male, 60% were White, 18% were Black, and 12% were Asian. The mean baseline plasma HIV-1 RNA was 4.8 log10 copies/mL (range 3.2–6.4). Forty percent of patients had baseline viral loads >100,000 copies/mL. The mean baseline CD4+ cell count was 352 cells/mm3 (range 1–1455) and 17% had CD4+ cell counts ≤200 cells/mm3.

Virologic outcomes in Trial 114 through Week 144 are presented in Table 12. In Trial 114, the mean increase from baseline in CD4+ cell count at Week 144 was 281 cells/mm3 in the TYBOST group and 297 cells/mm3 in the ritonavir group.

14.2 Clinical Trial Results in HIV-1 Infected Virologically Suppressed Pediatric Subjects – Trial 128

Trial 128 was a Phase 2/3 multicenter, open-label trial to evaluate the pharmacokinetics, safety, and efficacy of TYBOST coadministered with atazanavir or darunavir in HIV-1 infected virologically suppressed pediatric subjects ages 12 years and older with baseline estimated creatinine clearance ≥90 mL/min/1.73 m2. Subjects were on a stable antiretroviral regimen (for at least 3 months), consisting of atazanavir or darunavir, both administered with ritonavir, combined with 2 nucleotide reverse transcriptase inhibitors (NRTIs). They were switched from ritonavir to TYBOST 150 mg once daily and continued atazanavir (N=14) or darunavir once daily (N=7) and 2 NRTIs.

The mean age of subjects was 14 years (range 12–17 years); median weight was 55 kg; 62% were male, 38% were Asian, 33% were White, 19% were Black, and 67% were not Hispanic or Latino. At baseline, 20/21 subjects had plasma HIV-1 RNA <50 copies/mL and 1 subject had plasma HIV-1 RNA of 50 copies/mL.

In subjects who switched to TYBOST coadministered with atazanavir, 93% (13/14) of subjects remained suppressed (HIV-1 RNA <50 copies/mL), and 1 subject experienced virologic failure at Week 48. From a median baseline CD4+ cell count and CD4+% of 770 cells/mm3 (range 486 to 1765 cells/mm3) and 33% (range 23% to 45%), respectively, the median change from baseline in CD4+ cell count and CD4+% at Week 48 was -60 cells/mm3 (range -500 to 705 cells/mm3) and -0.3% (range -6% to 8%), respectively.

In subjects who switched to TYBOST coadministered with darunavir, 86% (6/7) of subjects remained suppressed (HIV-1 RNA <50 copies/mL), and 1 subject had missing data at Week 48. From a median baseline CD4+ cell count and CD4+% of 1117 cells/mm3 (range 658 to 2416 cells/mm3) and 45% (range 28% to 56%), respectively, the median change from baseline in CD4+ cell count and CD4+% at Week 48 was -342 cells/mm3 (range -1389 to 219 cells/mm3) and -6% (range -12% to 5%), respectively. All 6 subjects with available data had CD4+ cell counts above 800 cells/mm3 at Week 48.

Store at 25 °C (77 °F); excursions permitted to 15–30 °C (59–86 °F) (see USP Controlled Room Temperature).

• Keep container tightly closed.
• Dispense only in original container.
• Do not use if seal over bottle opening is broken or missing.

Drug Interaction

Inform patients that TYBOST coadministered with atazanavir or darunavir may interact with many drugs with potential serious implications and that some drugs are contraindicated with TYBOST coadministered with atazanavir or darunavir. Advise patients to report to their healthcare provider the use of any other prescription or nonprescription medication, including acid-modifying medications or herbal products, including St. John's wort [see Contraindications (4), Warnings and Precautions (5.3), and Drug Interactions (7)].

New Onset or Worsening Renal Impairment

Inform patients that renal impairment, including cases of acute renal failure and Fanconi syndrome, has been reported when TYBOST is used in combination with a TDF containing regimen [see Warnings and Precautions (5.2)].

Pregnancy

Advise patients that TYBOST is not recommended during pregnancy and to alert their healthcare provider if they get pregnant while taking TYBOST [see Use in Specific Populations (8.1)].

Inform patients that there is a pregnancy exposure registry that monitors fetal outcomes in pregnant individuals exposed to TYBOST during pregnancy [see Use in Specific Populations (8.1)].

Lactation

Instruct mothers with HIV-1 infection not to breastfeed because HIV-1 can be passed to the baby in breast milk [see Use in Specific Populations (8.2)].

Dosing Instructions

Inform patients that TYBOST must be taken at the same time as atazanavir or darunavir and with food once daily as prescribed. It is important to take TYBOST and atazanavir or darunavir together on a regular dosing schedule and to avoid missing doses. Counsel patients about the risks of developing resistance to their HIV-1 medications.