12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Darunavir is an HIV-1 antiviral drug [see Microbiology (12.4)] .

12.2 Pharmacodynamics

Cardiac Electrophysiology

In a thorough QT/QTc study in 40 healthy subjects, PREZISTA/ritonavir doses of 1.33 times the maximum recommended dose did not affect the QT/QTc interval.

12.3 Pharmacokinetics

Pharmacokinetics in Adults

General

Darunavir is primarily metabolized by CYP3A. Ritonavir inhibits CYP3A, thereby increasing the plasma concentrations of darunavir. When a single dose of PREZISTA 600 mg was given orally in combination with 100 mg ritonavir twice daily, there was an approximate 14-fold increase in the systemic exposure of darunavir. Therefore, PREZISTA should only be used in combination with 100 mg of ritonavir to achieve sufficient exposures of darunavir.

The pharmacokinetics of darunavir, co-administered with low dose ritonavir (100 mg), has been evaluated in healthy adult volunteers and in HIV-1-infected subjects. Table 11 displays the population pharmacokinetic estimates of darunavir after oral administration of PREZISTA/ritonavir 600/100 mg twice daily (based on sparse sampling in 285 patients in trial TMC114-C214, 278 patients in trial TMC114-C229 and 119 patients [integrated data] from trials TMC114-C202 and TMC114-C213) and PREZISTA/ritonavir 800/100 mg once daily (based on sparse sampling in 335 patients in trial TMC114-C211 and 280 patients in trial TMC114-C229) to HIV-1-infected patients.

Table 11: Population Pharmacokinetic Estimates of Darunavir at PREZISTA/ritonavir 800/100 mg Once Daily (Trial TMC114-C211, 48-Week Analysis and Trial TMC114-C229, 48-Week Analysis) and PREZISTA/ritonavir 600/100 mg Twice Daily (Trial TMC114-C214, 48-Week Analysis, Trial TMC114-C229, 48-Week Analysis and Integrated Data from Trials TMC114-C213 and TMC114-C202, Primary 24-Week Analysis)
	PREZISTA/ritonavir 800/100 mg once daily		PREZISTA/ritonavir 600/100 mg twice daily
Parameter	TMC114-C211 N=335	TMC114-C229 N=280	TMC114-C214 N=285	TMC114-C229 N=278	TMC114-C213 + TMC114-C202 (integrated data) N=119
N=number of subjects with data
* AUC 24h is calculated as AUC 12h*2.
AUC 24h(ng.h/mL) *
Mean ± Standard Deviation	93026 ± 27050	93334 ± 28626	116796 ± 33594	114302 ± 32681	124698 ± 32286
Median (Range)	87854 (45000–219240)	87788 (45456–236920)	111632 (64874–355360)	109401 (48934–323820)	123336 (67714–212980)
C 0h(ng/mL)
Mean ± Standard Deviation	2282 ± 1168	2160 ± 1201	3490 ± 1401	3386 ± 1372	3578 ± 1151
Median (Range)	2041 (368–7242)	1896 (184–7881)	3307 (1517–13198)	3197 (250–11865)	3539 (1255–7368)

Absorption and Bioavailability

Darunavir, co-administered with 100 mg ritonavir twice daily, was absorbed following oral administration with a T maxof approximately 2.5–4 hours. The absolute oral bioavailability of a single 600 mg dose of darunavir alone and after co-administration with 100 mg ritonavir twice daily was 37% and 82%, respectively. In vivodata suggest that PREZISTA/ritonavir is an inhibitor of the P-glycoprotein (P-gp) transporters.

Effects of Food on Oral Absorption

When PREZISTA tablets were administered with food, the C maxand AUC of darunavir, co-administered with ritonavir, is approximately 40% higher relative to the fasting state. Within the range of meals studied, darunavir exposure is similar. The total caloric content of the various meals evaluated ranged from 240 Kcal (12 gms fat) to 928 Kcal (56 gms fat).

Distribution

Darunavir is approximately 95% bound to plasma proteins. Darunavir binds primarily to plasma alpha 1-acid glycoprotein (AAG).

Metabolism

In vitroexperiments with human liver microsomes (HLMs) indicate that darunavir primarily undergoes oxidative metabolism. Darunavir is extensively metabolized by CYP enzymes, primarily by CYP3A. A mass balance study in healthy volunteers showed that after a single dose administration of 400 mg 14C-darunavir, co-administered with 100 mg ritonavir, the majority of the radioactivity in the plasma was due to darunavir. At least 3 oxidative metabolites of darunavir have been identified in humans; all showed activity that was at least 90% less than the activity of darunavir against wild-type HIV-1.

Elimination

A mass balance study in healthy volunteers showed that after single dose administration of 400 mg 14C-darunavir, co-administered with 100 mg ritonavir, approximately 79.5% and 13.9% of the administered dose of 14C-darunavir was recovered in the feces and urine, respectively. Unchanged darunavir accounted for approximately 41.2% and 7.7% of the administered dose in feces and urine, respectively. The terminal elimination half-life of darunavir was approximately 15 hours when co-administered with ritonavir. After intravenous administration, the clearance of darunavir, administered alone and co-administered with 100 mg twice daily ritonavir, was 32.8 L/h and 5.9 L/h, respectively.

Special Populations

Hepatic Impairment

Darunavir is primarily metabolized by the liver. The steady-state pharmacokinetic parameters of darunavir were similar after multiple dose co-administration of PREZISTA/ritonavir 600/100 mg twice daily to subjects with normal hepatic function (n=16), mild hepatic impairment (Child-Pugh Class A, n=8), and moderate hepatic impairment (Child-Pugh Class B, n=8). The effect of severe hepatic impairment on the pharmacokinetics of darunavir has not been evaluated [see Dosage and Administration (2.6)and Use in Specific Populations (8.6)] .

Hepatitis B or Hepatitis C Virus Co-infection

The 48-week analysis of the data from Studies TMC114-C211 and TMC114-C214 in HIV-1-infected subjects indicated that hepatitis B and/or hepatitis C virus co-infection status had no apparent effect on the exposure of darunavir.

Renal Impairment

Results from a mass balance study with 14C-PREZISTA/ritonavir showed that approximately 7.7% of the administered dose of darunavir is excreted in the urine as unchanged drug. As darunavir and ritonavir are highly bound to plasma proteins, it is unlikely that they will be significantly removed by hemodialysis or peritoneal dialysis. Population pharmacokinetic analysis showed that the pharmacokinetics of darunavir were not significantly affected in HIV-1-infected subjects with moderate renal impairment (CrCL between 30–60 mL/min, n=20). There are no pharmacokinetic data available in HIV-1-infected patients with severe renal impairment or end stage renal disease [see Use in Specific Populations (8.7)] .

Gender

Population pharmacokinetic analysis showed higher mean darunavir exposure in HIV-1-infected females compared to males. This difference is not clinically relevant.

Race

Population pharmacokinetic analysis of darunavir in HIV-1-infected subjects indicated that race had no apparent effect on the exposure to darunavir.

Geriatric Patients

Population pharmacokinetic analysis in HIV-1-infected subjects showed that darunavir pharmacokinetics are not considerably different in the age range (18 to 75 years) evaluated in HIV-1-infected subjects (n=12, age greater than or equal to 65) [see Use in Specific Populations (8.5)] .

Pediatric Patients

PREZISTA/ritonavir administered twice daily

The pharmacokinetics of darunavir in combination with ritonavir in 93 antiretroviral treatment-experienced HIV-1-infected pediatric subjects 3 to less than 18 years of age and weighing at least 10 kg showed that the administered weight-based dosages resulted in similar darunavir exposure when compared to the darunavir exposure achieved in treatment-experienced adults receiving PREZISTA/ritonavir 600/100 mg twice daily [see Dosage and Administration (2.5)] .

PREZISTA/ritonavir administered once daily

The pharmacokinetics of darunavir in combination with ritonavir in 12 antiretroviral treatment-naïve HIV-1-infected pediatric subjects 12 to less than 18 years of age and weighing at least 40 kg receiving PREZISTA/ritonavir 800/100 mg once daily resulted in similar darunavir exposures when compared to the darunavir exposure achieved in treatment-naïve adults receiving PREZISTA/ritonavir 800/100 mg once daily [see Dosage and Administration (2.5)] .

Based on population pharmacokinetic modeling and simulation, the proposed PREZISTA/ritonavir once daily dosing regimens for pediatric patients 3 to less than 12 years of age is predicted to result in similar darunavir exposures when compared to the darunavir exposures achieved in treatment-naïve adults receiving PREZISTA/ritonavir 800/100 mg once daily [see Dosage and Administration (2.5)] .

The population pharmacokinetic parameters in pediatric subjects with PREZISTA/ritonavir administered once or twice daily are summarized in the table below:

Table 12: Population Pharmacokinetic Estimates of Darunavir Exposure (Trials TMC114-C230, TMC114-C212 and TMC114-C228) Following Administration of Doses in Tables 2 and 3
	PREZISTA/ritonavir once daily	PREZISTA/ritonavir twice daily
			TMC114-C228 *
Parameter	TMC114-C230 † N=12	TMC114-C212 N=74
Parameter	TMC114-C230 † N=12	TMC114-C212 N=74	10 to less than 15 kg ‡ N=10	15 to less than 20 kg § N=13
N=number of subjects with data.
* Subjects may have contributed pharmacokinetic data to both the 10 kg to less than 15 kg weight group and the 15 kg to less than 20 kg weight group. † Summary statistics for population pharmacokinetic parameter estimates for DRV after administration of DRV/rtv at 800/100 mg once daily in treatment-naïve HIV-1 infected subjects from 12 to <18 years of age – Week-48 Analyses. ‡ Calculated from individual pharmacokinetic parameters estimated for Week 2 and Week 4, based on the Week 48 analysis that evaluated a darunavir dose of 20 mg/kg twice daily with ritonavir 3 mg/kg twice daily. § The 15 kg to less than 20 kg weight group received 380 mg (3.8 mL) PREZISTA oral suspension twice daily with 48 mg (0.6 mL) ritonavir oral solution twice daily in TMC114-C228. Calculated from individual pharmacokinetic parameters estimated for Week 2 post-dose adjustment visit; Week 24 and Week 48 based on the – Week 48 analysis that evaluated a darunavir dose of 380 mg twice daily. ¶ AUC 24h is calculated as AUC 12h*2.
AUC 24h(ng∙h/mL) ¶)
Mean ± Standard Deviation	84390 ± 23587	126377 ± 34356	137896 ± 51420	157760 ± 54080
Median (Range)	86741 (35527–123325)	127340 (67054–230720)	124044 (89688–261090)	132698 (112310–294840)
C 0h(ng/mL)
Mean ± Standard Deviation	2141 ± 865	3948 ± 1363	4510 ± 2031	4848 ± 2143
Median (Range)	2234 (542–3776)	3888 (1836–7821)	4126 (2456–9361)	3927 (3046–10292)

Pregnancy and Postpartum

The exposure to total darunavir and ritonavir after intake of PREZISTA/ritonavir 600/100 mg twice daily and PREZISTA/ritonavir 800/100 mg once daily as part of an antiretroviral regimen was generally lower during pregnancy compared with postpartum (see Table 13, Table 14and Figure 1).

Table 13: Pharmacokinetic Results of Total Darunavir After Administration of PREZISTA/ritonavir at 600/100 mg Twice Daily as Part of an Antiretroviral Regimen, During the 2 ndTrimester of Pregnancy, the 3 rdTrimester of Pregnancy and Postpartum
Pharmacokinetics of total darunavir (mean ± standard deviation)	2 ndTrimester of pregnancy (n=12) *	3 rdTrimester of pregnancy (n=12)	Postpartum (6–12 Weeks) (n=12)
* n=11 for AUC 24h † AUC 24h is calculated as AUC 12h*2.
C max, ng/mL	4668 ± 1097	5328 ± 1631	6659 ± 2364
AUC 24h, ng.h/mL †	78740 ± 19194	91760 ± 34720	113780 ± 52680
C min, ng/mL	1922 ± 825	2661 ± 1269	2851 ± 2216

Table 14: Pharmacokinetic Results of Total Darunavir After Administration of PREZISTA/ritonavir at 800/100 mg Once Daily as Part of an Antiretroviral Regimen, During the 2 ndTrimester of Pregnancy, the 3 rdTrimester of Pregnancy and Postpartum
Pharmacokinetics of total darunavir (mean ± standard deviation)	2 ndTrimester of pregnancy (n=17)	3 rdTrimester of pregnancy (n=15)	Postpartum (6–12 Weeks) (n=16)
C max, ng/mL	4964 ± 1505	5132 ± 1198	7310 ± 1704
AUC 24h, ng.h/mL	62289 ± 16234	61112 ± 13790	92116 ± 29241
C min, ng/mL	1248 ± 542	1075 ± 594	1473 ± 1141

Due to an increase in the unbound fraction of darunavir during pregnancy compared to postpartum, unbound darunavir exposures were less reduced during pregnancy as compared to postpartum. Exposure reductions during pregnancy were greater for the once daily regimen as compared to the twice daily regimen (see Figure 1).

Figure 1: Pharmacokinetic Results (Within-Subject Comparison) of Total and Unbound Darunavir After Administration of PREZISTA/ritonavir at 600/100 mg Twice Daily or 800/100 mg Once Daily as Part of an Antiretroviral Regimen, During the 2 ndand 3 rdTrimester of Pregnancy Compared to Postpartum

Legend: 90% CI: 90% confidence interval; GMR: geometric mean ratio. Solid vertical line: ratio of 1.0; dotted vertical lines: reference lines of 0.8 and 1.25.

Drug Interactions

[See also Contraindications (4), Warnings and Precautions (5.5)and Drug Interactions (7). ]

Darunavir co-administered with ritonavir is an inhibitor of CYP3A, CYP2D6, and P-gp. Co-administration of darunavir and ritonavir with drugs primarily metabolized by CYP3A and CYP2D6, or are transported by P-gp, may result in increased plasma concentrations of such drugs, which could increase or prolong their therapeutic effect and adverse events.

Darunavir and ritonavir are metabolized by CYP3A. In vitrodata indicate that darunavir may be a P-gp substrate. Drugs that induce CYP3A activity would be expected to increase the clearance of darunavir and ritonavir, resulting in lowered plasma concentrations of darunavir and ritonavir. Co-administration of darunavir and ritonavir and other drugs that inhibit CYP3A or P-gp may decrease the clearance of darunavir and ritonavir and may result in increased plasma concentrations of darunavir and ritonavir.

Drug interaction studies were performed with darunavir and other drugs likely to be co-administered and some drugs commonly used as probes for pharmacokinetic interactions. The effects of co-administration of darunavir on the AUC, C max, and C minvalues are summarized in Table 15 (effect of other drugs on darunavir) and Table 16 (effect of darunavir on other drugs). For information regarding clinical recommendations, see Drug Interactions (7).

Several interaction studies have been performed with a dose other than the recommended dose of the co-administered drug or darunavir; however, the results are applicable to the recommended dose of the co-administered drug and/or darunavir.

Table 15: Drug Interactions: Pharmacokinetic Parameters for Darunavir in the Presence of Co-Administered Drugs
Co-administered drug	Dose/Schedule		N	PK	LS Mean ratio (90% CI) of darunavir Pharmacokinetic parameters with/without co-administered drug no effect =1.00
Co-administered drug	Co-administered Drug	Darunavir/ritonavir	N	PK	C max	AUC	C min
N = number of subjects with data
* q.d. = once daily † b.i.d. = twice daily ‡ The pharmacokinetic parameters of darunavir in this study were compared with the pharmacokinetic parameters following administration of PREZISTA/ritonavir 600/100 mg twice daily. § Ratio based on between-study comparison. ¶ q.o.d. = every other day
Co-administration with other HIV protease inhibitors
Atazanavir	300 mg q.d. *	400/100 mg b.i.d. †	13	↔	1.02 (0.96–1.09)	1.03 (0.94–1.12)	1.01 (0.88–1.16)
Indinavir	800 mg b.i.d.	400/100 mg b.i.d.	9	↑	1.11 (0.98–1.26)	1.24 (1.09–1.42)	1.44 (1.13–1.82)
Lopinavir/ritonavir	400/100 mg b.i.d.	1200/100 mg b.i.d. ‡	14	↓	0.79 (0.67–0.92)	0.62 (0.53–0.73)	0.49 (0.39–0.63)
	533/133.3 mg b.i.d.	1200 mg b.i.d. ‡	15	↓	0.79 (0.64–0.97)	0.59 (0.50–0.70)	0.45 (0.38–0.52)
Saquinavir hard gel capsule	1000 mg b.i.d.	400/100 mg b.i.d.	14	↓	0.83 (0.75–0.92)	0.74 (0.63–0.86)	0.58 (0.47–0.72)
Co-administration with other HIV antiretrovirals
Didanosine	400 mg q.d.	600/100 mg b.i.d.	17	↔	0.93 (0.86–1.00)	1.01 (0.95–1.07)	1.07 (0.95–1.21)
Efavirenz	600 mg q.d.	300/100 mg b.i.d.	12	↓	0.85 (0.72–1.00)	0.87 (0.75–1.01)	0.69 (0.54–0.87)
Etravirine	200 mg b.i.d.	600/100 mg b.i.d.	15	↔	1.11 (1.01–1.22)	1.15 (1.05–1.26)	1.02 (0.90–1.17)
Nevirapine	200 mg b.i.d.	400/100 mg b.i.d.	8	↑	1.40 § (1.14–1.73)	1.24 § (0.97–1.57)	1.02 § (0.79–1.32)
Rilpivirine	150 mg q.d.	800/100 mg q.d.	15	↔	0.90 (0.81–1.00)	0.89 (0.81–0.99)	0.89 (0.68–1.16)
Tenofovir disoproxil fumarate	300 mg q.d.	300/100 mg b.i.d.	12	↑	1.16 (0.94–1.42)	1.21 (0.95–1.54)	1.24 (0.90–1.69)
Co-administration with other drugs
Artemether/lumefantrine	80/480 mg (6 doses at 0, 8, 24, 36, 48, and 60 hours)	600/100 mg b.i.d.	14	↔	1.00 (0.93–1.07)	0.96 (0.90–1.03)	0.87 (0.77–0.98)
Carbamazepine	200 mg b.i.d.	600/100 mg b.i.d.	16	↔	1.04 (0.93–1.16)	0.99 (0.90–1.08)	0.85 (0.73–1.00)
Clarithromycin	500 mg b.i.d.	400/100 mg b.i.d.	17	↔	0.83 (0.72–0.96)	0.87 (0.75–1.01)	1.01 (0.81–1.26)
Ketoconazole	200 mg b.i.d.	400/100 mg b.i.d.	14	↑	1.21 (1.04–1.40)	1.42 (1.23–1.65)	1.73 (1.39–2.14)
Omeprazole	20 mg q.d.	400/100 mg b.i.d.	16	↔	1.02 (0.95–1.09)	1.04 (0.96–1.13)	1.08 (0.93–1.25)
Paroxetine	20 mg q.d.	400/100 mg b.i.d.	16	↔	0.97 (0.92–1.02)	1.02 (0.95–1.10)	1.07 (0.96–1.19)
Pitavastatin	4 mg q.d.	800/100 mg q.d.	27	↔	1.06 (1.00–1.12)	1.03 (0.95–1.12)	NA
Ranitidine	150 mg b.i.d.	400/100 mg b.i.d.	16	↔	0.96 (0.89–1.05)	0.95 (0.90–1.01)	0.94 (0.90–0.99)
Rifabutin	150 mg q.o.d. ¶	600/100 mg b.i.d.	11	↑	1.42 (1.21–1.67)	1.57 (1.28–1.93)	1.75 (1.28–2.37)
Sertraline	50 mg q.d.	400/100 mg b.i.d.	13	↔	1.01 (0.89–1.14)	0.98 (0.84–1.14)	0.94 (0.76–1.16)

Table 16: Drug Interactions: Pharmacokinetic Parameters for Co-Administered Drugs in the Presence of PREZISTA/ritonavir
Co-administered drug	Dose/Schedule		N	PK	LS Mean ratio (90% CI) of co-administered drug pharmacokinetic parameters with/without darunavir no effect =1.00
Co-administered drug	Co-administered drug	Darunavir/ritonavir	N	PK	C max	AUC	C min
N = number of subjects with data;- = no information available
* q.d. = once daily † b.i.d. = twice daily ‡ The pharmacokinetic parameters of lopinavir in this study were compared with the pharmacokinetic parameters following administration of lopinavir/ritonavir 400/100 mg twice daily. § Noted as C τ or C 24 in the dolutegravir U.S. prescribing information ¶ Ratio is for buprenorphine; mean C max and AUC 24 for naloxone were comparable when buprenorphine/naloxone was administered with or without PREZISTA/ritonavir # 800/100 mg q.d. for 14 days before co-administered with dabigatran etexilate. Þ q.o.d. = every other day ß In comparison to rifabutin 300 mg once daily.
Co-administration with other HIV protease inhibitors
Atazanavir	300 mg q.d. */100 mg ritonavir q.d. when administered alone	400/100 mg b.i.d. †	13	↔	0.89 (0.78–1.01)	1.08 (0.94–1.24)	1.52 (0.99–2.34)
	300 mg q.d. when administered with darunavir/ritonavir
Indinavir	800 mg b.i.d. /100 mg ritonavir b.i.d. when administered alone	400/100 mg b.i.d.	9	↑	1.08 (0.95–1.22)	1.23 (1.06–1.42)	2.25 (1.63–3.10)
	800 mg b.i.d. when administered with darunavir/ ritonavir
Lopinavir/ritonavir	400/100 mg b.i.d. ‡	1200/100 mg b.i.d.	14	↔	0.98 (0.78–1.22)	1.09 (0.86–1.37)	1.23 (0.90–1.69)
	533/133.3 mg b.i.d.. ‡	1200 mg b.i.d.	15	↔	1.11 (0.96–1.30)	1.09 (0.96–1.24)	1.13 (0.90–1.42)
Saquinavir hard gel capsule	1000 mg b.i.d. /100 mg ritonavir b.i.d. when administered alone	400/100 mg b.i.d.	12	↔	0.94 (0.78–1.13)	0.94 (0.76–1.17)	0.82 (0.52–1.30)
	1000 mg b.i.d. when administered with darunavir/ritonavir
Co-administration with other HIV antiretrovirals
Didanosine	400 mg q.d.	600/100 mg b.i.d.	17	↔	0.84 (0.59–1.20)	0.91 (0.75–1.10)	-
Dolutegravir	30 mg q.d	600/100 mg b.i.d.	15	↓	0.89 (0.83–0.97)	0.78 (0.72–0.85)	0.62 § (0.56–0.69)
Dolutegravir	50 mg q.d.	600/100 mg b.i.d. with 200 mg b.i.d. etravirine	9	↓	0.88 (0.78–1.00)	0.75 (0.69–0.81)	0.63 § (0.52–0.76)
Efavirenz	600 mg q.d.	300/100 mg b.i.d.	12	↑	1.15 (0.97–1.35)	1.21 (1.08–1.36)	1.17 (1.01–1.36)
Etravirine	100 mg b.i.d.	600/100 mg b.i.d.	14	↓	0.68 (0.57–0.82)	0.63 (0.54–0.73)	0.51 (0.44–0.61)
Nevirapine	200 mg b.i.d.	400/100 mg b.i.d.	8	↑	1.18 (1.02–1.37)	1.27 (1.12–1.44)	1.47 (1.20–1.82)
Rilpivirine	150 mg q.d.	800/100 mg q.d.	14	↑	1.79 (1.56–2.06)	2.30 (1.98–2.67)	2.78 (2.39–3.24)
Tenofovir disoproxil fumarate	300 mg q.d.	300/100 mg b.i.d.	12	↑	1.24 (1.08–1.42)	1.22 (1.10–1.35)	1.37 (1.19–1.57)
Maraviroc	150 mg b.i.d.	600/100 mg b.i.d.	12	↑	2.29 (1.46–3.59)	4.05 (2.94–5.59)	8.00 (6.35–10.1)
		600/100 mg b.i.d. with 200 mg b.i.d. etravirine	10	↑	1.77 (1.20–2.60)	3.10 (2.57–3.74)	5.27 (4.51–6.15)
Co-administration with other drugs
Atorvastatin	40 mg q.d. when administered alone	300/100 mg b.i.d.	15	↑	0.56 (0.48–0.67)	0.85 (0.76–0.97)	1.81 (1.37–2.40)
	10 mg q.d. when administered with darunavir/ritonavir
Artemether	80 mg single dose	600/100 mg b.i.d.	15	↓	0.85 (0.68–1.05)	0.91 (0.78–1.06)	-
Dihydroartemisinin			15	↑	1.06 (0.82–1.39)	1.12 (0.96–1.30)	-
Artemether	artemether/lumefantrine 80/480 mg (6 doses at 0, 8, 24, 36, 48, and 60 hours)	600/100 mg b.i.d.	15	↓	0.82 (0.61–1.11)	0.84 (0.69–1.02)	0.97 (0.90–1.05)
Dihydroartemisinin			15	↓	0.82 (0.66–1.01)	0.82 (0.74–0.91)	1.00 (0.82–1.22)
Lumefantrine			15	↑	1.65 (1.49–1.83)	2.75 (2.46–3.08)	2.26 (1.92–2.67)
Buprenorphine/Naloxone	8/2 mg to 16/4 mg q.d.	600/100 mg b.i.d.	17	↔	0.92 ¶ (0.79–1.08)	0.89 ¶ (0.78–1.02)	0.98 ¶ (0.82–1.16)
Norbuprenorphine			17	↑	1.36 (1.06–1.74)	1.46 (1.15–1.85)	1.71 (1.29–2.27)
Carbamazepine	200 mg b.i.d.	600/100 mg b.i.d.	16	↑	1.43 (1.34–1.53)	1.45 (1.35–1.57)	1.54 (1.41–1.68)
Carbamazepine epoxide			16	↓	0.46 (0.43–0.49)	0.46 (0.44–0.49)	0.48 (0.45–0.51)
Clarithromycin	500 mg b.i.d.	400/100 mg b.i.d.	17	↑	1.26 (1.03–1.54)	1.57 (1.35–1.84)	2.74 (2.30–3.26)
Dabigatran etexilate	150 mg	800/100 mg single dose	14	↑	1.64 (1.21–2.23)	1.72 (1.33–2.23)	-
		800/100 mg q.d. #	13	↑	1.22 (0.89–1.67)	1.18 (0.90–1.53)	-
Dextromethorphan	30 mg	600/100 mg b.i.d.	12	↑	2.27 (1.59–3.26)	2.70 (1.80–4.05)	-
Dextrorphan				↓	0.87 (0.77–0.98)	0.96 (0.90–1.03)	-
Digoxin	0.4 mg	600/100 mg b.i.d.	8	↑	1.15 (0.89–1.48)	1.36 (0.81–2.27)	-
Ethinyl estradiol (EE)	Ortho-Novum 1/35 (35 µg EE /1 mg NE)	600/100 mg b.i.d.	11	↓	0.68 (0.61–0.74)	0.56 (0.50–0.63)	0.38 (0.27–0.54)
Norethindrone (NE)			11	↓	0.90 (0.83–0.97)	0.86 (0.75–0.98)	0.70 (0.51–0.97)
Ketoconazole	200 mg b.i.d.	400/100 mg b.i.d.	15	↑	2.11 (1.81–2.44)	3.12 (2.65–3.68)	9.68 (6.44–14.55)
R-Methadone	55–150 mg q.d.	600/100 mg b.i.d.	16	↓	0.76 (0.71–0.81)	0.84 (0.78–0.91)	0.85 (0.77–0.94)
Omeprazole	40 mg single dose	600/100 mg b.i.d.	12	↓	0.66 (0.48–0.90)	0.58 (0.50–0.66)	-
5-hydroxy omeprazole				↓	0.93 (0.71–1.21)	0.84 (0.77–0.92)	-
Paroxetine	20 mg q.d.	400/100 mg b.i.d.	16	↓	0.64 (0.59–0.71)	0.61 (0.56–0.66)	0.63 (0.55–0.73)
Pitavastatin	4 mg q.d.	800/100 mg q.d.	27	↓	0.96 (0.84–1.09)	0.74 (0.69–0.80)	NA
Pravastatin	40 mg single dose	600/100 mg b.i.d.	14	↑	1.63 (0.95–2.82)	1.81 (1.23–2.66)	-
Rifabutin	150 mg q.o.d. Þwhen administered with PREZISTA/ritonavir	600/100 mg b.i.d. ß	11	↑	0.72 (0.55–0.93)	0.93 (0.80–1.09)	1.64 (1.48–1.81)
25- O-desacetyl-rifabutin	300 mg q.d. when administered alone		11	↑	4.77 (4.04–5.63)	9.81 (8.09–11.9)	27.1 (22.2–33.2)
Sertraline	50 mg q.d.	400/100 mg b.i.d.	13	↓	0.56 (0.49–0.63)	0.51 (0.46–0.58)	0.51 (0.45–0.57)
Sildenafil	100 mg (single dose) administered alone	400/100 mg b.i.d.	16	↑	0.62 (0.55–0.70)	0.97 (0.86–1.09)	-
	25 mg (single dose)when administered with darunavir/ritonavir
S-warfarin	10 mg single dose	600/100 mg b.i.d.	12	↓	0.92 (0.86–0.97)	0.79 (0.73–0.85)	-
7-OH-S-warfarin			12	↑	1.42 (1.24–1.63)	1.23 (0.97–1.57)	-

12.4 Microbiology

Mechanism of Action

Darunavir is an inhibitor of the HIV-1 protease. It selectively inhibits the cleavage of HIV-1 encoded Gag-Pol polyproteins in infected cells, thereby preventing the formation of mature virus particles.

Antiviral Activity

Darunavir exhibits activity against laboratory strains and clinical isolates of HIV-1 and laboratory strains of HIV-2 in acutely infected T-cell lines, human peripheral blood mononuclear cells and human monocytes/macrophages with median EC 50values ranging from 1.2 to 8.5 nM (0.7 to 5.0 ng/mL). Darunavir demonstrates antiviral activity in cell culture against a broad panel of HIV-1 group M (A, B, C, D, E, F, G), and group O primary isolates with EC 50values ranging from less than 0.1 to 4.3 nM. The EC 50value of darunavir increases by a median factor of 5.4 in the presence of human serum. Darunavir did not show antagonism when studied in combination with the PIs amprenavir, atazanavir, indinavir, lopinavir, nelfinavir, ritonavir, saquinavir, or tipranavir, the N(t)RTIs abacavir, didanosine, emtricitabine, lamivudine, stavudine, tenofovir, zalcitabine, or zidovudine, the NNRTIs delavirdine, rilpivirine, efavirenz, etravirine, or nevirapine, and the fusion inhibitor enfuvirtide.

Resistance

Cell Culture: HIV-1 isolates with a decreased susceptibility to darunavir have been selected in cell culture and obtained from subjects treated with PREZISTA/ritonavir. Darunavir-resistant virus derived in cell culture from wild-type HIV-1 had 21- to 88-fold decreased susceptibility to darunavir and developed 2 to 4 of the following amino acid substitutions S37D, R41E/T, K55Q, H69Q, K70E, T74S, V77I, or I85V in the protease. Selection in cell culture of darunavir resistant HIV-1 from nine HIV-1 strains harboring multiple PI resistance-associated mutations resulted in the overall emergence of 22 mutations in the protease gene, coding for amino acid substitutions L10F, V11I, I13V, I15V, G16E, L23I, V32I, L33F, S37N, M46I, I47V, I50V, F53L, L63P, A71V, G73S, L76V, V82I, I84V, T91A/S, and Q92R, of which L10F, V32I, L33F, S37N, M46I, I47V, I50V, L63P, A71V, and I84V were the most prevalent. These darunavir-resistant viruses had at least eight protease substitutions and exhibited 50- to 641-fold decreases in darunavir susceptibility with final EC 50values ranging from 125 nM to 3461 nM.

Clinical trials of PREZISTA/ritonavir in treatment-experienced subjects: In a pooled analysis of the 600/100 mg PREZISTA/ritonavir twice daily arms of trials TMC114-C213, TMC114-C202, TMC114-C215, and the control arms of etravirine trials TMC125-C206 and TMC125-C216, the amino acid substitutions V32I and I54L or M developed most frequently on PREZISTA/ritonavir in 41% and 25%, respectively, of the treatment-experienced subjects who experienced virologic failure, either by rebound or by never being suppressed (less than 50 copies/mL). Other substitutions that developed frequently in PREZISTA/ritonavir virologic failure isolates occurred at amino acid positions V11I, I15V, L33F, I47V, I50V, and L89V. These amino acid substitutions were associated with decreased susceptibility to darunavir; 90% of the virologic failure isolates had a greater than 7-fold decrease in susceptibility to darunavir at failure. The median darunavir phenotype (fold change from reference) of the virologic failure isolates was 4.3-fold at baseline and 85-fold at failure. Amino acid substitutions were also observed in the protease cleavage sites in the Gag polyprotein of some PREZISTA/ritonavir virologic failure isolates. In trial TMC114-C212 of treatment-experienced pediatric subjects, the amino acid substitutions V32I, I54L and L89M developed most frequently in virologic failures on PREZISTA/ritonavir.

In the 96-week as-treated analysis of the Phase 3 trial TMC114-C214, the percent of virologic failures (never suppressed, rebounders and discontinued before achieving suppression) was 21% (62/298) in the group of subjects receiving PREZISTA/ritonavir 600/100 mg twice daily compared to 32% (96/297) of subjects receiving lopinavir/ritonavir 400/100 mg twice daily. Examination of subjects who failed on PREZISTA/ritonavir 600/100 mg twice daily and had post-baseline genotypes and phenotypes showed that 7 subjects (7/43; 16%) developed PI substitutions on PREZISTA/ritonavir treatment resulting in decreased susceptibility to darunavir. Six of the 7 had baseline PI resistance-associated substitutions and baseline darunavir phenotypes greater than 7. The most common emerging PI substitutions in these virologic failures were V32I, L33F, M46I or L, I47V, I54L, T74P and L76V. These amino acid substitutions were associated with 59- to 839-fold decreased susceptibility to darunavir at failure. Examination of individual subjects who failed in the comparator arm on lopinavir/ritonavir and had post-baseline genotypes and phenotypes showed that 31 subjects (31/75; 41%) developed substitutions on lopinavir treatment resulting in decreased susceptibility to lopinavir (greater than 10-fold) and the most common substitutions emerging on treatment were L10I or F, M46I or L, I47V or A, I54V and L76V. Of the 31 lopinavir/ritonavir virologic failure subjects, 14 had reduced susceptibility (greater than 10-fold) to lopinavir at baseline.

In the 48-week analysis of the Phase 3 trial TMC114-C229, the number of virologic failures (including those who discontinued before suppression after Week 4) was 26% (75/294) in the group of subjects receiving PREZISTA/ritonavir 800/100 mg once daily compared to 19% (56/296) of subjects receiving PREZISTA/ritonavir 600/100 mg twice daily. Examination of isolates from subjects who failed on PREZISTA/ritonavir 800/100 mg once daily and had post-baseline genotypes showed that 8 subjects (8/60; 13%) had isolates that developed IAS-USA defined PI resistance-associated substitutions compared to 5 subjects (5/39; 13%) on PREZISTA/ritonavir 600/100 mg twice daily. Isolates from 2 subjects developed PI resistance associated substitutions associated with decreased susceptibility to darunavir; 1 subject isolate in the PREZISTA/ritonavir 800/100 mg once daily arm, developed substitutions V32I, M46I, L76V and I84V associated with a 24-fold decreased susceptibility to darunavir, and 1 subject isolate in the PREZISTA/ritonavir 600/100 mg twice daily arm developed substitutions L33F and I50V associated with a 40-fold decreased susceptibility to darunavir. In the PREZISTA/ritonavir 800/100 mg once daily and PREZISTA/ritonavir 600/100 mg twice daily groups, isolates from 7 (7/60; 12%) and 4 (4/42; 10%) virologic failures, respectively, developed decreased susceptibility to an NRTI included in the treatment regimen.

Clinical trials of PREZISTA/ritonavir in treatment-naïve subjects: In the 192-week as-treated analysis censoring those who discontinued before Week 4 of the Phase 3 trial TMC114-C211, the percentage of virologic failures (never suppressed, rebounders and discontinued before achieving suppression) was 22% (64/288) in the group of subjects receiving PREZISTA/ritonavir 800/100 mg once daily compared to 29% (76/263) of subjects receiving lopinavir/ritonavir 800/200 mg per day. In the PREZISTA/ritonavir arm, emergent PI resistance-associated substitutions were identified in 11 of the virologic failures with post-baseline genotypic data (n=43). However, none of the darunavir virologic failures had a decrease in darunavir susceptibility (greater than 7-fold change) at failure. In the comparator lopinavir/ritonavir arm, emergent PI resistance-associated substitutions were identified in 17 of the virologic failures with post-baseline genotypic data (n=53), but none of the lopinavir/ritonavir virologic failures had decreased susceptibility to lopinavir (greater than 10-fold change) at failure. The reverse transcriptase M184V substitution and/or resistance to emtricitabine, which was included in the fixed background regimen, was identified in 4 virologic failures from the PREZISTA/ritonavir arm and 7 virologic failures in the lopinavir/ritonavir arm.

Cross-resistance

Cross-resistance among PIs has been observed. Darunavir has a less than 10-fold decreased susceptibility in cell culture against 90% of 3309 clinical isolates resistant to amprenavir, atazanavir, indinavir, lopinavir, nelfinavir, ritonavir, saquinavir and/or tipranavir showing that viruses resistant to these PIs remain susceptible to darunavir.

Darunavir-resistant viruses were not susceptible to amprenavir, atazanavir, indinavir, lopinavir, nelfinavir, ritonavir or saquinavir in cell culture. However, six of nine darunavir-resistant viruses selected in cell culture from PI-resistant viruses showed a fold change in EC 50values less than 3 for tipranavir, indicative of limited cross-resistance between darunavir and tipranavir. In trials TMC114-C213, TMC114-C202, and TMC114-C215, 34% (64/187) of subjects in the PREZISTA/ritonavir arm whose baseline isolates had decreased susceptibility to tipranavir (tipranavir fold change greater than 3) achieved less than 50 copies/mL serum HIV-1 RNA levels at Week 96. Of the viruses isolated from subjects experiencing virologic failure on PREZISTA/ritonavir 600/100 mg twice daily (greater than 7-fold change), 41% were still susceptible to tipranavir and 10% were susceptible to saquinavir while less than 2% were susceptible to the other protease inhibitors (amprenavir, atazanavir, indinavir, lopinavir or nelfinavir).

In trial TMC114-C214, the 7 PREZISTA/ritonavir virologic failures with reduced susceptibility to darunavir at failure were also resistant to the approved PIs (fos)amprenavir, atazanavir, lopinavir, indinavir, and nelfinavir at failure. Six of these 7 were resistant to saquinavir and 5 were resistant to tipranavir. Four of these virologic failures were already PI-resistant at baseline.

Cross-resistance between darunavir and nucleoside/nucleotide reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors, fusion inhibitors, CCR5 co-receptor antagonists, or integrase inhibitors is unlikely because the viral targets are different.

Baseline Genotype/Phenotype and Virologic Outcome Analyses

Genotypic and/or phenotypic analysis of baseline virus may aid in determining darunavir susceptibility before initiation of PREZISTA/ritonavir 600/100 mg twice daily therapy. The effect of baseline genotype and phenotype on virologic response at 96 weeks was analyzed in as-treated analyses using pooled data from the Phase 2b trials (Trials TMC114-C213, TMC114-C202, and TMC114-C215) (n=439). The findings were confirmed with additional genotypic and phenotypic data from the control arms of etravirine trials TMC125-C206 and TMC125-C216 at Week 24 (n=591).

Diminished virologic responses were observed in subjects with 5 or more baseline IAS-defined primary protease inhibitor resistance-associated substitutions (D30N, V32I, L33F, M46I/L, I47A/V, G48V, I50L/V, I54L/M, L76V, V82A/F/L/S/T, I84V, N88S, L90M) (see Table 17).

Table 17: Response to PREZISTA/ritonavir 600/100 mg Twice Daily by Baseline Number of IAS-Defined Primary PI Resistance-Associated Substitutions: As-treated Analysis of Trials TMC114-C213, TMC114-C202, and TMC114-C215
# IAS-defined primary PI substitutions	Proportion of subjects with <50 copies/mL at Week 96 N=439
# IAS-defined primary PI substitutions	Overall	de novoENF	Re-used/No ENF
ENF=enfuvirtide
All	44% (192/439)	54% (61/112)	40% (131/327)
0 – 4	50% (162/322)	58% (49/85)	48% (113/237)
5	22% (16/74)	47% (9/19)	13% (7/55)
≥6	9% (3/32)	17% (1/6)	8% (2/26)

IAS Primary PI Substitutions (2008): D30N, V32I, L33F, M46I/L, I47A/V, G48V, I50L/V, I54L/M, L76V, V82A/F/L/S/T, I84V, N88S, L90M.

The presence at baseline of two or more of the substitutions V11I, V32I, L33F, I47V, I50V, I54L or M, T74P, L76V, I84V or L89V was associated with a decreased virologic response to PREZISTA/ritonavir. In subjects not taking enfuvirtide de novo, the proportion of subjects achieving viral load less than 50 plasma HIV-1 RNA copies/mL at 96 weeks was 59%, 29%, and 12% when the baseline genotype had 0–1, 2 and greater than or equal to 3 of these substitutions, respectively.

Baseline darunavir phenotype (shift in susceptibility relative to reference) was shown to be a predictive factor of virologic outcome. Response rates assessed by baseline darunavir phenotype are shown in Table 18. These baseline phenotype groups are based on the select patient populations in the trials TMC114-C213, TMC114-C202, and TMC114-C215, and are not meant to represent definitive clinical susceptibility breakpoints for PREZISTA/ritonavir. The data are provided to give clinicians information on the likelihood of virologic success based on pre-treatment susceptibility to darunavir.

Table 18: Response (HIV-1 RNA <50 copies/mL at Week 96) to PREZISTA/ritonavir 600/100 mg Twice Daily by Baseline Darunavir Phenotype and by Use of Enfuvirtide: As-treated Analysis of Trials TMC114-C213, TMC114-C202, and TMC114-C215
Baseline DRV phenotype	Proportion of subjects with <50 copies/mL at Week 96 N=417
Baseline DRV phenotype	All	de novoENF	Re-used/No ENF
ENF=enfuvirtide
Overall	175/417 (42%)	61/112 (54%)	131/327 (40%)
0 – 7	148/270 (55%)	44/65 (68%)	104/205 (51%)
>7 – 20	16/53 (30%)	7/17 (41%)	9/36 (25%)
>20	11/94 (12%)	6/23 (26%)	5/71 (7%)