The bioavailability of all components of Symtuza was comparable to that when darunavir 800 mg, cobicistat 150 mg, and emtricitabine/tenofovir alafenamide 200/10 mg were co-administered as separate formulations; bioequivalence was established following single-dose administration under fed conditions in healthy subjects (N = 96).
Absorption
The absolute bioavailability of a single 600 mg dose of darunavir alone was approximately 37% and increased to approximately 82% in the presence of 100 mg twice daily ritonavir. The absolute bioavailability of the emtricitabine 200 mg capsule was 93%.
All components were rapidly absorbed following oral administration of Symtuza in healthy subjects. Maximum plasma concentrations of darunavir, cobicistat, emtricitabine and tenofovir alafenamide were achieved at 4.00, 4.00, 2.00, and 1.50 hours after dosing, respectively. The bioavailability of the components of Symtuza was not affected when administered orally as a split tablet compared to administration as a tablet swallowed whole.
The exposure to darunavir and cobicistat administered as the Symtuza was 30-45% lower and 16-29% lower, respectively, in fasted compared to fed condition. For emtricitabine, the Cmax was 1.26-fold higher in a fasted condition, while the AUC was comparable in fed and fasted condition. For tenofovir alafenamide, the Cmax was 1.82-fold higher in fasted condition, while the area under the curve (AUC) was 20% lower to comparable in a fasted compared to fed condition. Symtuza tablets should be taken with food. The type of food does not affect exposure to Symtuza.
Distribution
Darunavir
Darunavir is approximately 95% bound to plasma protein. Darunavir binds primarily to plasma α1-acid glycoprotein.
Following intravenous administration, the volume of distribution of darunavir alone was 88.1 ± 59.0 L (mean ± SD) and increased to 131 ± 49.9 L (mean ± SD) in the presence of 100 mg twice-daily ritonavir.
Cobicistat
Cobicistat is 97% to 98% bound to human plasma proteins and the mean plasma to blood concentration ratio was approximately 2.
Emtricitabine
In vitro binding of emtricitabine to human plasma proteins was < 4% and independent of concentration over the range of 0.02-200 mcg/mL. At peak plasma concentration, the mean plasma to blood drug concentration ratio was approximately 1.0 and the mean semen to plasma drug concentration ratio was approximately 4.0.
Tenofovir alafenamide
In vitro binding of tenofovir to human plasma proteins is < 0.7% and is independent of concentration over the range of 0.01-25 mcg/mL. Ex vivo binding of tenofovir alafenamide to human plasma proteins in samples collected during clinical trials was approximately 80%.
Biotransformation
Darunavir
In vitro experiments with human liver microsomes (HLMs) indicate that darunavir primarily undergoes oxidative metabolism. Darunavir is extensively metabolised by the hepatic CYP system and almost exclusively by isozyme CYP3A4. A [14C]-darunavir trial in healthy volunteers showed that a majority of the radioactivity in plasma after a single 400/100 mg darunavir with ritonavir dose was due to the parent active substance. At least 3 oxidative metabolites of darunavir have been identified in humans; all showed activity that was at least 10-fold less than the activity of darunavir against wild type HIV.
Cobicistat
Cobicistat is metabolised via CYP3A (major)- and CYP2D6 (minor)-mediated oxidation and does not undergo glucuronidation. Following oral administration of [14C]-cobicistat, 99% of circulating radioactivity in plasma was unchanged cobicistat. Low levels of metabolites are observed in urine and faeces and do not contribute to the CYP3A inhibitory activity of cobicistat.
Emtricitabine
In vitro studies indicate that emtricitabine is not an inhibitor of human CYP enzymes. Following administration of [14C]-emtricitabine, complete recovery of the emtricitabine dose was achieved in urine (approximately 86%) and faeces (approximately 14%). Thirteen percent of the dose was recovered in the urine as three putative metabolites. The biotransformation of emtricitabine includes oxidation of the thiol moiety to form the 3'-sulfoxide diastereomers (approximately 9% of dose) and conjugation with glucuronic acid to form 2'-O-glucuronide (approximately 4% of dose). No other metabolites were identifiable.
Tenofovir alafenamide
Metabolism is a major elimination pathway for tenofovir alafenamide in humans, accounting for > 80% of an oral dose. In vitro studies have shown that tenofovir alafenamide is metabolised to tenofovir (major metabolite) by cathepsin A in PBMCs (including lymphocytes and other HIV target cells) and macrophages; and by carboxylesterase-1 in hepatocytes. In vivo, tenofovir alafenamide is hydrolysed within cells to form tenofovir (major metabolite), which is phosphorylated to the active metabolite tenofovir diphosphate.
In vitro, tenofovir alafenamide is not metabolised by CYP1A2, CYP2C8, CYP2C9, CYP2C19, or CYP2D6. Tenofovir alafenamide is minimally metabolised by CYP3A4. Upon co-administration with the moderate CYP3A inducer probe efavirenz, tenofovir alafenamide exposure was not significantly affected. Following administration of tenofovir alafenamide, plasma [14C]-radioactivity showed a time-dependent profile with tenofovir alafenamide as the most abundant species in the initial few hours and uric acid in the remaining period.
Elimination
Darunavir
After a 400/100 mg [14C]-darunavir with ritonavir dose, approximately 79.5% and 13.9% of the administered dose of [14C]-darunavir could be retrieved in faeces and urine, respectively. Unchanged darunavir accounted for approximately 41.2% and 7.7% of the administered dose in faeces and urine, respectively.
The intravenous clearance of darunavir alone (150 mg) and in the presence of low dose (100 mg) ritonavir was 32.8 l/h and 5.9 l/h, respectively. The median terminal plasma half-life of darunavir following administration of Symtuza is 5.5 hours.
Cobicistat
Following oral administration of [14C]-cobicistat, 86% and 8.2% of the dose were recovered in faeces and urine, respectively. The median terminal plasma half-life of cobicistat following administration of Symtuza is 3.6 hours.
Emtricitabine
Emtricitabine is primarily excreted by the kidneys with complete recovery of the dose achieved in urine (approximately 86%) and faeces (approximately 14%). Thirteen percent of the emtricitabine dose was recovered in urine as three metabolites. The systemic clearance of emtricitabine averaged 307 mL/min. Following oral administration of Symtuza, the median terminal elimination half-life of emtricitabine is 17.2 hours.
Tenofovir alafenamide
Tenofovir alafenamide is mainly eliminated following metabolism to tenofovir. The median terminal elimination half–life of tenofovir alafenamide was 0.3 hours when administered as Symtuza. Tenofovir is eliminated from the body by the kidneys by both glomerular filtration and active tubular secretion. Tenofovir has a median plasma half-life of approximately 32 hours. Renal excretion of intact tenofovir alafenamide is a minor pathway with less than 1% of the dose eliminated in urine. The pharmacologically active metabolite, tenofovir diphosphate, has a half-life of 150-180 hours within PBMCs.
Special populations
Paediatric population
The pharmacokinetics of Symtuza have not been investigated in paediatric patients. However, there are pharmacokinetic data for the different components of Symtuza, indicating that doses of 800 mg darunavir, 150 mg cobicistat, 200 mg emtricitabine and 10 mg tenofovir alafenamide result in similar exposures in adults and adolescents aged 12 years and older, weighing at least 40 kg.
Elderly
Limited PK information is available in the elderly (age ≥ 65 years of age) for Symtuza as well as its individual components.
Population pharmacokinetic analysis in HIV infected patients showed that darunavir pharmacokinetics are not considerably different in the age range (18 to 75 years) evaluated in HIV infected patients (N = 12, age ≥ 65 years) (see section 4.4).
No clinically relevant pharmacokinetic differences due to age have been identified for cobicistat, emtricitabine or tenofovir alafenamide in the age range ≤ 65 years.
Gender
Population pharmacokinetic analysis showed a slightly higher darunavir exposure (16.8%) in HIV-1 infected females compared to males. This difference is not clinically relevant.
No clinically relevant pharmacokinetic differences due to gender have been identified for cobicistat, emtricitabine or tenofovir alafenamide.
Renal impairment
Symtuza has not been investigated in patients with renal impairment. There are pharmacokinetic data for the (individual) components of Symtuza.
Darunavir
Results from a mass balance study with [14C]-darunavir with ritonavir showed that approximately 7.7% of the administered dose of darunavir is excreted in the urine unchanged.
Although darunavir has not been studied in patients with renal impairment, population pharmacokinetic analysis showed that the pharmacokinetics of darunavir were not significantly affected in HIV infected patients with moderate renal impairment (eGFRCG between 30-60 mL/min, N = 20) (see sections 4.2 and 4.4).
Cobicistat
A trial of the pharmacokinetics of cobicistat was performed in non-HIV-1 infected subjects with severe renal impairment (eGFRCG below 30 mL/min). No meaningful differences in cobicistat pharmacokinetics were observed between subjects with severe renal impairment and healthy subjects, consistent with low renal clearance of cobicistat.
Emtricitabine
Mean systemic emtricitabine exposure was higher in patients with severe renal impairment (eGFRCG < 30 mL/min) (33.7 mcg•h/mL) than in subjects with normal renal function (11.8 mcg•h/mL).
Tenofovir alafenamide
No clinically relevant differences in tenofovir alafenamide, or tenofovir pharmacokinetics were observed between healthy subjects and patients with severe renal impairment (eGFRCG > 15 but < 30 mL/min) in studies of tenofovir alafenamide. There are no pharmacokinetic data on tenofovir alafenamide in patients with eGFRCG < 15 mL/min.
Hepatic impairment
Symtuza has not been investigated in patients with hepatic impairment. There are pharmacokinetic data for the (individual) components of Symtuza.
Darunavir
Darunavir is primarily metabolised and eliminated by the liver. In a multiple dose trial with darunavir/ritonavir (600/100 mg) twice daily, it was demonstrated that the total plasma concentrations of darunavir in subjects with mild (Child-Pugh Class A, N = 8) and moderate (Child-Pugh Class B, N = 8) hepatic impairment were comparable with those in healthy subjects. However, unbound darunavir concentrations were approximately 55% (Child-Pugh Class A) and 100% (Child-Pugh Class B) higher, respectively. The clinical relevance of this increase is unknown. The effect of severe hepatic impairment on the pharmacokinetics of darunavir has not been studied (see sections 4.2, 4.3 and 4.4).
Cobicistat
Cobicistat is primarily metabolised and eliminated by the liver. A trial of the pharmacokinetics of cobicistat was performed in non-HIV-1 infected subjects with moderate hepatic impairment (Child-Pugh Class B). No clinically relevant differences in cobicistat pharmacokinetics were observed between subjects with moderate impairment and healthy subjects. The effect of severe hepatic impairment (Child-Pugh Class C) on the pharmacokinetics of cobicistat has not been studied.
Emtricitabine
The pharmacokinetics of emtricitabine have not been studied in patients with hepatic impairment; however, emtricitabine is not significantly metabolised by liver enzymes, so the impact of liver impairment should be limited.
Tenofovir alafenamide
Clinically relevant changes in tenofovir pharmacokinetics in patients with hepatic impairment were not observed in patients with mild to moderate hepatic impairment. The effect of severe hepatic impairment (Child-Pugh Class C) on the pharmacokinetics of tenofovir alafenamide has not been studied.
Hepatitis B and/or hepatitis C virus co-infection
There were insufficient pharmacokinetic data in the clinical trials to determine the effect of hepatitis B and/or C virus infection on the pharmacokinetics of darunavir,cobicistat, emtricitabine, or tenofovir alafenamide (refer to sections 4.4 and 4.8).
Pregnancy and postpartum
Treatment with darunavir/cobicistat 800/150 mg once daily during pregnancy results in low darunavir exposure (see Table 8). In women receiving darunavir/cobicistat during the second trimester of pregnancy, mean intra-individual values for total darunavir Cmax, AUC24h and Cmin were 49%, 56% and 92% lower, respectively, as compared with postpartum; during the third trimester of pregnancy, total darunavir Cmax, AUC24h and Cmin values were 37%, 50% and 89% lower, respectively, as compared with postpartum. The unbound fraction was also substantially reduced, including around 90% reductions of Cmin levels. The main cause of these low exposures is a marked reduction in cobicistat exposure as a consequence of pregnancy-associated enzyme induction (see below).
Table 8
| Pharmacokinetic results of total darunavir after administration of darunavir/cobicistat 800/150 mg once daily as part of an antiretroviral regimen, during the second trimester of pregnancy, the third trimester of pregnancy, and postpartum |
| Pharmacokinetics of total darunavir (mean ± SD) | Second trimester of pregnancy N = 7 | Third trimester of pregnancy N = 6 | Postpartum (6-12 weeks) N = 6 |
| Cmax, ng/mL | 4 340 ± 1 616 | 4 910 ± 970 | 7 918 ± 2 199 |
| AUC24h, ng.h/mL | 47 293 ± 19 058 | 47 991 ± 9 879 | 99 613 ± 34 862 |
| Cmin, ng/mL | 168 ± 149 | 184 ± 99 | 1 538 ± 1 344 |
The exposure to cobicistat was lower during pregnancy, potentially leading to suboptimal boosting of darunavir. During the second trimester of pregnancy, cobicistat Cmax, AUC24h, and Cmin were 50%, 63%, and 83% lower, respectively, as compared with postpartum. During the third trimester of pregnancy, cobicistat Cmax, AUC24h, and Cmin, were 27%, 49%, and 83% lower, respectively, as compared with postpartum.
No pharmacokinetic data are available for emtricitabine and tenofovir alafenamide during pregnancy.