Etravirine

Etravirine is an NNRTI of human immunodeficiency virus type 1 (HIV-1). Etravirine binds directly to reverse transcriptase (RT) and blocks the RNA-dependent and DNA-dependent DNA polymerase activities by causing a disruption of the enzyme’s catalytic site.

Antiviral activity in vitro

Etravirine exhibits activity against wild type HIV-1 in T-cell lines and primary cells with median EC₅₀ values ranging from 0.9 to 5.5 nM. Etravirine demonstrates activity against HIV-1 group M (subtypes A, B, C, D, E, F, and G) and HIV-1 group O primary isolates with EC₅₀ values ranging from 0.3 to 1.7 nM and from 11.5 to 21.7 nM, respectively. Although etravirine demonstrates in vitro activity against wild type HIV-2 with median EC₅₀ values ranging from 5.7 to 7.2 μM, treatment of HIV-2 infection with etravirine is not recommended in the absence of clinical data. Etravirine retains activity against HIV-1 viral strains resistant to nucleoside reverse transcriptase and/or protease inhibitors. In addition, etravirine demonstrates a fold change (FC) in EC₅₀ ≤3 against 60% of 6,171 NNRTI-resistant clinical isolates.

Resistance

Etravirine efficacy in relation to NNRTI resistance at baseline has mainly been analysed with etravirine given in combination with darunavir/ritonavir (DUET-1 and DUET-2). Boosted protease inhibitors, like darunavir/ritonavir, show a higher barrier to resistance compared to other classes of antiretrovirals. The breakpoints for reduced efficacy with etravirine (>2 etravirine-associated mutations at baseline) applies when etravirine is given in combination with a boosted protease inhibitor. This breakpoint might be lower in antiretroviral combination therapy not including a boosted protease inhibitor.

In the Phase III trials DUET-1 and DUET-2, mutations that developed most commonly in patients with virologic failure to the etravirine containing regimen were V108I, V179F, V179I, Y181C and Y181I, which usually emerged in a background of multiple other NNRTI resistance-associated mutations (RAMs). In all the other trials conducted with etravirine in HIV-1 infected patients, the following mutations emerged most commonly: L100I, E138G, V179F, V179I, Y181C and H221Y.

Cross-resistance

Following virologic failure of an etravirine-containing regimen it is not recommended to treat patients with efavirenz and/or nevirapine.

The pharmacokinetic properties of etravirine have been evaluated in adult healthy subjects and in adult and paediatric treatment-experienced HIV-1 infected patients. Exposure to etravirine was lower (35-50%) in HIV-1 infected patients than in healthy subjects.

Table 1. Population pharmacokinetic estimates of etravirine 200 mg twice daily in HIV-1 infected adult subjects (integrated data from Phase III trials at week 48)*:

* All HIV-1 infected subjects enrolled in Phase III clinical trials received darunavir/ritonavir 600/100 mg twice daily as part of their background regimen. Therefore, the pharmacokinetic parameter estimates shown in the table account for reductions in the pharmacokinetic parameters of etravirine due to co-administration of etravirine with darunavir/ritonavir.
Note: The median protein binding adjusted EC 50 for MT4 cells infected with HIV-1/IIIB in vitro = 4 ng/ml.

Absorption

An intravenous formulation of etravirine is unavailable, thus, the absolute bioavailability of etravirine is unknown. After oral administration with food, the maximum plasma concentration of etravirine is generally achieved within 4 hours. In healthy subjects, the absorption of etravirine is not affected by co-administration of oral ranitidine or omeprazole, medicinal products that are known to increase gastric pH.

Effect of food on absorption

The systemic exposure (AUC) to etravirine was decreased by about 50% when etravirine was administered under fasting conditions, as compared to administration following a meal. Therefore, etravirine should be taken following a meal.

Distribution

Etravirine is approximately 99.9% bound to plasma proteins, primarily to albumin (99.6%) and α₁-acid glycoprotein (97.66%-99.02%) in vitro. The distribution of etravirine into compartments other than plasma (e.g. cerebrospinal fluid, genital tract secretions) has not been evaluated in humans.

Biotransformation

In vitro experiments with human liver microsomes (HLMs) indicate that etravirine primarily undergoes oxidative metabolism by the hepatic cytochrome CYP450 (CYP3A) system and, to a lesser extent, by the CYP2C family, followed by glucuronidation.

Elimination

After administration of a radiolabeled ¹⁴C-etravirine dose, 93.7% and 1.2% of the administered dose of ¹⁴C-etravirine could be retrieved in faeces and urine, respectively. Unchanged etravirine accounted for 81.2% to 86.4% of the administered dose in faeces. Unchanged etravirine in faeces is likely to be unabsorbed drug. Unchanged etravirine was not detected in urine. The terminal elimination half-life of etravirine was approximately 30-40 hours.

Special populations

Paediatric population (6 years to less than 18 years of age)

The pharmacokinetics of etravirine in 101 treatment-experienced HIV-1 infected paediatric patients, 6 years to less than 18 years of age and weighing at least 16 kg, showed that the administered weight-based dosages resulted in etravirine exposure comparable to that in adults receiving etravirine 200 mg twice daily when administered at a dose corresponding to 5.2 mg/kg twice daily. The population pharmacokinetic estimates for etravirine AUC_12h and C_0h are summarised in the table below.

Table 2. Population pharmacokinetic estimates for etravirine (all doses combined) in treatment-experienced HIV-1 infected paediatric patients 6 years to less than 18 years of age (PIANO 48 week analysis):

Paediatric population (less than 6 years of age)

The pharmacokinetics of etravirine in paediatric patients less than 6 years of age are under investigation. There are insufficient data at this time to recommend a dose in paediatric patients less than 6 years of age or weighing less than 16 kg.

Elderly

Population pharmacokinetic analysis in HIV infected patients showed that etravirine pharmacokinetics are not considerably different in the age range (18 to 77 years) evaluated, with 6 subjects aged 65 years or older.

Gender

No significant pharmacokinetic differences have been observed between males and females. A limited number of females were included in the studies.

Race

Population pharmacokinetic analysis of etravirine in HIV infected patients indicated no apparent difference in the exposure to etravirine between Caucasian, Hispanic and Black subjects. The pharmacokinetics in other races have not been sufficiently evaluated.

Hepatic impairment

Etravirine is primarily metabolised and eliminated by the liver. In a study comparing 8 patients with mild (Child-Pugh Class A) hepatic impairment to 8 matched controls and 8 patients with moderate (Child-Pugh Class B) hepatic impairment to 8 matched controls, the multiple dose pharmacokinetic disposition of etravirine was not altered in patients with mild to moderate hepatic impairment. However, unbound concentrations have not been assessed. Increased unbound exposure could be expected. No dose adjustment is suggested but caution is advised in patients with moderate hepatic impairment. Etravirine has not been studied in patients with severe hepatic impairment (Child-Pugh Class C) and is therefore not recommended.

Hepatitis B and/or hepatitis C virus co-infection

Population pharmacokinetic analysis of the DUET-1 and DUET-2 trials showed reduced clearance (potentially leading to increased exposure and alteration of the safety profile) for etravirine in HIV-1 infected patients with hepatitis B and/or hepatitis C virus co-infection. In view of the limited data available in hepatitis B and/or C co-infected patients, particular caution should be paid when etravirine is used in these patients.

Renal impairment

The pharmacokinetics of etravirine have not been studied in patients with renal insufficiency. Results from a mass balance study with radioactive 14 C-etravirine showed that <1.2% of the administered dose of etravirine is excreted in the urine. No unchanged drug was detected in urine so the impact of renal impairment on etravirine elimination is expected to be minimal. As etravirine is highly bound to plasma proteins, it is unlikely that it will be significantly removed by haemodialysis or peritoneal dialysis.

Pregnancy and postpartum

Study TMC114HIV3015 evaluated etravirine 200 mg twice daily in combination with other antiretroviral medicinal products in 15 pregnant women during the second and third trimesters of pregnancy and postpartum. The total etravirine exposure after intake of etravirine 200 mg twice daily as part of an antiretroviral regimen was generally higher during pregnancy compared with postpartum (see Table 3). The differences were less pronounced for unbound etravirine exposure. In women receiving etravirine 200 mg twice daily, higher mean values for C_max, AUC_12h and C_min were observed during pregnancy compared to postpartum. During the 2^nd and 3^rd trimester of pregnancy mean values of these parameters were comparable.

Table 3. Pharmacokinetic results of total etravirine after administration of etravirine 200 mg twice daily as part of an antiretroviral regimen, during the 2^nd trimester of pregnancy, the 3^rd trimester of pregnancy, and postpartum:

^a n=9 for AUC_12h

Each subject served as her own control, and with an intra-individual comparison, the total etravirine C_min, C_max and AUC_12h values were 1.2-, 1.4- and 1.4-fold higher, respectively, during the 2^nd trimester of pregnancy as compared to postpartum, and 1.1-, 1.4- and 1.2-fold higher, respectively, based during the 3^rd trimester of pregnancy as compared to postpartum.

Animal toxicology studies have been conducted with etravirine in mice, rats, rabbits and dogs. In mice, the key target organs identified were the liver and the coagulation system. Haemorrhagic cardiomyopathy was only observed in male mice and was considered to be secondary to severe coagulopathy mediated via the vitamin K pathway. In the rat, the key target organs identified were the liver, the thyroid and the coagulation system. Exposure in mice was equivalent to human exposure while in rats it was below the clinical exposure at the recommended dose. In the dog, changes were observed in the liver and gall bladder at exposures approximately 8-fold higher than human exposure observed at the recommended dose (200 mg twice daily).

In a study conducted in rats, there were no effects on mating or fertility at exposure levels equivalent to those in humans at the clinically recommended dose. There was no teratogenicity with etravirine in rats and rabbits at exposures equivalent to those observed in humans at the recommended clinical dose. Etravirine had no effect on offspring development during lactation or post weaning at maternal exposures equivalent to those observed at the recommended clinical dose.

Etravirine was not carcinogenic in rats and in male mice. An increase in the incidences of hepatocellular adenomas and carcinomas were observed in female mice. The observed hepatocellular findings in female mice are generally considered to be rodent specific, associated with liver enzyme induction, and of limited relevance to humans. At the highest tested doses, the systemic exposures (based on AUC) to etravirine were 0.6-fold (mice) and between 0.2- and 0.7-fold (rats), relative to those observed in humans at the recommended therapeutic dose (200 mg twice daily). In vitro and in vivo studies with etravirine revealed no evidence of a mutagenic potential.