Emtricitabine (Emtriva)

Adverse Reactions from Clinical Trials Experience in Adults

More than 2,000 adult subjects with HIV-1 infection have been treated with EMTRIVA alone or in combination with other antiretroviral agents for periods of 10 days to 200 weeks in clinical trials.

The most common adverse reactions (incidence greater than or equal to 10%, any severity) identified from any of the three large, controlled clinical trials include headache, diarrhea, nausea, fatigue, dizziness, depression, insomnia, abnormal dreams, rash, abdominal pain, asthenia, increased cough, and rhinitis.

In Trials 301A and 303, the most common adverse reactions that occurred in subjects receiving EMTRIVA with other antiretroviral agents were headache, diarrhea, nausea, and rash, which were generally mild to moderate. Approximately 1% of subjects discontinued participation in the clinical trials due to these events. All adverse reactions were reported with similar frequency in EMTRIVA and control treatment groups except for skin discoloration, which was reported with higher frequency in the EMTRIVA-treated group.

Skin discoloration, manifested by hyperpigmentation on the palms or soles, was generally mild and asymptomatic. The mechanism and clinical significance are unknown.

A summary of EMTRIVA treatment-emergent clinical adverse reactions in Trials 301A and 303 is provided in Table 2.

Adverse Reactions from Clinical Trials Experience in Pediatric Subjects

Assessment of adverse reactions in pediatric subjects is based on data from Trial 203, an open label, uncontrolled trial of 116 HIV-1 infected subjects who received FTC through 48 weeks. The adverse reaction profile in pediatric subjects was generally comparable to that observed in clinical trials of EMTRIVA in adult subjects [see Adverse Reactions (6.1)]. Hyperpigmentation was more frequent in children. Additional adverse reactions identified from this trial include anemia.

Selected treatment-emergent adverse events, regardless of causality, reported in subjects during 48 weeks of treatment were the following: infection (44%), hyperpigmentation (32%), increased cough (28%), vomiting (23%), otitis media (23%), rash (21%), rhinitis (20%), diarrhea (20%), fever (18%), pneumonia (15%), gastroenteritis (11%), abdominal pain (10%), and anemia (7%). Treatment-emergent Grades 3−4 laboratory abnormalities were experienced by 9% of pediatric subjects, including elevated amylase (>2.0 × ULN) (n=4), decreased neutrophils (<750/mm³) (n=3), elevated ALT (>5 × ULN) (n=2), elevated CPK (>4 × ULN) (n=2) and one subject each with elevated bilirubin (>3.0 × ULN), elevated GGT (>10 × ULN), elevated lipase (>2.5 × ULN), decreased hemoglobin (<7 g/dL), and decreased glucose (<40 mg/dL).

Pregnancy Exposure Registry

There is a pregnancy exposure registry that monitors pregnancy outcomes in women exposed to EMTRIVA during pregnancy. Healthcare providers are encouraged to register patients by calling the Antiretroviral Pregnancy Registry (APR) at 1-800-258-4263.

Risk Summary

Available data from the APR show no increase in the overall risk of major birth defects with first trimester exposure for emtricitabine (FTC) (2.3%) compared with the background rate for major birth defects of 2.7% in a U.S. reference population of the Metropolitan Atlanta Congenital Defects Program (MACDP) (see Data). The rate of miscarriage for individual drugs is not reported in the APR. In the U.S. general population, the estimated background risk of miscarriage in clinically recognized pregnancies is 15–20%.

In animal reproduction studies, no adverse developmental effects were observed when FTC was administered at exposures ≥60 times that of the recommended daily dose of EMTRIVA (see Data).

Data

Risk Summary

The Centers for Disease Control and Prevention recommend that HIV-1 infected mothers not breastfeed their infants to avoid risking postnatal transmission of HIV-1.

Based on published data, FTC has been shown to be present in human breast milk. It is not known if FTC affects milk production or has effects on the breastfed child.

Because of the potential for: (1) HIV transmission (in HIV-negative infants); (2) developing viral resistance (in HIV-positive infants); and (3) adverse reactions in a breastfed infant similar to those seen in adults, instruct mothers not to breastfeed if they are taking EMTRIVA.

Adults

The pharmacokinetic properties of FTC were evaluated in healthy subjects and HIV-1-infected subjects. Emtricitabine pharmacokinetics are similar between these populations.

Figure 1 shows the mean steady-state plasma FTC concentration-time profile in 20 HIV-1-infected subjects receiving EMTRIVA capsules.

Figure 1 Mean (± 95% CI) Steady-State Plasma FTC Concentrations in HIV-1 Infected Adults (N=20)

Effects of Food on Oral Absorption

EMTRIVA capsules and oral solution may be taken with or without food. Emtricitabine systemic exposure (AUC) was unaffected while C_max decreased by 29% when EMTRIVA capsules were administered with food (an approximately 1000 kcal high-fat meal). Emtricitabine systemic exposure (AUC) and C_max were unaffected when 200 mg EMTRIVA oral solution was administered with either a high-fat or low-fat meal.

Specific Populations

Assessment of Drug Interactions

At concentrations up to 14-fold higher than those observed in vivo, FTC did not inhibit in vitro drug metabolism mediated by any of the following human CYP isoforms: CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4. FTC did not inhibit the enzyme responsible for glucuronidation (uridine-5'-disphosphoglucuronyl transferase). Based on the results of these in vitro experiments and the known elimination pathways of FTC, the potential for CYP-mediated interactions involving FTC with other medicinal products is low.

EMTRIVA has been evaluated in healthy volunteers in combination with TDF, AZT, indinavir, famciclovir, and d4T. Tables 8 and 9 summarize the pharmacokinetic effects of coadministered drug on FTC pharmacokinetics and effects of FTC on the pharmacokinetics of coadministered drug.

Mechanism of Action

FTC, a synthetic nucleoside analog of cytidine, is phosphorylated by cellular enzymes to form emtricitabine 5'-triphosphate (FTC-TP), which inhibits the activity of the HIV-1 reverse transcriptase (RT) by competing with the natural substrate deoxycytidine 5'-triphosphate and by being incorporated into nascent viral DNA resulting in chain termination. FTC-TP is a weak inhibitor of mammalian DNA polymerases α, β, ε, and mitochondrial DNA polymerase γ.

Antiviral Activity

The antiviral activity of FTC against laboratory and clinical isolates of HIV-1 was assessed in lymphoblastoid cell lines, the MAGI-CCR5 cell line, and peripheral blood mononuclear cells. The 50% effective concentration (EC₅₀) values for FTC were in the range of 0.0013–0.64 µM (0.0003–0.158 µg/mL). The median EC₅₀, range, and number of isolates for the laboratory isolates were 0.07, 0.009−0.62, 10; 0.011, 0.002−0.03, 12; 0.055, 0.0015−0.09, 4 respectively for lymphoblastoid, PBMC, and reporter cells. The median EC₅₀, range, and number of isolates for the clinical isolates were 0.05, 0.0105−0.64, 15; 0.015, 0.004−0.028, 6 respectively for lymphoblastoid cells and PBMCs. No antagonism was observed in drug combination studies of emtricitabine with nucleoside reverse transcriptase inhibitors (NRTIs) (abacavir, lamivudine, stavudine, tenofovir, zidovudine), non-nucleoside reverse transcriptase inhibitors (NNRTIs) (delavirdine, efavirenz, nevirapine), and protease inhibitors (amprenavir, nelfinavir, ritonavir, saquinavir). FTC displayed antiviral activity in cell culture against HIV-1 clades A, B, C, D, E, F, and G (EC₅₀ values ranged from 0.007–0.075 µM) and showed strain-specific activity against HIV-2 (EC₅₀ values ranged from 0.007–1.5 µM in PBMCs and MAGI cells).

Resistance

FTC-resistant isolates of HIV-1 have been selected in cell culture and in vivo. Genotypic analysis of these isolates showed that the reduced susceptibility to FTC was associated with a valine or isoleucine (M184V/I) substitution in the HIV-1 RT.

FTC-resistant isolates of HIV-1 have been recovered from some subjects treated with FTC alone or in combination with other antiretroviral agents. In a clinical trial of treatment-naïve subjects treated with EMTRIVA, didanosine, and efavirenz (EFV) [see Clinical Studies (14.2)], viral isolates from 37.5% of subjects with virologic failure showed reduced susceptibility to FTC. Genotypic analysis of these isolates showed that the resistance was due to M184V/I substitutions in the HIV-1 RT.

In a clinical trial of treatment-naïve subjects treated with either EMTRIVA, TDF, and EFV or AZT/3TC and EFV [see Clinical Studies (14.2)], resistance analysis was performed on HIV-1 isolates from all confirmed virologic failure subjects with greater than 400 copies/mL of HIV-1 RNA at Week 144 or early discontinuation. Development of EFV resistance-associated substitutions occurred most frequently and was similar between the treatment arms. The M184V amino acid substitution, associated with resistance to EMTRIVA and 3TC, was observed in 2/19 analyzed subject isolates in the EMTRIVA + TDF group and in 10/29 analyzed subject isolates in the AZT/3TC group. Through 144 weeks of Trial 934, no subjects have developed a detectable K65R substitution in their HIV-1 as analyzed through standard genotypic analysis.

Cross Resistance

Cross-resistance among certain NRTIs has been recognized. FTC-resistant isolates (M184V/I) were cross-resistant to 3TC but retained susceptibility in cell culture to AZT, didanosine, d4T, and tenofovir, and to NNRTIs (delavirdine, EFV, and nevirapine). HIV-1 isolates containing the K65R substitution, selected in vivo by abacavir, didanosine, and tenofovir, demonstrated reduced susceptibility to inhibition by FTC. Viruses harboring substitutions conferring reduced susceptibility to AZT and d4T (M41L, D67N, K70R, L210W, T215Y/F, K219Q/E) or didanosine (L74V) remained sensitive to FTC. HIV-1 containing the K103N substitution associated with resistance to NNRTIs was susceptible to FTC.

Trial 934

Data through 144 weeks are reported for Trial 934, a randomized, open-label, active-controlled multicenter clinical trial comparing EMTRIVA + TDF administered in combination with EFV versus AZT/3TC fixed-dose combination administered in combination with EFV in 511 antiretroviral-naïve subjects. From Weeks 96 to 144 of the trial, subjects received FTC/TDF fixed-dose combination with EFV in place of EMTRIVA + TDF with EFV. Subjects had a mean age of 38 years (range 18–80); 86% were male, 59% were Caucasian, and 23% were Black. The mean baseline CD4+ cell count was 245 cells/mm³ (range 2–1191) and median baseline plasma HIV-1 RNA was 5.01 log₁₀ copies/mL (range 3.56–6.54). Subjects were stratified by baseline CD4+ cell count (< or ≥200 cells/mm³); 41% had CD4+ cell counts <200 cells/mm³ and 51% of subjects had baseline viral loads >100,000 copies/mL. Table 11 provides treatment outcomes through 48 and 144 weeks for those subjects who did not have EFV resistance at baseline.

Through Week 48, 84%, and 73% of subjects in the EMTRIVA + TDF group and the AZT/3TC group, respectively, achieved and maintained HIV-1 RNA <400 copies/mL (71% and 58% through Week 144). The difference in the proportion of subjects who achieved and maintained HIV-1 RNA <400 copies/mL through 48 weeks largely results from the higher number of discontinuations due to adverse events and other reasons in the AZT/3TC group in this open-label trial. In addition, 80% and 70% of subjects in the EMTRIVA + TDF group and the AZT/3TC group, respectively, achieved and maintained HIV-1 RNA <50 copies/mL through Week 48 (64% and 56% through Week 144). The mean increase from baseline in CD4+ cell count was 190 cells/mm³ in the EMTRIVA + TDF group and 158 cells/mm³ in the AZT/3TC group at Week 48 (312 and 271 cells/mm³ at Week 144).

Through 48 weeks, 7 subjects in the EMTRIVA + TDF group and 5 subjects in the AZT/3TC group experienced a new CDC Class C event (10 and 6 subjects through 144 weeks).

Trial 301A

Trial 301A was a 48-week double-blind, active-controlled, multicenter clinical trial comparing EMTRIVA (200 mg once daily) administered in combination with didanosine and EFV versus d4T, didanosine, and EFV in 571 antiretroviral naïve adult subjects. Subjects had a mean age of 36 years (range 18–69); 85% were male, 52% Caucasian, 16% African-American, and 26% Hispanic. Subjects had a mean baseline CD4+ cell count of 318 cells/mm³ (range 5–1317) and a median baseline plasma HIV-1 RNA of 4.9 log₁₀ copies/mL (range 2.6–7.0). Thirty-eight percent of subjects had baseline viral loads >100,000 copies/mL and 31% had CD4+ cell counts <200 cells/mL. Table 12 provides treatment outcomes through 48 weeks.

The mean increase from baseline in CD4+ cell count was 168 cells/mm³ for the EMTRIVA arm and 134 cells/mm³ for the d4T arm.

Through 48 weeks, 5 subjects (1.7%) in the EMTRIVA group experienced a new CDC Class C event compared to 7 subjects (2.5%) in the d4T group.

Trial 303

Trial 303 was a 48-week, open-label, active-controlled, multicenter clinical trial comparing EMTRIVA (200 mg once daily) to 3TC, in combination with d4T or AZT and a protease inhibitor or NNRTI in 440 adult subjects who were on a 3TC-containing triple-antiretroviral drug regimen for at least 12 weeks prior to trial entry and had HIV-1 RNA ≤400 copies/mL.

Subjects were randomized 1:2 to continue therapy with 3TC (150 mg twice daily) or to switch to EMTRIVA (200 mg once daily). All subjects were maintained on their stable background regimen. Subjects had a mean age of 42 years (range 22–80); 86% were male, 64% Caucasian, 21% African-American, and 13% Hispanic. Subjects had a mean baseline CD4+ cell count of 527 cells/mm³ (range 37–1909), and a median baseline plasma HIV-1 RNA of 1.7 log₁₀ copies/mL (range 1.7–4.0).

The median duration of prior antiretroviral therapy was 27.6 months. Table 13 provides treatment outcomes through 48 weeks.

The mean increase from baseline in CD4+ cell count was 29 cells/mm³ for the EMTRIVA arm and 61 cells/mm³ for the 3TC arm.

Through 48 weeks, in the EMTRIVA group 2 subjects (0.7%) experienced a new CDC Class C event compared to 2 subjects (1.4%) in the 3TC group.