Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1   Pharmacodynamic properties

Pharmacotherapeutic group: Antiviral for systemic use; nucleoside and nucleotide reverse transcriptase inhibitors, ATC code: J05AF07

Mechanism of action and pharmacodynamic effects
Tenofovir disoproxil fumarate is the fumarate salt of the prodrug tenofovir disoproxil. Tenofovir disoproxil is absorbed and converted to the active substance tenofovir, which is a nucleoside monophosphate (nucleotide) analogue. Tenofovir is then converted to the active metabolite, tenofovir diphosphate, an obligate chain terminator, by constitutively expressed cellular enzymes. Tenofovir diphosphate has an intracellular half-life of 10 hours in activated and 50 hours in resting peripheral blood mononuclear cells (PBMCs). Tenofovir diphosphate inhibits HIV-1 reverse transcriptase and the HBV polymerase by direct binding competition with the natural deoxyribonucleotide substrate and, after incorporation into DNA, by DNA chain termination. Tenofovir diphosphate is a weak inhibitor of cellular polymerases α, β, and γ. At concentrations of up to 300 µmol/l, tenofovir has also shown no effect on the synthesis of mitochondrial DNA or the production of lactic acid in in vitro assays.

Data pertaining to HIV
HIV antiviral activity in vitro: The concentration of tenofovir required for 50% inhibition (EC50) of the wild-type laboratory strain HIV-1IIIB is 1-6 µmol/l in lymphoid cell lines and 1.1 µmol/l against primary HIV-1 subtype B isolates in PBMCs. Tenofovir is also active against HIV-1 subtypes A, C, D, E, F, G, and O and against HIVBaL in primary monocyte/macrophage cells. Tenofovir shows activity in vitro against HIV-2, with an EC50 of 4.9 µmol/l in MT-4 cells.

Resistance: Strains of HIV-1 with reduced susceptibility to tenofovir and a K65R mutation in reverse transcriptase have been selected in vitro and in some patients (see Clinical efficacy and safety).
Tenofovir disoproxil should be avoided in antiretroviral-experienced patients with strains harbouring the K65R mutation (see section 4.4). In addition, a K70E substitution in HIV-1 reverse transcriptase has been selected by tenofovir and results in low-level reduced susceptibility to tenofovir.

Clinical studies in treatment-experienced patients have assessed the anti-HIV activity of tenofovir disoproxil 245 mg against strains of HIV-1 with resistance to nucleoside inhibitors. The results indicate that patients whose HIV expressed 3 or more thymidine-analogue associated mutations (TAMs) that included either the M41L or L210W reverse transcriptase mutation showed reduced response to tenofovir disoproxil 245 mg therapy.

Clinical efficacy and safety
The effects of tenofovir disoproxil in treatment-experienced and treatment-naïve HIV-1 infected adults have been demonstrated in trials of 48 weeks and 144 weeks duration, respectively.

In study GS-99-907, 550 treatment-experienced adult patients were treated with placebo or tenofovir disoproxil 245 mg for 24 weeks. The mean baseline CD4 cell count was 427 cells/mm3, the mean baseline plasma HIV-1 RNA was 3.4 log10 copies/ml (78% of patients had a viral load of < 5,000 copies/ml) and the mean duration of prior HIV treatment was 5.4 years. Baseline genotypic analysis of HIV isolates from 253 patients revealed that 94% of patients had HIV-1 resistance mutations associated with nucleoside reverse transcriptase inhibitors, 58% had mutations associated with protease inhibitors and 48% had mutations associated with non-nucleoside reverse transcriptase inhibitors.

At week 24 the time-weighted average change from baseline in log10 plasma HIV-1 RNA levels (DAVG24) was -0.03 log10 copies/ml and -0.61 log10 copies/ml for the placebo and tenofovir disoproxil 245 mg recipients (p < 0.0001). A statistically significant difference in favour of tenofovir disoproxil
245 mg was seen in the time-weighted average change from baseline at week 24 (DAVG24) for CD4 count (+13 cells/mm3 for tenofovir disoproxil 245 mg versus -11 cells/mm3 for placebo, p-value = 0.0008). The antiviral response to tenofovir disoproxil was durable through 48 weeks (DAVG48 was -0.57 log10 copies/ml, proportion of patients with HIV-1 RNA below 400 or 50 copies/ml was 41% and 18% respectively). Eight (2%) tenofovir disoproxil 245 mg treated patients developed the K65R mutation within the first 48 weeks.

The 144-week, double-blind, active controlled phase of study GS-99-903 evaluated the efficacy and safety of tenofovir disoproxil 245 mg versus stavudine when used in combination with lamivudine and efavirenz in HIV-1 infected adult patients naïve to antiretroviral therapy. The mean baseline CD4 cell count was 279 cells/mm3, the mean baseline plasma HIV-1 RNA was 4.91 log10 copies/ml, 19% of patients had symptomatic HIV-1 infection and 18% had AIDS. Patients were stratified by baseline HIV-1 RNA and CD4 count. Forty-three percent of patients had baseline viral loads > 100,000 copies/ml and 39% had CD4 cell counts < 200 cells/ml.

By intent to treat analysis (missing data and switch in antiretroviral therapy (ART) considered as failure), the proportion of patients with HIV-1 RNA below 400 copies/ml and 50 copies/ml at 48 weeks of treatment was 80% and 76% respectively in the tenofovir disoproxil 245 mg arm,
compared to 84% and 80% in the stavudine arm. At 144 weeks, the proportion of patients with HIV-1 RNA below 400 copies/ml and 50 copies/ml was 71% and 68% respectively in the tenofovir disoproxil 245 mg arm, compared to 64% and 63% in the stavudine arm.

The average change from baseline for HIV-1 RNA and CD4 count at 48 weeks of treatment was similar in both treatment groups (-3.09 and -3.09 log10 copies/ml; +169 and 167 cells/mm3 in the tenofovir disoproxil 245 mg and stavudine groups, respectively). At 144 weeks of treatment, the average change from baseline remained similar in both treatment groups (-3.07 and -3.03 log10 copies/ml; +263 and +283 cells/mm3 in the tenofovir disoproxil 245 mg and stavudine groups, respectively). A consistent response to treatment with tenofovir disoproxil 245 mg was seen regardless of baseline HIV-1 RNA and CD4 count.

The K65R mutation occurred in a slightly higher percentage of patients in the tenofovir disoproxil group than the active control group (2.7% versus 0.7%). Efavirenz or lamivudine resistance either preceded or was coincident with the development of K65R in all cases. Eight patients had HIV that expressed K65R in the tenofovir disoproxil 245 mg arm, 7 of these occurred during the first 48 weeks of treatment and the last one at week 96. No further K65R development was observed up to week 144.
One patient in the tenofovir disoproxil arm developed the K70E substitution in the virus. From both the genotypic and phenotypic analyses there was no evidence for other pathways of resistance to tenofovir.

Data pertaining to HBV
HBV antiviral activity in vitro: The in vitro antiviral activity of tenofovir against HBV was assessed in the HepG2 2.2.15 cell line. The EC50 values for tenofovir were in the range of 0.14 to 1.5 µmol/l, with CC50 (50% cytotoxicity concentration) values > 100 µmol/l.

Resistance: No HBV mutations associated with tenofovir disoproxil resistance have been identified (see Clinical efficacy and safety). In cell based assays, HBV strains expressing the rtV173L, rtL180M, and rtM204I/V mutations associated with resistance to lamivudine and telbivudine showed a susceptibility to tenofovir ranging from 0.7- to 3.4-fold that of wild-type virus. HBV strains 
expressing the rtL180M, rtT184G, rtS202G/I, rtM204V and rtM250V mutations associated with resistance to entecavir showed a susceptibility to tenofovir ranging from 0.6- to 6.9-fold that of wild- type virus. HBV strains expressing the adefovir-associated resistance mutations rtA181V and rtN236T showed a susceptibility to tenofovir ranging from 2.9- to 10-fold that of wild-type virus. Viruses containing the rtA181T mutation remained susceptible to tenofovir with EC50 values 1.5-fold that of wild-type virus.

Clinical efficacy and safety
The demonstration of benefit of tenofovir disoproxil in compensated and decompensated disease is based on virological, biochemical and serological responses in adults with HBeAg positive and HBeAg negative chronic hepatitis B. Treated patients included those who were treatment-naïve, lamivudine-experienced, adefovir dipivoxil-experienced and patients with lamivudine and/or adefovir dipivoxil resistance mutations at baseline. Benefit has also been demonstrated based on histological responses in compensated patients.

Experience in patients with compensated liver disease at 48 weeks (studies GS-US-174-0102 and GS-US-174-0103)
Results through 48 weeks from two randomised, phase 3 double-blind studies comparing tenofovir disoproxil to adefovir dipivoxil in adult patients with compensated liver disease are presented in Table 3 below. Study GS-US-174-0103 was conducted in 266 (randomised and treated) HBeAg positive patients while study GS-US-174-0102 was conducted in 375 (randomised and treated) patients negative for HBeAg and positive for HBeAb.

In both of these studies tenofovir disoproxil was significantly superior to adefovir dipivoxil for the primary efficacy endpoint of complete response (defined as HBV DNA levels < 400 copies/ml and Knodell necroinflammatory score improvement of at least 2 points without worsening in Knodell fibrosis). Treatment with tenofovir disoproxil 245 mg was also associated with significantly greater proportions of patients with HBV DNA < 400 copies/ml, when compared to adefovir dipivoxil 10 mg treatment. Both treatments produced similar results with regard to histological response (defined as Knodell necroinflammatory score improvement of at least 2 points without worsening in Knodell fibrosis) at week 48 (see Table 3 below).

In study GS-US-174-0103 a significantly greater proportion of patients in the tenofovir disoproxil group than in the adefovir dipivoxil group had normalised ALT and achieved HBsAg loss at week 48 (see Table 3 below).



Table 3: Efficacy parameters in compensated HBeAg negative and HBeAg positive patients at week 48

Study 174-0102 (HBeAg negative)                Study 174-0103 (HBeAg positive) Parameter                    Tenofovir       Adefovir dipivoxil             Tenofovir       Adefovir dipivoxil disoproxil 245 mg        10 mg                 disoproxil 245 mg        10 mg n = 250            n = 125                     n = 176             n = 90 Complete                        71*                 49                         67*                 12 response (%)a
Histology
Histological response             72                     69                     74                      68 (%)b
Median HBV DNA                  -4.7*                   -4.0                   -6.4*                   -3.7 reduction from baselinec
(log10 copies/ml)
HBV DNA (%)
< 400 copies/ml                  93*                     63                     76*                     13 (< 69 IU/ml)
ALT (%)
Normalised ALTd                   76                     77                     68*                     54 Serology (%)
HBeAg                            n/a                     n/a                   22/21                  18/18 loss/seroconversion
HBsAg                            0/0                     0/0                   3*/1                    0/0 loss/seroconversion
* p-value versus adefovir dipivoxil < 0.05.
a Complete response defined as HBV DNA levels < 400 copies/ml and Knodell necroinflammatory score improvement of at  least 2 points without worsening in Knodell fibrosis.
b Knodell necroinflammatory score improvement of at least 2 points without worsening in Knodell fibrosis.
c Median change from baseline HBV DNA merely reflects the difference between baseline HBV DNA and the limit of  detection (LOD) of the assay.
d The population used for analysis of ALT normalisation included only patients with ALT above ULN at baseline.
 n/a = not applicable.
Tenofovir disoproxil was associated with significantly greater proportions of patients with undetectable HBV DNA (< 169 copies/ml [< 29 IU/ml]; the limit of quantification of the Roche Cobas Taqman HBV assay), when compared to adefovir dipivoxil (study GS-US-174-0102; 91%, 56% and study GS-US-174-0103; 69%, 9%), respectively.

Response to treatment with tenofovir disoproxil was comparable in nucleoside-experienced (n = 51) and nucleoside-naïve (n = 375) patients and in patients with normal ALT (n = 21) and abnormal ALT (n = 405) at baseline when studies GS-US-174-0102 and GS-US-174-0103 were combined. Forty-nine of the 51 nucleoside-experienced patients were previously treated with lamivudine. Seventy-three percent of nucleoside-experienced and 69% of nucleoside-naïve patients achieved complete response to treatment; 90% of nucleoside-experienced and 88% of nucleoside-naïve patients achieved HBV DNA suppression < 400 copies/ml. All patients with normal ALT at baseline and 88% of patients with abnormal ALT at baseline achieved HBV DNA suppression < 400 copies/ml.

Experience beyond 48 weeks in studies GS-US-174-0102 and GS-US-174-0103 In studies GS-US-174-0102 and GS-US-174-0103, after receiving double-blind treatment for 48 weeks (either tenofovir disoproxil 245 mg or adefovir dipivoxil 10 mg), patients rolled over with no interruption in treatment to open-label tenofovir disoproxil. In studies GS-US-174-0102 and GS-US-174-0103, 77% and 61% of patients continued in the study through to 384 weeks, respectively.
At weeks 96, 144, 192, 240, 288 and 384, viral suppression, biochemical and serological responses were maintained with continued tenofovir disoproxil treatment (see Tables 4 and 5 below).



Table 4: Efficacy parameters in compensated HBeAg negative patients at week 96, 144, 192, 240, 288 and 384 open-label treatment

Study 174-0102 (HBeAg negative)
Parametera                    Tenofovir disoproxil 245 mg             Adefovir dipivoxil 10 mg roll over to n = 250                           tenofovir disoproxil 245 mg n = 125
Week                  96b     144e 192g      240i    288l   384o   96c 144f 192h 240j 288m                384p HBV DNA (%)           90       87    84       83      80     74    89    88       87      84     84        76 < 400 copies/ml
(< 69 IU/ml)
ALT (%)               72       73       67       70       68        64       68      70      77       76       74        69 Normalised
ALTd
Serology (%)
HBeAg loss/           n/a      n/a      n/a      n/a      n/a       n/a     n/a     n/a      n/a      n/a      n/a      n/a seroconversion
HBsAg loss/           0/0      0/0      0/0      0/0      0/0       1/1n    0/0     0/0      0/0     0/0k     1/1n      1/1n seroconversion a Based upon Long Term Evaluation algorithm (LTE Analysis) - Patients who discontinued the study at any time prior to week 384 due to a protocol defined endpoint, as well as those completing week 384, are included in the denominator.
b 48 weeks of double-blind tenofovir disoproxil followed by 48 weeks open-label.
c 48 weeks of double-blind adefovir dipivoxil followed by 48 weeks open-label tenofovir disoproxil.
d The population used for analysis of ALT normalisation included only patients with ALT above ULN at baseline.
e 48 weeks of double-blind tenofovir disoproxil followed by 96 weeks open-label.
f 48 weeks of double-blind adefovir dipivoxil followed by 96 weeks open-label tenofovir disoproxil.
g 48 weeks of double-blind tenofovir disoproxil followed by 144 weeks open-label.
h 48 weeks of double-blind adefovir dipivoxil followed by 144 weeks open-label tenofovir disoproxil.
i 48 weeks of double-blind tenofovir disoproxil followed by 192 weeks open-label.
j
48 weeks of double-blind adefovir dipivoxil followed by 192 weeks open-label tenofovir disoproxil.
k One patient in this group became HBsAg negative for the first time at the 240 week visit and was ongoing in the study at  the time of the data cut-off. However, the subject’s HBsAg loss was ultimately confirmed at the subsequent visit.
l 48 weeks of double-blind tenofovir disoproxil followed by 240 weeks open-label.
m 48 weeks of double-blind adefovir dipivoxil followed by 240 weeks open-label tenofovir disoproxil.
n Figures presented are cumulative percentages based upon a Kaplan Meier analysis excluding data collected after the  addition of emtricitabine to open-label tenofovir disoproxil (KM-tenofovir disoproxil).
o 48 weeks of double-blind tenofovir disoproxil followed by 336 weeks open-label.
p 48 weeks of double-blind adefovir dipivoxil followed by 336 weeks open-label tenofovir disoproxil.
 n/a = not applicable.
Table 5: Efficacy parameters in compensated HBeAg positive patients at week 96, 144, 192, 240, 288 and 384 open-label treatment

Study 174-0103 (HBeAg positive)
Parametera                    Tenofovir disoproxil 245 mg              Adefovir dipivoxil 10 mg roll over to n = 176                            tenofovir disoproxil 245 mg n = 90
Week                  96b     144e 192h 240j 288m           384o    96c   144f    192i 240k 288n 384p HBV DNA (%)           76       72    68       64      61     56     74     71      72      66      65       61 < 400 copies/ml
(< 69 IU/ml)
ALT (%)               60       55       56       46       47        47       65      61       59       56       57       56 Normalised
ALTd
Serology (%)
HBeAg loss/           26/      29/      34/     38/      37/        30/     24/      33/      36/      38/      40/     35/ seroconversion        23       23       25      30       25         20      20       26       30       31       31      24 HBsAg loss/           5/       8/       11/     11/      12/        15/     6/        8/      8/       10/      11/     13/ seroconversion         4       6g       8g       8l       8l        12l      5       7g       7g       10l      10l     11l a Based upon Long Term Evaluation algorithm (LTE Analysis) - Patients who discontinued the study at any time prior to week 384 due to a protocol defined endpoint, as well as those completing week 384, are included in the denominator.
b 48 weeks of double-blind tenofovir disoproxil followed by 48 weeks open-label.
c 48 weeks of double-blind adefovir dipivoxil followed by 48 weeks open-label tenofovir disoproxil.



d The population used for analysis of ALT normalisation included only patients with ALT above ULN at baseline.
e 48 weeks of double-blind tenofovir disoproxil followed by 96 weeks open-label.
f 48 weeks of double-blind adefovir dipivoxil followed by 96 weeks open-label tenofovir disoproxil.
g Figures presented are cumulative percentages based upon a Kaplan Meier analysis including data collected after the  addition of emtricitabine to open-label tenofovir disoproxil (KM-ITT).
h 48 weeks of double-blind tenofovir disoproxil followed by 144 weeks open-label.
i 48 weeks of double-blind adefovir dipivoxil followed by 144 weeks open-label tenofovir disoproxil .
j 48 weeks of double-blind tenofovir disoproxil followed by 192 weeks open-label.
k 48 weeks of double-blind adefovir dipivoxil followed by 192 weeks open-label tenofovir disoproxil.
l Figures presented are cumulative percentages based upon a Kaplan Meier analysis excluding data collected after the  addition of emtricitabine to open-label tenofovir disoproxil (KM-tenofovir disoproxil).
m 48 weeks of double-blind tenofovir disoproxil followed by 240 weeks open-label.
n 48 weeks of double-blind adefovir dipivoxil followed by 240 weeks open-label tenofovir disoproxil.
o 48 weeks of double-blind tenofovir disoproxil followed by 336 weeks open-label.
p 48 weeks of double-blind adefovir dipivoxil followed by 336 weeks open-label tenofovir disoproxil.


Paired baseline and week 240 liver biopsy data were available for 331/489 patients who remained in studies GS-US-174-0102 and GS-US-174-0103 at week 240 (see Table 6 below). Ninety-five percent (225/237) of patients without cirrhosis at baseline and 99% (93/94) of patients with cirrhosis at baseline had either no change or an improvement in fibrosis (Ishak fibrosis score). Of the 94 patients with cirrhosis at baseline (Ishak fibrosis score: 5 - 6), 26% (24) experienced no change in Ishak fibrosis score and 72% (68) experienced regression of cirrhosis by week 240 with a reduction in Ishak fibrosis score of at least 2 points.

Table 6: Histological response (%) in compensated HBeAg negative and HBeAg positive subjects at week 240 compared to baseline

Study 174-0102                                       Study 174-0103
(HBeAg negative)                                     (HBeAg positive) Tenofovir disoproxil        Adefovir dipivoxil      Tenofovir disoproxil        Adefovir dipivoxil 245 mg               10 mg roll over to             245 mg               10 mg roll over to n = 250c             tenofovir disoproxil            n = 176c            tenofovir disoproxil 245 mg                                              245 mg n = 125d                                             n = 90d
Histological                        88                       85                         90                        92 responsea,b (%)                [130/148]                   [63/74]                   [63/70]                   [36/39] a The population used for analysis of histology included only patients with available liver biopsy data (Missing = Excluded)  by week 240. Response after addition of emtricitabine is excluded (total of 17 subjects across both studies).
b Knodell necroinflammatory score improvement of at least 2 points without worsening in Knodell fibrosis score.
c 48 weeks double-blind tenofovir disoproxil followed by up to 192 weeks open-label.
d 48 weeks double-blind adefovir dipivoxil followed by up to 192 weeks open-label tenofovir disoproxil.


Experience in patients with HIV co-infection and prior lamivudine experience In a randomised, 48-week double-blind, controlled study of tenofovir disoproxil 245 mg in adult patients co-infected with HIV-1 and chronic hepatitis B with prior lamivudine experience (study ACTG 5127), the mean serum HBV DNA levels at baseline in patients randomised to the tenofovir arm were 9.45 log10 copies/ml (n = 27). Treatment with tenofovir disoproxil 245 mg was associated with a mean change in serum HBV DNA from baseline, in the patients for whom there was 48-week data, of -5.74 log10 copies/ml (n = 18). In addition, 61% of patients had normal ALT at week 48.

Experience in patients with persistent viral replication (study GS-US-174-0106) The efficacy and safety of tenofovir disoproxil 245 mg or tenofovir disoproxil 245 mg plus 200 mg emtricitabine has been evaluated in a randomised, double-blind study (study GS-US-174-0106), in HBeAg positive and HBeAg negative adult patients who had persistent viraemia (HBV DNA ≥ 1,000 copies/ml) while receiving adefovir dipivoxil 10 mg for more than 24 weeks. At baseline, 57% of patients randomised to tenofovir disoproxil versus 60% of patients randomised to emtricitabine plus tenofovir disoproxil treatment group had previously been treated with lamivudine.
Overall at week 24, treatment with tenofovir disoproxil resulted in 66% (35/53) of patients with HBV DNA < 400 copies/ml (< 69 IU/ml) versus 69% (36/52) of patients treated with emtricitabine plus tenofovir disoproxil (p = 0.672). In addition 55% (29/53) of patients treated with tenofovir disoproxil had undetectable HBV DNA (< 169 copies/ml [< 29 IU/ml]; the limit of quantification of the Roche Cobas TaqMan HBV assay) versus 60% (31/52) of patients treated with emtricitabine plus 
tenofovir disoproxil (p = 0.504). Comparisons between treatment groups beyond week 24 are difficult to interpret since investigators had the option to intensify treatment to open-label emtricitabine plus tenofovir disoproxil. Long-term studies to evaluate the benefit/risk of bitherapy with emtricitabine plus tenofovir disoproxil in HBV monoinfected patients are ongoing.

Experience in patients with decompensated liver disease at 48 weeks (study GS-US-174-0108) Study GS-US-174-0108 is a randomised, double-blind, active controlled study evaluating the safety and efficacy of tenofovir disoproxil (n = 45), emtricitabine plus tenofovir disoproxil (n = 45), and entecavir (n = 22), in patients with decompensated liver disease. In the tenofovir disoproxil treatment arm, patients had a mean CPT score of 7.2, mean HBV DNA of 5.8 log10 copies/ml and mean serum ALT of 61 U/l at baseline. Forty-two percent (19/45) of patients had at least 6 months of prior lamivudine experience, 20% (9/45) of patients had prior adefovir dipivoxil experience and 9 of 45 patients (20%) had lamivudine and/or adefovir dipivoxil resistance mutations at baseline. The co-primary safety endpoints were discontinuation due to an adverse event and confirmed increase in serum creatinine ≥ 0.5 mg/dl or confirmed serum phosphate of < 2 mg/dl.

In patients with CPT scores ≤ 9, 74% (29/39) of tenofovir disoproxil, and 94% (33/35) of emtricitabine plus tenofovir disoproxil treatment groups achieved HBV DNA < 400 copies/ml after 48 weeks of treatment.

Overall, the data derived from this study are too limited to draw any definitive conclusions on the comparison of emtricitabine plus tenofovir disoproxil versus tenofovir disoproxil, (see Table 7 below).

Table 7: Safety and efficacy parameters in decompensated patients at week 48 
Study 174-0108
Parameter                           Tenofovir disoproxil           Emtricitabine 200 mg/             Entecavir 245 mg                     tenofovir disoproxil         (0.5 mg or 1 mg) (n = 45)                         245 mg                      n = 22
(n = 45)
Tolerability failure                       3 (7%)                          2 (4%)                    2 (9%) (permanent discontinuation of study drug due to a treatment emergent AE) n (%)a
Confirmed increase in                      4 (9%)                         3 (7%)                     1 (5%) serum creatinine
≥ 0.5 mg/dl from baseline or confirmed serum phosphate of
< 2 mg/dl n (%)b
HBV DNA n (%)                           31/44 (70%)                    36/41 (88%)                 16/22 (73%) < 400 copies/ml n (%)
ALT n (%)                               25/44 (57%)                    31/41 (76%)                 12/22 (55%) Normal ALT
≥ 2 point decrease in                    7/27 (26%)                    12/25 (48%)                 5/12 (42%) CPT from baseline n (%)
Mean change from                             -0.8                          -0.9                        -1.3 baseline in CPT score
Mean change from                             -1.8                          -2.3                        -2.6 baseline in MELD score a   p-value comparing the combined tenofovir-containing arms versus the entecavir arm = 0.622, b   p-value comparing the combined tenofovir-containing arms versus the entecavir arm = 1.000.



Experience beyond 48 weeks in study GS-US-174-0108
Using a noncompleter/switch = failure analysis, 50% (21/42) of subjects receiving tenofovir disoproxil, 76% (28/37) of subjects receiving emtricitabine plus tenofovir disoproxil and 52% (11/21) of subjects receiving entecavir achieved HBV DNA < 400 copies/ml at week 168.

Experience in patients with lamivudine-resistant HBV at 240 weeks (study GS-US-174-0121) The efficacy and safety of 245 mg tenofovir disoproxil was evaluated in a randomised, double-blind study (GS-US-174-0121) in HBeAg positive and HBeAg negative patients (n = 280) with compensated liver disease, viraemia (HBV DNA ≥ 1,000 IU/ml), and genotypic evidence of lamivudine resistance (rtM204I/V +/- rtL180M). Only five had adefovir-associated resistance mutations at baseline. One hundred forty-one and 139 adult subjects were randomised to a tenofovir disoproxil and emtricitabine plus tenofovir disoproxil treatment arm, respectively. Baseline demographics were similar between the two treatment arms: At baseline, 52.5% of subjects were HBeAg negative, 47.5% were HBeAg positive, mean HBV DNA level was 6.5 log10 copies/ml, and mean ALT was 79 U/l, respectively.

After 240 weeks of treatment, 117 of 141 subjects (83%) randomised to tenofovir disoproxil had HBV DNA < 400 copies/ml, and 51 of 79 subjects (65%) had ALT normalisation. After 240 weeks of treatment with emtricitabine plus tenofovir disoproxil, 115 of 139 subjects (83%) had HBV DNA < 400 copies/ml, and 59 of 83 subjects (71%) had ALT normalisation. Among the HBeAg positive subjects randomised to tenofovir disoproxil, 16 of 65 subjects (25%) experienced HBeAg loss, and 8 of 65 subjects (12%) experienced anti-HBe seroconversion through week 240. In the HBeAg positive subjects randomised to emtricitabine plus tenofovir disoproxil, 13 of 68 subjects (19%) experienced HBeAg loss, and 7 of 68 subjects (10%) experienced anti-HBe seroconversion through week 240. Two subjects randomised to tenofovir disoproxil experienced HBsAg loss by Week 240, but not seroconversion to anti-HBs. Five subjects randomised to emtricitabine plus tenofovir disoproxil experienced HBsAg loss, with 2 of these 5 subjects experiencing seroconversion to anti- HBs.

Clinical resistance
Four hundred and twenty-six HBeAg negative (GS-US-174-0102, n = 250) and HBeAg positive (GS-US-174-0103, n = 176) patients initially randomised to double-blind tenofovir disoproxil treatment and then switched to open-label tenofovir disoproxil treatment were evaluated for genotypic changes in HBV polymerase from baseline. Genotypic evaluations performed on all patients with HBV DNA > 400 copies/ml at week 48 (n = 39), 96 (n = 24), 144 (n = 6), 192 (n = 5), 240 (n = 4), 288 (n = 6) and 384 (n = 2) of tenofovir disoproxil monotherapy showed that no mutations associated with tenofovir disoproxil resistance have developed.

Two hundred and fifteen HBeAg negative (GS-US-174-0102, n = 125) and HBeAg positive (GS-US-174-0103, n = 90) patients initially randomised to double-blind adefovir dipivoxil treatment and then switched to open-label tenofovir disoproxil treatment were evaluated for genotypic changes in HBV polymerase from baseline. Genotypic evaluations performed on all patients with HBV DNA > 400 copies/ml at week 48 (n = 16), 96 (n = 5), 144 (n = 1), 192 (n = 2), 240 (n = 1), 288 (n = 1) and 384 (n = 2) of tenofovir disoproxil monotherapy showed that no mutations associated with tenofovir disoproxil resistance have developed.

In study GS-US-174-0108, 45 patients (including 9 patients with lamivudine and/or adefovir dipivoxil resistance mutations at baseline) received tenofovir disoproxil for up to 168 weeks. Genotypic data from paired baseline and on treatment HBV isolates were available for 6/8 patients with HBV DNA > 400 copies/ml at week 48. No amino acid substitutions associated with resistance to tenofovir disoproxil were identified in these isolates. Genotypic analysis was conducted for 5 subjects in the tenofovir disoproxil arm post week 48. No amino acid substitutions associated with tenofovir disoproxil resistance were detected in any subject.

In study GS-US-174-0121, 141 patients with lamivudine resistance substitutions at baseline received tenofovir disoproxil for up to 240 weeks. Cumulatively, there were 4 patients who experienced a viremic episode (HBV DNA>400 copies/ml) at their last timepoint on tenofovir disoproxil. Among 
them, sequence data from paired baseline and on treatment HBV isolates were available for 2 of 4 patients. No amino acid substitutions associated with resistance to tenofovir disoproxil were identified in these isolates.


Paediatric population
HIV-1: In study GS-US-104-0321, 87 HIV-1 infected treatment-experienced patients 12 to < 18 years of age were treated with tenofovir disoproxil (n = 45) or placebo (n = 42) in combination with an optimised background regimen (OBR) for 48 weeks. Due to limitations of the study, a benefit of tenofovir disoproxil over placebo was not demonstrated based on plasma HIV-1 RNA levels at week 24. However, a benefit is expected for the adolescent population based on extrapolation of adult data and comparative pharmacokinetic data (see section 5.2).

In patients who received treatment with tenofovir disoproxil or placebo, mean lumbar spine BMD Z-score was -1.004 and -0.809, and mean total body BMD Z-score was -0.866 and -0.584, respectively, at baseline. Mean changes at week 48 (end of double-blind phase) were -0.215 and -0.165 in lumbar spine BMD Z-score, and -0.254 and -0.179 in total body BMD Z-score for the tenofovir disoproxil and placebo groups, respectively. The mean rate of BMD gain was less in the tenofovir disoproxil group compared to the placebo group. At week 48, six adolescents in the tenofovir disoproxil group and one adolescent in the placebo group had significant lumbar spine BMD loss (defined as > 4% loss). Among 28 patients receiving 96 weeks of treatment with tenofovir disoproxil, BMD Z-scores declined by -0.341 for lumbar spine and -0.458 for total body.

Pharmacokinetic Properties

5.2   Pharmacokinetic properties

Tenofovir disoproxil is a water soluble ester prodrug which is rapidly converted in vivo to tenofovir and formaldehyde.

Tenofovir is converted intracellularly to tenofovir monophosphate and to the active component, tenofovir diphosphate.

Absorption
Following oral administration of tenofovir disoproxil to HIV infected patients, tenofovir disoproxil is rapidly absorbed and converted to tenofovir. Administration of multiple doses of tenofovir disoproxil with a meal to HIV infected patients resulted in mean (%CV) tenofovir Cmax, AUC, and Cmin values of 326 (36.6%) ng/ml, 3,324 (41.2%) ng·h/ml and 64.4 (39.4%) ng/ml, respectively. Maximum tenofovir concentrations are observed in serum within one hour of dosing in the fasted state and within two hours when taken with food. The oral bioavailability of tenofovir from tenofovir disoproxil in fasted patients was approximately 25%. Administration of tenofovir disoproxil with a high fat meal enhanced the oral bioavailability, with an increase in tenofovir AUC by approximately 40% and Cmax by approximately 14%. Following the first dose of tenofovir disoproxil in fed patients, the median Cmax in serum ranged from 213 to 375 ng/ml. However, administration of tenofovir disoproxil with a light meal did not have a significant effect on the pharmacokinetics of tenofovir.

Distribution
Following intravenous administration the steady-state volume of distribution of tenofovir was estimated to be approximately 800 ml/kg. After oral administration of tenofovir disoproxil, tenofovir is distributed to most tissues with the highest concentrations occurring in the kidney, liver and the intestinal contents (preclinical studies). In vitro protein binding of tenofovir to plasma or serum protein was less than 0.7 and 7.2%, respectively, over the tenofovir concentration range 0.01 to 25 µg/ml.

Biotransformation
In vitro studies have determined that neither tenofovir disoproxil nor tenofovir are substrates for the CYP450 enzymes. Moreover, at concentrations substantially higher (approximately 300-fold) than 
those observed in vivo, tenofovir did not inhibit in vitro drug metabolism mediated by any of the major human CYP450 isoforms involved in drug biotransformation (CYP3A4, CYP2D6, CYP2C9, CYP2E1, or CYP1A1/2). Tenofovir disoproxil at a concentration of 100 µmol/l had no effect on any of the CYP450 isoforms, except CYP1A1/2, where a small (6%) but statistically significant reduction in metabolism of CYP1A1/2 substrate was observed. Based on these data, it is unlikely that clinically significant interactions involving tenofovir disoproxil and medicinal products metabolised by CYP450 would occur.

Elimination
Tenofovir is primarily excreted by the kidney by both filtration and an active tubular transport system with approximately 70-80% of the dose excreted unchanged in urine following intravenous administration. Total clearance has been estimated to be approximately 230 ml/h/kg (approximately 300 ml/min). Renal clearance has been estimated to be approximately 160 ml/h/kg (approximately 210 ml/min), which is in excess of the glomerular filtration rate. This indicates that active tubular secretion is an important part of the elimination of tenofovir. Following oral administration the terminal half-life of tenofovir is approximately 12 to 18 hours.

Studies have established the pathway of active tubular secretion of tenofovir to be influx into proximal tubule cell by the human organic anion transporters (hOAT) 1 and 3 and efflux into the urine by the multidrug resistant protein 4 (MRP 4).

Linearity/non-linearity
The pharmacokinetics of tenofovir were independent of tenofovir disoproxil dose over the dose range 75 to 600 mg and were not affected by repeated dosing at any dose level.

Age
Pharmacokinetic studies have not been performed in the elderly (over 65 years of age).

Gender
Limited data on the pharmacokinetics of tenofovir in women indicate no major gender effect.
Ethnicity
Pharmacokinetics have not been specifically studied in different ethnic groups.

Paediatric population
HIV-1: Steady-state pharmacokinetics of tenofovir were evaluated in 8 HIV-1 infected adolescent patients (aged 12 to < 18 years) with body weight ≥ 35 kg. Mean (± SD) Cmax and AUCtau are 0.38 ± 0.13 μg/ml and 3.39 ± 1.22 μg·h/ml, respectively. Tenofovir exposure achieved in adolescent patients receiving oral daily doses of tenofovir disoproxil 245 mg was similar to exposures achieved in adults receiving once-daily doses of tenofovir disoproxil 245 mg.


Renal impairment
Pharmacokinetic parameters of tenofovir were determined following administration of a single dose of tenofovir disoproxil 245 mg to 40 non-HIV, non-HBV infected adult patients with varying degrees of renal impairment defined according to baseline creatinine clearance (CrCl) (normal renal function when CrCl > 80 ml/min; mild with CrCl = 50-79 ml/min; moderate with CrCl = 30-49 ml/min and severe with CrCl = 10-29 ml/min). Compared with patients with normal renal function, the mean (%CV) tenofovir exposure increased from 2,185 (12%) ng·h/ml in subjects with CrCl > 80 ml/min to respectively 3,064 (30%) ng·h/ml, 6,009 (42%) ng·h/ml and 15,985 (45%) ng·h/ml in patients with mild, moderate and severe renal impairment. The dosing recommendations in patients with renal impairment, with increased dosing interval, are expected to result in higher peak plasma concentrations and lower Cmin levels in patients with renal impairment compared with patients with normal renal function. The clinical implications of this are unknown.



In patients with end-stage renal disease (ESRD) (CrCl < 10 ml/min) requiring haemodialysis, between dialysis tenofovir concentrations substantially increased over 48 hours achieving a mean Cmax of 1,032 ng/ml and a mean AUC0-48h of 42,857 ng·h/ml.

It is recommended that the dosing interval for tenofovir disoproxil 245 mg is modified in adult patients with creatinine clearance < 50 ml/min or in patients who already have ESRD and require dialysis (see section 4.2).

The pharmacokinetics of tenofovir in non-haemodialysis patients with creatinine clearance < 10 ml/min and in patients with ESRD managed by peritoneal or other forms of dialysis have not been studied.

The pharmacokinetics of tenofovir in paediatric patients with renal impairment have not been studied.
No data are available to make dose recommendations (see sections 4.2 and 4.4).

Hepatic impairment
A single 245 mg dose of tenofovir disoproxil was administered to non-HIV, non-HBV infected adult patients with varying degrees of hepatic impairment defined according to Child-Pugh-Turcotte (CPT) classification. Tenofovir pharmacokinetics were not substantially altered in subjects with hepatic impairment suggesting that no dose adjustment is required in these subjects. The mean (%CV) tenofovir Cmax and AUC0-∞ values were 223 (34.8%) ng/ml and 2,050 (50.8%) ng·h/ml, respectively, in normal subjects compared with 289 (46.0%) ng/ml and 2,310 (43.5%) ng·h/ml in subjects with moderate hepatic impairment, and 305 (24.8%) ng/ml and 2,740 (44.0%) ng·h/ml in subjects with severe hepatic impairment.

Intracellular pharmacokinetics
In non-proliferating human peripheral blood mononuclear cells (PBMCs) the half-life of tenofovir diphosphate was found to be approximately 50 hours, whereas the half-life in phytohaemagglutinin- stimulated PBMCs was found to be approximately 10 hours.