A total of 49 HIV-1-infected subjects (8 females, 41 males) were enrolled in the four cohorts between 6 May 1997 and 18 May 1999 (15 in the 75-mg cohort, 10 in the 150-mg cohort, 11 in the 300-mg cohort, and 13 in the 600-mg cohort). Thirty-eight subjects were assigned to receive the active drug (12 at 75 mg, 8 at 150 mg, 8 at 300 mg, and 10 at 600 mg). All of the 11 other study subjects received a placebo.
The five study groups (pooled placebo and 75, 150, 300, and 600 mg of tenofovir DF) were similar in age and race (Table ). Although the proportion of subjects who had received prior antiretroviral therapy varied in the four groups, the differences were not significant (Table ). Most of the antiretroviral agents used prior to study were nucleoside analogues. There were no significant differences in median baseline log10 HIV-1 RNA levels or median baseline CD4 counts among the four groups (Table ).
Characteristics of the study subject population at study entry
Median steady-state concentration-versus-time curves on day 15 are shown in Fig. . Median tenofovir pharmacokinetic parameters obtained on study days 1, 8, 15, and 35 are shown in Table . Median peak tenofovir concentrations (Cmax) were proportional to dose. The times required to reach maximum drug concentrations (Tmax) were similar for all doses in the fasted state (0.5 to 1.0 h) and were increased by 0.5 to 2.2 h when the drug was administered with food. In the 75- and 150-mg dose cohorts, many tenofovir concentrations during the pharmacokinetic sampling period were below the limit of quantitation of the bioanalytical assay, resulting in limited calculation of pharmacokinetic parameters (Cmax, Tmax) for these cohorts on some visits.
Steady-state concentrations of tenofovir in serum after 7 days of daily oral dosing of HIV-1-infected subjects with tenofovir DF. Data are the median and range for the evaluable (eight or nine) subjects at each dose level.
Median tenofovir pharmacokinetic parameters on study days 1, 8, 15, and 35
Median steady-state pharmacokinetic parameters evaluated on day 15 (and day 35 where applicable) were dose linear across all dose groups. There were no changes in pharmacokinetic parameters over time as assessed by comparison of total drug exposure following the first dose versus at steady state. The total tenofovir exposure over the dosing interval at steady state for the 300- and 600-mg doses was similar to the total tenofovir exposure following the first dose, indicating no unexpected drug accumulation. For the 300- and 600-mg dose cohorts, following the achievement of Cmax, tenofovir concentrations in serum declined in a biphasic manner with terminal half-lives between 12 and 15 h, regardless of the feeding state or pharmacokinetic sampling period. The apparent serum and renal clearances of tenofovir exceeded the calculated creatinine clearance, indicating active tubular secretion of tenofovir by the kidneys.
Oral bioavailability of tenofovir was estimated by using historical data obtained in an evaluation of a 1-mg/kg intravenous dose (3
). Oral bioavailability was enhanced by administration with a high-fat meal. The oral bioavailability of the 300- and 600-mg doses of tenofovir DF were estimated to be 25 and 21%, respectively, in the fasted state and 39 and 34%, respectively, in the fed state. The median steady-state levels of tenofovir in serum after administration of eight consecutive doses of 150, 300, and 600 mg of tenofovir DF were 35, 63, and 131%, respectively, of that measured following the administration of a 1-mg/kg intravenous tenofovir dose. Calculated creatinine clearance was not affected by repeated administration of tenofovir DF at any dose level.
The plasma HIV-1 RNA responses in the subjects in the four tenofovir DF arms and the combined placebo arm are shown in Fig. . After administration of a single oral dose of tenofovir DF, median decreases in HIV-1 RNA levels in plasma at day 4 were seen in the 150-mg dose group (−0.20 log10 copies/ml) and in the 300-mg dose group (−0.33 log10 copies/ml). Compared to the placebo group, statistically significant median changes were seen for all tenofovir dose groups at day 35: −0.33 log10 copies/ml (P = 0.003) for the 75-mg dose group, −0.44 log10 copies/ml (P = 0.0002) for the 150-mg dose group, −1.22 log10 copies/ml (P = 0.0004) for the 300-mg dose group, and −0.80 log10 copies/ml (P = 0.0002) for the 600-mg dose group. The median decrease in log10 HIV-1 RNA after 28 days of dosing was greater for subjects in the 300-mg dose group than for those the 150-mg dose group (P = 0.03) and those in the 75-mg dose group (P = 0.0005) but not statistically significantly different for those in the 600-mg dose group.
Median changes in HIV-1 RNA in plasma from the baseline among placebo-treated subjects and the three tenofovir DF (TDF)-treated dose groups of patients (as-treated analysis).
The 300-mg dose group contained eight patients, of whom four had had no previous treatment. The median decrease in log10 HIV-1 RNA after 28 days of dosing in the untreated patients was −1.57 log10 copies/ml, while the median decrease in the previously treated patients was −0.97 log10 copies/ml.
Although all of the groups experienced increases in CD4 counts that ranged from 17 to 64 cells/mm3 in the 300- and 600-mg dose group, respectively, none of these changes were significant.
Baseline and day 35 RT sequences (amino acids 1 to 300) of HIV-1 from the plasma of all tenofovir-treated subjects in the 75-, 150-, 300-, and 600-mg dosing cohorts were analyzed. No subject developed detectable RT sequence changes during the 4-week dosing period. A total of nine subjects had HIV-1 expressing nucleoside-associated RT mutations at baseline (Table ). The 3TC-associated M184V mutation was identified in the baseline plasma HIV-1 from eight subjects (75 mg, one subject; 150 mg, five subjects; 600 mg, two subjects) treated with tenofovir. By day 35, this mutation was no longer detectable in four of the eight subjects, consistent with previous reports of impaired fitness of M184V-expressing HIV-1. Three subjects expressed 3TC-thymidine analog-associated resistance mutations at baseline, either as mixtures or as full mutants (75 mg, one subject; 600 mg, two subjects; Table ). These mutations were maintained through day 35 in most subjects; one subject (subject I) demonstrated the loss of an unusual T69A mutation but maintained the M41L and T215Y mutations as mixtures of the mutant and the wild type. Sequence data from patients with detectable mutations have been deposited with GenBank (accession numbers AF375228 to AF375241).
Genotypic analysis of RT of tenofovir DF-treated subjects with baseline nucleoside-associated RT mutations
Safety and tolerance.
Forty-nine subjects entered the study; 41 subjects completed the study. Four subjects discontinued the study drug due to laboratory abnormalities according to protocol: 1 in the placebo group, 1 in the 75-mg group, and 2 in the 300-mg group. One additional subject in the placebo group was removed from the study after administration of a single dose due to high amylase and lipase levels at baseline. Other reasons for removal were patient request and noncompliance (two patients in the placebo group and two in the 600-mg dose group).
Adverse events and laboratory abnormalities of severe or life-threatening severity (grade III or IV) judged to be possibly or probably related to the study drug are shown in Table . A total of six subjects had grade III or greater elevations in serum creatine kinase (CK) levels (i.e., CK levels greater than four times the upper limit of normal) during the study; five of these subjects received tenofovir, and one subject was in the placebo group (Table ). In one subject, CK elevation resolved despite continuation of the active study drug (75-mg group). In four of the other five tenofovir-treated subjects with CK elevation, the CK rise was associated with recent exercise. In two of these four subjects, elevations of serum CK recurred upon repetition of similar exercise 2 to 3 weeks after discontinuation of the study drug. In the remaining subject, CK elevation was associated with cocaine use and alcohol intoxication. Only mild symptoms of fatigue were reported at the time of the CK elevations. There were no sequelae, and no dose relationship was apparent.
Grade III or IV adverse events (severe or life threatening) possibly or probably related to the study drug
Three of the five subjects with grade III or IV elevations in CK had concurrent elevations in aspartate aminotransferase (AST) or alanine aminotransferase (ALT) (to greater than five times the upper limit of normal). Two of these episodes were judged possibly or probably related to the study drug. In each, the timing of the rise and fall of AST and ALT was similar to that of serum CK levels, suggestive of a skeletal muscle rather than a hepatic etiology.
Two subjects experienced severe peripheral neuropathy that occurred when they were off the study drug. One subject in the placebo group had a prior history of peripheral neuropathy and was one of the subjects who experienced a grade IV CK elevation. The other subject, who also had a history of peripheral neuropathy, was in the 300-mg tenofovir DF dose group. Because the recurrence was consistent with the subject's “flares” in the past, his physician considered the event to be possibly related to the study drug.
One subject in the 300-mg group had an isolated rise in serum creatinine (1.7 mg/dl) on day 35. Screening and baseline creatinine values were 0.9 and 1.2 mg/dl, respectively. On the following day, the level was 0.9 mg/dl. All subsequent serum creatinine values were normal in this subject, and there was no proteinuria. No subject in the study had grade III or greater (i.e., >3+) proteinuria.