Saquinavir clinical pharmacology

# Clinical Pharmacology

## Mechanism of Action
INVIRASE is an antiviral agent 

## Pharmacodynamics
QTcS interval was evaluated in a randomized, placebo and active (moxifloxacin 400 mg once daily) controlled crossover study in 59 healthy adults, with ECG measurements on Day 3. The maximum mean (95% upper confidence bound) differences in QTcS interval from placebo after baseline-correction were 18.9 (22.0) and 30.2 (33.4) ms for 1000/100 mg twice daily and supratherapeutic 1500/100 mg twice daily of INVIRASE/ritonavir, respectively. There is a delayed effect between QTc interval change and drug concentrations, with the maximum placebo-adjusted baseline-corrected QTcS observed at about 12-20 h post-dose. INVIRASE/ritonavir 1500/100 mg twice daily resulted in a Day 3 mean Cmax of INVIRASE approximately 1.4-fold higher than the mean Cmax observed on Day 3 with the approved therapeutic dose in healthy volunteers (within the same study). QTcS in this study was QT/RR0.319 for males and QT/RR0.337 for females, which are similar to Fridericia's correction (QTcF=QT/RR0.3333).
PR and QRS interval prolongations were also noted in subjects receiving INVIRASE/ritonavir in the same study on Day 3. The maximum mean (95% upper confidence bound) difference from placebo in the PR interval after baseline-correction were 28.6 (31.6) and 38.4 (41.4) ms for 1000/100 mg twice daily and supratherapeutic 1500/100 mg twice daily saquinavir/ritonavir respectively. The maximum mean (95% upper confidence bound) difference from placebo in QRS interval after baseline correction were 2.9 (3.9) and 4.4 (5.3) ms for 1000/100 mg twice daily and supratherapeutic 1500/100 mg twice daily INVIRASE/ritonavir respectively. In this study using healthy subjects, PR interval prolongation of >200 ms was also observed in 40% and 47% of subjects receiving INVIRASE/ritonavir 1000/100 mg bid and 1500/100 mg bid, respectively, on Day 3. Three (3%) of subjects in the active control moxifloxacin arm and 5% in the placebo arm experienced PR prolongation of >200 ms.

## Pharmacokinetics
The pharmacokinetics of INVIRASE/ritonavir 1000/100 mg twice daily have been evaluated in HIV-1-infected subjects and healthy subjects. Steady-state saquinavir AUC, Cmax, and Cmin in healthy subjects are approximately 50% higher than observed in HIV-1-infected subjects.

### Adults
Similar bioavailability was demonstrated when INVIRASE 500 mg film-coated tablet (2  500 mg) and INVIRASE 200 mg capsule (5  200 mg) were administered with low-dose ritonavir (100 mg) under fed conditions. The ratio of mean exposures (90% confidence intervals) of tablets vs capsules was 1.10 (1.04-1.16) for AUC0- and 1.19 (1.14-1.25) for Cmax.
Absolute bioavailability of saquinavir administered as INVIRASE averaged 4% (CV 73%, range: 1% to 9%) in 8 healthy volunteers who received a single 600-mg dose (3  200 mg) of saquinavir mesylate following a high-fat breakfast (48 g protein, 60 g carbohydrate, 57 g fat; 1006 kcal). The low bioavailability is thought to be due to a combination of incomplete absorption and extensive first-pass metabolism.
INVIRASE in combination with ritonavir at a dose of 1000/100 mg twice daily provides saquinavir systemic exposures over a 24-hour period that are similar to those achieved with saquinavir soft gel capsules with ritonavir 1000/100 mg twice daily and greater than that achieved with saquinavir soft gel capsules 1200 mg three times daily (see Table 4).
The mean 24-hour AUC after a single 600-mg oral dose (6  100 mg) in healthy volunteers (n=6) was increased from 24 ngh/mL (CV 33%), under fasting conditions, to 161 ngh/mL (CV 35%) when INVIRASE was given following a high-fat breakfast (48 g protein, 60 g carbohydrate, 57 g fat; 1006 kcal). Saquinavir 24-hour AUC and Cmax (n=6) following the administration of a higher calorie meal (943 kcal, 54 g fat) were on average 2 times higher than after a lower calorie, lower fat meal (355 kcal, 8 g fat). The effect of food has been shown to persist for up to 2 hours.
INVIRASE/ritonavir should be taken within 2 hours after a meal.
The mean steady-state volume of distribution following intravenous administration of a 12-mg dose of saquinavir (n=8) was 700 L (CV 39%), suggesting saquinavir partitions into tissues. Saquinavir was approximately 98% bound to plasma proteins over a concentration range of 15 to 700 ng/mL. In 2 subjects receiving saquinavir mesylate 600 mg three times daily, cerebrospinal fluid concentrations were negligible when compared to concentrations from matching plasma samples.
In vitro studies using human liver microsomes have shown that the metabolism of saquinavir is cytochrome P450 mediated with the specific isoenzyme, CYP3A4, responsible for more than 90% of the hepatic metabolism. Based on in vitro studies, saquinavir is rapidly metabolized to a range of mono- and di-hydroxylated inactive compounds. In a mass balance study using 600 mg 14C-saquinavir mesylate (n=8), 88% and 1% of the orally administered radioactivity was recovered in feces and urine, respectively, within 5 days of dosing. In an additional 4 subjects administered 10.5 mg 14C-saquinavir intravenously, 81% and 3% of the intravenously administered radioactivity was recovered in feces and urine, respectively, within 5 days of dosing. In mass balance studies, 13% of circulating radioactivity in plasma was attributed to unchanged drug after oral administration and the remainder attributed to saquinavir metabolites. Following intravenous administration, 66% of circulating radioactivity was attributed to unchanged drug and the remainder attributed to saquinavir metabolites, suggesting that saquinavir undergoes extensive first-pass metabolism.
Systemic clearance of saquinavir was rapid, 1.14 L/h/kg (CV 12%) after intravenous doses of 6, 36, and 72 mg. The mean residence time of saquinavir was 7 hours (n=8).

## Special Populations

### Renal Impairment
Saquinavir pharmacokinetics in patients with renal impairment has not been investigated. Only 1% of saquinavir is excreted in the urine, so the impact of renal impairment on saquinavir elimination would likely be minimal. However, subjects with severe renal impairment or end-stage renal disease (ESRD) have not been studied, and concentrations of saquinavir may be elevated in these populations.

### Hepatic Impairment
The effect of hepatic impairment on the steady state pharmacokinetics of INVIRASE/ritonavir (1000/100 mg bid for 14 days) was investigated in 7 HIV-1-infected subjects with moderate liver impairment (6 with Child-Pugh score of 7 and 1 with Child-Pugh score of 9). The study included a control group consisting of 7 HIV-1-infected subjects with normal hepatic function matched with hepatically impaired subjects for age, gender, weight and tobacco use. The mean (% coefficient of variation in parentheses) values for INVIRASE AUC0-12 and Cmax were 24.3 (102%) ghr/mL and 3.6 (83%) g/mL, respectively, for HIV-1-infected subjects with moderate hepatic impairment. The corresponding values in the control group were 28.5 (71%) ghr/mL and 4.3 (68%) g/mL. The geometic mean ratio (ratio of pharmacokinetic parameters in hepatically impaired subjects to subjects with normal liver function) (90% confidence interval) was 0.7 (0.3 to 1.6) for both AUC0-12 and Cmax, which suggests approximately 30% reduction in saquinavir exposure in subjects with moderate hepatic impairment. No dose adjustment is warranted for INVIRASE in HIV-1-infected patients with mild or moderate hepatic impairment .

### Gender, Race, and Age
A gender difference was observed, with females showing higher saquinavir exposure than males (mean AUC 56% higher, mean Cmax 26% higher), in the relative bioavailability study comparing INVIRASE 500 mg film-coated tablets to the INVIRASE 200 mg capsules in combination with ritonavir. There was no evidence that age and body weight explained the gender difference in this study. A clinically significant difference in safety and efficacy between men and women has not been reported with the approved dosage regimen (saquinavir 1000-mg/ritonavir 100-mg twice daily).
The effect of race on the pharmacokinetics of saquinavir has not been investigated.
The pharmacokinetics of saquinavir have not been evaluated in the elderly.

### Pediatric Subjects
Steady-state pharmacokinetic information is available from HIV-1 infected pediatric subjects from study NV20911. In this study, 5 subjects less than 2 years of age and 13 subjects between 2 and less than 6 years of age received 50 mg per kg saquinavir twice daily (not to exceed 1000 mg twice daily) boosted with ritonavir at 3 mg/kg for subjects with body weight ranging from 5 to <15 kg or 2.5 mg per kg for subjects with body weight ranging from 15 to 40 kg (not to exceed 100 mg twice daily). For subjects unable to swallow the INVIRASE capsules, the contents of INVIRASE 200 mg capsules were mixed with sugar syrup, or sorbitol syrup (for subjects with Type I diabetes or glucose intolerance), jam, or baby formula. The mean steady state saquinavir PK parameters for pediatric subjects 2 to less than 6 years of age were: AUC0-12h 37269  18232 ngh/mL; Ctrough 1811  998 ng/mL; Cmax 5464  2782 ng/mL, and day 3 exposures may be within the range of exposure associated with QT and PR prolongation . The subject number was too low and the pharmacokinetic data too variable in the subjects less than 2 years to establish an appropriate dosing recommendation for this age group. Pharmacokinetic data for subjects ages 6 to 16 years were not available for comparisons with observations from NV20911  as the data from HIVNAT 017 could not be validated.

## Drug Interactions
Table 5 summarizes the effect of saquinavir soft gel capsules and INVIRASE with and without ritonavir on the geometric mean AUC and Cmax of coadministered drugs. Table 6 summarizes the effect of coadministered drugs on the geometric mean AUC and Cmax of saquinavir.