Sildenafil (Page 5 of 7)

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Sildenafil was not carcinogenic when administered to rats for up to 24 months at 60 mg/kg/day, a dose resulting in total systemic exposure (AUC) to unbound sildenafil and its major metabolite 33 and 37 times, for male and female rats respectively, the human exposure at the RHD of 20 mg TID. Sildenafil was not carcinogenic when administered to male and female mice for up to 21 and 18 months, respectively, at doses up to a maximally tolerated level of 10 mg/kg/day, a dose equivalent to the RHD on a mg/m2 basis.

Sildenafil was negative in in vitro bacterial and Chinese hamster ovary cell assays to detect mutagenicity, and in vitro human lymphocytes and in vivo mouse micronucleus assays to detect clastogenicity.

There was no impairment of fertility in male or female rats given up to 60 mg sildenafil/kg/day, a dose producing a total systemic exposure (AUC) to unbound sildenafil and its major metabolite of 19 and 38 times for males and females, respectively, the human exposure at the RHD of 20 mg TID.

14 CLINICAL STUDIES

Studies of Adults with Pulmonary Arterial Hypertension

Study 1

A randomized, double-blind, placebo-controlled study of sildenafil (Study 1) was conducted in 277 patients with PAH (defined as a mean pulmonary artery pressure of greater than 25 mmHg at rest with a pulmonary capillary wedge pressure less than 15 mmHg). Patients were predominantly World Health Organization (WHO) functional classes II-III. Allowed background therapy included a combination of anticoagulants, digoxin, calcium channel blockers, diuretics, and oxygen. The use of prostacyclin analogues, endothelin receptor antagonists, and arginine supplementation were not permitted. Subjects who had failed to respond to bosentan were also excluded. Patients with left ventricular ejection fraction less than 45% or left ventricular shortening fraction less than 0.2 also were not studied.

Patients were randomized to receive placebo (n=70) or sildenafil tablets 20 mg (n = 69), 40 mg (n = 67) or 80 mg (n = 71) TID for a period of 12 weeks. They had either primary pulmonary hypertension (PPH) (63%), PAH associated with CTD (30%), or PAH following surgical repair of left-to-right congenital heart lesions (7%). The study population consisted of 25% men and 75% women with a mean age of 49 years (range: 18-81 years) and baseline 6-minute walk distance between 100 and 450 meters (mean 343).

The primary efficacy endpoint was the change from baseline at week 12 (at least 4 hours after the last dose) in the 6-minute walk distance. Placebo-corrected mean increases in walk distance of 45-50 meters were observed with all doses of sildenafil tablets. These increases were significantly different from placebo, but the sildenafil dose groups were not different from each other (see Figure 9), indicating no additional clinical benefit from doses higher than 20 mg TID. The improvement in walk distance was apparent after 4 weeks of treatment and was maintained at week 8 and week 12.

Figure 9. Change from Baseline in 6-Minute Walk Distance (meters) at Weeks 4, 8, and 12 in Study 1: Mean (95% Confidence Interval)
(click image for full-size original)

Figure 9. Change from Baseline in 6-Minute Walk Distance (meters) at Weeks 4, 8, and 12 in Study 1: Mean (95% Confidence Interval)

Figure 10 displays subgroup efficacy analyses in Study 1 for the change from baseline in 6-Minute Walk Distance at Week 12 including baseline walk distance, disease etiology, functional class, gender, age, and hemodynamic parameters.

Figure 10. Placebo-Corrected Change From Baseline in 6-Minute Walk Distance (meters) at Week 12 by study subpopulation in Study 1: Mean (95% Confidence Interval)
(click image for full-size original)

Figure 10. Placebo-Corrected Change From Baseline in 6-Minute Walk Distance (meters) at Week 12 by study subpopulation in Study 1: Mean (95% Confidence Interval)

Key: PAH = pulmonary arterial hypertension; CTD = connective tissue disease; PH = pulmonary hypertension; PAP = pulmonary arterial pressure; PVRI = pulmonary vascular resistance index; TID = three times daily.

Patients on all sildenafil doses achieved a statistically significant reduction in mean pulmonary arterial pressure (mPAP) compared to those on placebo. Data from other hemodynamic parameters for the sildenafil 20 mg TID and placebo dosing regimens is displayed in Table 3. The relationship between these effects and improvements in 6-minute walk distance is unknown.

Table 3. Changes from Baseline in Hemodynamic Parameters at Week 12 [mean (95% CI)] for the Sildenafil 20 mg TID and Placebo Group
Placebo (n = 65) *Sildenafil 20 mg TID (n = 65) *
mPAP (mmHg) 0.6 (-0.8, 2.0) -2.1 (-4.3, 0.0)
PVR ( dyns /cm 5 ) 49 (-54, 153) -122 (-217, -27)
SVR ( dyns /cm 5 ) -78 (-197, 41) -167 (-307, -26)
RAP (mmHg) 0.3 (-0.9, 1.5) -0.8 (-1.9, 0.3)
CO (L/min) -0.1 (-0.4, 0.2) 0.4 (0.1, 0.7)
HR (beats/min) -1.3 (-4.1, 1.4) -3.7 (-5.9, -1.4)

mPAP = mean pulmonary arterial pressure; PVR= pulmonary vascular resistance; SVR = systemic vascular resistance; RAP = right atrial pressure; CO = cardiac output; HR = heart rate

*The number of patients per treatment group varied slightly for each parameter due to missing assessments.

Of the 277 treated patients, 259 entered a long-term, uncontrolled extension study. At the end of 1 year, 94% of these patients were still alive. Additionally, walk distance and functional class status appeared to be stable in patients taking sildenafil. Without a control group, these data must be interpreted cautiously.

16 HOW SUPPLIED/STORAGE AND HANDLING

Sildenafil tablets are supplied as white, round shaped convex film-coated tablets containing sildenafil citrate, USP equivalent to the nominally indicated amount of sildenafil as follows:

Sildenafil Tablets
Package Configuration Strength NDC Engraving on Tablet
Bottle of 90 20 mg 0591-3780-19 “WPI” on one side and “3780” on other side

Recommended Storage for Sildenafil Tablets: Store at 20°C to 25°C (68°F to 77°F) [See USP Controlled Room Temperature].

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