Natesto (Page 4 of 5)


12.1. Mechanism of Action

Endogenous androgens, including testosterone and dihydrotestosterone (DHT), are responsible for the normal growth and development of the male sex organs and for maintenance of secondary sex characteristics. These effects include the growth and maturation of the prostate, seminal vesicles, penis, and scrotum; the development of male hair distribution, such as facial, pubic, chest, and axillary hair; laryngeal enlargement, vocal cord thickening, alterations in body musculature, and fat distribution. Testosterone and DHT are necessary for the normal development of secondary sex characteristics.

Male hypogonadism, a clinical syndrome resulting from insufficient secretion of testosterone, has two main etiologies. Primary hypogonadism is caused by defects of the gonads, such as Klinefelter’s syndrome or Leydig cell aplasia, whereas secondary hypogonadism is the failure of the hypothalamus (or pituitary) to produce sufficient gonadotropins (FSH, LH).

12.2. Pharmacodynamics

No specific pharmacodynamic studies were conducted using Natesto.

12.3. Pharmacokinetics


Natesto delivers physiologic amounts of testosterone, producing circulating concentrations that approximate normal testosterone concentrations (i.e., 300 to 1,050 ng/dL) seen in healthy men. The maximum concentration for Natesto is achieved within approximately 40 minutes of administration and has a half-life ranging from 10 to 100 minutes.

Figure 1 summarizes the pharmacokinetic profiles of total testosterone in patients completing 90 days of Natesto treatment administered as 33 mg of testosterone daily (11 mg three times daily).

Figure 1: Mean Serum Total Testosterone Concentrations on Day 90 Following Natesto Administered As 11 mg of Testosterone Three Times Daily (N=69)

Figure 1
(click image for full-size original)

The average daily testosterone concentration produced by Natesto administered as 11 mg of testosterone three times daily on Day 90 was 421 (± 116) ng/dL.


Circulating testosterone is primarily bound in the serum to sex hormone-binding globulin (SHBG) and albumin. Approximately 40% of testosterone in plasma is bound to SHBG, 2% remains unbound (free), and the rest is loosely bound to albumin and other proteins.


Testosterone is metabolized to various 17-keto steroids through 2 different pathways. The major active metabolites of testosterone are estradiol and dihydrotestosterone (DHT).

DHT concentrations increased in parallel with testosterone concentrations during Natesto treatment. After 90 days of treatment, the mean DHT/testosterone ratio was 0.09 which was within the normal range.


About 90% of a dose of testosterone given intramuscularly is excreted in the urine as glucuronic and sulfuric acid conjugates of testosterone and its metabolites; about 6% of a dose is excreted in the feces, mostly in the unconjugated form. Inactivation of testosterone occurs primarily in the liver.

Drug Interactions

Use in patients with allergic rhinitis and oxymetazoline: The effects of allergic rhinitis and the use of oxymetazoline on the absorption of testosterone were investigated in a 3-way cross-over clinical study. Eighteen males with seasonal allergic rhinitis received 3 doses of 11 mg of testosterone intranasally (testosterone dose of 33 mg/day) while they were in the asymptomatic, symptomatic, and symptomatic but treated (with oxymetazoline) states using an environmental challenge chamber model.

Serum total testosterone concentrations were decreased by 21 to 24% in males with symptomatic allergic rhinitis. A 2.6% decrease in mean AUC(0-24) and 3.6% decrease in mean Cmax of total testosterone was observed in males with symptomatic seasonal rhinitis when treated with oxymetazoline 30 minutes prior to Natesto compared to when left untreated. Oxymetazoline does not impact the absorption of testosterone when concomitantly administered with Natesto [see Clinical Pharmacology ( 12.3)]. Drug interaction potential with nasally administered drugs other than oxymetazoline has not been studied.


13.1. Carcinogenesis, Mutagenesis, and Impairment of Fertility


Testosterone has been tested by subcutaneous injection and implantation in mice and rats. In mice, the implant induced cervical-uterine tumors, which metastasized in some cases. There is suggestive evidence that injection of testosterone into some strains of female mice increases their susceptibility to hepatoma. Testosterone is also known to increase the number of tumors and decrease the degree of differentiation of chemically induced carcinomas of the liver in rats.


Testosterone was negative in the in vitro Ames and in the in vivo mouse micronucleus assays.

Impairment of Fertility

The administration of exogenous testosterone has been reported to suppress spermatogenesis in the rat, dog and non-human primates, which was reversible on cessation of the treatment.


14.1. Testosterone Replacement Therapy

Natesto was evaluated for efficacy in a 90-day, open-label, multicenter study of 306 hypogonadal men. Eligible patients were 18 years of age and older (mean age 54 years) and had morning serum total testosterone concentrations less than 300 ng/dL. Patients were Caucasian (89%), African-American (6%), Asian (5%), or of other ethnicities (less than 1%).

Patients were instructed to self-administer Natesto (11 mg of testosterone) intranasally either two or three times daily.

The primary endpoint was the percentage of patients with an average serum total testosterone concentration (Cavg ) within the normal range (300 to 1050 ng/dL) on Day 90.

The secondary endpoint was the percentage of patients with a maximum total testosterone concentration (Cmax ) above three predetermined limits: greater than 1500 ng/dL, between 1800 and 2500 ng/dL, and greater than 2500 ng/dL.

A total of 78 hypogonadal men received Natesto (11 mg of testosterone) three times daily (33 mg of testosterone daily). Of these, a total of 73 hypogonadal men were included in the statistical evaluation of efficacy (total testosterone pharmacokinetics) on Day 90 based on the intent-to-treat (ITT) population with last observation carried forward (LOCF). Ninety percent (90%) of these 73 patients had a Cavg within the normal range (300 to 1050 ng/dL) on Day 90. The percentages of patients with Cavg below the normal range (less than 300 ng/dL) and above the normal range (greater than 1050 ng/dL) on Day 90 were 10% and 0%, respectively.

Table 3 summarizes the mean (SD) serum total testosterone concentrations on Day 90 in 69 patients who had a full pharmacokinetic sampling profile and were treated with Natesto (11 mg of testosterone) three times daily for 90 days.

Table 3: Mean (SD) Serum Total Testosterone Concentrations on Day 90 Following Administration of Natesto (11 mg of testosterone) Three Times Daily

Cavg = average concentration; Cmax = maximum concentration; Cmin = minimum concentration.

Natesto (11 mg of testosterone) Three Times Daily (N=69)
Cavg (ng/dL) 421 (116)
Cmax (ng/dL) 1044 (378)
Cmin (ng/dL) 215 (74)

The percentages of patients with Cmax greater than 1500 ng/dL and between 1800 and 2500 ng/dL were 15.9% and 1.4%, respectively. No patient had a Cmax greater than 2500 ng/dL.

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