Edex

EDEX- alprostadil injection, powder, lyophilized, for solution
Actient Pharmaceuticals, LLC

For Intracavernous Use Only

Sterile Powder and Diluent (sterile 0.9% sodium chloride) in Cartridges

Rx Only

DESCRIPTION

edex® (alprostadil for injection) is a sterile, pyrogen-free powder containing alprostadil in an alfadex (α-cyclodextrin) inclusion complex. Alprostadil is an endogenous substance known as prostaglandin E1 (PGE1 ). edex® is supplied in single-dose, dual-chamber cartridges.

edex® is lyophilized in single-dose, dual-chamber cartridges intended for use with the reusable edex® injection device. One chamber of the cartridge contains alprostadil, alfadex and lactose as a sterile, pyrogen-free powder. The other chamber contains 1.075 mL of sterile 0.9% sodium chloride. The edex® cartridges are supplied in three strengths: 10 mcg cartridge (10.75 mcg alprostadil, 347.55 mcg α-cyclodextrin, 51.06 mg lactose); 20 mcg cartridge (21.5 mcg alprostadil, 695.2 mcg α-cyclodextrin, 51.06 mg lactose); 40 mcg cartridge (43.0 mcg alprostadil, 1,390.3 mcg α-cyclodextrin, 51.06 mg lactose). The edex® injection device is used to reconstitute the sterile powder in one chamber with the sterile 0.9% sodium chloride in the other chamber. After reconstitution, the edex® injection device is used to administer the intracavernous injection of alprostadil.

The chemical name for alprostadil is (1R,2R,3R)-3-Hydroxy-2-[(E)-(3S)-3-hydroxy-1-octenyl]-5-oxocyclopentane heptanoic acid. The empirical formula is C20 H34 O5 and the molecular weight is 354.49. The chemical structure is:

alprostadil chemical structure

The α-cyclodextrin inclusion complex improves the water solubility of alprostadil. The empirical formula of α-cyclodextrin is C36 H60 O30 and the molecular weight is 972.85.

The chemical structure is:

 α-cyclodextrin chemical structure

Alprostadil alfadex is a white, odorless, hygroscopic powder. It is freely soluble in water and practically insoluble in ethanol, ethyl acetate and ether. After reconstitution, the active ingredient, alprostadil, immediately dissociates from the α-cyclodextrin inclusion complex. The reconstituted solution is clear and colorless and has a pH between 4.0 and 8.0. When the single-dose, dual-chamber cartridge containing either 10.75, 21.5 or 43.0 mcg of alprostadil is placed into the edex® injection device and reconstituted, the deliverable amount of alprostadil in each milliliter is 10, 20 or 40 micrograms, respectively.

CLINICAL PHARMACOLOGY

Alprostadil (PGE1 ) is one of the prostaglandins, a family of naturally occurring acidic lipids with various pharmacological effects. Endogenous PGE1 is derived from dihomo-gamma-linolenic acid, a fatty acid found within the phospholipids of cellular membranes. As an endogenous substance, PGE1 exerts its biological effects either directly or indirectly by regulating and modifying the synthesis and effects of other hormones and mediators.

Mode of Action

Alprostadil is a smooth muscle relaxant. Precontracted isolated preparations of the human corpus cavernosum, corpus spongiosum and cavernous artery are relaxed by alprostadil. Alprostadil has been shown to bind to specific receptors in human penile tissue. Two types of receptors that differ in their PGE1 binding affinity have been identified. The binding of alprostadil to its receptors is accompanied by an increase in intracellular cAMP levels. Human cavernous smooth muscle cells respond to alprostadil by releasing intracellular calcium into the surrounding medium. Smooth muscle relaxation is associated with a reduction of the cytoplasmic free calcium concentration. Alprostadil also attenuates presynaptic noradrenaline release in the corpus cavernosum which is essential for the maintenance of a flaccid and non-erect penis.

Alprostadil induces erection by relaxation of trabecular smooth muscle and by dilation of cavernous arteries. This leads to expansion of lacunar spaces and entrapment of blood by compressing the venules against the tunica albuginea, a process referred to as the corporal veno-occlusive mechanism.

Pharmacokinetics

Alpha-Cyclodextrin

After reconstitution, PGE1 immediately dissociates from the α-cyclodextrin inclusion complex; the in vivo disposition of both components occurs independently after administration. After intravenous infusion of radiolabeled α-cyclodextrin to healthy volunteers, the radiolabeled components were rapidly eliminated within 24-hours, urine accounting for 81-83% of radioactivity and feces for 0.1%. There was no evidence of significant accumulation of radiolabeled α-cyclodextrin in the body even after 7 days of repeated intravenous injection. After intracavernous administration in monkeys, radiolabeled α-cyclodextrin was rapidly distributed from the injection site with less than 0.1% of the dose remaining in the penis 1 hour after administration. There was no evidence of tissue retention of radiolabeled α-cyclodextrin in monkeys.

Alprostadil

Absorption

After intracavernous injection of 20 mcg of edex® in 24 patients with erectile dysfunction, mean systemic plasma concentrations of PGE1 increased from baseline of 0.8 ± 0.6 pg/mL to a peak (Cmax ) of 16.8 ± 18.9 pg/mL (corrected for baseline) within 2 to 5 minutes and dropped to endogenous plasma levels within 2 hours (Table 1). The absolute bioavailability of alprostadil estimated from systemic exposure was about 98% as compared to the same dose given by a short-term intravenous infusion.

Distribution

The volume of distribution for PGE1 was not estimated. Approximately 93% of PGE1 found in plasma is protein-bound.

Metabolism

PGE1 is metabolized in the corpus cavernosum after intracavernous administration. PGE1 entering the systemic circulation is rapidly and extensively metabolized in the lungs with a first-pass pulmonary elimination of 60 to 90% of PGE1 . Enzymatic oxidation of the C15-hydroxy group followed by reduction of the C13, 14-double bond produces the primary metabolites, 15-keto-PGE1 , 15-keto-PGE0 , and PGE0 . 15-keto-PGE1 has only been detected in vitro in homogenized lung preparations, whereas 15-keto-PGE0 and PGE0 have been measured in plasma. Unlike the 15-keto metabolites which are less pharmacologically active than the parent compound, PGE0 is similar in potency to PGE1 in vitro using isolated animal organs.

After intracavernous injection of 20 mcg of edex® to 24 patients with erectile dysfunction, mean systemic plasma 15-keto-PGE0 levels increased within 7 minutes from endogenous levels of 12.9 ± 11.8 pg/mL to a Cmax of 421 ± 337 pg/mL (corrected for baseline) followed by a decrease to baseline levels in several hours. Mean systemic plasma PGE0 levels increased within 20 minutes from endogenous levels of 0.6 ± 0.5 pg/mL to a Cmax of 3.9 ± 2.3 pg/mL (corrected for baseline) followed by a decrease to baseline levels in several hours.

Excretion

After further degradation of PGE1 by beta and omega oxidation, the main metabolites are excreted primarily in urine (88%) and feces (12%) over 72 hours, and total excretion is essentially complete (92%) within 24 hours after administration. No unchanged PGE1 has been found in the urine and there is no evidence of tissue retention of PGE1 and its metabolites. After intracavernous injection of 20 mcg of edex® in patients with erectile dysfunction, the terminal half-lives (t½ ) of 15-keto-PGE0 and PGE0 were calculated to be 40.9 ± 16.5 minutes and 63.2 ± 31.1 minutes, respectively. The terminal half-life of PGE1 in healthy volunteers was calculated to be around 9-11 minutes which is consistent with that reported in the literature (8 minutes).

Mean total body clearance of PGE1 in patients with erectile dysfunction was calculated to be around 115 L/min after an intravenous infusion of 20 mcg alprostadil. The above value exceeded cardiac output indicating extensive and rapid elimination of PGE1 in the lungs and/or blood.

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