Prescription Drug Information: DepoDur

DEPODUR- morphine sulfate injection, lipid complex
Pacira Pharmaceuticals Inc.

DESCRIPTION

DepoDur (morphine sulfate extended-release liposome injection) is a sterile suspension of multivesicular liposomes using proprietary DepoFoam® formulation technology containing morphine sulfate, intended for epidural administration.

Chemically, morphine sulfate is 7, 8-didehydro-4, 5α-epoxy-17-methylmorphinan-3, 6α -diol sulfate (2:1) (salt) pentahydrate with a molecular weight of 758. Morphine sulfate pentahydrate has the following structural formula:

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Morphine base has a pKa of 7.9, with an octanol/water partition coefficient of 1.42 at physiologic pH 7.4. At this pH, morphine’s tertiary amino group is mostly ionized, making the molecule water-soluble.

DepoDur is a sterile, non-pyrogenic, white to off-white, preservative-free suspension of multivesicular lipid-based particles containing Morphine Sulfate, USP. The median diameter of the liposome particles is in the range of 17 to 23 μm. The liposomes are suspended in a 0.9% sodium chloride solution. Each vial contains morphine sulfate (expressed as the pentahydrate) at a nominal concentration of 10 mg/mL. Inactive ingredients and their approximate concentrations are: 1,2-dioleoyl-sn -glycero-3‑phosphocholine (DOPC), 4.2 mg/mL; cholesterol, 3.3 mg/mL; 1,2-dipalmitoyl-sn -glycero-3‑phospho-rac -(1-glycerol) (DPPG), 0.9 mg/mL; tricaprylin, 0.3 mg/mL; and triolein, 0.1 mg/mL. The pH of DepoDur is in the range of 5.0 to 8.0.

After the administration of DepoDur into the epidural space, morphine sulfate is released from the multivesicular liposomes over a period of time.

Liposomal encapsulation or incorporation in a lipid complex can substantially affect a drug’s functional properties relative to those of the unencapsulated or nonlipid-associated drug. In addition, different liposomal or lipid-complexed products with a common active ingredient may vary from one another in the chemical composition and physical form of the lipid component. Such differences may affect functional properties of these drug products. DO NOT SUBSTITUTE.

CLINICAL PHARMACOLOGY

Mechanism of Action

Epidural administration of morphine sulfate results in analgesia without attendant loss of motor, sensory, or sympathetic function.

Morphine released from DepoDur is absorbed both neuraxially and systemically.

Morphine, a pure opiate agonist, is relatively selective for the μ-receptor, although it can interact with other opiate receptors at higher doses. In addition to analgesia, the widely diverse effects of morphine include respiratory depression, drowsiness, changes in mood, decreased gastrointestinal motility, nausea, vomiting, and alterations of the endocrine and autonomic nervous system.

Pharmacodynamics

The effects described below are common to all morphine-containing products.

Effects on the Central Nervous System (CNS): The principal therapeutic action of morphine is analgesia. Other therapeutic effects of morphine include anxiolysis, euphoria and feelings of relaxation. Although the precise mechanism of the analgesic action is unknown, specific CNS opiate receptors and endogenous compounds with morphine-like activity have been identified throughout the brain and spinal cord and are likely to play a role in the expression and perception of analgesic effects. As with all drugs in the opiate class, morphine can cause respiratory depression, in part by a direct effect on the brainstem respiratory centers. Morphine and related opiates depress the cough reflex by direct effect on the cough center in the medulla. Antitussive effects may occur with doses lower than those usually required for analgesia. Morphine may cause miosis, even in total darkness. Pinpoint pupils are a sign of opiate overdose; however, when asphyxia is present during opiate overdose, marked mydriasis occurs.

Effects on the Gastrointestinal Tract and on Other Smooth Muscle: Gastric, biliary and pancreatic secretions are decreased by morphine. Morphine causes a reduction in motility and is associated with an increase in tone in the antrum of the stomach and duodenum. Digestion of food in the small intestine is delayed and propulsive contractions are decreased. Propulsive peristaltic waves in the colon are decreased, while tone can be increased to the point of spasm, often resulting in constipation. Morphine can cause a marked increase in biliary tract pressure as a result of spasm of the sphincter of Oddi. Morphine may also cause spasm of the sphincter of the urinary bladder.

Effects on the Cardiovascular System: In therapeutic doses, morphine does not usually exert major effects on the cardiovascular system. Morphine, like other opiates, produces peripheral vasodilatation that may result in orthostatic hypotension and fainting. Release of histamine can occur, which may play a role in opiate-induced hypotension. Manifestations of histamine release and/or peripheral vasodilatation may include pruritus, flushing, red eyes and sweating.

Pharmacokinetics

Epidural administration of DepoDur results in both systemic absorption of morphine sulfate and absorption of morphine sulfate through the meninges into the intrathecal space. The relative absorption systemically versus intrathecally is unknown for DepoDur.

Absorption

Relative systemic bioavailability of DepoDur compared to epidurally administered morphine injection was determined in 19 patients (Table 1).

Table 1: Pharmacokinetics of DepoDur and Morphine Sulfate Injection (Mean ± SD)

* Median (range)

DepoDur 5 mg

(n = 10)

Morphine Sulfate Injection

5 mg

(n = 9)

Parameter

Mean

SD

Mean

SD

Cmax (ng/mL)

7.1

3.4

23.8

12.8

tmax (hr)*

1.0

(0.3–4.0)

0.3

(0.3–2.0)

AUC (ng•hr/mL)

38.8

10.4

42.8

8.4

t1/2 (hr)

3.8

1.0

2.2

0.5

DepoDur systemic AUC was comparable to that of morphine sulfate injection (approximately 90%), however, systemic Cmax was 30 % of that of morphine sulfate injection.

Based on systemic AUC, DepoDur appears to exhibit dose proportionality over a dose range of 5 to 25 mg. In contrast, systemic Cmax did not exhibit dose-proportionality and tended to increase by an amount less than the proportional change in dose (Table 2).

Table 2: Morphine Plasma Pharmacokinetic Parameters (Mean, SD) Following Epidural Administration of DepoDur
Parameter DepoDur5 mg (n=14) DepoDur10 mg (n=36) DepoDur15 mg (n=71) DepoDur20 mg (n=63) DepoDur25 mg (n=32) DepoDur30 mg (n=25)
Cmax (ng/mL) 9.4 (5.7) 20.0 (9.5) 18.6 (10.4) 26.4 (18.6) 22.6 (15.4) 47.3 (28.9)

AUC0–∞ (ng•hr/mL)

41.0 (10.6) 124.9 (98.1) 131.6 (73.7) 185.9 (81.4) 207.3 (77.7) 341.5 (136.9)
t1/2 (hr) 4.2 (2.1) 16.2 (19.7) 20.0 (20.6) 23.9 (25.4) 32.9 (24.2) 25.6 (14.6)

Distribution

After morphine sulfate has been released from DepoDur and is absorbed systemically, morphine distribution is expected to be the same as for other morphine formulations.

Once absorbed, morphine is distributed to skeletal muscle, kidneys, liver, intestinal tract, lungs, spleen and brain. The volume of distribution of morphine is approximately 1 to 4 L/kg. Morphine is 20 to 35% reversibly bound to plasma proteins. Morphine also crosses the placental membranes and has been found in breast milk.

Metabolism

After morphine sulfate has been released from DepoDur and is absorbed systemically, morphine metabolism is expected to be the same as for other morphine formulations.

The major pathway of the detoxification of morphine is conjugation, either with D‑glucuronic acid in the liver to produce glucuronides or with sulfuric acid to give morphine-3-etheral sulfate. Although a small fraction (less than 5%) of morphine is demethylated, for all practical purposes, virtually all morphine is converted to glucuronide metabolites including morphine-3-glucuronide, M3G (about 50%) and morphine-6-glucuronide, M6G (about 5 to 15%). M3G has no significant analgesic activity. M6G has been shown to have opiate agonist and analgesic activity in humans.

Excretion

After morphine sulfate has been released from DepoDur and is absorbed systemically, morphine excretion is expected to be the same as for other morphine formulations. DepoDur is intended for single dose administration, therefore, accumulation of morphine or its metabolites is not expected even in patients with impaired hepatic or renal function.

Approximately 10% of morphine dose is excreted unchanged in the urine. Most of the dose is excreted in the urine as M3G and M6G. A small amount of the glucuronide metabolites is excreted in the bile and there is some minor enterohepatic cycling. Seven to 10% of administered morphine is excreted in the feces. The mean adult plasma clearance is about 20–30 mL/minute/kg. The effective terminal half-life of morphine after IV administration is reported to be approximately 2 hours. In some studies involving longer periods of plasma sampling, a longer terminal half-life of morphine of about 15 hours was reported.

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