MORPHINE SULFATE EXTENDED-RELEASE (Page 2 of 6)

PHARMACOKINETICS AND METABOLISM

Morphine sulfate extended-release tablets are extended-release tablets containing morphine sulfate. Morphine is released from morphine sulfate extended-release tablets somewhat more slowly than from conventional oral preparations. Following oral administration of a given dose of morphine, the amount ultimately absorbed is essentially the same whether the source is morphine sulfate extended-release tablets or a conventional formulation. Because of pre-systemic elimination (i.e., metabolism in the gut wall and liver) only about 40% of the administered dose reaches the central compartment.

Variation in the physical/mechanical properties of a formulation of an oral morphine drug product can affect both its absolute bioavailability and its absorption rate constant (ka ). The formulation employed in morphine sulfate extended-release tablets has not been shown to affect morphine’s oral bioavailability, but does decrease its apparent ka . Other basic pharmacokinetic parameters (e.g., volume of distribution [Vd], elimination rate constant [ke ], clearance [Cl]), are unchanged as they are fundamental properties of morphine in the organism. However, in chronic use, the possibility that shifts in metabolite to parent drug ratios may occur cannot be excluded.

When immediate-release oral morphine or morphine sulfate extended-release tablets are given on a fixed dosing regimen, steady-state is achieved in about a day.

For a given dose and dosing interval, the AUC and average blood concentration of morphine at steady-state (Css ) will be independent of the specific type of oral formulation administered so long as the formulations have the same absolute bioavailability. The absorption rate of a formulation will, however, affect the maximum (Cmax ) and minimum (Cmin ) blood levels and the times of their occurrence.

Absorption

Following the administration of conventional oral morphine products, approximately fifty percent of the morphine that will reach the central compartment intact reaches it within 30 minutes. Following the administration of an equal amount of morphine sulfate extended-release tablets to normal volunteers, however, this extent of absorption occurs, on average, after 1.5 hours.

Food Effects

The possible effect of food upon the systemic bioavailability of morphine sulfate extended-release tablets has not been systematically evaluated for all strengths. One study, conducted with the 30 mg morphine sulfate extended-release tablets, showed no significant differences in Cmax and AUC(0-24h) values, whether the tablet was taken while fasting or with a high-fat breakfast.

Distribution

The volume of distribution (Vd) for morphine is approximately 4 liters per kilogram. Once absorbed, morphine is distributed to skeletal muscle, kidneys, liver, intestinal tract, lungs, spleen, and brain. Morphine also crosses the placental membranes and has been found in breast milk.

Metabolism

Although a small fraction (less than 5%) of morphine is demethylated, for all practical purposes, virtually all morphine is converted to the 3- and 6- (M3G and M6G) glucuronide metabolites. M3G is present in the highest plasma concentration following oral administration and possesses no significant analgesic activity. M6G, while possessing analgesic activity, is present in the plasma in low concentrations.

Excretion

The elimination of morphine occurs primarily as renal excretion of morphine-3-glucuronide and its terminal elimination half-life after intravenous administration is normally 2 to 4 hours. In some studies involving longer periods of plasma sampling, a longer terminal half-life of about 15 hours was reported. A small amount of the glucuronide conjugate is excreted in the bile, and there is some minor enterohepatic recycling. As with any drug, caution should be taken to guard against unanticipated accumulation if renal and/or hepatic function is seriously impaired.

Special Populations

Renal Impairment

Morphine pharmacokinetics are altered in patients with renal failure. Clearance is decreased and the metabolites, M3G and M6G, may accumulate to much higher plasma levels in these patients as compared to patients with normal renal function.

Drug-Drug Interactions

Known drug-drug interactions involving morphine are pharmacodynamic not pharmacokinetic.

INDICATIONS AND USAGE

Morphine sulfate extended-release tablets are an extended-release oral formulation of morphine sulfate indicated for the management of moderate to severe pain when a continuous, around-the-clock opioid analgesic is needed for an extended period of time.

Morphine sulfate extended-release tablets are NOT intended for use as a prn analgesic.

The morphine sulfate extended-release tablets 100 mg and 200 mg strengths are high dose, extended-release, oral morphine formulations indicated for the relief of pain in opioid-tolerant patients only.

Morphine sulfate extended-release tablets are not indicated for pain in the immediate postoperative period (the first 12 to 24 hours following surgery) for patients not previously taking the drug, because its safety in this setting has not been established.

Morphine sulfate extended-release tablets are not indicated for pain in the postoperative period if the pain is mild, or not expected to persist for an extended period of time.

Morphine sulfate extended-release tablets are only indicated for postoperative use if the patient is already receiving the drug prior to surgery or if the postoperative pain is expected to be moderate to severe and persist for an extended period of time. Physicians should individualize treatment, moving from parenteral to oral analgesics as appropriate. (See American Pain Society guidelines.)

CONTRAINDICATIONS

Morphine sulfate extended-release tablets are contraindicated in patients with known hypersensitivity to morphine or in any situation where opioids are contraindicated. This includes patients with respiratory depression (in the absence of resuscitative equipment or in unmonitored settings), and in patients with acute or severe bronchial asthma or hypercarbia.

Morphine sulfate extended-release tablets are contraindicated in any patient who has or is suspected of having a paralytic ileus.

WARNINGS

(see CLINICAL PHARMACOLOGY)

MORPHINE SULFATE EXTENDED-RELEASE TABLETS ARE TO BE SWALLOWED WHOLE AND ARE NOT TO BE BROKEN, CHEWED, DISSOLVED, OR CRUSHED. TAKING BROKEN, CHEWED, DISSOLVED, OR CRUSHED MORPHINE SULFATE EXTENDED-RELEASE TABLETS LEADS TO RAPID RELEASE AND ABSORPTION OF A POTENTIALLY FATAL DOSE OF MORPHINE.

Morphine sulfate extended-release 100 mg AND 200 mg tablets ARE FOR USE IN OPIOID-TOLERANT PATIENTS ONLY. These tablet strengths may cause fatal respiratory depression when administered to patients not previously exposed to opioids.

Morphine sulfate extended-release 100 mg AND 200 mg tablets are for use only in opioid-tolerant patients requiring daily morphine equivalent dosages of 200 mg or more for the 100 mg tablet and 400 mg or more for the 200 mg tablet. Care should be taken in the prescribing of these tablet strengths. Patients should be instructed against use by individuals other than the patient for whom it was prescribed, as such inappropriate use may have severe medical consequences, including death.

Misuse, Abuse and Diversion of Opioids

Morphine is an opioid agonist and a Schedule II controlled substance. Such drugs are sought by drug abusers and people with addiction disorders and are subject to criminal diversion.

Morphine can be abused in a manner similar to other opioid agonists, legal or illicit. This should be considered when prescribing or dispensing morphine sulfate extended-release tablets in situations where the physician or pharmacist is concerned about an increased risk of misuse, abuse, or diversion.

Morphine sulfate extended-release tablets can be abused by crushing, chewing, snorting or injecting the dissolved product. These practices will result in the uncontrolled delivery of the opioid and pose a significant risk to the abuser that could result in overdose and death (see WARNINGS, Drug Abuse and Addiction).

Concerns about abuse, addiction, and diversion should not prevent the proper management of pain.

Healthcare professionals should contact their State Professional Licensing Board or State Controlled Substances Authority for information on how to prevent and detect abuse or diversion of this product.

Interactions with Alcohol and Drugs of Abuse

Morphine may be expected to have additive effects when used in conjunction with alcohol, other opioids, or illicit drugs that cause central nervous system depression because respiratory depression, hypotension, and profound sedation or coma may result (see WARNINGS, Interactions with Other CNS Depressants).

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