Description<\/h3>\n\n\n\n
Morphine is a drug commonly used in the \nmanagement of moderate to severe nociceptive pain, such as pain due to \ncancer, surgery or trauma. \n<\/p>\n\n\n\n
Morphine is well absorbed through the gastrointestinal mucosa. However, it undergoes substantial hepatic first-pass effect<\/a>. Therefore, its oral bioavailability<\/a>\n is relatively low (~25%). Peak plasma drug concentrations are reached \n30 to 90 min after oral administration and 15 to 20 minutes after \nsubcutaneous or intramuscular administration. Slow release oral \nformulations have been developed, which deliver the dose over 8 to 12 \nhours (MST Continus\u00ae) or up to 24 hours (Kapanol\u00ae)\n<\/p>\n\n\n\n After absorption<\/a>, morphine is rapidly distributed<\/a> within the body, including the brain. Morphine has a large volume of distribution<\/a>, and only one third of the circulating amount binds to plasma proteins. \n<\/p>\n\n\n\n Morphine has a high systemic clearance<\/a> and an accordingly short half-life<\/a> of approximately two hours. The primary site of morphine metabolism<\/a>\n is the liver, where it undergoes rapid glucuronidation. However, \nextrahepatic metabolism of the drug can account for up to 30% of its \ntotal clearance<\/a>.\n This extrahepatic metabolism may play a relatively important role in \nmorphine metabolism in patients with severe liver failure. In the liver,\n the principal metabolite is the morphine-3-glucuronide (M3G). This \nmetabolite has no pharmacological effect and is primarily excreted in \nthe urine. Another important metabolite is morphine-6-glucuronide (M6G),\n which appears to be at least as potent as morphine. M6G has a half-life\n of approximately 1-2 hours. This active metabolite is also excreted in \nthe urine and may accumulate significantly in case of renal \ninsufficiency. Less than 10% of the dose is excreted unchanged in the \nurine.<\/p>\n\n\n\n When deciding for the appropriate schedule of \nadministration, several factors must be evaluated. The approximate \nrelative potency of parenteral to oral morphine is 1:3. Patients with \nacute pain will be more readily relieved with parenteral administration \nof morphine (e.g iv injection<\/a>, i.m or sc injection, or constant rate infusion<\/a>).\n On the other hand considering the greater convenience of oral \nadministration, this route is the first choice for treatment of patients\n with sustained pain. Changing from parenteral to oral route \nnecessitates the administration of double to triple doses. To further \nincrease the convenience of oral administration, controlled-release preparations<\/a> have been developed, which provide prolonged analgesia for 8 to 24 hours.\n<\/p>\n\n\n\n Due to its short half-life, dosing must be repeated on a frequent basis (q 4 hours in general). The frequency must however be decreased in hepatic failure patients and also in renal failure patients, due to the accumulation of an active metabolite.<\/p>\n\n\n\n Morphine pharmacokinetic parameters Oral bioavailability (F) 25% Clearance (CL) 72 L\/h Volume of Distribution (Vd) 245 L Half-life (t1\/2) 2.5 h Description Morphine is a drug commonly used in the management of moderate to severe nociceptive pain, such as pain due to cancer, surgery or trauma. Morphine is well absorbed through the gastrointestinal mucosa. However, … <\/p>\nClinical implications<\/h3>\n\n\n\n
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