Opium Morphine Pharmacokinetics ADME opioids classification
Channel: alok bains
Date: 17/01/2021

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Pharmacokinetics: Morphine is readily absorbed from S.C. injection, I.M. injection as well as from GIT. But morphine undergoes the first metabolism in the gut wall and liver. Thus its GIT absorption is considered slow, erratic, and unreliable. The oral bioavailability of morphine is 25% if compared with parenteral route bioavailability. An oral dose of morphine requires twice of morphine parenteral dose. Opiates are also consumed for nonmedical purposes very commonly. These opiates are administered by inhalation of smoke from burning opium. This route has a rapid onset of action.

30% of morphine present in the blood binds with plasma proteins. It is widely distributed throughout the body and rapidly enters into tissues.  Morphine concentration in liver, kidney, spleen remains higher than in blood plasma. It crosses the placental barrier to enter into fetus circulation Effects of morphine on the fetus will be much more than on the body of pregnant women. The newly born baby of an opium-addicted mother shows opium dependence. Opium withdrawal symptoms appear in the newly born baby. Morphine is low lipophilic and a very small amount enters into the brain. But morphine's primary site of action is CNS. Fentanyl and heroin are lipophilic. They rapidly enter into CNS and produce more intense euphoric action. 

Morphine is metabolized in the liver by conjugation with glucuronic acid to form both active and inactive metabolites. These are morphine-6-glucuronide and morphine-3-glucuronide. The former is an active metabolite and the latter is an inactive metabolite. Morphine-6-glucuronic acid is a more potent analgesic than morphine. It accumulates in the body upon chronic administration of morphine. Morphine half-life is 2 hours and the duration of action is 4-6 hours. Heroin (Diacetyl morphi ne) is hydrolyzed to 6-mono acetyl morphine. 6- mono acetyl morphine is further hydrolyzed to morphine. Both heroin and 6-mono acetyl morphine are lipid-soluble.
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