Morphine is an opiate drug named after the god of dreams and sleep - Morpheus. The drug eases pain, alters mood and induces sleep.

Chemical structure and source

The chemical formula for morphine is C17H19NO3. It is a benzylisoquinoline alkaloid and is the most abundant opiate present in opium.

The three dimensional structure has five rings. Of these, three lie approximately in the same plane. The other nitrogen-containing ring and the remaining ring are at right angles to the other three.

All opioid analgesics have some similarities in their structure which include:

• An aromatic ring
• A quaternary carbon atom linked to a tertiary amine group by two other carbon atoms

Together, these properties make up "the morphine rule". Morphine also has a methyl group attached to a nitrogen atom. If this methyl group is replaced by a propenyl group, an antagonist of morphine called nalorphine is formed.

Properties

Morphine and its hydrated form, C17H19NO3.H2O, are not vey soluble in water or lipids. In five litres of water, only around one gram of morphine can be dissolved. Morphine can cross the blood-brain barrier but due its poor lipid solubility along with its rapid conjugation with glucaronic acid, it does not cross this barrier easily.

The commercially available forms of morphine are the morphine salts such as hydrochloride and sulfate that are around 300 times more water soluble that the parent molecule. These salts are much more acidic (with pH around 5) than the saturated morphine hydrate solution which has a pH of 8.5. The salts are therefore neutralized with small amounts of sodium hydroxide to make them suitable for injection.