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Opiates Learning out comes Understand what is meant by an opiate Understand the mode of action of strong analgesics such as morphine and codeine Compare the structures of morphine, codeine and diamorphine Explain why diamorphine is more potent than morphine Understand how diamorphine and codeine can be synthesised from morphine Explain the advantages and disadvantages of using opiates Analgesics Analgesics are common pain relievers. Many analgesics also have antipyretic properties as well. They can be used to reduce fever Some analgesics are also anti-inflammatory drugs as well Classification of Analgesics Analgesics Strong Mild Analgesics Aspirin Analgesics Ibuprofen Acetaminophen Opium Heroin Codeine Strong analgesics Whereas mild analgesics, such as aspirin, are used for relatively mild pain, such as headache or toothache, opiate/opioid analgesics are strong analgesics used for moderate to severe pain, such as in terminally ill patients. Mild analgesics may be combined with strong analgesics in some preparations – for example, paracetamol and codeine are often used together. Strong Analgesics Only Available by prescription Used to relieve severe pain associated with injuries, heart attacks, or chronic diseases such as cancer Most strong analgesics are derived from the opium poppy or synthetically produced Basically three types: Natural, semi-synthetic, synthetic Opiates Opiates are natural narcotic (sleep-inducing) analgesics derived from the opium poppy. The term ‘narcotic’ can be used in different ways. It is used here to describe analgesic drugs derived from opium, but nowadays it is often used in everyday language to indicate any illicit/strictly controlled drug. Origin of Opiates Opiates are derived from the juice of the unripe seed pods of the poppy Papaver somniferum. This juice is known as opium (the Greek word for ‘juice’) and contains morphine as one of the ingredient. Morphine was first isolated in 1803 and is chiefly responsible for the biological effects of opium How it works Morphine and codeine are Strong analgesics work by temporarily bonding to receptor sites in the brain, preventing the transmission of pain impulses without depressing the central nervous system. strong analgesics, which act by temporarily binding to opioid receptors in the brain. This blocks the transmission of pain signals in the brain and increases the pain perception threshold Even though pain in the affected tissue is still occurring and being transmitted via the peripheral nervous system, the patient is not as aware of it Opiates cause a number of effects on the body through binding to opioid receptors. These include analgesia, sedation, a feeling of well-being and suppression of the cough reflex. They are used medically for pain relief and the treatment of coughs and diarrhea. Structures of morphine and its derivatives Morphine Naturally occurring in the poppy- Only needs to be isolated Very strong pain reliever but also very addictive (2nd to Heroin) Usually injected but can be smoked, sniffed or swallowed Commonly used in hospitals Large illegal street culture Codeine Most commonly used strong analgesic Similar to Morphine except for the replacement of a (OH-) group for (OCH3) group Commonly used with Tylenol as a more mild analgesic 1/6 as strong as Morphine and less addictive Synthesis of codeine Codeine synthesis Codeine can also be synthesised from morphine In the original process, morphine was reacted with iodomethane (the methylating agent) in the presence of a base. Phenols are slightly acidic and so the presence of a strong base converts the OH of the phenol to O−. The reaction is nucleophilic substitution, with the O− attacking the δ+ carbon atom of the CH3I. Heroin ( diamorphine) Originally sold as cough suppressant and pain killer 10 times stronger than Morphine Incredibly addictive (many times, other strong analgesics are needed for withdrawal) Synthesis of diamorphine Synthesized from morphine in a esterification reaction with acetyl chloride Heroin It is absorbed by the brain very quickly resulting in a potent high Many other problems are associated with heroin addiction including as prostitution and AIDS. Advantages of opiates Opiates such as morphine and diamorphine are used medically for the relief of severe pain – they are especially effective in visceral pain (pain in internal organs, such as the liver and lungs). They are commonly used to relieve the pain associated with cancer in terminally ill patients. Morphine may also be used for the short-term control of diarrhea due to its constipating effect, and to control distressing coughing by lung cancer patients, due to its cough-suppressant effect. Milder opiates such as codeine are used to relieve moderate pain. Codeine is also used as a cough suppressant for dry coughs and as an anti diarrhea drug. Side Effects of Opiates Analgesics Short term Dulling of Pain Euphoria Slow Nervous system Slowed heart rate Loss of cough reflex Nausea Overdoses can lead to death Possibility of stroke Overall slowdown of biological systems Long Term Addiction and very strong withdrawal effects Constipation Loss of libido Disruptions in menstruation “Cross-tolerance” Loss of appetite Problems associated with buying street drugs i.e. sharing needles AIDS and prostitution. Methadone Compared to most strong analgesics it is weaker. Has been synthesized to not have euphoric properties and mild withdrawal effects but is still addictive. Used as an analgesic but most commonly to help in the withdrawal for Heroin addicts.
