Opioids, specific agents morphine

Few studies have explored the efficacy of opioids specifically for OA. The APS recommends against the use of codeine and propoxyphene for OA because of the high incidence of adverse effects and limited analgesic effectiveness. Oxycodone is the most extensively studied of the agents recommended for OA. However, other narcotic analgesics such as morphine, hydromorphone, methadone, and transdermal fentanyl are also effective. 

The following section describes the most important and widely used opioid analgesics, along with features peculiar to specific agents. Data about doses approximately equivalent to 10 mg of intramuscular morphine, oral versus parenteral efficacy, duration of analgesia, and intrinsic activity (maximum efficacy) are presented in Table 31-2. 

Alkaloids such as boldine, codeine, narceine and morphine are active factors in their receptors. Boldine has morphine-like properties and is active on opioid receptors. It may be used to treat stomach disorders and as metabolic stimulant. As it is similar to morphine, boldine can also be considered in the possible development of treatments for narcotic dependence. Codeine also binds to opiate receptors, and specifically functions to reduce bronchial secretions. Codeine can also be used as a cough suppressant when acting on the centre of the medulla oblongata and as a sedative agent. 

A study of the effect of several opioid antagonists on food intake and their ability to block opioid agonist-induced behaviors, demonstrates a degree of specificity which suggests that the mechanisms for these two activities may differ. Naloxone, naltrexone, diprenorphine, Mr 1452 (16) and Mr 2266 (17) decrease food intake whereas WIN 44,441 (18) does not. Diprenorphine is the most potent of these agents in blocking the antinociceptive effect of morphine, whereas (lb), (]J) and (lb) are weaker antagonists in this test. ... 

Exogenously administered substances are not the only agents which might interfere with a receptor binding assay. For example, opiate receptor binding as a radioreceptor assay for morphine would appear to be a relatively specific procedure since only opiates can interfere with the attachment to this receptor site. However, the discovery of endogenous opioid peptides makes the morphine assay less feasible with brain tissue because of the potential for these substances to be present in the tissue extracts. 

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