Opioid, Opioid

The receptors in these two organ systems mediate both the beneficial effects, and the side effects of opioids.

The side effects of opioids include sedation, respiratory depression, and constipation. Opioids can cause cough suppression, which can be both an indication for opioid administration or an unintended side effect. Physical dependence can develop with ongoing administration of opioids, leading to a withdrawal syndrome with abrupt discontinuation. Opioids can produce a feeling of euphoria, and this effect, coupled with physical dependence, can lead to the abuse of opioids by some individuals. However, abuse of opiods is uncommon in patients prescribed opioids for the treatment of pain.

Noscapine is a marginal case as it does have CNS effects but not necessarily similar to morphine, and it is probably in a category all its own. Dextromethorphan (the stereoisomer of levomethorphan, a semi-synthetic opioid agonist) and its metabolite dextrorphan have no opioid agonist effects at all despite their structure similarity to other opioids, instead they are potent NMDA antagonist and sigma 1 and 2 agonists and are used in many over-the-counter cough suppressants.

In most countries the use of opioids is subject to complex legal and medical regulations.

In palliative care, opioids are not recommended for sedation or anxiety because experience has found them to be ineffective agents in these roles.

Since then, nearly all non-clinical use of opioids has been rated zero on the scale of approval of nearly every social institution. However, in United Kingdom the 1926 report of the Departmental Committee on Morphine and Heroin Addiction under the Chairmanship of the President of the Royal College of Physicians reasserted medical control and established the "British system" of controlwhich lasted until the 1960s; in the U.S. the Controlled Substances Act of 1970 markedly relaxed the harshness of the Harrison Act.

In some cultures, approval of opioids was significantly higher than approval of alcohol.

The amount of raw poppy materials that each country can demand annually based on these provisions must correspond to an estimate of the country's needs taken from the national consumption within the preceding two years. In many countries, underprescription of morphine is rampant because of the high prices and the lack of training in the prescription of poppy-based drugs. The World Health Organization is now working with different countries' national administrations to train healthworkers and to develop national regulations regarding drug prescription in order to facilitate a greater prescription of poppy-based medicines. The World Health Organization "Assuring Availability of Opioid Analgesics" [2] Another idea to increase morphine availability is proposed by the Senlis Council, who suggest, through their proposal for Afghan Morphine, that Afghanistan could provide cheap pain relief solutions to emerging countries as part of a second-tier system of supply that would complement the current INCB regulated system by maintaining the balance and closed system that it establishes while providing finished product morphine to those suffering from severe pain and unable to access poppy-based drugs under the current system.

Non-sedating antihistamines such as fexofenadine are preferable so as to avoid increasing opioid induced drowsiness, although some sedating antihistamines such as orphenadrine may be helpful as they produce a synergistic analgesic effect which allows smaller doses of opioids to be used while still producing effective analgesia. For this reason some opioid/antihistamine combination products have been marketed, such as Meprozine (meperidine/promethazine) and Diconal (dipipanone/cyclizine), which may also have the added advantage of reducing nausea as well.

Peripherally acting opioid antagonists such as alvimopan and methylnaltrexone (Relistor) are currently under development which have been found to effectively relieve opioid induced constipation without affecting analgesia or triggering withdrawal symptoms. McNicol E, Boyce D, Schumann R, Carr D. Mu-opioid antagonists for opioid-induced bowel dysfunction.

Several drugs have been developed which can block respiratory depression completely even from high doses of potent opioids, without affecting analgesia, although the only respiratory stimulant currently approved for this purpose is doxapram, which has only limited efficacy in this application. Yost CS. A new look at the respiratory stimulant doxapram.

In patients taking opioids regularly it is essential that the opioid is only partially reversed to avoid a severe and distressing reaction of waking in excruciating pain. This is achieved by not giving a full dose (e.g. naloxone 400 g) but giving this in small doses (e.g. naloxone 40 g) until the respiratory rate has improved. An infusion is then started to keep the reversal at that level, while maintaining pain relief.

In the UK two studies have shown that double doses of bedtime morphine did not increase overnight deaths, Regnard C and Badger C. Opioids, sleep and the time of death.

Good PD, Ravenscroft PJ, Cavenagh J. Effects of opioids and sedatives on survival in an Australian inpatient palliative care population.

Morita T, Tsunoda J, Inoue S, Chihara S. Effects of high dose opioids and sedatives on survival in terminally ill cancer patients.

The withdrawal symptoms include severe dysphoria, sweating, nausea, rhinorrea, depression, severe fatigue, vomiting and pain. Slowly reducing the intake of opioids over days and weeks will reduce or eliminate the withdrawal symptoms.

The acute withdrawal phase is often followed by a protracted phase of depression and insomnia that can last for months. The symptoms of opioid withdrawal can also be treated with other medications, but with a low efficacy.

Opioids are abused due to their ability to produce euphoria and because individuals can become physically dependent. However, abuse of opioids is uncommon in patients being treated with opioids for pain relief.

Source: Wikipedia > Opioid