OPIOID ANALGESICS

 

Introduction: Successful treatment of pain is a challenging task that begins with careful attempts to assess the source and magnitude of the pain. The amount of pain experienced by the patient is often measured by means of a pain Numeric Rating Scale (NRS) or less frequently by marking a line on a Visual Analog Scale (VAS) with word descriptors ranging from no pain (0) to excruciating pain (10). In either case, values indicate the magnitude of pain as: mild (1–3), moderate (4–6), or severe (7–10).  For a patient in severe pain, the administration of an opioid analgesic is usually considered a primary part of the overall management plan. Determining the route of administration, duration of drug action, ceiling effect also known as maximal intrinsic activity, duration of therapy, potential for adverse effects, and the patient’s past experience with opioids all should be addressed.  Use of opioid drugs in acute situations may be contrasted with their use in chronic pain management, in which a multitude of other factors must be considered, including the development of tolerance to and physical dependence on opioid analgesics.

Clinical Use of Opioid Analgesics:  1)  Analgesia: Severe, constant pain is usually relieved with opioid analgesics with high intrinsic activity. This includes the pain associated with cancer and other terminal illnesses. Such conditions may require continuous use of potent opioid analgesics and are associated with some degree of tolerance and dependence. Opioid analgesics are also often used during obstetric labor. Because opioids cross the placental barrier and reach the fetus, however care must be taken to minimize neonatal depression. If it occurs, immediate injection of the antagonist naloxone will reverse the depression.  

2)  Acute Pulmonary Edema: The relief produced by intravenous morphine in dyspnea from pulmonary edema associated with left ventricular heart failure is remarkable. Proposed mechanisms include reduced anxiety and reduced cardiac preloa and afterload. However, if respiratory depression is a problem, furosemide may be preferred for the treatment of pulmonary edema. On the other hand, morphine can be particularly useful when treating painful myocardial ischemia with pulmonary edema.  

3) Cough: Suppression of cough can be obtained at doses lower than those needed for analgesia. However, in recent years the use of opioid analgesics to allay cough has diminished largely because a number of effective synthetic compounds have been developed that are neither analgesic nor addictive.  

4)  Diarrhea: Diarrhea from almost any cause can be controlled with the opioid analgesics, but if diarrhea is associated with infection such use must not substitute for appropriate chemotherapy. Crude opium preparations were used in the past to control diarrhea, but now synthetic surrogates with more selective gastrointestinal effects and few or no CNS effects, such as diphenoxylate or loperamide, are used.  

5)  Shivering: Although all opioid agonists have some propensity to reduce shivering, meperidine is reported to have the most pronounced anti-shivering properties. Meperidine apparently blocks shivering mainly through an action on subtypes of the α2 adrenoceptor.  

6)  Applications in Anesthesia: The opioids are frequently used as premedicant drugs before anesthesia and surgery because of their sedative, anxiolytic, and analgesic properties. They are also used intra-operatively both as adjuncts to other anesthetic agents and, in high doses, as a primary component of the anesthetic regimen . Opioids are most commonly used in cardiovascular surgery and other types of high-risk surgery in which a primary goal is to minimize cardiovascular depression. In such situations, mechanical respiratory assistance must be provided.

RELATED; 

1.  CORTICOSTEROIDS  

2.  CHRONIC INFLAMMATION

3.  MORPHINE

4.  PHARMACOLOGY AND THERAPEUTICS

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