Opioid analgesics- introduction, classification

Opioid analgesics

Opioids, or opioid analgesics, are a family of pharmaceuticals that are either synthetically or generated from opium to replicate its effects. To reduce pain, these chemicals interact with certain receptors in the brain and spinal cord. Strong analgesics, opioids are frequently recommended to treat excruciating pain brought on by surgery, trauma, or specific medical disorders. Opioids are useful in treating pain, but they come with hazards as well, such the possibility of dependency and addiction as well as side effects like nausea, diarrhea, and sleepiness. Owing to these concerns, medical practitioners and government regulators keep a strict eye on the prescription and usage of opioids. The opioid crisis, which has resulted in an increase in overdoses and fatalities linked to opioids, has increased awareness of the significance of appropriate opioid prescription practices and alternative pain treatment techniques.

Opioid analgesics classification:

Opioid analgesics are classified based on various factors, including their potency, chemical structure, and clinical use. Here is a general classification of opioid analgesics:

1.Natural Opioids:

Natural opioids are derived directly from the opium poppy plant (Papaver somniferum). These substances have been used for centuries for their analgesic (pain-relieving) properties. The two primary natural opioids are morphine and codeine. Here’s an overview of each:

  1. Morphine:

    • Source: Morphine is extracted from the latex sap of the opium poppy.
    • Potency: It is one of the most potent natural opioids and is often considered the standard against which other opioids are measured.
    • Clinical Use: Morphine is commonly used for managing severe pain, such as post-surgical pain, pain associated with certain medical conditions, and cancer-related pain.
    • Forms: It is available in various formulations, including oral tablets, injectables, and extended-release formulations.
  2. Codeine:

    • Source: Codeine is also derived from the opium poppy, and it can be found in the sap of the plant.
    • Potency: Codeine is less potent than morphine.
    • Clinical Use: Codeine is often used for milder to moderate pain relief and is commonly found in combination with other medications, such as acetaminophen or ibuprofen.
    • Forms: It is available in oral formulations, including tablets and syrups.

Both morphine and codeine work by binding to specific receptors in the central nervous system called opioid receptors, modulating the perception of pain. It’s important for healthcare professionals to consider factors such as the severity of pain, individual patient characteristics, and potential side effects when prescribing natural opioids. Additionally, due to the potential for dependence and misuse, these medications are typically used under close medical supervision.

2.Semi-Synthetic Opioids:

Semi-synthetic opioids are a category of opioid analgesics that are derived from natural opioids but undergo chemical modification to create new compounds with specific properties. These modifications are made to enhance or alter the pharmacological effects of the drug. Here are some examples of semi-synthetic opioids:

  1. Oxycodone: Derived from thebaine, a natural alkaloid found in the opium poppy, oxycodone is a potent semi-synthetic opioid. It is commonly used for the management of moderate to severe pain. Oxycodone is available in various formulations, including immediate-release and extended-release forms.

  2. Hydrocodone: Hydrocodone is synthesized from codeine, a natural alkaloid obtained from the opium poppy. It is often combined with acetaminophen or ibuprofen in various formulations for the treatment of moderate to moderately severe pain. Hydrocodone is commonly prescribed in oral medications.

  3. Hydromorphone: This semi-synthetic opioid is derived from morphine and is more potent than its parent compound. Hydromorphone is used for the treatment of moderate to severe pain. It is available in various formulations, including immediate-release tablets and extended-release formulations.

  4. Oxymorphone: Similar to hydromorphone, oxymorphone is derived from morphine and is used to treat moderate to severe pain. It is available in various formulations, including immediate-release tablets and extended-release forms.

These semi-synthetic opioids are commonly prescribed by healthcare professionals for pain management, especially in situations where other pain relievers may be insufficient. It’s important to note that the use of opioids, including semi-synthetic opioids, comes with potential risks and side effects, and their prescription should be carefully monitored by healthcare providers to minimize the risk of dependence and misuse. Patients should follow their healthcare provider’s instructions closely and report any adverse effects promptly.

3.Synthetic Opioids:

Synthetic opioids are a category of opioids that are chemically synthesized rather than being derived directly from the opium poppy plant. These drugs are designed to mimic the effects of natural opioids, such as morphine and codeine, which are found in opium. Synthetic opioids may be created to be more potent or have specific pharmacological properties. Here are some examples of synthetic opioids:

  1. Fentanyl:

    • Fentanyl is a potent synthetic opioid that is many times more potent than morphine. It is used medically for managing severe pain, especially in situations like surgery or cancer-related pain.
    • Various formulations of fentanyl are available, including patches, lozenges, and injectable forms. Illicitly produced fentanyl has also been a significant contributor to the opioid epidemic, often found mixed with other drugs.
  2. Methadone:

    • Methadone is a synthetic opioid with a long duration of action. It is commonly used for the treatment of opioid addiction (as part of medication-assisted treatment) and for managing chronic pain. Methadone has unique pharmacological properties that can make it effective in certain clinical settings.
  3. Tramadol:

    • Tramadol is a synthetic opioid with a dual mechanism of action. In addition to its opioid activity, it also affects serotonin and norepinephrine levels in the brain. Tramadol is used to treat moderate to moderately severe pain.
    • It is considered to have a lower risk of dependence compared to some other opioids, but it still carries the potential for abuse and dependence.

Synthetic opioids, like all opioids, have the potential for side effects, including respiratory depression, sedation, and constipation. When prescribed by healthcare professionals, they are typically administered with careful consideration of the patient’s medical history, the severity of pain, and the potential risks and benefits.

It’s crucial to note that misuse or abuse of synthetic opioids, especially those obtained illicitly, can lead to serious health consequences, including overdose and death. Illicitly manufactured synthetic opioids, such as fentanyl analogs, have been associated with a significant number of opioid-related fatalities in recent years, contributing to public health concerns.

4.Mixed Agonist-Antagonist Opioids:

Mixed agonist-antagonist opioids are a specific class of opioids that exhibit both agonist and antagonist properties at opioid receptors. These drugs interact with opioid receptors in a way that can stimulate some receptors (agonist activity) while simultaneously blocking or inhibiting others (antagonist activity). This dual action can make them useful in certain clinical situations, such as pain management and treatment of opioid dependence. One notable member of this class is buprenorphine.


  • Agonist Activity: Buprenorphine acts as a partial agonist at the mu-opioid receptor. This means that it can activate the receptor to produce analgesic (pain-relieving) effects, but its efficacy is limited compared to full agonists like morphine.

  • Antagonist Activity: Buprenorphine also has antagonist activity at the kappa-opioid receptor. This antagonistic effect can mitigate the potential for respiratory depression and overdose seen with full opioid agonists.

  • Clinical Uses:

    • Pain Management: Buprenorphine is used for the treatment of moderate to severe pain, often in situations where other opioids might be too potent.

    • Opioid Dependence Treatment: Buprenorphine is approved for use in medication-assisted treatment (MAT) for opioid dependence. In this context, it helps reduce cravings and withdrawal symptoms, allowing individuals to taper off more gradually and with less severe withdrawal effects.

  • Formulations: Buprenorphine is available in various formulations, including sublingual tablets, sublingual films, and long-acting implants.

  • Lower Abuse Potential: Buprenorphine has a lower abuse potential compared to full opioid agonists, making it a preferred option for certain patients, particularly those at risk of opioid misuse.

It’s important to note that while mixed agonist-antagonist opioids like buprenorphine can offer advantages, they are not without risks. Healthcare providers carefully assess each patient’s medical history, pain level, and potential for opioid misuse before prescribing these medications. Additionally, these drugs should be used under close supervision and in accordance with established guidelines to ensure safe and effective management of pain or opioid dependence.

                                          It’s important to remember that several formulations, strengths, and delivery methods may exist within each category. When prescribing opioids for pain management, medical practitioners carefully analyze each opioid’s unique properties, taking into account patient tolerance, potential side effects, and the degree of the patient’s pain.

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