Opiates
A review of terminology, types of opiates, routes of administration, and effects on organ systems and specific receptors.
Three common terms are used to describe a patient’s interaction with opiates: dependence (presence of withdrawal symptoms if a drug is withheld), tolerance (the need to increase the dose of a drug to keep the same level of analgesia), and addiction (compulsive drug seeking or drug use despite harmful consequences).
Opiates can be divided into 3 major groups by their pharmacodynamic property. Pure agonists, such as morphine and fentanyl. Pure antagonists, such as nalaxone. And mixed agonist/antagonists, such as buprenorephine and nalbuphine.
There are multiple routes of administration for opiates for have analgesic effects. These include oral, intravenous, intramuscular, transmucosal, intrathecal, and epidural.
Opiates affect almost every organ system in the body. Neurologically, they cause supraspinal analgesia, spinal analgesia, sedation, euphoria, miosis, and nausea. In the cardiovascular system, they cause vasodilation and bradycardia. In the pulmonary system, they cause cough suppression and ventilation depression. In the gastric system, opiates cause delayed gastric emptying, increased biliary pressure, and constipation. They also cause urinary retention, muscle rigidity, and decreased cellular immunity.
Opiates work on different receptors, each leading to a different effect. Mu1-receptors are responsible for supraspinal analgesia, bradycardia, sedation, pruritus, and nausea. Mu2-receptors are responsible for respiratory depression, euphoria, physical dependence, pruritus, constipation. Kappa-receptors are responsible for spinal analgesia, respiratory depression, sedation, and miosis. And delta-receptors are responsible for spinal anesthesia, and respiratory depression.
