Analgesic Agents Flashcards
What can cause prolonged narcosis and ventilatory depression in patients with kidney failure when taking morphine?
The accumulation of morphine metabolites, morphine 3-glucuronide and morphine 6-glucuronide, in patients with kidney failure can cause prolonged narcosis and ventilatory depression lasting several days.
What is a dangerous effect of rapidly administering large doses of opioids like fentanyl, sufentanil, remifentanil, and alfentanil?
Rapid administration of large doses of opioids can induce chest wall rigidity severe enough to prevent adequate bag-and-mask ventilation.
What is opioid-induced hyperalgesia?
Opioid-induced hyperalgesia is a condition in which patients become more sensitive to painful stimuli after prolonged opioid dosing.
What is the effect of large doses of opioids on the neuroendocrine stress response during surgery?
Large doses of opioids block the release of specific hormones, such as catecholamines, antidiuretic hormone, and cortisol, more completely than volatile anesthetics.
How does aspirin inhibit COX-1?
Aspirin irreversibly inhibits COX-1 by acetylating a serine residue in the enzyme, leading to prolonged effects even after the drug is discontinued.
What is the goal of multimodal analgesia in postoperative care?
The goal of multimodal analgesia is to provide pain relief using a combination of medications, often emphasizing COX inhibitors and local anesthetic techniques while minimizing opioid use.
What receptors do opioids bind to in the body?
Opioids bind to specific receptors throughout the central nervous system, including mu (µ), kappa (κ), delta (δ), and sigma (σ) receptors.
What is the cellular mechanism by which opioids work?
Opioids inhibit the presynaptic release and postsynaptic response to excitatory neurotransmitters, including acetylcholine and substance P, from nociceptive neurons.
What type of analgesia is provided by opioids when administered intrathecally or epidurally?
Opioids provide analgesia by selectively modifying the transmission of pain impulses at the level of the dorsal horn of the spinal cord.
What is the difference between full opioid agonists and agonist–antagonists?
Full opioid agonists (e.g., fentanyl) have greater efficacy than agonist–antagonists (e.g., nalbuphine, nalorphine, butorphanol, and pentazocine), which may antagonize the actions of full agonists in some situations.
What are the common effects of opioids when administered peripherally, such as in the gastrointestinal system?
Opioids can reduce gastrointestinal motility, which may result in constipation and biliary colic due to contraction of the sphincter of Oddi.
What is the role of opioid receptor activation in pain management?
Opioid receptor activation inhibits the transmission of pain signals by blocking the release of excitatory neurotransmitters and modulating pain perception via descending inhibitory pathways.
What structural characteristics do opioids generally share?
Opioids share common structural characteristics, and small changes in their chemical structure can convert an agonist into an antagonist.
What is the pharmacokinetics of opioid absorption through intramuscular injection?
Opioids like hydromorphone, morphine, and meperidine are rapidly and completely absorbed via intramuscular injection, with peak plasma levels usually achieved in 20–60 minutes.
How is fentanyl absorbed transdermally?
Fentanyl, a lipid-soluble opioid, can be absorbed through the skin using a transdermal patch, with peak serum levels occurring within 14–24 hours of application.
How does the lipid solubility of fentanyl and sufentanil affect their onset and duration?
The increased lipid solubility of fentanyl and sufentanil leads to a faster onset and shorter duration of action when administered in small doses.
What is the role of pulmonary uptake in opioid distribution?
Significant amounts of lipid-soluble opioids can be retained by the lungs (first-pass uptake) and released into the bloodstream as systemic concentrations fall.
How do opioids undergo biotransformation?
Opioids are primarily metabolized in the liver by the cytochrome P450 system, with some metabolites being active, like morphine 6-glucuronide, while others are inactive.
What is unique about remifentanil’s metabolism compared to other opioids?
Remifentanil has an ester structure and is hydrolyzed by nonspecific esterases in red blood cells and tissues, resulting in a very short elimination half-life of less than 10 minutes.
What cardiovascular effects do opioids generally have?
Opioids typically cause a decrease in arterial blood pressure due to bradycardia, venodilation, and decreased sympathetic reflexes, often requiring vasopressor support.
What is the effect of opioids on the respiratory system?
Opioids depress ventilation, particularly respiratory rate, and shift the CO2 response curve downward, leading to a higher apneic threshold and decreased hypoxic drive.
How do opioids affect the cerebral circulation?
Opioids reduce cerebral oxygen consumption, cerebral blood flow, and intracranial pressure, but to a much lesser extent than barbiturates, propofol, or benzodiazepines.
How do opioids interact with the gastrointestinal system?
Opioids reduce peristalsis in the gastrointestinal tract, causing constipation, and can induce biliary colic due to contraction of the sphincter of Oddi.
What is the risk of using meperidine in patients with renal failure?
Meperidine’s active metabolite, normeperidine, can accumulate in patients with renal failure, leading to seizures that are not reversed by naloxone.
