Opioid analgesics

Opioids activate mu-opioid receptors, the G protein-coupled receptors used by the body's own opioids in the brain, spinal cord and gut. In nerve cells this opens potassium channels and closes calcium channels, so neurons fire less and release less pain transmitter such as substance P. They also depress the brainstem breathing center, narrow the pupils and slow the gut; tolerance and dependence build with regular use.

• MorphineUnlike tramadol, it releases histamine, which accounts for the itching, flushing and drop in blood pressure it can cause.
• CodeineAlso sold combined with paracetamol (co-codamol) or with ibuprofen.
• TramadolIts dual action sets it apart from other opioids, and unlike morphine it has not been shown to release histamine.
• FentanylMost common serious reactions to the injection are respiratory depression, apnea, muscle rigidity and slow heart rate, which is why it is given where breathing can be supported.
• OxycodoneIts oral bioavailability is high, 60 to 87%, compared with about 20 to 40% for oral morphine.

• Severe pain after surgery or injury
• Cancer pain
• Moderate pain when other painkillers fail
• Pain relief during anesthesia
• Dry cough (codeine)

• Slowed, shallow breathing (respiratory depression)Known forSerious
• ConstipationKnown for
• Pinpoint pupils (miosis)Known for
• Nausea and vomiting
• Drowsiness and sedation
• Addiction, misuse and dependenceSerious
• Withdrawal symptoms if stopped suddenly
• Low blood pressureSerious
• Itching
• Difficulty passing urine

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• With benzodiazepines, alcohol or other CNS depressants they can cause profound sedation, respiratory depression and death.
• Respiratory depression is most likely when starting or raising the dose, in older people and in chronic lung disease.
• Long use in pregnancy can cause neonatal opioid withdrawal syndrome, which can be life-threatening.
• Naloxone reverses an overdose; after regular use, taper slowly rather than stopping, to avoid withdrawal.

Written for biofideX in plain words, after checking these references:

• Opioid (NCI Thesaurus)
• Codeine (NCI Thesaurus)
• Morphine sulfate extended-release tablets: label (DailyMed)
• Morphine (NHS)
• Fentanyl citrate injection: label (DailyMed)

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.