Codeine
A weak opioid prodrug that CYP2D6 turns into morphine, used for mild to moderate pain, dry cough and diarrhea.
Drug card
- Class
- Opioid
- How it works
- Activating mu-opioid receptors in the brain and spinal cord to dull pain
- Used for
- Mild to moderate pain
- Dry or painful cough
- Diarrhea
- Known for
- Constipation
- Slowed breathing, worst in ultra-rapid metabolizers
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does codeine work?
Codeine binds mu-opioid receptors far more weakly than morphine; its pain relief is thought to come mostly from the part CYP2D6 converts to morphine. Ultra-rapid CYP2D6 metabolizers make morphine faster and can be poisoned. It also calms the medullary cough center and slows gut movement.
Like other 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.
Uses
What is codeine used for?
- Mild to moderate pain
- Dry or painful cough
- Diarrhea
Side effects
Side effects of codeine
- ConstipationKnown for
- Slowed breathing, worst in ultra-rapid metabolizersKnown forSerious
- Nausea and vomiting
- Drowsiness and tiredness
- Dizziness and lightheadedness
- Headache
- Dry mouth
- Itching
- Low blood pressureSerious
- Addiction, misuse and dependenceSerious
- Withdrawal symptoms if stopped suddenly
- Serotonin syndrome with serotonergic drugsSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Contraindicated under 12 years, and under 18 after tonsil or adenoid removal, because of fatal breathing depression.
- Breastfeeding is not advised: an ultra-rapid metabolizer mother can pass harmful amounts of morphine to her baby.
- CYP3A4 inhibitors raise levels and morphine production; benzodiazepines or alcohol add to breathing depression.
Good to know: Also sold combined with paracetamol (co-codamol) or with ibuprofen.
Remember it
A way to remember it
MORPHINE
- M
- Miosis (pinpoint pupils)
- O
- Opioid withdrawal if stopped suddenly
- R
- Respiratory depression
- P
- Pruritus (itching)
- H
- Hypotension
- I
- Intestinal slowing: constipation
- N
- Nausea and vomiting
- E
- Euphoria, then dependence and addiction
Written for biofideX
Its class
Opioid analgesics
Easily mixed up with opioid antagonists, benzodiazepines and antimotility drugs.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
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.
Pain, fever and inflammation
Codeine is one of 15 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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