Codeine
**Codeine** is a phenanthrene-derivative opiate agonist used in veterinary medicine primarily as an **antitussive** (cough suppressant) and mild **analgesic**. It is also occasionally used as an antidiarrheal agent. * **Analgesia**: Used for mild to moderate pain, often when NSAIDs are ineffective or contraindicated. * **Antitussive**: Highly effective for suppressing non-productive coughs (e.g., tracheal collapse, chronic bronchitis). * **Antidiarrheal**: Decreases gastrointestinal motility. > **Clinical Pearl**: While widely used in human medicine, codeine's use in dogs is controversial. Dogs absorb oral codeine very poorly and lack the robust enzymatic pathways to convert it to its active metabolite (morphine). Therefore, its analgesic efficacy in dogs is highly variable and generally considered inferior to other opioids like buprenorphine or methadone.
Mecanismo: Codeine acts as a weak agonist at **mu (μ) opioid receptors**. * **Analgesia**: Binds to **μ-receptors** in the central nervous system → inhibits the release of excitatory neurotransmitters (such as Substance P) in ascending pain pathways → alters the perception of and response to pain. * **Antitussive**: Causes direct depression of the **medullary cough center** in the brainstem. * **Antidiarrheal**: Binds to **enteric μ-receptors** → decreases gastrointestinal motility and increases sphincter tone. * **Metabolism Note**: In humans, codeine is a prodrug metabolized by the enzyme **CYP2D6** → **morphine**. Dogs lack significant CYP2D6-equivalent activity, relying mostly on codeine-6-glucuronide for any analgesic effect, which explains its limited efficacy in this species.
Dosificación por especie
- Analgesic (mild to moderate acute pain) · 0.5-2 mg/kg PO titrated to effect q6-12h · PO · q6-12h · May use for chronic pain at lowest effective dose. Do NOT use combination products containing acetaminophen.
- Analgesic · 0.5-2 mg/kg PO q6-8h · PO · q6-8h · Do NOT use combination products containing acetaminophen.
- Analgesic · 0.5 mg/kg PO q6h · PO · q6h · Do NOT use combination products containing acetaminophen.
- Antitussive / Analgesia · 0.5 - 2 mg/kg · PO · q6h-q8h · As directed · Rarely used. MUST ensure the product does NOT contain paracetamol.
- Analgesic · 1 mL in 10-20 mL of drinking water · PO · Continuous · Using acetaminophen and codeine elixir. Add dextrose to enhance palatability.
- Antitussive · 1-2 mg/kg PO q6-12h · PO · q6-12h
- Antitussive · 0.1-0.3 mg/kg PO q8-12h up to 1-2 mg/kg PO q6-12h · PO · q6-12h · Whatever the starting point, the dose may need to be increased to achieve a satisfactory effect.
- Analgesic (mild to moderate acute pain) · 0.5-2 mg/kg PO titrated to effect q6-12h · PO · q6-12h · May use for chronic pain at lowest effective dose.
- Analgesic (in combination with acetaminophen) · 1-2 mg/kg (of the codeine) PO q6-8h · PO · q6-8h · Using a 60 mg codeine and 300 mg acetaminophen fixed-dose tablet. Do not use in cats.
Vías de administración
Contraindicaciones
- Hypersensitivity to narcotic analgesics
- Patients receiving monoamine oxidase inhibitors (MAOIs) like amitraz or selegiline
- Diarrhea caused by toxic ingestion (until toxin is eliminated)
- Repeated use in severe inflammatory bowel disease
- Scorpion stings (Centruroides sculpturatus and C. gertschi) as it may potentiate venom
- Combination products containing acetaminophen are STRICTLY CONTRAINDICATED in cats
- Hypersensitivity to opioids
- Severe respiratory depression or asthma
- Cats (especially if using combination products containing paracetamol)
Efectos adversos
- Sedation (most common)
- Constipation
- Anorexia
- Vomiting
- Ileus
- Biliary and pancreatic duct spasms
- Respiratory depression (at high doses)
- Cats: CNS stimulation, hyperexcitability, tremors, seizures
- Sedation
- Nausea
Interacciones farmacológicas
- Anticholinergic drugs · May increase the chances of constipation developing
- Antidepressants (TCAs/MAOIs) · May potentiate CNS depressant effects
- CNS Depressants (anesthetics, antihistamines, phenothiazines, barbiturates, tranquilizers) · May cause increased CNS or respiratory depression
- Quinidine · May inhibit the transformation of codeine to morphine in the liver, decreasing its efficacy
- CNS Depressants (e.g., phenobarbital, diazepam) · Additive CNS and respiratory depression · moderate
- SSRIs / MAOIs · Increased risk of serotonin syndrome · major
- CNS Depressants (e.g., sedatives, anesthetics, antihistamines) · Additive CNS and respiratory depression · major
- Monoamine Oxidase Inhibitors (MAOIs) · May cause severe, unpredictable reactions (serotonin syndrome or severe respiratory depression) · major
Monitoreo
- Efficacy (pain relief, reduction in coughing, or resolution of diarrhea)
- Adverse effects (sedation, respiratory rate, GI signs)
- Respiratory rate and depth
- Level of sedation
- Pain score or coughing frequency
- Bowel movements (monitor for constipation)
Sobredosis
Opiate overdosage may produce profound **respiratory and/or CNS depression**. Other effects can include cardiovascular collapse, hypothermia, and skeletal muscle hypotonia. * **Decontamination**: Oral ingestions should be removed using standard gut removal protocols. Inducing vomiting should be attempted with caution due to rapid changes in CNS status. * **Antidote**: **Naloxone** is the agent of choice for treating respiratory depression. In massive overdoses, naloxone doses may need to be repeated, as its effects may diminish before subtoxic levels of codeine are attained. * **Supportive Care**: Mechanical respiratory support should be considered in cases of severe respiratory depression. Contact an animal poison control center for further guidance.
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