可待因
**可待因 (Codeine)** 是一種菲衍生物鴉片類促效劑，在獸醫學中主要用作**鎮咳藥**（止咳）和輕度**鎮痛藥**。偶爾也用作止瀉劑。 * **鎮痛**：用於輕度至中度疼痛，通常在非類固醇消炎止痛藥 (NSAIDs) 無效或有禁忌時使用。 * **鎮咳**：對抑制無痰乾咳（例如氣管塌陷、慢性支氣管炎）非常有效。 * **止瀉**：可降低胃腸道蠕動。 > **臨床要點**：雖然在人類醫學中廣泛使用，但可待因在犬隻的使用存在爭議。犬對口服可待因的吸收極差，且缺乏將其轉化為活性代謝物（嗎啡）的強效酵素途徑。因此，其在犬隻的鎮痛效果變異極大，通常被認為不如丁基原啡因 (Buprenorphine) 或美沙酮 (Methadone) 等其他鴉片類藥物。
作用機制: 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.
各物種劑量
- 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.
給藥途徑
禁忌症
- 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)
不良反應
- 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
藥物相互作用
- 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
監測
- 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)
過量
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.
VetSheet 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。