Meperidine
Meperidine (also known as pethidine) is a synthetic **opiate agonist** primarily used for analgesia. **Clinical Pearls:** * While historically popular, its use in modern veterinary medicine has significantly declined due to its very short duration of action (<1-2 hours in dogs and cats) and high propensity to cause **histamine release** and hypotension, especially when administered intravenously. * Unlike most other opioids, meperidine possesses **vagolytic (anticholinergic) and negative inotropic properties**, which can lead to tachycardia rather than the bradycardia typically seen with pure mu agonists. * It is approximately 1/3 to 1/8th as potent as morphine but produces equivalent respiratory depression at equi-analgesic doses. * It is a C-II controlled substance.
Mecanismo: Meperidine acts primarily as an agonist at the **mu (μ) opioid receptors** in the central nervous system (CNS) and peripheral tissues. * **Receptor Binding:** Binds to G-protein coupled mu receptors → inhibits adenylate cyclase → decreases intracellular cAMP. * **Ion Channel Modulation:** Promotes opening of potassium channels (causing hyperpolarization) and inhibits voltage-gated calcium channels (decreasing neurotransmitter release). * **Analgesia:** Inhibits ascending nociceptive pathways and alters the perception of pain. * **Unique Mechanisms:** Exhibits **anticholinergic (vagolytic)** effects and can cause direct mast cell degranulation leading to **histamine release**.
Dosificación por especie
- Perioperative pain · 3-5 mg/kg · IM, SC · 1-2 hours
- Analgesia · 2-5 mg/kg · IM, SC · short (30 minutes to an hour)
- Pre-medication · 3-4 mg/kg · IM · In healthy cats
- Post-op analgesia · 1-2 mg/kg · IM · In healthy cats
- General Note · Not recommended for cats
- Analgesia (mild to moderate pain) · 5-10 mg/kg · IM, SC · q1-2h · Depending on pain assessment · Frequent redosing is required.
- Restraining agent (preanesthetic) · 1-2 mg/kg · IM · 45-60 minutes before anesthesia · Used in combination with promazine (2 mg/kg IM) and atropine (0.07-0.09 mg/kg IM) in separate sites.
- Analgesia · 2 mg/kg · IM · q4h · as needed
- Analgesia · 5-10 mg/kg · SC, IM · q2-3h
- Analgesia · Up to 200 mg total dose · IM
Vías de administración
Contraindicaciones
- Hypersensitivity to narcotic analgesics
- Patients receiving monamine oxidase inhibitors (MAOIs)
- Diarrhea caused by a toxic ingestion (until toxin is eliminated)
- Envenomations from Centruroides scorpion species, Gila monsters, or Mexican beaded lizards
- Intravenous (IV) administration
- Animals at risk from histamine release (e.g., skin allergies, asthma, mast cell tumours)
Efectos adversos
- Respiratory depression
- Histamine release
- Bronchoconstriction (dogs)
- CNS depression
- Nausea and vomiting
- Decreased intestinal peristalsis
- Mydriasis (dogs)
- Salivation (especially cats)
- Physical dependence (chronic use)
- Tachycardia with PVCs (horses)
- Profuse sweating (horses)
- Hyperpnea (horses)
- Severe hypotension (if given IV rapidly)
- Hypotension (especially if given IV)
- Tachycardia
- Bronchoconstriction
Interacciones farmacológicas
- CNS Depressants (anesthetics, antihistamines, phenothiazines, barbiturates, tranquilizers) · May cause increased CNS or respiratory depression when used with meperidine.
- Diuretics · Opiates may decrease efficacy in CHF patients.
- Isoniazid · Meperidine may enhance INH adverse effects.
- Monamine Oxidase Inhibitors (MAOIs) (e.g., amitraz, selegiline) · Contraindicated. Can cause severe opiate overdose signs; avoid meperidine for at least 14 days after receiving MAOIs.
- Skeletal Muscle Relaxants · Meperidine may enhance neuromuscular blockade.
- Tricyclic Antidepressants (clomipramine, amitriptyline) · Meperidine may exacerbate the effects of tricyclic antidepressants.
- Warfarin · Opiates may potentiate anticoagulant activity.
- CNS depressants (anaesthetics, antihistamines, barbiturates, phenothiazines, tranquillizers) · Increased CNS or respiratory depression · moderate
- Monoamine oxidase inhibitors (MAOIs) · Serious interaction resulting in coma, convulsions, and hyperpyrexia · major
Monitorización
- Respiratory rate and depth
- CNS level of depression or excitation
- Blood pressure (especially with IV use)
- Analgesic activity
- Pain score
- Heart rate
- Blood pressure
- Signs of histamine release (urticaria, bronchoconstriction)
Sobredosis
Overdosage may produce profound **respiratory and/or CNS depression**. Other effects can include cardiovascular collapse, hypothermia, and skeletal muscle hypotonia. * **Species Differences:** Some species (especially cats) may demonstrate CNS excitability (hyperreflexia, tremors) and seizures at doses >20 mg/kg. * **Treatment:** **Naloxone** is the agent of choice for respiratory depression. In massive overdoses, naloxone doses may need to be repeated, as its effects can diminish before subtoxic levels of meperidine are attained. Mechanical respiratory support should be considered. Pentobarbital has been suggested for CNS excitement/seizures in cats, but extreme caution is required as barbiturates and narcotics have additive respiratory depressant effects.
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