Hydromorphone
Hydromorphone is a potent, semi-synthetic **pure mu-opioid receptor agonist** used extensively in veterinary medicine as a sedative, restraining agent, analgesic, and preanesthetic. Key clinical features include: - **Potency**: Approximately 5 times more potent than morphine on a per-weight basis, and roughly equipotent to oxymorphone. - **Advantages over Morphine**: Generally causes less sedation, minimal histamine release following intravenous administration, and rarely induces significant vasodilation or hypotension. - **Clinical Utility**: Rapidly replacing oxymorphone in veterinary practice due to comparable analgesic efficacy and duration of action, but at a significantly lower cost. - **Regulatory Status**: It is a **Schedule II (C-II)** controlled substance due to its high potential for abuse and physical dependence.
Mecanismo: Hydromorphone exerts its effects by binding to opioid receptors, primarily the **mu (μ) receptors**, with some affinity for **delta (δ) receptors**. Mechanism pathway: Agonist binding to **mu-receptors** in the CNS (limbic system, spinal cord, thalamus, midbrain) and peripheral tissues (GI tract, smooth muscle) → activation of G-proteins → inhibition of **adenylate cyclase** → decreased intracellular cAMP → opening of **potassium channels** (causing hyperpolarization) and closing of **voltage-gated calcium channels** → decreased presynaptic release of excitatory neurotransmitters (e.g., **Substance P**, glutamate) → profound **analgesia** and altered pain perception. Secondary effects include respiratory depression (decreased sensitivity of the respiratory center to CO2), antitussive activity, and increased GI sphincter tone leading to decreased motility.
Dosificación por especie
- As an analgesic · 0.05-0.1 mg/kg IM, IV or SC q2-6 hours · IM/IV/SC · q2-6h
- For cancer pain · 0.08-0.2 mg/kg IV, IM, or SC · IV/IM/SC · Not specified
- For moderate to severe pain · 0.08-0.3+ mg/kg IV, IM or SC q2-6 hours · IV/IM/SC · q2-6h
- As a premed prior to moderately painful procedures · 0.1 mg/kg · Not specified · Once · May be combined with acepromazine (0.05-0.2 mg/kg) in young, healthy patients.
- As an alternate induction method (especially in critical patients) · 0.05-0.2 mg/kg IV, slowly to effect followed by diazepam 0.02 mg/kg IV · IV · Once · Do not mix two drugs together. Positive pressure ventilation likely necessary.
- As a pre-op · 0.05-0.1 mg/kg IV · IV · Once
- As a CRI post-op · 0.05 mg/kg IV loading dose, then 0.05-0.1 mg/kg/hr · IV · CRI
- As a pre-op (Rabbits) · 0.05-0.1 mg/kg IV · IV · Once
- As a CRI post-op (Rabbits) · 0.05 mg/kg IV loading dose, then 0.05-0.1 mg/kg/hr · IV · CRI
Vías de administración
Contraindicaciones
- Hypersensitivity to narcotic analgesics
- Diarrhea caused by toxic ingestion (until toxin is eliminated)
- Prior to GI obstructive surgery (due to vomiting risk)
- Patients stung by scorpion species Centruroides sculpturatus Ewing and C. gertschi Stahnke (may potentiate venom)
Efectos adversos
- Dogs: Nausea, vomiting, defecation, panting, vocalization, sedation, CNS depression, respiratory depression, bradycardia, decreased GI motility (constipation with chronic use)
- Cats: Nausea, ataxia, hyperesthesia, hyperthermia, behavioral changes (mania/excitement if given without tranquilization)
- Mild histamine release (infrequent compared to morphine)
Interacciones farmacológicas
- Butorphanol, Nalbuphine · Potentially could antagonize opiate effects
- CNS Depressants · Additive CNS depression effects possible
- Diuretics · Opiates may decrease diuretic efficacy in CHF patients
- Monoamine Oxidase Inhibitors (e.g., amitraz, selegiline) · Severe and unpredictable opiate potentiation; not recommended if MAOI used within 14 days
- Skeletal Muscle Relaxants · Hydromorphone may enhance muscle relaxant effects
- Phenothiazines · May antagonize analgesic effects and increase risk for hypotension
- Tricyclic Antidepressants (clomipramine, amitriptyline) · Hydromorphone may exacerbate the effects of tricyclic antidepressants
- Warfarin · Opiates may potentiate anticoagulant activity
Monitoreo
- Respiratory rate and depth (pulse oximetry highly recommended)
- CNS level of depression or excitation
- Blood pressure (especially with IV use)
- Cardiac rate (monitor for bradycardia)
- Analgesic efficacy
Sobredosis
Massive overdoses may produce profound **respiratory and/or CNS depression** in most species. Other potential effects include: - Cardiovascular collapse - Hypothermia - Skeletal muscle hypotonia - Mania (especially in cats) **Treatment**: - **Naloxone** is the specific reversal agent of choice for treating respiratory depression. - In massive overdoses, naloxone doses may need to be repeated, as naloxone's duration of action may be shorter than that of hydromorphone. - Mechanical respiratory support should be considered in cases of severe respiratory depression. - Provide supportive care as needed.
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