Isoflurane
Dosage & Administration Guidelines
| Species | Route | Dose | Frequency | Duration & Clinical Notes |
|---|---|---|---|---|
| Dog | Inhalation | Induction: 2-3% (with oxygen); Maintenance: 1.5-2.5% | Continuous | Duration: As needed for procedure Notes: Use vaporizer calibrated for isoflurane. Adjust based on anesthetic depth and patient response. |
| Cat | Inhalation | Induction: 2-3% (with oxygen); Maintenance: 1.5-2.5% | Continuous | Duration: As needed for procedure Notes: Cats may require higher concentrations for induction; use mask or chamber. |
| Horse | Inhalation | Maintenance: 1.5-2.5% (after IV induction) | Continuous | Duration: As needed for procedure Notes: Usually used for maintenance after induction with injectable agents. |
| Cattle | Inhalation | Maintenance: 1.5-2.5% (after IV induction) | Continuous | Duration: As needed for procedure Notes: May require higher concentrations due to larger body size; monitor cardiovascular status. |
| Small Ruminants (sheep, goats) | Inhalation | Maintenance: 1.5-2.5% (after IV induction) | Continuous | Duration: As needed for procedure Notes: Similar to cattle; use appropriate vaporizer settings. |
| Rabbit | Inhalation | Induction: 3-4% (in chamber); Maintenance: 1.5-3% | Continuous | Duration: As needed for procedure Notes: Rabbits are prone to respiratory depression; monitor closely. |
| Bird/Poultry | Inhalation | Maintenance: 1-2% (after mask induction) | Continuous | Duration: As needed for procedure Notes: Birds have high metabolic rates; use precision vaporizer and non-rebreathing circuit. |
| Exotic/Other (reptiles, small mammals) | Inhalation | Maintenance: 1-3% (species-dependent) | Continuous | Duration: As needed for procedure Notes: Adjust based on species and response; use appropriate equipment. |
Clinical Indications & Species Uses
- General anesthesia for surgical and diagnostic procedures
- Induction and maintenance of general anesthesia
- Anesthesia for surgical procedures
- Induction and maintenance of general anesthesia
- Anesthesia for surgical procedures
- Maintenance of general anesthesia
- Anesthesia for surgical procedures
- Maintenance of general anesthesia
- Anesthesia for surgical procedures
- Maintenance of general anesthesia
- Anesthesia for surgical procedures
- Induction and maintenance of general anesthesia
- Anesthesia for surgical procedures
- Maintenance of general anesthesia
- Anesthesia for surgical procedures
- Maintenance of general anesthesia in various exotic species (reptiles, small mammals)
Pharmacology & Mechanism of Action
Drug Class: Inhalation Anesthetic | Pharmacological Group: Halogenated Ether
Mechanism of Action: Isoflurane produces dose-dependent central nervous system depression by enhancing inhibitory GABAergic neurotransmission and inhibiting excitatory glutamatergic neurotransmission. It acts on multiple ion channels, including GABA-A receptors, glycine receptors, and N-methyl-D-aspartate (NMDA) receptors, leading to decreased neuronal excitability and induction of anesthesia. The exact molecular targets are not fully understood, but it is believed to disrupt synaptic transmission in the brain and spinal cord, resulting in unconsciousness, amnesia, and immobility.
Pharmacodynamics: Isoflurane causes a dose-dependent decrease in blood pressure primarily due to peripheral vasodilation, with minimal direct myocardial depression at clinical doses. It increases cerebral blood flow and intracranial pressure, but reduces cerebral metabolic rate. It produces dose-dependent respiratory depression, with a decrease in tidal volume and an increase in respiratory rate. It also causes skeletal muscle relaxation and potentiates the effects of neuromuscular blocking agents. The minimum alveolar concentration (MAC) varies by species: approximately 1.28% in dogs, 1.63% in cats, 1.31% in horses, 1.2% in cattle, and 1.5% in rabbits.
β‘ Pharmacokinetics Summary
Available Formulations & Strengths
Contraindications & Clinical Warnings
- Known hypersensitivity to isoflurane or other halogenated anesthetics
- History of malignant hyperthermia (in susceptible species, e.g., pigs, dogs, horses)
- Severe hypotension or hypovolemia (use with caution)
- Increased intracranial pressure (unless adequately managed)
- Use only with calibrated vaporizers and appropriate anesthesia equipment.
- Monitor vital signs (heart rate, respiratory rate, blood pressure, oxygen saturation, end-tidal CO2) continuously.
- Isoflurane is a potent respiratory depressant; provide assisted ventilation if needed.
- May cause dose-dependent hypotension; use with caution in patients with cardiovascular compromise.
- Use in well-ventilated areas to minimize occupational exposure; use scavenging systems.
- Pregnant animals: use with caution; may cause uterine relaxation and fetal depression.
- In horses, isoflurane can cause hypotension and respiratory depression; monitor closely.
- In birds, use non-rebreathing circuits to reduce dead space and resistance.
- Malignant hyperthermia risk: discontinue immediately if signs (hyperthermia, muscle rigidity, tachycardia) occur and treat with dantrolene.
Adverse Effects & Reactions
Common:
- Hypotension
- Respiratory depression
- Hypothermia
- Shivering during recovery
- Nausea and vomiting (in some species)
Serious / Severe:
- Malignant hyperthermia (rare but life-threatening)
- Cardiac arrhythmias
- Severe hypotension
- Respiratory arrest
- Hepatic injury (rare)
Rare:
- Seizures (during induction or recovery)
- Hyperkalemia (in susceptible individuals)
- Metabolic acidosis
Key Drug Interactions
| Interacting Drug / Class | Clinical Effect & Mechanism | Severity |
|---|---|---|
| Neuromuscular blocking agents (e.g., atracurium, vecuronium) | Isoflurane potentiates the effects of neuromuscular blockers, leading to prolonged muscle relaxation. | Moderate |
| Opioids (e.g., fentanyl, morphine) | Additive respiratory depression and sedation; may reduce MAC requirements. | Moderate |
| Benzodiazepines (e.g., diazepam, midazolam) | Additive CNS depression; may reduce MAC. | Mild |
| Alpha-2 agonists (e.g., xylazine, dexmedetomidine) | Additive hypotension and bradycardia; may reduce MAC significantly. | Moderate |
| Epinephrine and other sympathomimetics | Increased risk of cardiac arrhythmias. | Moderate |
| Aminoglycoside antibiotics (e.g., gentamicin) | May enhance neuromuscular blockade. | Mild |
Overdose & Toxicity Management
Signs of Toxicity:
- Severe hypotension
- Respiratory depression or apnea
- Cardiac arrhythmias
- Hypothermia
- Cyanosis
- Coma
Emergency Treatment Protocol: Immediately discontinue isoflurane administration, provide 100% oxygen, and institute assisted or controlled ventilation. Support cardiovascular function with intravenous fluids and vasopressors (e.g., dopamine, norepinephrine) as needed. Treat arrhythmias with appropriate antiarrhythmic agents. Monitor body temperature and provide active warming if hypothermic. In cases of malignant hyperthermia, administer dantrolene (2-3 mg/kg IV) and initiate cooling measures.
Food Animal Withdrawal Times
Isoflurane is rapidly eliminated via exhalation; no withdrawal times are required for food animals. However, follow label recommendations and local regulations.
Storage, Handling & Regulatory Information
Storage Temperature: Store at controlled room temperature (15-30Β°C)
Handling & Special Conditions: Keep container tightly closed. Protect from moisture. Do not use if discolored or if container is damaged.
Dispensing Status: Prescription Required (Rx Only)
Approval Status: Approved for veterinary use in dogs, cats, and horses (FDA-approved).
Extra-Label (Off-Label) Use: In the US, isoflurane is approved for use in dogs, cats, and horses. Extra-label use in other species is permitted under AMDUCA with appropriate veterinary oversight and withdrawal times.
Clinical Pearls & Practice Notes
References & Literature
- π Plumb's Veterinary Drug Handbook
- π Papich Veterinary Pharmacology and Therapeutics
- π Compendium of Veterinary Products (CVP)