Isoflurane is a halogenated methyl ethyl ether used as a volatile inhalation general anesthetic. It is a non-flammable, non-explosive, clear, colorless liquid with a pungent, ethereal odor. It provides rapid induction and recovery from anesthesia with minimal metabolism (<0.2%), making it a preferred agent for maintenance of general anesthesia in various surgical procedures. It offers good muscle relaxation and is less arrhythmogenic than halothane.
Adult: Induction: 1.5-3.0% v/v with oxygen/nitrous oxide mixture. Maintenance: 1.0-2.5% v/v, adjusted based on patient response, surgical stimulus, and use of adjuncts (opioids, N2O). In 100% oxygen, MAC (Minimum Alveolar Concentration) is 1.15%.
Note: Administered ONLY via a calibrated, agent-specific, temperature-compensated vaporizer in an anesthesia delivery system. Must be used with adequate oxygenation and ventilation. Inspired concentration should be monitored. Use scavenging systems to minimize occupational exposure.
Isoflurane produces a reversible depression of the central nervous system leading to loss of consciousness, amnesia, analgesia, and muscle relaxation. Its exact mechanism is complex and involves potentiation of inhibitory neurotransmission (GABA-A, glycine receptors) and inhibition of excitatory neurotransmission (NMDA, AMPA receptors). It also activates potassium channels (TREK, TASK).
Pregnancy: Pregnancy Category C (US FDA). Animal studies show teratogenicity. Use during pregnancy only if potential benefit justifies potential risk to the fetus. Avoid during first trimester unless essential. Not recommended for obstetric analgesia due to uterine relaxation and increased blood loss.
Driving: Patients must be advised not to drive, operate machinery, or make important decisions for at least 24 hours after general anesthesia.
| Non-depolarizing Neuromuscular Blockers (e.g., Atracurium, Vecuronium) | Potentiates neuromuscular blockade, prolongs duration of action. | Major |
| Opioid Analgesics (e.g., Fentanyl, Morphine) | Additive CNS and respiratory depression; reduces MAC requirement. | Major |
| Beta-blockers (e.g., Atenolol, Metoprolol) | Additive negative inotropic and chronotropic effects, risk of severe bradycardia/hypotension. | Moderate |
| Calcium Channel Blockers (e.g., Verapamil, Diltiazem) | Enhanced myocardial depression and hypotension. | Moderate |
| Aminoglycosides (e.g., Gentamicin) | May enhance neuromuscular blockade. | Moderate |
| Theophylline | May lower seizure threshold. | Moderate |
Same composition (Isoflurane (100%)), different brands: