Isoflurane is compatible with all commonly used muscle relaxants. The effects of which may be markedly potentiated by isoflurane. The effect is most notable in nondepolarising agents. Thus, lower doses should be used in the presence of isoflurane. The effect of nondepolarising muscle relaxants can be counteracted by administering neostigmine as this has no effect on the relaxant properties of isoflurane. Administration of adrenaline (epinephrine) by any route, and some other β-sympathomimetic drugs during isoflurane anaesthesia may cause supraventricular or ventricular arrhythmias.
Isoflurane can cause marked hypotension in patients receiving concomitant therapy with calcium antagonists, especially those of the dihydropyridine class. Patients receiving chronic therapy with other vasodilators eg, ACT inhibitors (eg, captopril, enalapril, lisinopril) or α1-adrenoreceptor antagonists (eg, prazosin) may show unpredictable hypotension with any type of anaesthesia.