Severe Hypotension from Lisinopril plus Tizanidine
“Dramatic” hypotension in a patient who was taking drug lisinopril (Zestril generic, AstraZeneca), an ACE-inhibitor, might have been caused by an interaction with tizanidine (Zanaflex®, Elan), a muscle relaxant, say physicians from Taipei Veterans General Hospital in Taiwan. A 48-year-old woman was admitted to the hospital with a cerebral hemorrhage. Five days after the onset of stroke, her abnormal body posture improved but her blood pressure was still fairly high (160/100 mm Hg). The medical team started antihypertensive therapy, including generic lisinopril. Three weeks later, they added tizanidine in hopes of improving the patient’s rigidity and still-high blood pressure by reducing muscle tone.
Her blood pressure plummeted within two hours, from 130/85 to 66/42 mm Hg. The physicians did not find any newly developed focal deficits or worsening systemic infection. Because of the acute hypotension and deterioration in consciousness, they started dopamine therapy to maintain blood pressure. They withdrew tizanidine and all antihyper-tensive agents. Within five hours, the patient’s blood pressure increased to 120/50 mm Hg. Dopamine was stopped 20 hours later. The alpha-beta blocker labetolol (e.g., Trandate®, Prometheus), the calcium-channel blocker amlodipine besylate (e.g., Norvasc®, Pfizer), the cerebral artery spasm inhibitor nimodipine (e.g., Nimotop®, Bayer), and tizanidine were successively resumed 42 hours later when her blood pressure reached 152/85 mm Hg, but they did not produce similar problems.
Tizanidine drug is an alpha2-adrenergic agonist much like clonidine (Catapres generic, Boehringer Ingelheim) but with less severe side effects. Because clonidine drug can depress blood pressure through volume depletion and an ACE-inhibitor may further compromise the renin-angio-tensin system, the authors theorize that tizanidine might provoke the same response. The authors concede that the drastic decrease in blood pressure might have been an idiosyncratic reaction. The use of ACE-inhibitors in post-stroke patients is not rare, and tizanidine is increasingly chosen for its antispastic effect with few hemodynamic influences. However, they add, significant hypotensive events are seldom reported.
