Drugs or dissection? Unraveling a diagnostic puzzle in the ED: A case report on Tizanidine-Nifedipine interaction.

Lower back pain is among the top ten reasons patients visit the emergency department (ED). Tizanidine, a centrally acting alpha-2 adrenergic receptor agonist, is commonly prescribed for managing spasticity in patients with cerebral or spinal injuries. It is also used as an effective treatment for nonspecific lower back pain. One of the most critical and life-threatening causes of lower back pain is abdominal aortic dissection, particularly in patients with hypertension. Nifedipine, a 1,4-dihydropyridine calcium channel blocker (CCB), is a widely used oral antihypertensive and antianginal agent. It lowers systemic vascular resistance and dilates coronary arteries by inhibiting calcium ion (Ca²⁺) entry into the smooth muscle cells of small arteries (arterioles), thereby reducing systemic blood pressure and improving myocardial oxygen delivery. We report a compelling case of a male patient presenting to the ED with high blood pressure and lower back pain. Shortly after the administration of tizanidine and nifedipine, his blood pressure dropped significantly within an hour. Initially suspected to be a ruptured abdominal aortic dissection, the cause was later identified as a drug-drug interaction. The synergistic effects of tizanidine and nifedipine resulted in a rapid and critical drop in blood pressure. The Drug Interaction Probability Scale (DIPS) score of 4 suggests the hypotensive episode was possibly caused by a drug interaction. This case also highlights the importance of point of care ultrasound (POCUS) and repeated examinations in excluding life-threatening conditions like aortic rupture.