Major
Colchicine × Verapamil
Antigout agents×Non-dihydropyridine calcium channel blocker
Mechanism
Verapamil blocks CYP3A4 and the P-glycoprotein transporter – two colchicine clearance routes. Colchicine plasma levels rise; myopathy, neuropathy, and pancytopenia risks grow.
Symptoms
Profuse diarrhoea, vomiting, abdominal pain. With prolonged combination: muscle weakness, peripheral neuropathy, falling leukocytes and platelets.
Management
In chronic kidney disease or hepatic impairment, do not prescribe. With preserved function: colchicine 0.3 mg every other day for no more than 5 days. Alternative for gout on verapamil: intra-articular or short systemic glucocorticoid.