Concomitant intake of tetracyclines and zinc may decrease the Gl absorption and serum levels of tetracyclines. Similarly concomitant administration of zinc and fluroquinolones may decrease the Gl absorption and serum? levels of some fluroquinolones. Coadministration of Niacin and HMG-CoA reductase inhibitors (eg. lovastatin) may result mayopathy and rhabdomyolysis. Pyridoxine reduces levodopa’s effectiveness by increasing its peripheral metabolism. Co-administration of pyridoxine with phenytoin may decrease serum levels of phenytoin.