<p>Diltiazem is about 70-80% bound to plasma proteins, according to <em>in vitro</em> binding studies.<sup class="text-reference-group"><a class="reference-popover-link" data-content="CARDIZEM® LA (diltiazem hydrochloride) extended-release tablets - FDA Label" href="#reference-L10556">12</a></sup> About 40% of the drug is thought to bind to alpha-1-glycoprotein at clinically significant concentrations while about 30% of the drug is bound to albumin.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Diltiazem Hydrochloride Injection Label - Bedford Laboratories" href="#reference-L6292">10</a></sup></p>