<p>Diltiazem is readily absorbed from the gastrointestinal tract. Minimum therapeutic plasma diltiazem concentrations appear to be in the range of 50 to 200 ng/mL. Following oral administration of extended formulations of 360 mg diltiazem, the drug in plasma was detectable within 3 to 4 hours and the peak plasma concentrations were reached between 11 and 18 hours post-dose. Diltiazem peak and systemic exposures were not affected by concurrent food intake.<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> Due to hepatic first-pass metabolism, the absolute bioavailability following oral administration is about 40%,<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> with the value ranging from 24 to 74% due to high interindividual variation in the first pass effect.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Hermann P, Rodger SD, Remones G, Thenot JP, London DR, Morselli PL: Pharmacokinetics of diltiazem after intravenous and oral administration. Eur J Clin Pharmacol. 1983;24(3):349-52. (PubMed ID 6861848)" href="#reference-A178420">1</a></sup> The bioavailability may increase in patients with hepatic impairment.<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></p>