should be avoided in patients with SA or AV nodal abnormalities, because of its negative chronotropic and dromotropic effects. Low blood pressure patients, with systolic blood pressures below 90 mm Hg, should not be treated with diltiazem. Diltiazem may paradoxically increase ventricular rate in patients with Wolff-Parkinson-White syndrome because of accessory conduction pathways. Diltiazem is relatively contraindicated in the presence of sick sinus syndrome, atrioventricular node conduction disturbances, bradycardia, impaired left ventricle function, peripheral artery occlusive disease, and chronic obstructive pulmonary disease. Side effects A reflex sympathetic response, caused by the peripheral dilation of vessels and the resulting drop in blood pressure, works to counteract the negative inotropic, chronotropic and dromotropic effects of diltiazem. Undesirable effects include hypotension, bradycardia, dizziness, flushing, fatigue, headaches and edema. Rare side effects are congestive heart failure, myocardial infarction, and hepatotoxicity. Diltiazem is one of the most common drugs that cause drug-induced lupus, along with hydralazine, procainamide, isoniazid, minocycline. Drug interactions Because of its inhibition of hepatic cytochromes CYP3A4, CYP2C9 and CYP2D6, there are a number of drug interactions. Some of the more important interactions are listed below. Beta-blockers Intravenous diltiazem should be used with caution with beta-blockers because, while the combination is most potent at reducing heart rate, there are rare instances of dysrhythmia and AV node block. Quinidine Quinidine should not be used concurrently with calcium channel blockers because of reduced clearance of both drugs and potential pharmacodynamic effects at the SA and AV nodes. Fentanyl Concurrent use of fentanyl with diltiazem, or any other CYP3A4 inhibitors, as these medications decrease the breakdown of fentanyl and thus increase its effects. Mechanism Diltiazem, also known as (2S,3S)-3-acetoxy-5-[2-(dimethylamino)ethyl]-2,3-dihydro-2-(4-methoxyphenyl)-1,5-benzothiazepin-4(5H)-one hydrochlorid has a vasodilating activity attributed to the (2S,3S)-isomer. Diltiazem is a potent vasodilator, increasing blood flow and variably decreasing the heart rate via strong depression of A-V node conduction. It binds to the alpha-1 subunit of L-type calcium channels in a fashion somewhat similar to verapamil, another nondihydropyridine (non-DHP) calcium channel blocker. Chemically, it is based upon a 1,4-thiazepine ring, making it a benzothiazepine-type calcium channel blocker. It is a potent and mild vasodilator of coronary and peripheral vessels, respectively, which reduces peripheral resistance and afterload, though not as potent as the dihydropyridine (DHP) calcium channel blockers. This results in minimal reflexive sympathetic changes. Diltiazem has negative inotropic, chronotropic, and dromotropic effects. This means diltiazem causes a decrease in heart muscle contractility – how strong the