Diltiazem is an oral and parenteral non-dihydropyridine calcium channel blocker. It is used in many clinical scenarios as an antihypertensive, anti-arrhythmic, and as an anti-anginal.
Diltiazem is also used for numerous off-label indications. A select few are listed below.
Diltiazem is available in many dosage forms and strengths making it imperative to be cautious when prescribing, dispensing and administering this medication. Numerous brand names for oral diltiazem (capsules and tablets) include:
Available strengths include 30mg, 60mg, 90mg, 120mg, 180mg, 240mg, 300mg, 360mg, 420mg.
Diltiazem is a non-dihydropyridine calcium channel blocker. Therapeutic effects are seen through various mechanisms. Primarily, diltiazem inhibits the inflow of calcium ions into the cardiac smooth muscle during depolarization. Reduced intracellular calcium concentrations equate to increased smooth muscle relaxation resulting in arterial vasodilation and therefore, decreased blood pressure. Diltiazem is a potent coronary artery vasodilator and is therefore used for chronic angina and in those patients with coronary vasospasm. Vasospasm of the coronary arteries can lead to debilitating conditions such as myocardial infarction.
Diltiazem is classified as a negative inotrope (decreased force) and negative chronotrope (decreased rate). The combination along with coronary artery vasodilation leads to decreased myocardial oxygen demand, decreased heart rate, and reduced blood pressure.
Chronic Stable Angina
Atrial Arrhythmia/Paroxysmal Supraventricular Tachycardia
*Increase based on clinical response to 180mg-360mg/day
Common adverse effects of diltiazem therapy include edema, bradycardia, dizziness, headache, and fatigue. Rarer, yet more severe adverse effects include congestive heart failure, myocardial infarction, and hepatotoxicity. Diltiazem is indicated for the treatment of arrhythmias and consequently the potential to worsen or create new arrhythmias such as extrasystole and AV block.
Diltiazem is extensively metabolized through the CYP450 system and requires careful medication profile review. Concomitant use alongside potent CYP450 inhibitors may increase diltiazem concentrations leading to adverse effects even at clinically recommended doses. Concomitant administration with agents that slow cardiac conduction can further potentiate adverse effects such as AV block or bradycardia.
Specific clinical scenarios are contraindicated to the use of diltiazem. Due to its mechanism of actions, patients with a systolic blood pressure of less than 90mmHg are ineligible for diltiazem pharmacotherapy. Additional contraindications include sick sinus syndrome and second/third degree AV block, without a functioning ventricular pacemaker and acute myocardial infarction with pulmonary congestion on X-ray.
Additional contraindications are in place for intravenous administration. These include concomitant or recent administration of intravenous beta blockers; cardiogenic shock; atrial fibrillation or flutter associated with an accessory bypass tract (i.e., Wolff-Parkinson-White syndrome); and ventricular tachycardia.
Therapeutic monitoring includes periodic assessments of blood pressure, heart rate, and electrocardiograms. When treating hypertension and arrhythmias, objective findings are used to assess the efficacy of therapy while subjective findings, such as a patient's frequency and severity of chest pain, are used to assess efficacy when treating chronic angina. A complete blood count (CBC) lab test is also performed at baseline to track potential changes in electrolytes and kidney and liver function.
For treatment of hypertension during pregnancy, recommendations state to use an alternative agent as diltiazem has shown adverse fetal effects in animal studies. If a patient is controlled on diltiazem for the treatment of hypertrophic cardiomyopathy, diltiazem may be continued, but additional fetal monitoring is required.
Additional monitoring is required when using diltiazem parenterally. When treating arrhythmias, an IV bolus is administered over two minutes. Continuous blood pressure and ECG monitoring are warranted during the bolus administration.
Potential diltiazem overdose can lead to profound bradycardia and conduction delays by suppression of SA and AV nodes. These may manifest as dizziness, lightheadedness, and fatigue. Further toxicities can lead to worsened arrhythmias, hyperglycemia and end-organ dysfunction. Moderate toxicity can be treated with fluids but ACLS protocol may be required when treating severe bradycardia and hypotension. 
Diltiazem is a substrate of the CYP450 enzyme and careful monitoring is warranted when given concomitantly with inducers or inhibitors. Potent inducers/inhibitors can lead to new arrhythmias or worsen existing arrhythmias. Potent inhibitors can increase diltiazem concentration leading to mentioned toxicities. A medication profile review should be conducted when initiating new medications for patients on diltiazem. 
Diltiazem has been widely used in practice for many clinical indications. Proper dosage and frequency are essential to enhance patient care and improve outcomes. Providers should verify drug, dose, and patient factors prior to administration. One common error that occurs with diltiazem therapy is incorrect dose administered to the patient. Diltiazem is available in many brand names with differing recommended dosages and differing maximum daily doses. Double-checking doses can help ensure the patient is being therapeutically managed in both the inpatient and outpatient setting. Pharmacists and other providers should also check for potential drug interactions with other medications of the patient's profile. This will limit the potential drug interactions.
Diltiazem possesses negative inotropic effects and is generally avoided in patients with congestive heart failure, but diltiazem is also on the Beers Criteria. This highlights the importance to avoid diltiazem in heart failure patients, especially in the elderly, due to potential fluid retention and heart failure exacerbation.