GENERAL DESCRIPTION
Calcium Channel Blockers are used to block voltage-dependent Ca2+ channel are called Calcium channel blockers. The main action of this drug is vasodilation. These drugs are used to treat many cardio vascular disease including hypertension, arrhythmia and angina pectoris. Dihyropyridines are more potent vasodilators than Verapamil, which is more potent than diltiazem.
TYPES OF CALCIUM CHANNEL BLOCKERS
There are three types of Calcium channel blockers available so far. Although these drugs are commonly grouped in Calcium channel blockers, but they have different in pharmacological characters, drug interactions and toxicities.
| Class of Calcium channel blockers | Generic Name | Brand Name |
| Dihydropyridine | Nifedipine | Adalat CC, Procardia, Nifediac CC |
| Amlodipine | Norvasc, Acord, Amlibon | |
| Nimodipine | Nimotop, Nymalize | |
| Nicardipine | Cardene | |
| Benzothiazepine | Diltiazem | Cartia, Dilacor, Tiazac, Cardizem |
| Phenylalkylamine | Verapamil | Calan, Isoptin, Verelan |
MECHANISM OF ACTION
The mechanism of action of calcium channel blockers in hypertension is inhibition of calcium influx into arterial smooth muscles.
The L-type calcium channel is the dominant type in cardiac and smooth muscles. In smooth muscles, calcium influx from these calcium channels is responsible for normal resting tone and contractility. When these channels blocked by calcium channel blockers then inhibit the calcium influx resulted in relaxation of vascular, bronchiolar, gastrointestinal and urinary smooth muscles. Calcium channel blockers also reduce the tonicity of coronary arteries which is befitted for the patient of Variant angina.
Cardiac muscles are highly dependent upon calcium influx for normal function. Impulse generation in Atrioventricular node (AV node) and sinoatrial node (SA node) is highly dependent on calcium dependent, action potential. Firstly, Calcium channel blocker reduce the impulse generation in atrioventricular node and sinoatrial node. Secondly, calcium channel blockers reduce the excitation-contraction coupling in all cardiac cells and reduce cardiac contractility. This reduction in cardiac mechanical function by calcium channel blockers reduce the oxygen requirement in patients with angina.
PHARMACOKINETICS
The calcium channel blockers have complete absorption after oral administration. These drugs have 70-98% bioavailability. Some drugs undergo the first-pass metabolism which reduce their bioavailability. The duration of action of calcium channel blockers is 30-60 min of an oral dose except amlodipine. Most of the calcium channel blockers metabolized by an enzyme CYP3A4.
INDICATIONS
- Supraventricular tachyarrhythmia (only verapamil and diltiazem)
- Decrease coronary vascular resistance
- Dysrhythmia
- Variant Angina
- Exertional Angina
- Unstable angina
- SR preparation for hypertension
- Myocardial Infarction
- Hypertension
- Heart Failure (only amlodipine)
- Prophylaxis of migraine (only verapamil)
CONTRAINDICATIONS
- Hypersensitivity
- Hepatic cirrhosis (can use with dose adjustment)
- Second or third degree heart block
- Bradycardia
- Ventricular dysfunction
- SA and AV nodal conduction disturbance
- Systolic blood pressure below 90 mmHg
SIDE EFFECTS & ADVERSE EFFECTS
- Ankle swelling (oedema)
- Negative ionotropic effects (only with verapamil exacerbate heart failure)
- Constipation (Verapamil)
- Dizziness
- Flushing
- Urinary retention (less)
- Headache
- Dizziness
- Nausea
- Vomiting
DRUG INTERACTION
- Verapamil IV and beta blockers when given concurrently, can cause circulatory collapse
- Grape fruit juice may increase the bioavailability of calcium channel blockers.
- Calcium channel blockers can cause digoxin toxicity when given concurrently.
- When use with Quinidine, calcium channel blockers can cause hypotension.
- The absorption of Verapamil may be modestly reduced when given with antineoplastic regimen containing cyclophosphamide, vincristine, procarbazine or doxorubicin, vindesine, cisplatin.
- The concurrent use of aprepitant and diltiazem increases the plasma level of both drugs.
- NSAIDs may reduce the hypotensive effects of Calcium channel blockers. NSAIDs may cause internal bleeding and bruises when used with verapamil.
- Drugs containing azole can increase the serum level of calcium channel blockers, which further increase adverse effect of oedema in patients
- Verapamil given orally with Calcium or calciferol have shown the antagonizing effects on antiarrhythmic effects of verapamil.
- Chlorpromazine and other phenothiazine can cause severe hypotension when used with calcium channel blockers.
- Dantrolene may cause acute hyperkalemia and cardiovascular collapse when given with verapamil or diltiazem.
- Combination of diuretics and calcium channel blockers case increase antihypertensive effects.
- Verapamil and Nifedipine may increase adverse effects (oedema, headache, vomiting, flushing, and orthostatic hypotension) when use with Fluoxetine.
NURSING INTERVENTION
- Inquire complete health history of patient.
- Monitor blood pressure and pulse before and during therapy
- Check fluid intake and output.
- Check peripheral oedema, rashes and other s/s related to the medicine
- Monitor BUN, serum potassium, creatinine, AST, ALT, serum bilirubin level
PATIENT EDUCATION
- Counsel the right time and dosage of medicine.
- Instruct patient how to count pulse and if pulse is less than 55 inform health practitioner.
- If patient taking Nifedipine, forbid to use grapefruit juice.
- Avoid the use of alcohol while taking medicine.
- Don’t adjust the missed dose.
- Avoid OTC and NSAIDs concurrently with medicine.
- Consult doctor prior to the use of herbal or other multivitamins supplements
- Instruct patient to take caution while changing the posture.
- Counsel patient with the possible side effects of the medicine and inform if feel any.