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Calcium channel blockers

Calcium channel blockers (CCBs) work by blocking the influx of calcium through L-type calcium channels in cardiac and vascular smooth muscle. This leads to vasodilation, decreased blood pressure, and reduced cardiac contractility. The main classes of CCBs are dihydropyridines like nifedipine, benzothiazepines like diltiazem, and diphenylalkylamines like verapamil. They are used to treat hypertension, angina, and arrhythmias. Common side effects include headache, flushing, edema, and constipation. Cautions include hypotension, heart failure, and avoiding grapefruit juice with some CCBs.

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CALCIUM CHANNEL BLOCKERS MEDICAL STUDENT: MOHAMMAD TAILAKH . 4TH YEAR AT JU.
CCB ā€¢ It has been known since the late 1800s that transmembrane calcium influx is necessary for the contraction of smooth and cardiac muscle. The discovery of a calcium channel in cardiac muscle was followed by the finding of several different types of calcium channels in different tissues. ā€¢ Although the blockers currently available for clinical use in cardiovascular conditions are exclusively L-type calcium channel blockers.
Type Channel Name Where Found Properties of the Calcium Current Blocked By L CaV1.1ā€“CaV1.3 Cardiac, skeletal, smooth muscle, neurons (CaV1.4 is found in retina), endocrine cells, bone Long, large, high threshold Verapamil, DHPs, Cd2+, -aga-IIIA T CaV3.1ā€“CaV3.3 Heart, neurons Short, small, low threshold sFTX, flunarizine, mibefradil1 N CaV2.2 Neurons, sperm2 Short, high threshold Ziconotide,3 gabapen tin,4 -CTX- GVIA, -aga-IIIA, Cd2+ P/Q CaV2.1 Neurons Long, high threshold -CTX-MVIIC, - aga-IVA
CCB ā€¢ They divided into three chemical classes: ā€¢ a. Diphenylalkylamines, Varapamil. ā€¢ b. Benzothiazepines, Diltiazem ā€¢ c. Dihydropyridines, Nifedipine
ā€¢ MECHANISM OF ACTION ā€¢ Calcium enters muscle cell through special voltage sensitive calcium channel. ā€¢ Normally, L-Type of channels admit Ca+ and causes depolarization ā€“ excitation- contraction coupling through phosphorylation of myosin light chain ā€“ contraction of vascular smooth muscle ā€“ elevation of BP CCBs block L-Type ā€¢ These agents exert their effect by antagonists block for the inward movement of calcium by binding to the L-type channels in the heart and peripheral vasculature
ORGAN SYSTEM EFFECTS ā€¢ 1. Smooth muscle: dependent on transmembrane calcium influx for normal resting tone and contractile responses. ā€¢ Vascular smooth muscles (most sensitive) relaxed by the calcium channel blockers. ā€¢ reduction in peripheral vascular resistance . ā€¢ Reduction of coronary artery spasm .
2. CARDIAC MUSCLE ā€¢ Normally: highly dependent on calcium influx during each action potential for normal function(plateau). ā€¢ Impulse generation in the sinoatrial node and conduction in the atrioventricular node. ā€¢ reduce cardiac contractility , decrease CO, reduce oxygen requirement in with angina.
3. SKELETAL MUSCLE ā€¢ Skeletal muscle is not depressed by the calcium channel blockers because it uses intracellular pools of calcium to support excitation-contraction coupling and does not require as much transmembrane calcium influx.
CLINICAL EFFECTS ā€¢ decrease myocardial contractile force. ā€¢ reduces myocardial oxygen requirements. ā€¢ Decrease peripheral resistance . ā€¢ Decreased heart rate with the use of verapamil or diltiazem causes a further decrease in myocardial oxygen demand.
NIFEDIPINE DILTIAZEM VERAPAMIL coronary arteries dilation ++ ++ ++ peripheral arteries dilation ++++ ++ +++ negative inotropic + ++ +++ slowing AV cond ļ‚« +++ ++++ heart rate ļ‚­ ļ‚« ļ‚Æ ļ‚« ļ‚Æ ļ‚« ā†“ blood pressure ++++ ++ +++ depression of SA increase in cardiac output ļ‚« ++ ++ ļ‚« ++ ļ‚«
INDICATIONS ā€¢ Angina. ā€¢ Hypertension. ā€¢ Raynaud's phenomenon. (Nifedipine is the mainstay of medical treatment). ā€¢ Supraventricular tachycardias, including atrial fibrillation. ā€¢ Ischaemic neurological deficit after subarachnoid haemorrhage. ā€¢ Delay of preterm labour(prevent premature labour has been with nifedipine) ā€¢ Prophylaxis for cluster headache.
USAGE ā€¢ Verapamil and Diltiazem are used in arrhythmias because they have an effect on the heart. They both are not great antihypertensive drugs ā€¢ because they have negative inotropic and chronotropic effects, ā€¢ however are used in patients who have palpitations/arrhythmias and suffer from HTN since they can reduce heart rate and blood pressure simultaneously. ā€¢ Dihydropyridines: depend on JNC-8, found in first line theraby espically in black population have a high efficacy of 40 mmHg, regarding that the highest reduction in blood pressure an orally taken anti-hypertensive drug can cause is 40 mmHg.
ADVERSE EFFECTS ā€¢ Common adverse effects ā€¢ These can be predicted from the type of CCB and mode of action, as already illustrated. Examples include: ā€¢ Myocardial effects ā€¢ Hypotension ā€¢ Heart failure ā€¢ Conduction effects ā€¢ Heart block ā€¢ Arrhythmias
ADVERSE EFFECTS ā€¢ Vascular smooth muscle ā€¢ Flushing ā€¢ Oedema ā€¢ Headaches ā€¢ Rashes ā€¢ Other effects ā€¢ Constipation ā€¢ Rashes ā€¢ Gynaecomastia ā€¢ Photosensitivit
ADVERSE EFFECTS drug Effect on heart rate Adverse effect Nifedipine ļ‚­ Headache, flushing, ankle swelling Amlodipine ļ‚­ Ankle swelling, Gingival hyperplasia Nimodipine Ā± Flushing, headache Diltiazem Ā± Generally mild Verapamil ļ‚Æ Constipation, marked negative inotropic action
CAUTIONS AND CONTRA-INDICATIONS ā€¢ Again, these can be predicted from the type of CCB and mode of action. Individual drug monographs need to be reviewed. Some examples include: ā€¢ Cardiovascular: shock, unstable angina, significant aortic stenosis, bradycardia, heart failure, etc. ā€¢ Avoidance of grapefruit juice with felodipine, lacidipine, lercanidipine, nicardipine, nifedipine, nimodipine and verapamil. This may affect metabolism. ā€¢ Sudden withdrawal of CCBs may exacerbate angina. ā€¢ These are best considered under each individual drug.
Calcium channel blockers