Calcium channel blockers: adverse effects and teaching

A calcium channel blocker lowers blood pressure and relieves angina by keeping calcium out of the smooth muscle of the arteries so that they relax, and — in the two agents that also act on the heart, verapamil and diltiazem — by slowing the sinus node, delaying conduction through the atrioventricular node and weakening the force of contraction, so its predictable harms follow from which of those two things the drug in hand does and the nurse anticipates, checks for and teaches every one of them: from the vessel-relaxing agents such as amlodipine and nifedipine, a flushing, headache and dizziness that are the vasodilation itself, a reflex quickening of the heart that is sharpest with the short-acting preparations, which is why an immediate-release dihydropyridine is never used to bring a high reading down and only the long-acting forms are used for blood pressure, and an ankle swelling that is fluid leaking from dilated capillaries rather than heart failure or salt and water overload, so it is not answered with a diuretic or a salt restriction but reported and met with a lower dose or a different drug once heart failure has been excluded; from the heart-acting agents, a heart rate driven too slow or a block at the atrioventricular node, and a heart failure made worse by the weakened contraction, which is why the apical pulse and the blood pressure are measured before every dose of verapamil or diltiazem and the dose held and the prescriber told when either falls below the ordered parameter, why neither is given to a patient whose heart failure comes from a weakened ventricle, and why their combination with a beta blocker or with digoxin — whose level verapamil also raises — is a deliberate prescription watched for bradycardia and block rather than an unremarked pairing; from verapamil above all, a constipation that is the drug's own and is managed with fluid, fibre and activity rather than endured; and from the whole class, a fall in pressure on standing, so the patient is taught to rise slowly, and an overgrowth of the gums that is met with dental hygiene and reported rather than blamed on the patient's brushing — while the patient is taught that grapefruit and its juice raise the level of most of the class and are left out of the diet, that an extended-release tablet or capsule is swallowed whole and never crushed, split or chewed because a whole day's supply released at once is an overdose, that dietary calcium and calcium supplements have nothing to do with the drug's action and are neither stopped nor needed, that ankle swelling and a slow or irregular pulse are reported rather than self-treated, and that the tablet is not stopped abruptly, because in angina the vessels it was holding open answer its sudden removal with a return of the chest pain, so a pressure that has come to normal is the drug working rather than the disease cured and any change is made by the prescriber.