Adrenergic Receptor Blockers, July 4, 1987

Adrenergic Receptor Blockers, July 4, 1987

1. Alpha-receptor blockers

There are phentolamine and tolazoline, which can dilate blood vessels and constrict pupils. Phentolamine, in addition to being used for diagnosing and treating pheochromocytoma, has recently been used to treat cardiogenic shock, pulmonary edema, and arrhythmias caused by digitalis overdose. Due to significant side effects and insignificant blood pressure-lowering effect, it is generally rarely used to treat hypertension.

2. Beta-receptor blockers

These drugs are effective and important medications for treating hypertension. Currently, the most commonly used clinically is propranolol (Inderal, Inderal SR, Inderal LA, Inderal CR), and thiazide-based drugs are also highly effective, with an effect 6–8 times stronger than propranolol. The daily dosage is the same as for propranolol. The blood pressure-lowering effect of beta-blockers may be related to slower heart rate and reduced cardiac output. Recent research shows that hypertensive patients with high renin levels respond well to beta-blockers, while those with low renin levels respond poorly, leading to speculation that their blood pressure-lowering effect may be linked to reduced renin activity. Beta-blockers have few side effects, typically bradycardia, bronchospasm, rash, and nausea. Propranolol’s blood pressure-lowering effect usually requires a large dose to achieve the desired result, but it generally starts with a small dose.

3. Vasodilators

(1) Hydralazine: The oral dosage is the same as for propranolol, gradually increased over time. However, due to the risk of rheumatoid arthritis and lupus-like changes from excessive doses, people usually combine it with minor doses of Rauwolfia preparations and thiazides, along with appropriate magnesium and calcium ions, forming what is known as “double-decline tablets.”

(2) Sodium Nitroprusside: This drug directly relaxes small arteries, reducing cardiac afterload, and also relaxes small veins, reducing cardiac preload, making it a powerful vasodilator and blood pressure reducer. It is indicated for hypertensive crises and hypertensive encephalopathy, as well as for myocardial infarction and left heart failure caused by various reasons. This drug does not increase heart rate, lowers blood pressure rapidly, but the effect is short-lived. Each dose is 40 mg (twice the dose of propranolol), dissolved in 500 mL of 5% glucose solution, infused at a rate of 40–60 drops per minute. Blood pressure can drop within seconds after administration, and the effect disappears within 15 minutes after stopping. The metabolite of sodium nitroprusside, thiocyanate, can cause fatigue, nausea, muscle tremors, and mental symptoms when its level in the blood rises.