Metoprolol

Pharmacological action

Metoprolo has selective blocking effect on beta 1 receptor, and has no partial activity and no function of membrane stability. It can significantly reduce the blood pressure of the people with hypertension, and do not cause erect hypotension and electrolyte disorder. It can reduce the number of episodes of angina pectoris and increase exercise tolerance. Long term use can reduce the incidence of myocardial infarction. After myocardial infarction, medication can reduce the incidence of re infarction and reduce the mortality after myocardial infarction. It can block the stimulation of adrenergic receptor at the point of cardiac ectopic pacing. It is used for supraventricular tachyarrhythmias, ventricular arrhythmias, digitalis and catecholamine induced tachyarrhythmias. Metoprolo is more effective for tachyarrhythmia caused by hypertension, coronary heart disease and catecholamine increase. It can antagonize the effect of catecholamine, and it can be used to treat arrhythmia caused by hyperthyroidism. The effect of the treatment dose on the contractile bronchus and the peripheral blood vessels is not obvious. The resistance to the trachea will be increased after individual drug use, which can be corrected by extra taking beta 2 receptor agonist. Metoprolo is suitable for treatment of hypertension, angina pectoris, myocardial infarction, hypertrophic cardiomyopathy, aortic dissection, arrhythmia, hyperthyroidism, cardiac neurosis, etc.

Pharmacokinetics

Absorption of oral administration is rapid and peak time is generally at 1.5h. The maximum action time is 1 ~ 2h. The absorption rate is >90%, but the metabolic rate of liver is 95%.The effect of the first pass is 25% to 60%, so the bioavailability is only 40% ~ 75%.
It is similar to propranolol and food can increase the oral absorption of this product.The plasma protein binding rate of this product is about 12% and it can penetrate the blood brain barrier and the placental barrier.It can also be secreted from milk. The decrease of blood pressure is not parallel to the concentration of blood, and the decrease of heart rate has a linear relationship with the concentration of blood.The metabolism of this product in the liver is influenced by genetic factors.The fast metabolic and slow metabolic half-life (t1/2) are 3 to 4h and 7.55h, respectively.It is excreted through the kidney and is mainly metabolites in the urine, only a small amount of (<5%) origin. It can not be discharged through dialysis.

Indication

Metoprolol belongs to class II antiarrhythmic drugs.It is used for the treatment of hypertension, angina pectoris, hypertrophic cardiomyopathy, aortic dissection, supraventricular arrhythmia, atrial fibrillation, ventricular rate, hyperthyroidism, pheochromocytoma and chronic heart failure.It can prevent and treat myocardial ischemia, rapid arrhythmia, and chest pain in acute myocardial infarction.

Adverse reaction

A few patients can have fatigue, gastrointestinal dysfunction and lethargy in the early stage of taking medicine, which can disappear after continuing to take the medicine.There were occasional nonspecific skin reactions and fear of cold in the limbs. Other adverse reactions include:

• Cardiovascular system: Slow heart rate, conduction block, lower blood pressure, aggravation of heart failure, cold limbs or unpalpable pulse caused by peripheral vasospasm and Reynolds phenomenon.Because of its fat solubility, this product is easily penetrated into the central nervous system, so there are more adverse reactions in the central nervous system. Fatigue and vertigo account for 10%, depression accounts for 5%, other adverse reactions include headache, dream, insomnia etc. With rare illusion.
• Digestive system: the ratio of people with symptoms of nausea, stomachache and constipation is <1%, and those with diarrhea account for 5%, but they are not serious and seldom affect the drug use.
• Other: such as shortness of breath, joint pain, pruritus, retroperitoneal fibrosis, deafness, eye pain, etc..

Drug interaction

• The combined use of Catecholamine depletion agent (such as reserpine) with this product can cause vertigo, or hypotension. 
• Its combined use with digitalis can cause the heart rate to be slow.
• It is forbidden to use with diltiazem for patients with heart failure.
• It is forbidden to combine with monoamine oxidase inhibitors for the cause of severe hypotension
• Its combined use of cimetidine or preuse of quinidine can increase the concentration of metoprolol in blood.
• It has similar side effects with calcium antagonists.

Precaution

1. Patients with the following circumstances can not be given immediate intravenous medication: The systolic pressure of supraventricular fast arrhythmia is lower than that of 110mmHg;  acute myocardial infarction and unstable angina with heart rate less than 70 bpm, when the systolic pressure is lower than 110mmHg, or with the atrioventricular conduction block.
2. The treatment of suspected or confirmed AMI should not be repeated if there is any aggravation of dyspnea or cold sweat.
3. Patients with pheochromocytoma should use alpha receptor antagonist first.
4. A moderate amount of beta 2 receptor agonist must be given to patienst with bronchial asthma or COPD.
5. For patients undergoing general anesthesia, it must be stopped at least 48h before anesthesia.
6. Careful use for patients with liver and kidney insufficiency, diabetes and hyperthyroidism. 

Uses

Anti-adrenergic.

Uses

rac Metoprolol is a β1 selective aryloxypropanolamine andrenergic antagonist. Used in the treatment of a variety of cardiovascular disorder.

Definition

ChEBI: Metoprolol is a propanolamine that is 1-(propan-2-ylamino)propan-2-ol substituted by a 4-(2-methoxyethyl)phenoxy group at position 1. It has a role as a beta-adrenergic antagonist, an antihypertensive agent, a xenobiotic, an environmental contaminant and a geroprotector. It is a propanolamine, an aromatic ether, a secondary alcohol and a secondary amino compound.