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Overdose
Toxicity: 7.5 g to an adult caused lethal intoxication. 100 mg to a 5-year old gave no symptoms after gastric lavage. 450 mg to a 12-year old and 1.4 g to an adult gave moderate intoxication, 2.5 g to an adult caused serious intoxication, and 7.5 g to an adult gave very serious intoxication.

Symptoms: Cardiovascular symptoms are most important, but in some cases, especially in children and young individuals, CNS symptoms and respiratory depression may dominate. Bradycardia, AV-block I-III, QT-prolongation (exceptional cases), asystole, fall in blood pressure, poor peripheral perfusion, cardiac insufficiency, cardiogenic shock. Respiratory depression, apnoea. Others: Fatigue, confusion, unconsciousness, fine tremor, cramps, perspiration, paraesthesiae, bronchospasm, nausea, vomiting, possibly oesophageal spasm, hypoglycaemia (especially in children) or hyperglycaemia, hyperkalaemia. Effect on the kidneys. Transient myasthenic syndrome. Concomitant ingestion of alcohol antihypertensives, quinidine or barbiturates may aggravate the patient's condition. The first signs of overdosing may be seen 20 minutes to 2 hours after ingestion.

Management: If justified, gastric lavage, charcoal. NB! Atropine (0.25-0.5 mg intravenously to adults, 10-20 mcg/kg to children) should be given before gastric lavage (due to risk of vagal stimulation). The indication should be very wide for intubation and treatment with respirator. Adequate volume substitution. Glucose infusion. ECG-monitoring. Atropine 1.0-2.0 mg intravenously, which may be repeated (primarily against vagal symptoms). In myocardial depression: Infusion of dobutamine or dopamine and calcium glubionate 9 mg/ml, 10-20 ml. Glucagone 50-150 mcg/kg intravenously over 1 minute, followed by infusion may also be tried, as well as amrinone. In some cases, addition of epinephrine (adrenaline) has been efficient. Infusion of sodium (chloride or bicarbonate) in widened QRS-complex and arrhythmias. Pacemaker may be used. In circulatory arrest, resuscitation actions for several hours could be required. In bronchospasm, terbutaline (injection or inhalation) may be used. Symptomatic therapy.

Pharmacodynamic properties
Pharmacotherapeutic group: Beta-receptor blocker, selective

ATC code: C07A B02

Metoprolol is a beta₁-selective receptor blocker, i.e. metoprolol affects the beta, receptors of the heart in lower doses than needed to affect beta₂-receptors in peripheral vessels and bronchi. At increasing doses the beta₁-selectivity may decrease.

Metoprolol has no beta-stimulating effect and has little membrane- stimulating effect. Beta-receptor blockers have negative inotropic and chronotropic effect.

Metoprolol therapy reduces the effect of catecholamines in association with physical and psychic strain and gives lower heart rate, cardiac output and blood pressure. In stress situations with an increased release of adrenaline from the adrenal glands, metoprolol does not prevent the normal physiological vascular dilation. In therapeutic doses, metoprolol has less contractile effect on the bronchial muscles than non-selective beta-blockers. This property enables treatment of patients with bronchial asthma or other pronounced obstructive lung diseases with metoprolol in combination with beta2-receptor stimulants. Metoprolol influences insulin release and carbohydrate metabolism to less extent than non-selective beta-blockers and therefore it can also be given to patients with diabetes mellitus. The cardiovascular reaction in hypoglycaemia, e.g. tachycardia, is less influenced by metoprolol and the return of blood sugar level to normal is faster than for nonselective beta-receptor blockers.

In hypertension, Betaloc lowers the blood pressure significantly for more than 24 hours both in lying and standing position as well as during exercise. In treatment with metoprolol an increase in the peripheral vascular resistance is observed initially. In long-term treatment, however, the obtained lowering in blood pressure may be due to reduced peripheral vascular resistance and unchanged cardiac output. In males with moderate/severe hypertension, metoprolol reduces the risk of cardiovascular death. There is no electrolyte imbalance.

In tachyarrhythmias the effect of increased sympatholytic activity is blocked and this gives a lower heart rate primarily by reduced automatisation in the pacemaker cells, but also through a prolonged supraventricular conduction time.

Betaloc has shown fast and effective amelioration of symptoms in thyrotoxicosis. Increased T₃-values may be decreased with high dose metoprolol. T₄ are not affected.

Metoprolol reduces the risk of reinfarction and cardiac death, especially sudden death after myocardial infarction.

Pharmacokinetic properties
The bioavailability of Betaloc is 40-50%. Maximal beta-blockade is reached after 1-2 hours. After per oral once-daily dosage of 100 mg the effect on the heart rate is still pronounced after 12 hours. Metoprolol is metabolised in the liver mainly by CYP2D6. Three main metabolites have been identified, though none has a beta-blocking effect of clinical importance. The half-life in plasma is 3-5 hours. Metoprolol is excreted to approximately 5% in unchanged form via the kidneys, the remaining dose as metabolites.

List of excipients
Lactose, magnesium stearate, microcrystalline cellulose, polyvinylpyrrolidone, silicon dioxide and sodium starch glycolate.

Shelf-life

3 years

Special precautions for storage

Store below 30°C

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