L17&18 Anti-hypertensive drugs - dr.naser online

Introduction to Arrhythmias and Hypertension

Overview of the Session

• The session begins with a focus on arrhythmias as the last topic, emphasizing the importance of connectivity during the lecture. Participants are encouraged to communicate any disconnection issues promptly.

Learning Objectives

• The instructor outlines learning objectives (ILOs), mentioning previous discussions on sympathetic antagonists, including alpha blockers, beta blockers, and centrally acting sympatholytics like alpha-methyl dopa. These drugs are part of anti-hypertensive treatment but will not be discussed in detail again unless questions arise.

Blood Pressure Basics

• Normal blood pressure is defined as less than 120/80 mmHg, while target control for aged hypertensives should ideally be below 130/80 mmHg but can vary based on conditions like arteriosclerosis. Adjustments may be necessary depending on individual cardiovascular health.

Understanding Arteriosclerosis

• Arteriosclerosis refers to hardening of blood vessels; atherosclerosis is a specific type caused by plaque buildup. This condition affects blood pressure management strategies due to reduced arterial elasticity.

Key Equation: Blood Pressure Regulation

• Blood pressure is determined by cardiac output multiplied by peripheral resistance, highlighting that both heart function and vascular health are critical in managing hypertension. Cardiac output itself consists of heart rate and stroke volume, which can all be influenced by various treatments aimed at lowering blood pressure.

Types of Hypertension

Primary vs Secondary Hypertension

• Primary hypertension (essential) lacks identifiable causes and often results from unmeasurable factors like stiffened blood vessels, while secondary hypertension typically arises from renal disease or other identifiable conditions such as hypothyroidism or substance abuse (e.g., cocaine).

Systemic vs Pulmonary Hypertension

• Hypertension can affect systemic arteries (aorta and its branches) or pulmonary arteries; it can also present as systolic or diastolic hypertension, with further discussion planned for congestive cardiac failure topics next week.

Pharmacological Approaches to Lowering Blood Pressure

First-Line Treatments

• Renin-angiotensin system blockers are first-line treatments for hypertension; they work by reducing angiotensin II production or blocking its receptors.

• Calcium channel blockers serve as common adjunct therapies when renin inhibitors alone do not suffice in controlling blood pressure levels.

Emergency Treatments

• Vasodilators are reserved for hypertensive emergencies where immediate intervention is required due to sudden spikes in blood pressure levels. They may also be used alongside other medications if initial treatments fail in cases like arteriosclerosis-related hypertension.

Mechanisms Involved in Renin-Angiotensin System

Role of Organs in Blood Pressure Regulation

• The liver produces angiotensinogen, which is converted into angiotensin I by renin from the kidneys; this is then converted into angiotensin II via an enzyme found primarily in the lungs.

Effects of Angiotensin II

• Angiotensin II acts as a potent vasoconstrictor and stimulates aldosterone secretion from adrenal glands leading to sodium retention—this increases circulatory volume and impacts cardiac function through mechanisms involving atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP).

Drug Classes Targeting the Renin-Angiotensin System

Angiotensin-Converting Enzyme Inhibitors

• ACE inhibitors reduce levels of angiotensin II while increasing bradykinin—a vasodilator—leading to decreased total peripheral resistance over time.

Classification of ACE Inhibitors

• Active drugs include captopril and lisinopril; prodrugs require conversion into active metabolites before exerting their effects on blood pressure regulation through ACE inhibition processes.

Adverse Effects Associated with Antihypertensive Drugs

Types of Adverse Reactions

1. Type A: Augmented responses leading to exaggerated hypotension.

2. Type B: Unpredictable reactions such as dysgeusia or neutropenia.

3. Type C: Continuous use effects like hyperkalemia due to aldosterone inhibition.

4. Type D: Delayed reactions manifesting after prolonged use.

5. Type E: Withdrawal symptoms upon cessation leading back to elevated blood pressure levels.

These adverse effects necessitate careful monitoring during treatment regimens involving antihypertensive medications such as ACE inhibitors or receptor blockers for optimal patient safety outcomes.

Endothelin Receptor Blockers

Mechanism & Benefits

• Endothelin receptor blockers specifically target AT1 receptors associated with vasoconstriction without causing bradykinin-related side effects seen with ACE inhibitors.

Clinical Considerations

• These agents may be preferred for patients prone to allergies or asthma since they avoid some common adverse reactions associated with traditional ACE inhibitor therapy options.

This structured approach provides clarity regarding pharmacological interventions available for managing hypertension effectively while considering potential risks involved with each class of medication discussed throughout the session's content.

Anti-Hypertensive Medications Overview

Classification of Calcium Channel Blockers

• T-type calcium channels are primarily found in neuronal tissue and play a role in CNS drugs for epilepsy.

• Calcium channel blockers (CCBs) are classified into two types: dihydropyridines (DHPs), which are selective for blood vessels, and non-dihydropyridines (non-DHPs), which affect both the heart and blood vessels.

• DHPs induce bronchodilation and inhibit smooth muscle in bronchial, gastrointestinal, and uterine tissues but mainly target arterial smooth muscle.

Commonly Used Dihydropyridines

• Amlodipine is the most commonly used DHP as an anti-hypertensive medication, along with isradipine and nifedipine; nifedipine is considered the prototype.

Side Effects of Calcium Channel Blockers

• Peripheral edema is a common side effect due to vasodilation; other side effects include flushing, dizziness, nausea, and constipation.

• Serious side effects from cardio-selective CCBs can include cardiac depression leading to bradycardia and hypotension when combined with other cardiodepressant medications.

Risks Associated with Short Acting Dihydropyridines

• Shorter acting DHPs may increase the risk of adverse cardiac events due to their short half-life causing fluctuations in blood pressure that can lead to angina or chest pain.

Vasodilators in Hypertension Management

• Direct vasodilators are used for hypertensive emergencies often combined with other anti-hypertensives; they reduce total peripheral resistance but can cause reflex tachycardia.

• Unlike other vasodilators, calcium channel blockers prevent reflex tachycardia by suppressing myocardial contractility.

Mechanisms of Action for Various Vasodilators

Oral vs. Parenteral Vasodilators

• Oral vasodilators like hydralazine are typically used for chronic conditions; parenteral options such as nitroprusside are utilized in acute settings.

Hydralazine's Role

• Hydralazine acts as an adjunct treatment for severe hypertension and congestive heart failure by reducing afterload through arterial dilation.

Adverse Drug Reactions (ADRs)

• Common ADRs from hydralazine include headache, nausea, palpitations, flushing, and potential autoimmune reactions like SLE-like syndrome.

Minoxidil: An Arterial Dilator

Mechanism of Action

• Minoxidil induces hyperpolarization by opening potassium channels in smooth muscle; it also has topical applications for hair growth due to its vasodilatory effects on skin.

Alpha Blockers Overview

Mechanism & Use Cases

• Alpha blockers induce vasodilation by blocking alpha adrenoceptors involved in vasoconstriction; phenoxybenzamine is an irreversible blocker used particularly for catecholamine-secreting tumors.

Side Effects

• Orthostatic hypotension is a notable side effect where patients experience dizziness upon standing due to impaired sympathetic response from alpha receptor blockade.

Beta Blockers: Functions & Considerations

Cardiac Effects

• Beta blockers decrease heart rate and cardiac output while reducing excitability through negative chronotropic effects. They also lower renin output over time.

Clinical Applications

• In cases of hypertension with comorbidities like diabetes or chronic kidney disease (CKD), ACE inhibitors or ARBs paired with calcium channel blockers are preferred treatments.

Summary of Treatment Approaches

First-Line Treatments

• The first choice medications include ACE inhibitors or ARBs based on patient demographics such as age or ethnicity. Additional medications may be added based on individual needs during treatment.