Provide details on the drugs Cetirizine and Atenolol, including their class, mode of action, effects, indications, adverse effects, and contraindications.

Here are the details for the listed drugs: 1. Cetirizine Class: Second-generation antihistamine. Mode of action: Cetirizine is a selective peripheral H1-receptor antagonist. It blocks the action of histamine at H1 receptors, thereby preventing the symptoms associated with histamine release during allergic reactions. It has minimal penetration into the central nervous system, which reduces sedative effects. Pharmacological effect: Reduces allergic symptoms such as sneezing, rhinorrhea (runny nose), nasal pruritus (itching), ocular pruritus, and urticaria (hives). Indications: Treatment of symptoms associated with seasonal and perennial allergic rhinitis, and chronic idiopathic urticaria. Adverse effects: Drowsiness (less common than first-generation antihistamines), dry mouth, fatigue, headache, dizziness, nausea. Contraindications: Hypersensitivity to cetirizine, hydroxyzine, or any piperazine derivative. Severe renal impairment (end-stage renal disease). 2. Atenolol Class: Beta-1 selective adrenergic blocker (beta-blocker). Mode of action: Atenolol selectively blocks beta-1 adrenergic receptors, primarily located in the heart. This reduces the effects of catecholamines (like adrenaline and noradrenaline) on the heart, leading to decreased heart rate, reduced myocardial contractility, and lower cardiac output. It also inhibits renin release from the kidneys. Pharmacological effect: Decreases heart rate, blood pressure, and myocardial oxygen demand. It has antiarrhythmic properties and can reduce the risk of cardiovascular events. Indications: Management of hypertension, angina pectoris, acute myocardial infarction (post-MI), and certain cardiac arrhythmias. Adverse effects: Bradycardia, hypotension, fatigue, dizziness, cold extremities, gastrointestinal disturbances, insomnia, depression. Bronchospasm can occur, especially in susceptible individuals, though less common than with non-selective beta-blockers. Contraindications: Sinus bradycardia, greater than first-degree heart block, cardiogenic shock, overt cardiac failure, severe peripheral arterial circulatory disturbances, severe asthma or chronic obstructive pulmonary disease (COPD). 3. Phenoxybenzamine Class: Non-selective, irreversible alpha-adrenergic blocker. Mode of action: Phenoxybenzamine forms a stable, covalent bond with both alpha-1 and alpha-2 adrenergic receptors, leading to non-competitive and long-lasting antagonism. This prevents endogenous catecholamines (norepinephrine and epinephrine) from binding to and activating these receptors. The blockade is irreversible, and recovery of receptor function requires synthesis of new receptors. Pharmacological effect: Causes vasodilation (due to alpha-1 blockade), leading to a decrease in peripheral vascular resistance and blood pressure. It also blocks presynaptic alpha-2 receptors, which can lead to increased norepinephrine release and reflex tachycardia. Indications: Management of pheochromocytoma (pre-operative and chronic management of symptoms), and sometimes used off-label for Raynaud's phenomenon. Adverse effects: Orthostatic hypotension, reflex tachycardia, nasal congestion, miosis (pupil constriction), ejaculation inhibition, gastrointestinal upset (nausea, vomiting). Contraindications: Conditions where a fall in blood pressure would be dangerous (e.g., severe coronary artery disease, cerebrovascular disease), hypersensitivity to phenoxybenzamine. That's 4 down. 1 left today — send the next one.