Therapeutic antihypertensives Flashcards
Classes of ACE inhibitors
1: Captopril
- active drug with active metabolites
2: Enalapril, ramipril
- prodrugs which become active after hepatic metabolism to diacid moiety
3: Lisinopril
- active drug that is not metabolised and is excreted unchanged in the urine
Class 1 CCBs
L-type calcium channels in the heart are targeted by phenylalkylamines, e.g. verapamil, and this slows conduction at SA and AV node reducing the heart rate. They also reduce the force of contraction. These drugs are not used to treat hypertension
Class 2 CCBs
The dihydropyridines, e.g. amlodipine, nifedipine, are selective for smooth muscle calcium channels and their effect is most pronounced in the arterial system. This causes arteriorlar relaxation and reduced blood pressure
Class 3 CCBs
Diltiazem works at both L-type calcium channels
Thiazides
Thiazides act on the early segment of the distal convoluted tubule and block Na+ and Cl- reabsorption. Water follows Na+ and thus more water is excreted. Reduced plasma volume and systemic vascular resistance lead to their antihypertensive effect.
The increased Na+ in the distal tubule is exchanged with K+ at the Na/K pump and thus a hypokalaemic hypochloraemic alkalosis is precipitated.
Thiazides reduce glycogenesis and insulin secretion and they enhance glycogenolysis and this may raise plasma glucose levels particularly in diabetic patients. Bendroflumethiazide may precipitate pancreatitis.
AAGBI HTN guidance
These aim to ensure that patients admitted to hospital for elective surgery are known to have blood pressure below 160 mmHg systolic and 100 mmHg diastolic in primary care. Secondary care should not attempt to diagnose hypertension in patients who are normotensive in primary care.
In patients with no documented primary care blood pressure, elective surgery should proceed if clinic blood pressures are below 180 mgHg systolic and 110 mmHg diastolic.
