antihypertensive drugs Flashcards
what blood pressure is considered to be hypertensive?
equal to or greater than 160/95 mmHg
what is the level of vascular smooth muscle tone dependent on
alpha 1 activity
what other physiological factors contribute to blood pressure (equation)
blood pressure= cardiac output x peripheral resistance
what are symptoms of hypertension
hypertension is asymptomatic but leads to increased risk of heart disease
what is treatment for mild hypertension
weight loss, give up smoking if a smoker, reduced alcohol intake
what is further treatment (drugs) of hypertension
diuretics, beta blockers, calcium channel blockers, ACE inhibitors
if^ inadequate then vasodilators may be given
what is mechanism of diuretics in reducing blood pressure
reduce blood volume by increasing sodium excretion
associated water loss then reduces blood volume and so cardiac output, reducing pressure
in long term cardiac output and plasma volumes return to original value however pressure remains lower due to reduced peripheral resistance (mechanism unclear, some relax vascular smooth muscle)
what is mechanism of vasodilators in blood pressure
they are K+ (atp) channel openers:
channels close when ATP binds, vasodilators block ATP binding to these ATP sensitive potassium channels
hyperpolarisation caused by their opening of vascular smooth muscle causes voltage gated L type calcium channels to close
this reduces calcium concentration in smooth muscle, causing relaxation
relaxation of vascular smooth muscle causes decrease in peripheral resistence
give examples of vasodilators used to treat hypertension and under what circumstances are they used
diazoxide: potent vasodilator, only used in hypertensive emergencies
minoxidil: only given in severe hypertension, causes hypertrichosis
what is mechanism of calcium channel blockers in reduction of blood pressure
reduce calcium influx into arterial smooth muscle and to an extent in myocardial cells
causes both vasodilator effect and reduction in strength of contraction of myocardial cells
give examples of calcium channel blocker drugs and their effect
nifedipine: selective for L-type calcium channels so targets vascular smooth muscle
verapamil used to decrease cardiac output
what is mechanism of nitrovasodilators in reduction of blood pressure, name a drug and when it is used
used to break down nitric oxide, relaxes smooth muscle
not for day to day treatment of hypertension
sodium nitroprusside is given via IV to control severe hypertensive crisis
give some examples of indirect vasodilators
alpha adrenoceptor antagonists: lower blood pressure by blocking effects of sympathetic stimulation on vasculature, e.g prazosin
adrenergic blocking agents: block release of NA from postganglionic sympathetic neurones, rarely used today, blocks sympathetic activity, not specific to vasculature, e.g guanethidine
ganglion blocking drugs: not used any more, formerly used in hypertensive crisis, side effects would be blockade of both sympathetic and parasympathetic systems
what do all antihypertensive drugs cause (aside from reduced blood pressure)
will cause baroreceptor reflex to be activated since beta 1 receptors are not blocked
this causes reflex tachycardia and activation of renin angiontensin system
give some examples of centrally acting antihypertensives
clonidine and alpha-methyl DOPA: have effects in CNS to cause decrease in sympathetic outflow, their action is on alpha 2 receptors in medulla
clonidine is alpha 2 selective agonist
alpha methyl DOPA is prodrug which is converted into alpha methyl noradrenaline which is highly selective for alpha 2 over alpha 1
there may be rebound hypertension if a patient is withdrawn abruptly from clonidine