Pharmacology for Dentistry

170 Section 4/ Drugs Acting on Cardiovascular & Urinary System

contractility and are not the primary effects
of digitalis.

Cardiac output: Digitalis increases the
cardiac output in CHF patients by increasing
the force of myocardial contraction. It also
increases the contractility of normal heart
but cardiac output remains unchanged or is
slightly decreased. In normal individuals, it
increases the tone of arteries as well as that
of the veins.

Heart rate: In CHF patients, the heart
rate is decreased. Digitalis produce a
decrease in heart rate by stimulation of
vagus. The ‘vagal effect’ is probably evoked
by sensitization of carotid baroreceptors,
and by direct stimulation of vagal centre.
The vagal action can be blocked by atropine
but after full digitalising dose the effect can
not be blocked by atropine and it is due to
its direct cardiac action. In CHF patients,
the sympathetic activity is increased as a
compensatory phenomenon which leads to
tachycardia. Digitalis decreases the

sympathetic tone and thus reducing the

heart rate.

Refractory period: It is a period after onset

of depolarization during which a stimulus can

not evoke a propagated action potential. In

atrium, refractory period is shortened by vagal

action and increased by direct action.

SA node: Digitalis sensitizes the SA node

to normal vagal impulse resulting in

bradycardia. In a patient suffering from

paroxysmal supraventricular tachycardia, it

decreases the heart rate due to vagal action on

SA node which is associated with decrease in

the slope of slow diastolic depolarisation and

increase in the transmembrane negativity and,

also lower the SA rate by antiadrenergic action.

Automaticity: It is the ability to generate

propagated impulse. Digitalis increases the

ability of the Purkinje cell and the

ventricular muscle to initiate impulses.

Conductivity: Conduction through AV

node is depressed whereas conduction is

slightly increased in the auricle and ventricles.

Table 4.1.1: Classification of cardiac glycosides.

I Natural glycosides

Digitoxin (DIGITALIN) 0.05-0.2 mg/day

Digoxin (LANOXIN) 0.125-0.5 mg/day oral

0.25-1.0 mg slow IV

Lanatoside-C (CEDILANID) 0.25-1.0 mg/day

Stropanthin-K (STROPHOSID) 0.25-0.5 mg IV

Stropanthin-G (OVABAIN) 0.25-0.5 mg IV

Proscillaridin-A 0.3-1.0 ml (Tr. Scilla)

Cavallotoxin

Thevetin

Bufotoxin

II. Semisynthetic

Acetyl digoxin (ACYLANID) 0.2-0.5 mg/day oral/IV

Desacetyl lanatoside-C (DESLANOSIDE) 0.25-1 mg IV

Acetyl stropanthidin (diagnostic use) 0.25 mg IV