page114
lar, nodal and ventricular tachycardias, atrial fibrillation
and flutter,
and ventricular fibrillation.
It
can also be
used for tachyarrhythmias associated with Wolff-Parkin-
son-White syndrome.
It should be initiated only under
hospital
or specialist supervision.
Amiodarone may be
given by intravenous infusion as well as by mouth,
and
has the advantage of
causing little or
no myocardial
depression.
Unlike oral
amiodarone,
intravenous amio-
darone acts relatively rapidly.
Intravenous injection of
amiodarone can be used in
cardiopulmonary resuscitation for
ventricular
fibrilla-
tion or
pulseless
tachycardia unresponsive to other
interventions (section 2.7.3).
Amiodarone has
a very long half-life (extending to
several
weeks) and only needs to be given once daily
(but high doses can cause nausea unless divided). Many
weeks or months may be required to achieve steady-
state plasma-amiodarone concentration; this is particu-
larly important
when drug interactions are likely (see
also Appendix 1).
Most
patients
taking
amiodarone
develop
corneal
microdeposits (reversible on withdrawal
of
treatment);
these rarely interfere with vision,
but
drivers may be
dazzled by headlights at
night.
However,
if
vision is
impaired or if optic neuritis or optic neuropathy occur,
amiodarone must be stopped to prevent blindness and
expert
advice sought.
Because of
the possibility of
phototoxic reactions,
patients
should be advised to
shield the skin from light
during treatment
and for
several
months
after
discontinuing
amiodarone;
a
wide-spectrum sunscreen (section 13.8.1)
to protect
against
both long-wave
ultraviolet
and visible
light
should be used.
Amiodarone contains iodine and can cause disorders of
thyroid
function;
both
hypothyroidism and
hyper-
thyroidism may occur.
Clinical
assessment
alone is
unreliable,
and laboratory tests should be performed
before treatment and every 6 months.
Thyroxine (T4)
may be raised in the absence of hyperthyroidism; there-
fore tri-iodothyronine (T3),
T4,
and thyroid-stimulating
hormone (thyrotrophin, TSH) should all be measured. A
raised T3 and T4 with a very low or undetectable TSH
concentration suggests the development of thyrotoxic-
osis.
The thyrotoxicosis may be very refractory,
and
amiodarone should usually be withdrawn at least tem-
porarily to help achieve control; treatment with carbim-
azole may be required.
Hypothyroidism can be treated
with replacement
therapy without
withdrawing amio-
darone if it is essential;
careful supervision is required.
Pneumonitis
should always
be suspected if
new or
progressive shortness of breath or cough develops in a
patient
taking amiodarone.
Fresh neurological
symp-
toms should raise the possibility of
peripheral
neuro-
pathy.
Amiodarone is also associated with hepatotoxicity and
treatment should be discontinued if severe liver function
abnormalities or clinical signs of liver disease develop.
Beta-blockers act as anti-arrhythmic drugs principally
by attenuating the effects of the sympathetic system on
automaticity and conductivity within the
heart,
for
details
see section 2.4.
For
special
reference to the
role of sotalol in ventricular arrhythmias,
see p.
98.
Disopyramide can be given by intravenous injection to
control arrhythmias after myocardial infarction (includ-
ing those not
responding to lidocaine),
but
it
impairs
cardiac contractility.
Oral
administration of
disopyr-
amide is
useful,
but
it
has
an antimuscarinic effect
which limits its use in patients susceptible to angle-
closure glaucoma or with prostatic hyperplasia.
Flecainide belongs to the same general
class as lido-
caine and may be of
value for
serious symptomatic
ventricular
arrhythmias.
It
may also be indicated for
junctional
re-entry tachycardias
and for
paroxysmal
atrial
fibrillation.
However,
it
can precipitate serious
arrhythmias in a small
minority of
patients (including
those with otherwise normal hearts).
Propafenone is used for the prophylaxis and treatment
of ventricular arrhythmias and also for some supraven-
tricular
arrhythmias.
It
has
complex mechanisms
of
action,
including weak beta-blocking activity (therefore
caution is needed in obstructive airways disease—con-
tra-indicated if severe).
Drugs for supraventricular arrhythmias include aden-
osine,
cardiac glycosides,
and verapamil;
see above
under Supraventricular Arrhythmias.
Drugs for ventri-
cular arrhythmias include lidocaine;
see under Ventri-
cular Arrhythmias,
p.
96.
Mexiletine and procainamide are both available from
‘special-order’
manufacturers
or
specialist
importing
companies,
see p.
988.
Mexiletine can be used for life-
threatening ventricular
arrhythmias;
procainamide is
given by intravenous injection to control
ventricular
arrhythmias.
AMIODARONE HYDROCHLORIDE
Indications
see notes above (should be initiated in
hospital or under specialist supervision)
Cautions
liver-function and thyroid-function tests
required before treatment and then every 6 months
(see notes above for tests of thyroid function);
hypo-
kalaemia (measure serum-potassium concentration
before treatment);
chest x-ray required before treat-
ment;
heart failure;
elderly;
severe bradycardia and
conduction disturbances in excessive dosage;
intra-
venous use may cause moderate and transient fall in
blood pressure (circulatory collapse precipitated by
rapid administration or overdosage) or severe hepa-
tocellular toxicity (monitor transaminases closely);
administration by central venous catheter recom-
mended if repeated or continuous infusion required—
infusion via peripheral veins may cause pain and
inflammation; ECG monitoring and resuscitation
facilities must be available during intravenous use;
acute porphyria (section 9.8.2);
interactions: Appen-
dix 1 (amiodarone)
Contra-indications
(except in cardiac arrest) sinus
bradycardia, sino-atrial heart block; unless pacemaker
fitted avoid in severe conduction disturbances or
sinus node disease; thyroid dysfunction;
iodine sen-
sitivity; avoid
intravenous use
in severe respiratory
failure,
circulatory collapse,
or severe arterial hypo-
tension;
avoid bolus injection in congestive heart
failure or cardiomyopathy
Pregnancy
possible risk of neonatal goitre; use only if
no alternative
Breast-feeding
avoid; present in milk in significant
amounts;
theoretical risk of neonatal hypothyroidism
from release of iodine
Side-effects
nausea,
vomiting,
taste disturbances,
raised serum transaminases (may require dose
reduction or withdrawal if accompanied by acute liver
disorders),
jaundice;
bradycardia (see Cautions);
94
2.3.2 Drugs for arrhythmias
BNF 61
2
Cardiovascular system