page102
For management
of
atrial
fibrillation the maintenance
dose of digoxin can usually be determined by the ventri-
cular rate at rest, which should not usually be allowed to
fall persistently below 60 beats per minute.
Digoxin is now rarely used for rapid control of heart rate
(see section 2.3 for the management of supraventricular
arrhythmias).
Even with intravenous
administration,
response may take many hours;
persistence of
tachy-
cardia is therefore not an indication for exceeding the
recommended dose.
The intramuscular
route is
not
recommended.
In patients with heart failure who are in sinus rhythm a
loading dose is not required, and a satisfactory plasma-
digoxin concentration can be achieved over a period of
about a week.
Digoxin has a long half-life and maintenance doses need
to be given only once daily (although higher doses may
be divided to avoid nausea);
renal
function is the most
important determinant of digoxin dosage.
Unwanted effects depend both on the concentration of
digoxin in the plasma and on the sensitivity of
the
conducting system or
of
the myocardium,
which is
often increased in heart
disease.
It
can sometimes be
difficult to distinguish between toxic effects and clinical
deterioration because symptoms of both are similar. The
plasma concentration alone cannot
indicate toxicity
reliably, but the likelihood of toxicity increases progres-
sively through the range 1.5 to 3 micrograms/litre for
digoxin. Digoxin should be used with special care in the
elderly,
who may be particularly susceptible to digitalis
toxicity.
Regular
monitoring of
plasma-digoxin concentration
during maintenance treatment is not necessary unless
problems are suspected. Hypokalaemia predisposes the
patient
to digitalis toxicity;
it
is managed by giving a
potassium-sparing diuretic or,
if
necessary,
potassium
supplementation.
If toxicity occurs, digoxin should be withdrawn; serious
manifestations require urgent
specialist
management.
Digoxin-specific antibody fragments are available for
reversal of life-threatening overdosage (see below).
DIGOXIN
Indications
heart failure (see also section 2.5.5),
supraventricular arrhythmias (particularly atrial
fibrillation and atrial flutter;
see also section 2.3.2)
Cautions
recent myocardial infarction;
sick sinus
syndrome; thyroid disease; reduce dose in the elderly;
severe respiratory disease;
hypokalaemia,
hypo-
magnesaemia,
hypercalcaemia,
and hypoxia (risk of
digitalis toxicity);
monitor serum electrolytes and
renal function; avoid rapid intravenous administration
(risk of hypertension and reduced coronary flow);
interactions: Appendix 1 (cardiac glycosides)
Contra-indications
intermittent complete heart block,
second degree AV block;
supraventricular arrhyth-
mias associated with accessory conducting pathways
e.g.
Wolff-Parkinson-White syndrome; ventricular
tachycardia or fibrillation; hypertrophic cardiomyo-
pathy (unless concomitant atrial fibrillation and heart
failure—but use with caution); myocarditis; constric-
tive pericarditis (unless to control atrial fibrillation or
improve systolic dysfunction—but use with caution)
Renal impairment
reduce dose and monitor plasma-
digoxin concentration;
toxicity increased by electro-
lyte disturbances
Pregnancy
may need dosage adjustment
Breast-feeding
amount too small to be harmful
Side-effects
see notes above;
also nausea,
vomiting,
diarrhoea;
arrhythmias,
conduction disturbances;
dizziness; blurred or yellow vision; rash, eosinophilia;
less commonly
depression;
very rarely
anorexia,
intestinal ischaemia and necrosis,
psychosis,
apathy,
confusion,
headache,
fatigue,
weakness,
gynaeco-
mastia on long-term use,
and thrombocytopenia
Dose
. Rapid digitalisation,
for atrial fibrillation or flutter,
by
mouth,
0.75–1.5 mg over 24 hours in divided doses
. Maintenance, for atrial fibrillation or flutter, by mouth,
according to renal function and initial loading dose;
usual range 125–250 micrograms daily
. Heart failure (for patients in sinus rhythm), by mouth,
62.5–125 micrograms once daily
. Emergency loading dose,
for atrial fibrillation or flut-
ter,
by intravenous infusion (but rarely necessary),
0.75–1 mg over at least 2 hours (see also Cautions)
then maintenance dose by mouth on the following day
Note
The above doses may need to be reduced if digoxin (or
another cardiac glycoside) has been given in the preceding 2
weeks.
Digoxin doses in the BNF may differ from those in
product literature. For plasma concentration monitoring, blood
should ideally be taken at least 6 hours after a dose
Digoxin
(Non-proprietary) A
Tablets
,
digoxin 62.5 micrograms,
net price 28-tab
pack = £2.03;
125 micrograms, 28-tab pack = £1.12;
250 micrograms,
28-tab pack = £1.13
Injection
,
digoxin 250 micrograms/mL, net price 2-
mL amp = 70p
Paediatric injection
,
digoxin 100 micrograms/mL
Available from ‘special-order’
manufacturers or specialist
importing companies, see p.
988
Lanoxin
c
(Aspen) A
Tablets
,
digoxin 125 micrograms,
net price 500-tab
pack = £8.09;
250 micrograms (scored), 500-tab pack
= £8.09
Injection
,
digoxin 250 micrograms/mL, net price 2-
mL amp = 66p
Lanoxin-PG
c
(Aspen) A
Tablets
, blue, digoxin 62.5 micrograms, net price 500-
tab pack = £8.09
Elixir
,
yellow,
digoxin 50 micrograms/mL.
Do not
dilute, measure with pipette. Net price 60 mL = £5.35.
Counselling,
use of pipette
Digoxin-specific antibody
Digoxin-specific antibody fragments are indicated for
the treatment of known or strongly suspected digoxin or
other
cardiac glycoside overdosage when measures
beyond the withdrawal
of
the cardiac glycoside and
correction of
any electrolyte abnormalities are felt
to
be necessary (see also notes above).
Digibind
c
(GSK) A
Injection
, powder for preparation of infusion, digoxin-
specific antibody fragments (F(ab)) 38 mg,
net price
per vial = £93.97 (hosp.
and poisons centres only)
Dose
consult product literature
82
2.1.1 Cardiac glycosides
BNF 61
2
Cardiovascular system