page212
antihistamines because they penetrate the blood brain
barrier only to a slight extent.
Cautions and contra-indications
Sedating antihist-
amines have significant antimuscarinic activity and they
should therefore be used with caution in prostatic hyper-
trophy, urinary retention, susceptibility to angle-closure
glaucoma,
and pyloroduodenal
obstruction.
Caution
may be required in epilepsy.
Children and the elderly
are more susceptible to side-effects.
Many antihist-
amines
should be
avoided in acute
porphyria
but
some are thought to be safe, see section 9.8.2. Interac-
tions: Appendix 1 (antihistamines).
Hepatic impairment
Sedating antihistamines should
be avoided in severe liver disease—increased risk of
coma.
Pregnancy
Most
manufacturers
of
antihistamines
advise avoiding their use during pregnancy;
however,
there
is
no
evidence
of
teratogenicity
except
for
hydroxyzine where toxicity has
been reported with
high doses in
animal
studies.
The use of sedating anti-
histamines in the latter part of the third trimester may
cause adverse effects in neonates such as irritability,
paradoxical excitability,
and tremor.
Breast-feeding
Most
antihistamines are present
in
breast milk in varying amounts; although not known to
be harmful,
most
manufacturers advise avoiding their
use in mothers who are breast-feeding.
Side-effects
Drowsiness is a significant
side-effect
with most
of
the older
antihistamines although para-
doxical
stimulation may occur
rarely,
especially with
high doses or in children and the elderly.
Drowsiness
may diminish after
a few days
of
treatment
and is
considerably less of a problem with the newer antihist-
amines
(see also notes
above).
Side-effects
that
are
more common with the older
antihistamines include
headache,
psychomotor
impairment,
and
anti-
muscarinic
effects
such
as
urinary
retention,
dry
mouth,
blurred
vision,
and
gastro-intestinal
distur-
bances.
Other rare side-effects of antihistamines include hypo-
tension,
palpitation,
arrhythmias,
extrapyramidal
effects,
dizziness,
confusion,
depression,
sleep distur-
bances,
tremor,
convulsions,
hypersensitivity reactions
(including bronchospasm,
angioedema,
and anaphy-
laxis,
rashes,
and photosensitivity reactions), blood dis-
orders,
liver dysfunction,
and angle-closure glaucoma.
Non-sedating antihistamines
Driving
Although drowsiness
is
rare,
nevertheless
patients should be advised that it can occur and may
affect performance of skilled tasks (e.g. driving); excess
alcohol should be avoided.
ACRIVASTINE
Indications
symptomatic relief of allergy such as hay
fever,
chronic idiopathic urticaria
Cautions
see notes above
Contra-indications
see notes above;
also hypersensi-
tivity to triprolidine;
elderly
Renal impairment
avoid in severe impairment
Pregnancy
see notes above
Breast-feeding
see notes above
Side-effects
see notes above
Dose
.
ADULT
and
CHILD
over 12 years,
8 mg 3 times daily
Acrivastine
(Non-proprietary)
Capsules
,
acrivastine 8 mg,
net price 12-cap pack =
£2.59,
24-cap pack = £4.49.
Counselling,
driving
Brands include
Benadryl
c
Allergy Relief
CETIRIZINE HYDROCHLORIDE
Indications
symptomatic relief of allergy such as hay
fever,
chronic idiopathic urticaria
Cautions
see notes above
Contra-indications
see notes above
Renal impairment
use half normal dose if eGFR 30–
50 mL/minute/1.73 m
2
;
use half normal dose and
reduce dose frequency to alternate days if eGFR 10–
30 mL/minute/1.73 m
2
;
avoid if eGFR less than
10 mL/minute/1.73 m
2
Pregnancy
see notes above
Breast-feeding
see notes above
Side-effects
see notes above
Dose
.
ADULT
and
CHILD
over 12 years, 10 mg once daily;
CHILD
1–2 years see
BNF for Children
,
2–6 years 2.5 mg
twice daily,
6–12 years 5 mg twice daily
Cetirizine
(Non-proprietary)
Tablets
,
cetirizine hydrochloride 10 mg,
net price 30-
tab pack = 95p.
Counselling,
driving
Dental
prescribing on NHS
Cetirizine 10 mg tablets
may be
prescribed
Oral solution
,
cetirizine hydrochloride 5 mg/5 mL,
net price 200 mL = £2.03.
Counselling,
driving
Note
Sugar-free versions are available and can be ordered by
specifying sugar-free on the prescription
Excipients
may include propylene glycol (see Excipients, p.
2)
DESLORATADINE
Note
Desloratadine is a metabolite of loratadine
Indications
symptomatic relief of allergic rhinitis and
urticaria
Cautions
see notes above
Contra-indications
see notes above;
also hypersensi-
tivity to loratadine
Renal impairment
use with caution in severe impair-
ment
Pregnancy
see notes above
Breast-feeding
see notes above
Side-effects
see notes above;
rarely
myalgia;
very
rarely
hallucinations
Dose
. 5 mg once daily;
CHILD
1–6 years 1.25 mg once daily,
6–12 years 2.5 mg once daily
Neoclarityn
c
(Schering-Plough) A
Tablets
, blue, f/c, desloratadine 5 mg, net price 30-tab
pack = £6.77.
Counselling,
driving
Oral solution
,
desloratadine 2.5 mg/5 mL,
net price
100 mL (bubblegum-flavour) = £6.77,
150 mL =
£10.15.
Counselling,
driving
Excipients
include propylene glycol (see Excipients, p.
2)
FEXOFENADINE HYDROCHLORIDE
Note
Fexofenadine is a metabolite of terfenadine
Indications
see under Dose
Cautions
see notes above
Contra-indications
see notes above
192
3.4.1 Antihistamines
BNF 61
3
Respiratory system