To:  Nancy Walker
As regards the use of beta-blockers and antihistamines, it is not clear what
you mean by RfightingS each other.
 
There are two types of antihistamines: H1-blockers and H2-blockers.
H1-blockers generally can be thought of as two types: the older ones (first
generation) and the newer ones (second generation). The older ones such as
chlorpheniramine, brompheniramine, diphenhydramine, tripelennamine,
hydroxyzine, cetirazine, meclizine, and many others, tend to be sedating. The
second generation or newer ones such as astemizole (Hismanal), loratadine
(Claritin), and terfenadine (Seldane) tend not to be sedating.
H2-blockers include some of the medications which decrease acid production in
the stomach such as cimetidine, famotidine, nizatidine, and ranitidine
(others such as omeprazole (Losec) are not H2-blockers).
Other drugs have antihistamine properties, but are usually classified
according to their major effect. For example, the phenothiazines such as
chlorpromazine have antihistamine effects, but are usually called major
tranquillizers or antipsychotic drugs, not antihistamines.
 
Beta-blockers also can be divided into subtypes according to their effect on
the cardiovascular system, their effect on the central nervous system (how
fat soluble they are determines to a large extent how readily they cross into
the brain), their effect in controlling (or causing) some types of abnormal
heart rhythms, and their undesirable effect on other tissues such as the
lungs (some types are more likely to cause asthma in people prone to asthma).
If you are on a Beta-blocker, can you take an antihistamine? It probably
depends on the type of Beta-blocker you are on, the reason for being on it,
other diseases you might have or are prone to, and the type of antihistamine
you wish to take.
There are no reports of any interactions between H1-blocker type
antihistamines and beta-blockers in the standard books having lists of drugs,
and at least the older types can be used relatively safely with
beta-blockers. However, there is a report on a beta-blocker called Sotalol
(Sotacor) in the Handbook of Adverse Drug Interactions: RSotalol has the
usual adverse effects of a beta-blocker, most commonly fatigue, bradycardia,
and dyspnea, and also can have a proarrhythmic effect [can cause the heart to
beat irregularly]; it causes torsades de pointes, a serious ventricular
arrhythmia [which can lead to death], in 3% to 5% of patients, particularly
those who have prolonged QTc intervals. Additive effects are likely with
other drugs that prolong the QTc interval, including the antihistamines
terfenadine (Seldane) and astemizole (Hismanal), phenothiazines, and
tricyclic antidepressants.S
There are a few reports of interactions between beta-blockers and H2-blocker
type antihistamines. Ranitidine and high doses of Cimetidine possibly may
cause beta-blocker toxicity.
 
Antihistamines with anticholinergic properties may be helpful in reducing
rigidity in PD, but tend not to have as much effect on tremor as other types
of anticholinergic drugs. Diphenhydramine (Benadryl), and Chlorpheniramine
are two examples. Other drugs with antihistamine properties, and
anticholinergic properties have been used as well. For example, Ethopropazine
(Parsidol, Parsitan), usually classified as a phenothiazine or major
tranquilliser but which has antihistamine and anticholinergic properties, is
approved as an antiparkinsonian agent. It is not commonly used however,
probably because of the concern about the potential side effects of this
class of drugs such as dyskinesias.
 
I believe your doctor probably told you to avoid beta-blocker type drugs
because if you are on them, they might precipitate asthma. Additionally, if
you were on a beta-blocker, and had a bad allergic reaction, the beta-blocker
could block the effects of some of the main drugs such as epinephrine
(adrenalin) used to treat severe allergic reactions.
 
Brian Symonds
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