1. Histamine Antagonists
GLOSSARY
arrhythmia general term for an irregularity or rapidity of the
heartbeat, an abnormal heart rhythm. palpitation rapid heart rate; the patient feels the heartbeat.
THESE WELL-KNOWN ANTIALLERGY MEDICATIONS may occasionally cause an increase in the pulse rate because they have an atropine-like effect. In some individuals, the heart rate may become rapid. These sensations, called palpitations and caused by arrhythmia, subside over time and usually cause no harm. Patients with angina, however, should be cautious with the use of antihistamines, because an increase in heart rate may trigger an attack of angina. Blood pressure is usually not increased by antihistamine use, but many remedies containing antihistamines contain the decongestant phenylpropanolamine, which elevates blood pressure. This should be avoided by patients with hypertension and angina.
I. HISTAMINE ANTAGONISTS
These newer agents differ from the general group of antihistamines in that they are more selective blockers of specific histamine H1 receptors. They do not produce the bothersome side effects usually noted with antihistamines, such as drowsiness and dry mouth. Unlike antihistamines, they are safe in patients with glaucoma or enlargement of the prostate. Older histamine H1 antagonists include astemizole and terfenadine. These agents are generally safe, but abnormal heart rhythms, palpitations, transient loss of consciousness, and cardiac arrest have been reported. The electrocardiographic findings include an increase in the QT interval. Agents that also increase the QT inter¬val should not be taken concurrently with these H1 antagonists.

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• BIBLIOGRAPHY
  Khan, M. Gabriel Effects of Drug Interactions. In Cardiac Drug Therapy, sixth edition. W. B. Saunders, Philadelphia, 2003.