Drug Classification & Information

Hyoscyamine is an oral anti-cholinergic.  It blocks vagal receptors and is typically used in humans for irritable bowel syndrome.  It has similar effects to atropine.  Vagal receptors on the heart lead to slower heart rates by affecting the pacemaker of the heart, the sino-atrial (SA) node.  Vagal receptors also lead to slower conduction of electrical signals through the atrio-ventricular (AV) node leading to the potential for heart block.

Indications for Use

Occasionally used for the treatment of bradycardias (slow heart rate) in dogs with sick sinus syndrome and AV block.

Potential Drug Interactions

Additive effects can be noted when given with anti-histamines (Benadryl) including urine retention, constipation, arrhythmias and lethargy.

Drug Side Effects

Hyoscyamine can cause pupil dilation, dry eye, constipation, urine retention and tachycardia. 

Therapeutic Monitoring

When used for the treatment of bradycardias, regular electrocardiogram (ECG) and Holter monitoring is used to assess treatment efficacy.

Dosage Forms

Human: 0.125 mg tablets