The plasma half-life in humans is 6 hours. The amount of dosage adjustment required in patients with renal impairment is unknown. Elimination of meclizine is not fully established. Due to the anticholinergic effects of meclizine, precautions must be exercised in certain patient populations such as elderly patients. Patients with bladder obstruction, particularly of the bladder neck or prostatic hypertrophy can develop symptomatic urinary retention.
Anticholinergic actions can cause an acute attack of narrow-angle glaucoma.
A decrease in gastric motility and tone can aggravate GI obstruction and retention in patients with pyloroduodenal obstruction. Caution should be used in patients with asthma or chronic obstructive pulmonary disease since anticholinergic actions can increase obstruction of respiratory passages secondary to effects on bronchial secretions. Lactation can be inhibited during breast-feeding due to the anticholinergic effects of meclizine. While this agent may be excreted in breast milk, no problems have been documented in the infant. The CNS depressant effects of meclizine can be potentiated by concurrent use of ethanol or other CNS depressant agents such as benzodiazepines, barbiturates, tricyclic antidepressants, opiate agonists, skeletal muscle relaxants, and antihistamines.