Diphenhydramine Contraindications and Precautions
- neonates
- asthma
- bladder obstruction
- breast-feeding
- cardiac disease
- children
- chronic obstructive pulmonary disease (COPD)
- closed-angle glaucoma
- contact lenses
- driving or operating machinery
- elderly
- GI obstruction
- hepatic disease
- ileus
- pregnancy
- prostatic hypertrophy
- urinary retention
Diphenhydramine Contraindications and Precautions
Use antihistamines with caution in patients with asthma. The anticholinergic activity of H1-antagonists may result in thickened bronchial secretions in the respiratory tract thereby aggravating an acute asthmatic attack or chronic obstructive pulmonary disease (COPD). Although antihistamines should be avoided during an acute asthmatic attack, these anticholinergic effects do not preclude the use of antihistamines in all asthmatic or COPD patients, particularly if the above respiratory symptom is not a primary component of the illness. Because diphenhydramine exhibits a significant amount of anticholinergic activity, the use of an H1-antagonist with less anticholinergic activity is preferable when therapy is indicated.
Diphenhydramine should be used cautiously in children since a paradoxical CNS stimulation can occur. There have been a number of cases of respiratory depression, sleep apnea, and SIDS in children receiving phenothiazine antihistamines. The mechanism of this reaction is not yet known; therefore, H1-antagonists should be used with extreme caution in children with a family history of SIDS or sleep apnea. H1-antagonists should not be used in neonates due to the possibility of paradoxical CNS stimulation or seizures.
Diphenhydramine is classified as pregnancy category B. Parenteral diphenydramine is typically the parenteral antihistamine of choice in managing acute or severe allergic reactions during pregnancy. The routine use of H1-antagonists generally is not recommended during pregnancy; there are no adequate well-controlled clinical trials available. H1-antagonists are not recommended for use in the last 2 weeks of pregnancy due to a possible association between these drugs and retrolental fibroplasia in premature neonates. Diphenhydramine should be administered during pregnancy only when the benefits of therapy outweigh the potential risks to the fetus, and use should be limited to short-term, ‘as needed’ administration under the prescription of a qualified health-care professional. First-trimester use is not recommended unless medically necessary. Non-pharmacologic methods (e.g., fluids, rest) are recommended to be tried first for symptomatic relief of colds or allergies.
H1-antagonists are not recommended for use during breast-feeding because they can induce a paradoxical CNS stimulation in neonates or seizures in premature infants. Inhibition of lactation may also occur. Alternative methods of feeding should be used if diphenhydramine therapy is necessary.
Diphenhydramine should be avoided, if possible, in patients with closed-angle glaucoma and an H1-antagonists with less anticholinergic effects should be substituted. An increase in intraocular pressure may occur from the anticholinergic actions of the drug, precipitating an acute attack of glaucoma. Elderly patients are more susceptible to the anticholinergic effects of diphenhydramine, including possible precipitation of undiagnosed glaucoma. Other ocular effects resulting from the anticholinergic effects of diphenhydramine include dry eyes or blurred vision. This may be of significance in the elderly and wearers of contact lenses.
Diphenhydramine has substantial anticholinergic effects and a worsening of symptoms may be seen in patients with bladder obstruction, GI obstruction or ileus, benign prostatic hypertrophy, or urinary retention. These precautions are most significant when using H1-antagonists such as diphenhydramine or those from the phenothiazine group. The elderly are more susceptible to the anticholinergic effects of drugs since there is a decline in endogenous cholinergic activity that occurs with age.
Diphenhydramine is extensively metabolized in the liver. The metabolism of diphenhydramine may be reduced in the presence of hepatic impairment. Those with significant hepatic disease receiving H1-antagonists should be monitored for liver function and side effects. Dosage reduction may be required in these patients.
The quinidine-like local anesthetic and anticholinergic effects of H1-antagonists are responsible for the adverse cardiac effects which have been observed including tachycardia, ECG changes, hypotension, and arrhythmias. Although these cardiovascular effects are uncommon, H1-antagonists should be used conservatively in patients with cardiac disease.
Diphenhydramine can cause drowsiness. Patients receiving diphenhydramine should be advised to avoid driving or operating machinery until the effects of the drug are known.
[ Last revised: 1/5/2003 6:45:00 PM ]
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