Antihistamine Injections (cont.)

Pharmacy Author:
Medical and Pharmacy Editor:

Effects of antihistamines are prolonged if combined with MAO inhibitors like:

  • phenelzine (Nardil),
  • selegiline (Zelapar, Emsam, and Eldepryl),
  • tranylcypromine (Parnate),
  • procarbazine (Matulane),
  • rasagiline (Azilect), and
  • isocarboxazid (Marplan).

Antihistamine injections should be used with caution with MAO inhibitors.

What formulations of antihistamine injections are available?

Antihistamine injections are available in injection form.

  • Diphenhydramine, promethazine, and dimenhydrinate are administered intramuscularly and intravenously.
  • Hydroxyzine hydrochloride is administered only intramuscularly.
  • Antihistamine injections are not recommended for administration via subcutaneous route.

What about taking antihistamine injections during pregnancy or while breastfeeding?

FDA lists diphenhydramine and dimenhydrinate as Pregnancy Category B and promethazine as Pregnancy Category C. Hydroxyzine does not have a Pregnancy Category. These categories mean that the safe and effective use of antihistamine injections is not established in during pregnancy; therefore, they should be used only if clearly needed.

It is not known whether injected antihistamine medication enters breast milk; therefore, it is best to be cautious before using antihistamine injections in women who are breastfeeding.

REFERENCE: FDA Prescribing Information.

Medically Reviewed by a Doctor on 11/18/2014

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