Why do vaccines have to be given intramuscularly? If nitroglycerin tablets are absorbed enough to have immediate effects on the heart, why can’t vaccines be given as droplets or transdermal patches?—CATHERINE PATNODE, ARNP, Yakima, Wash.

Administration route depends on the pharmacokinetic properties of the medication. Many agents, when given orally, undergo extensive metabolism via the GI tract and hepatic portal circulation and are rendered inactive after this “first pass” effect. Insulin is a good example of this activity. Many oral preparations of insulin have been attempted, but all undergo such thorough inactivation in the GI tract that there is no bioavailable drug remaining. 

A parenteral route of administration avoids this effect. Other medications are given parenterally because of their caustic effects on the GI tract. In the case of some vaccines, the intramuscular route also provides a slow absorption (especially depending on whether the drug is suspended in fat or water) and release of the vaccine and vaccine action.—Kathy Pereira, MSN, FNP-BC, assistant professor, co-coordinator, family nurse practitioner program, Duke University School of Nursing, Durham, N.C. (183-3)

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