The first 600,000 doses of swine flu vaccinations will become available in 21 states on Tuesday in the form of FluMist—a spray you squirt up your nose. Another 40 million injectable doses will be shipped by mid-October. How do doctors decide what form—spray, shot, pill, suppository—a drug will take?
Convenience and necessity. Drug companies cater to their clients' preferences. Adults prefer popping pills, so most medicines for adults come in small capsules. Kids, by contrast, often dislike swallowing tablets, so companies manufacture liquid alternatives. But not every drug can be taken any which way. It's better to take certain cancer medications—like the red-blood-cell booster Epogen—intravenously rather than via intramuscular injection, since the drugs may irritate tissue. Proteins such as human growth hormone or insulin can't be taken orally, since the stomach's acids and digestive enzymes would break these down as if they were food. Other drugs have to be taken orally. For example, if you're trying to treat a gastrointestinal issue like ulcerative colitis, you're going to want a pill rather than an ointment or an IV drip. *
Timing also matters. If a doctor needs to get a large dose of a drug into someone's bloodstream right away—say they're having a seizure or going into cardiac arrest—she'll give the patient an intravenous injection. Subcutaneous (under the skin) or intramuscular (into the muscle) shots, by contrast, get absorbed a little slower. Inhalers act quickly by entering the bloodstream through the lungs, while nasal sprays are rapidly absorbed through the mucus membrane. Liquids tend to get absorbed slightly faster than pills, which can either dissolve right away or resist digestion—as with so-called time-release capsules—for as long as a day. Suppositories, or capsules inserted into the rectum, get absorbed at about the same rate as pills. Finally, epidermal patches release medication very slowly—sometimes over the course of a whole week.
Drug companies often match delivery mechanisms with a medicine's target. While it's possible to take asthma medication in pill form, for example, it's far more effective to use an inhaler, which reaches your lungs more directly. Likewise, it makes sense to use creams and ointments rather than injections for external cuts and scrapes.
Cost is sometimes a factor, too. It's far cheaper to manufacture a pill than to make any other form of medication. Creating injectable doses is a lot more expensive, since you have to sterilize the drug itself—an elaborate process in a sealed laboratory environment—as well as the needle and the syringe.
Delivery methods will make a difference when it comes to swine flu. The injectable form of the vaccine is a "killed" virus—it's dead—whereas the inhaled version is an "attenuated," or living, virus that has been severely weakened. Pregnant women are better-off getting the injected form, since it's dangerous to expose a fetus to a live virus.
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Explainer thanks Alan Goldhammer of Pharmaceutical Research and Manufacturers of America, Larry Golightly of the University of Colorado Hospital, andJames Polli of the University of Maryland.
Correction, Oct. 5, 2009: This article originally suggested that treatment for heartburn comes only in pill form. Some treatments are administered through an IV. (Return to the corrected sentence.)