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 gastrointestinal issues like heartburn, 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.
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