Sunday, February 13, 2005

Will natural medicine be a pille or a needle?

From the skeptical inquirer:

Many alternative practitioners promise to reveal "secrets your doctor never told you." One secret is never mentioned: why alternative remedies are ingested rather than injected. Though most practitioners of alternative medicine are silent on this question, this "missing information," as previously described by Kardes and Sanbonmatsu (2003), is crucial for evaluating the promised cure.

So-called natural medicines, usually herbs or supplements, are invariably things to eat or drink. And why not? Ever since the appearance of pharmaceuticals in the early 1800s, the doctor's prescription, legible only to a pharmacist, would nearly always get you something to swallow--a liquid, a pill, or a powder; an extract of senna leaves to relieve constipation, for example, or a "headache powder." Only occasionally would the prescription get you something to rub on your skin, like a salve. Today, medication still comes mostly in pill or capsule form.

By the late 1800s, Louis Pasteur's work with microorganisms brought about the first vaccines, for anthrax and rabies. BCG (bacillus Calmette-Guerin) vaccine against tuberculosis appeared in 1921, and by 1955, Jonas Salk developed his polio vaccine. These vaccines could not be swallowed, they had to be injected. With a needle. But inflicting pain is unpleasant and discourages parents from bringing their children for vaccination. Therefore, Albert Sabin's 1965 oral polio vaccine was an important discovery.

The 1960s also brought the oral contraceptives--birth-control pills. Carl Djerassi, a chemistry professor at Stanford University known as "the father of the birth-control pill," preferred to call it "chemical fertility control." What was so special about oral polio vaccine and oral contraceptives? Did we not always swallow our medicines? Why were these oral medications such a breakthrough?

Although polio vaccine and birth-control pills are Far apart in the pharmaceutical spectrum, the reason for the importance of "oral" is the same. Research often yields promising compounds that act on microorganisms or on cell cultures in vitro, in the shallow glass vessels called petri dishes. Next, the potential remedy is tested on animals, usually via a syringe. How does it get to be a pill? Or does it?

From Needle to Pill

Progesterone is a hormone secreted during pregnancy. One of its functions is to prevent the fertilization of other egg cells. It is the natural form of birth control, but it cannot be used as a pill. Progesterone is absorbed readily through the intestinal wall and is quickly metabolized on its first pass through the liver. Its half-life in the blood stream is about five minutes (Katzung 1998). Chemically modifying the progesterone molecule avoids this problem. That modification allowed the development of the Pill.

The moment we swallow something, what we eat starts on an obstacle course toward its destination. Enzymes in saliva begin the attack. Then the strongly acidic environment in the stomach alters many food molecules. Chemicals that survive this far face the digestive enzymes on their way through the small intestine. Eventually, some useful products of the breakdown of our food are absorbed through the intestinal wall into the bloodstream. Others are fermented by the bacteria in our colon, and still others are excreted.

More hurdles wait in the bloodstream. Portal blood carries absorbed food-derived molecules first to the liver, which can metabolize a chemical, be it food or medicine, before it reaches the systemic circulation. It's quite a steeplechase for whatever we eat.

Like the family doctor of old, alternative healers also give us pills or teas. After all, we have been conditioned to accept medicine as something we eat, never mind who recommends or prescribes it. But there is a difference between the alternative and the conventional. We invariably eat or drink the herbalist's prescriptions. But physicians, although they prefer to prescribe pills or capsules, must sometimes reach for the needle, because many effective drugs do not cope well with the rigors of our digestive tract. A drug's susceptibility to digestion or its poor absorption through the intestinal wall result in poor bioavailability. Such drugs must be injected to bypass the digestive system. The alternative-medicine approach rarely considers the bioavailability question.

Of an annotated list of North American prescription drugs, fully one third cannot be taken orally for these reasons (Springhouse Corporation 1996). They are injected, usually by a nurse or a doctor. In contrast, the complementary approach holds to the view that good medicine, provided by nature, comes from plants. It should be eaten, even if the extract must be sealed in a capsule. Strangely, although chemical laboratories are not kindly thought of by herb users, buying herbal extracts sealed into laboratory-made capsules does not seem to be a problem.

An early step in testing new drugs is determining how the drug reaches the target organ, how much enters the circulation, and how quickly it is metabolized or excreted. Without knowing this pharmacokinetic behavior, we cannot predict what happens after we swallow the pill, the capsule, or the tea.

A chemical called amygdalin, extracted from peach or apricot pits, was touted throughout the 1970s as an anticancer drug under the name Laetrile and became the subject of much controversy. While some alternative healers still believe Laetrile is a cancer drug, conventional medicine has rejected it. Laetrile molecules consist, in the chemical sense, of three smaller building blocks: benzaldehyde, glucose, and hydrocyanic acid. The last one is a highly toxic chemical, the "cyanide" of detective stories and gas chambers.

The reason for rejecting Laetrile is its pharmacokinetic behavior. When injected into cancer patients, it was quickly and almost completely excreted in the urine (Moertel et al. 1981). Given orally, it is rapidly split into its building blocks by stomach acid, causing elevated but nonlethal blood levels of cyanide. Since injected Laetrile is not absorbed, and if orally administered, the drug is destroyed by digestion, whatever it does to cancer cells in a lab is irrelevant.

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