DEAR DR. DONOHUE: I am writing about an article you wrote. It was about medicines that promote saliva production, and you said a new one has just been released. My husband had throat cancer a year ago. He still can’t swallow. Would you repeat the name of that medicine? – J.T.

ANSWER: Did your husband have radiation as part of his treatment? Dry mouth often results from radiation to the head and neck. As hard as doctors try not to radiate normal tissue, it’s next to impossible to miss salivary glands with radiation when the target is the head or neck. Radiated salivary glands suffer a great reduction in their saliva production. The mouth becomes dry, and swallowing is difficult.

Since I wrote that article, two new products have appeared – Numoisyn Liquid and Numoisyn Lozenges. The liquid is a saliva replacement for those who make no to very little saliva. The lozenges are thin tablets that slowly dissolve in the mouth and stimulate saliva production in cases where the entire gland has not been completely put out of commission. Both medicines require a prescription.

The medicine I mentioned in the previous article is Evoxac (E-voh-zack). It, too, stimulates saliva production. Another salivary stimulant is Salogen.

Saliva does more than moisten food. It fights tooth decay. People with dry mouths have to be meticulous in taking care of their teeth. They have to make a close friend of their dentist.

Your husband would benefit from contacting the Sjogren’s Syndrome Foundation. He doesn’t have the syndrome, but one of its prominent features is dry mouth. The foundation is knowledgeable about the latest developments in keeping the mouth moist. I am sure your husband would learn much by contacting the foundation at 800-475-6473. If you have access to a computer, its Web site is www.sjogrens.org. The foundation’s bulletin is aptly named The Moisture Seekers.

DEAR DR. DONOHUE: I have been getting a monthly shot of vitamin B-12. I want to try the B-12 tablets, but I can’t get a straight answer about the correct dose. One person says two 500-microgram tablets a day. Another says one 500-microgram tablet a day. A third tells me to take the lowest possible dose, whatever that is.

Will you address this in a column?

How much B-12 does one get from eating cereals that have 100 percent of the recommended daily requirement of it? – M.G.

ANSWER: Vitamin B-12 is a strange vitamin. People usually become deficient in it not because they don’t get enough of the vitamin but because they don’t make a substance called intrinsic factor. The stomach produces intrinsic factor. It takes vitamin B-12 by the hand and leads it into the circulation. Without the factor, the vitamin isn’t absorbed well. Many conditions throw a monkey wrench into the stomach’s production of intrinsic factor. Age is one of them.

Without enough B-12, pernicious anemia develops.

Giving the vitamin by shot bypasses the need for intrinsic factor. The vitamin is directly shunted into the blood. That’s why oral B-12 has not been a standard treatment.

However, if the vitamin is given in high doses, enough does get into the blood. European doctors treat their pernicious anemia patients with oral B-12, and the oral treatment is becoming more common here. The dose is high – 2 milligrams. A milligram is 1,000 micrograms.

For healthy people, the daily recommended dose of vitamin B-12 is only 2.4 micrograms. A food enriched with the vitamin and having 100 percent of the recommended allotment, therefore, has 2.4 micrograms – a small amount.

DEAR DR. DONOHUE: When’s the best time to take a vitamin? There are no directions on the bottle, and all the doctors I ask simply shrug their shoulders. – B.W.

ANSWER: It’s the kind of question that prompts a shrug because there’s not a lot of information on the subject. I have been told to take a multivitamin on a full stomach — after eating. Many vitamins are absorbed better then.

I take a multivitamin early in the morning, before eating. It’s an act of defiance on my part.

DEAR DR. DONOHUE: I read that grapefruit lowers cholesterol. Can the same be said for grapefruit juice? – B.C.

ANSWER: How high is your cholesterol? If it’s high enough to call for medicines, choose the medicines to lower it. Grapefruit juice can lower it as much as the fruit itself does. Red grapefruit works somewhat better than the nonred variety. Don’t expect dramatic results.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com