Dr. Roach: Highly contagious tuberculosis still a threat worldwide

Keith Roach
To Your Health

Dear Dr. Roach: I recently read that tuberculosis kills more people than any other infectious illness. Can people who have no symptoms spread this disease?

— R.R.

Dear R.R.: Tuberculosis, an ancient disease, is caused by Mycobacterium tuberculosis. It infects 10 million people per year and kills 1.5 million people yearly worldwide, mostly in Africa and India. This is more than malaria and HIV combined. Although tuberculosis was the cause of death for 1 in 7 people during the 19th century in Europe and the U.S., there were only 9,000 cases of TB and 500 deaths in the U.S. in 2017.

Most cases of tuberculosis are spread person-to-person, with the primary route being inhalation of the bacteria a person has coughed. Household contacts of an infected person are at the highest risk of acquiring tuberculosis; if infected, 90% to 95% of those will successfully control the bacteria and enter a latent phase of infection, which has no symptoms. However, in 5% to 10% of those people, the bacteria will become active and cause clinical infection. Cough, fever, night sweats and weight loss are classic symptoms of active tuberculosis infection. Reactivation of tuberculosis is most likely to happen in the first two to three years after exposure, but may also happen if a person’s immune system becomes weakened due to serious illness or medication that suppresses it.

Only people with active tuberculosis infection can spread the disease. Latent disease cannot be spread. Cough is the most effective means of expelling tuberculosis, but recent research suggests cough is not necessary for tuberculosis to spread. Quick identification and quarantine of people with tuberculosis and rapid treatment are the keys to preventing its spread. Since tuberculosis is much less common than in the past, physicians need to be aware that this disease is still prevalent, and we need to be diligent about considering the diagnosis.

Dear Dr. Roach: What would cause melatonin to work faster: letting a flavored pill dissolve in your mouth or swallowing it?

— D.A.

Dear D.A.: Not all drugs are absorbed through the mucosal membrane of the mouth. Some drugs are, and they can get absorbed very rapidly. Nitroglycerine, for example, gets into the bloodstream faster through a sublingual (under the tongue) tablet than any other way -- unless you happen to already have an intravenous line in and intravenous nitroglycerine ready to go, which is almost never the case. When I was a resident on the cardiology inpatient service, I always kept a bottle of sublingual nitroglycerine in my pocket.

Other drugs are not absorbed well at all through the mouth, and must be swallowed in order for them to be absorbed. However, all medicine absorbed through the stomach and intestines must go through the bloodstream into the liver, where it may be metabolized into something inactive. In those cases, sublingual administration might lead to higher blood levels in the brain, where melatonin works.

In the case of melatonin, there are different preparations made specifically for administration under the tongue. At least one of these (a spray) was absorbed faster than oral administration; however, a different preparation (a patch made for the mouth) had both slower absorption than melatonin that was swallowed and half of the medicine was still in the patch when removed.

Because the absorption is variable depending on the type of delivery system used, I can’t answer your question directly. But since you are talking about a pill that dissolves in the mouth, what isn’t absorbed through the mouth will be swallowed and subsequently absorbed through the intestine. The sublingual route is therefore not likely to be much slower, and could be somewhat faster.

Readers may email questions to ToYourGoodHealth@med.cornell.edu.