The FDA has required that the labels of all carbidopa/levodopa-containing products (Crexont, Dhivy, Duopa, Rytary, Sinemet, Sinemet CR, Stalevo, Vyalev) include a warning about the risk of vitamin B6 (pyridoxine) deficiency and vitamin B6 deficiency-related seizures associated with their use. The combination of carbidopa/levodopa is the most effective treatment for the motor symptoms of Parkinson's disease and recent evidence favors its early use.

The FDA has approved Diclegis (Duchesnay), a fixed-dose, delayed-release combination of the H₁-antihistamine doxylamine and the vitamin B₆ analog pyridoxine, for treatment of nausea and vomiting of pregnancy in women who do not respond to conservative management. It is only available by prescription. Doxylamine and pyridoxine, both currently available over the counter, were previously available by prescription in a fixed-dose combination (Bendectin) for morning sickness. Bendectin was voluntarily withdrawn in the US in 1983 because of claims of teratogenicity that have since been disproven. The combination has continued to be available in Canada as Diclectin.

Many patients ask their physicians whether they should take vitamins. Since the last Medical Letter article on this subject, more data have become available on the benefits and risks of taking vitamin supplements.

High plasma homocysteine concentrations, like high cholesterol, have been associated with an increased risk of cardiovascular disease and death (O Nygσrd et al, N Engl J Med 1997; 337:230; RS Vasan et al, JAMA 2003; 289:1251). In one meta-analysis, 25% lower plasma homocysteine concentrations were associated with 11% less coronary heart disease and 19% less stroke (Homocysteine Studies Collaboration, JAMA 2002; 288:2015). Should we be trying to lower serum homocysteine concentrations in our patients?

Many patients ask their physicians whether they should take vitamins. In recent years, more data have become available on the risks and benefits of taking vitamin supplements.

After many years of decline, the incidence of tuberculosis has recently increased because the disease occurs in patients with AIDS (Morbid Mortal Weekly Rep, 36:817, Jan 1, 1988). For uncomplicated tuberculosis, the recent trend in tuberculosis treatment has been toward a shorter period of therapy and increased use of pyrazinamide.