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|Newsletters: Pending Changes in Adult Multivitamins|
Pending Changes in Adult Multivitamins
Todd Canada, PharmD, BCNSP
The importance of parenteral multivitamins for consumers who are unable to adequately absorb oral multivitamins has been emphasized in the last 15 years by the multiple national shortages of parenteral adult and pediatric multivitamins. Several cases of refractory lactic acidosis due to thiamin deficiency occurred in home parenteral nutrition (HPN) consumers and resulted in significant morbidity and mortality. Now that the latest shortage of both forms of parenteral multivitamins has been resolved, the US Food and Drug Administration (FDA) has notified manufacturers of the adult products to reformulate to “new” FDA specifications.
Why Change Now?Notably, the new specifications (see Table) are not from recently derived data, but rather from a public workshop that was held in August 1985 and sponsored by the FDA’s Division of Metabolic and Endocrine Drug Products and the American Medical Association’s (AMA) Division of Personal and Public Health Policy. Evidently, the clinical testing of the 1975 AMA multivitamin formulation prompted the new recommendations to increase the dosage of vitamins B1, B6, C, and folic acid and to add vitamin K to the available adult products. It is unclear why it has taken 15 years for these recommendations to be implemented, and why the FDA is implementing them without reviewing and incorporating research conducted since the 1985 meeting. Astra-Zeneca and Baxter have responded to the new FDA changes and do not expect to have updated products on the market for another 18 months unofficially.
Many health care practitioners have expressed concerns over the addition of vitamin K1 to the new adult multivitamin formulation. These concerns are related to the long-term complications associated with vascular access in HPN consumers. HPN consumers often use oral anticoagulants, such as warfarin (brand name Coumadin), to maintain catheter patency. Since low doses (0.5-2.0 mg) of vitamin K1 can fully reverse the anticoagulant effects of warfarin, the dosage increase (from 0 to 0.15 mg) in the new multivitamin formulation has many clinicians worried that loss of adequate anticoagulation may result in consumer morbidity and further malnutrition, possibly, after loss of venous access. It is often difficult to provide oral anticoagulation to consumers with significant gastrointestinal resections or malabsorptive syndromes, including short bowel syndrome, because of their erratic absorption of warfarin.
Consumers receiving home parenteral nutrition who are not on anticoagulants, will likely find it more convenient having vitamin K added to the multivitamins, as they will no longer be required to add it to their solutions. Theoretically, they may also benefit from the addition of Vitamin K since the vitamin K-dependent protein, osteocalcin, is one of the most abundant noncollagenous proteins in bone. Thus adding Vitamin K could impede or retard the development of metabolic bone disease in long-term HPN consumers.
The higher dose of vitamin C presents risks since it may lead to the development of hyperoxaluria (increased oxalate in the urine). In conditions such as short bowel syndrome with an intact/partial colon, there is increased absorption of oxalate from the oral diet (the colon is a major site of oxalate absorption). Normally, oxalate is bound by dietary calcium in the small intestine and forms an insoluble salt that is not available for absorption in the colon. However, when there is little small intestine left, such as with short bowel syndrome, unabsorbed fatty acids complex with the dietary calcium, leaving the oxalate free to be absorbed; it is then excreted in the urine where it can bind with endogenous calcium and cause kidney stones (nephrolithiasis). Since oxalate is a metabolite of vitamin C, extra vitamin C adds to the endogenous oxalate load. Consumers with short bowel syndrome are at risk for kidney stones because of the increased oxalate absorbed and because they are often close to dehydration. Consumers with renal insufficiency or renal disease and a prior history of nephrolithiasis may also be at added risk. If an oxalate- and fat-restricted diet does not reduce the hyperoxaluria, oral calcium supplements may help bind the oxalate in the foods consumed and facilitate losses in the stool of these consumers.
Vitamins B6 and Folic Acid
On the positive side, the new vitamins will include an increase in Vitamin B6 and folic acid. It is hoped that the increases in vitamin B6 and folic acid will prevent hyperhomocysteinemia in HPN consumers at risk for this problem, given the association of hyperhomocysteinemia with thrombosis and vascular disease. The increases in vitamin B6 and folic acid could also reduce the risk of catheter-associated thrombosis. The minimum most-effective dose of these cofactors is not yet determined.
Excerpted with permission from Medscape(http://www.medscape.com/Medscape/pharmacists/journal/2001/v02.n01/mph0212.cana/mph0212.cana-01.html) © 2000, Medscape, Inc.
New Adult Parenteral Multivitamin Formulation
Parenteral Vitamin Recommendations for Adults (Age 11+ yrs)
* Proposed by the AMA in 1975
** Proposed by the US FDA’s Division of Metabolic and Endocrine Drug Products and the AMA’s Division of Personal and Public Health Policy in 1985.