21-10-2021, 02:51 AM
Vitamins and minerals serve crucial functions in almost all bodily processes and must be obtained from foods or supplements, as our bodies are unable to make them. According to results of the National Health and Nutrition Examination Survey, 52% of adults take dietary supplements.1 Supplement use is typically a safe and effective method of maintaining a healthy body; however, supplements have the potential to interact with prescribed medications. In this article, common drug interactions with vitamins and minerals are discussed, along with suggestions on how the pharmacist should manage these interactions.
It is important for pharmacists to be able to identify patients who are most at risk. Risk factors for poor outcomes from drug interactions include use of multiple medications and/or supplements, older age, inadequate kidney or liver function, and the use of medications with narrow therapeutic indexes. Patients with these risk factors should be targeted for interventions to prevent drug interactions with vitamins and minerals.
When managing interactions between medications and vitamin/mineral supplements, the pharmacist has several factors to keep in mind. First, he or she needs to determine the need for the supplement during the time the medication is to be taken. For a short course of medication, it is usually possible to discontinue the supplement until the therapy is completed. Second, the pharmacist should identify alternatives. For example, if the interacting substance comes from an antacid that the patient needs to treat symptoms of gastroesophageal reflux disease, an alternative such as an H2-blocker or proton pump inhibitor can be used during the course of the medication. If the affected medication is to be taken chronically, and the supplement is deemed necessary, the pharmacist should work with the patient and the prescriber to suggest alternatives that would limit exposure to potentially dangerous drug interactions.
Vitamin B6 (Pyridoxine): Vitamin B6, or pyridoxine, is a water-soluble vitamin used to treat deficiencies in vitamin B6 and some types of anemia. Foods rich in pyridoxine include meats, whole grains, and certain fruits and vegetables. Pyridoxine has been shown to decrease the effects of both phenytoin and levodopa. However, this effect is not seen when levodopa is prescribed in combination with carbidopa, which prevents the interaction from occurring. In the rare instance that patients are taking levodopa in absence of carbidopa, pharmacists should advise their patients to avoid any products containing pyridoxine, because even smaller doses, such as 10 to 25 mg of pyridoxine, may be enough to inhibit levodopa.3 Pharmacists should strongly encourage the switch to a levodopa/carbidopa combination product if a patient is not already taking this combination therapy.
There is limited evidence that high doses of pyridoxine reduce phenytoin serum concentrations, thereby reducing the efficacy of phenytoin. One study of patients with seizure disorders found an association between pyridoxine 200 mg/day and reductions in phenytoin concentration of nearly 50%.4 Effects of pyridoxine doses lower than 200 mg/day on phenytoin serum concentration have not been established; however, lower doses can be considered if someone taking a multivitamin presents with low phenytoin serum concentrations. In these instances, it may be necessary to discontinue or lower the dosage of the multivitamin or to increase the dosage of phenytoin.
It is important for pharmacists to be able to identify patients who are most at risk. Risk factors for poor outcomes from drug interactions include use of multiple medications and/or supplements, older age, inadequate kidney or liver function, and the use of medications with narrow therapeutic indexes. Patients with these risk factors should be targeted for interventions to prevent drug interactions with vitamins and minerals.
When managing interactions between medications and vitamin/mineral supplements, the pharmacist has several factors to keep in mind. First, he or she needs to determine the need for the supplement during the time the medication is to be taken. For a short course of medication, it is usually possible to discontinue the supplement until the therapy is completed. Second, the pharmacist should identify alternatives. For example, if the interacting substance comes from an antacid that the patient needs to treat symptoms of gastroesophageal reflux disease, an alternative such as an H2-blocker or proton pump inhibitor can be used during the course of the medication. If the affected medication is to be taken chronically, and the supplement is deemed necessary, the pharmacist should work with the patient and the prescriber to suggest alternatives that would limit exposure to potentially dangerous drug interactions.
Vitamin B6 (Pyridoxine): Vitamin B6, or pyridoxine, is a water-soluble vitamin used to treat deficiencies in vitamin B6 and some types of anemia. Foods rich in pyridoxine include meats, whole grains, and certain fruits and vegetables. Pyridoxine has been shown to decrease the effects of both phenytoin and levodopa. However, this effect is not seen when levodopa is prescribed in combination with carbidopa, which prevents the interaction from occurring. In the rare instance that patients are taking levodopa in absence of carbidopa, pharmacists should advise their patients to avoid any products containing pyridoxine, because even smaller doses, such as 10 to 25 mg of pyridoxine, may be enough to inhibit levodopa.3 Pharmacists should strongly encourage the switch to a levodopa/carbidopa combination product if a patient is not already taking this combination therapy.
There is limited evidence that high doses of pyridoxine reduce phenytoin serum concentrations, thereby reducing the efficacy of phenytoin. One study of patients with seizure disorders found an association between pyridoxine 200 mg/day and reductions in phenytoin concentration of nearly 50%.4 Effects of pyridoxine doses lower than 200 mg/day on phenytoin serum concentration have not been established; however, lower doses can be considered if someone taking a multivitamin presents with low phenytoin serum concentrations. In these instances, it may be necessary to discontinue or lower the dosage of the multivitamin or to increase the dosage of phenytoin.