Vitamin interaction with drugs

All quinolones interact with multivalent cations, forming chelation complexes resulting in reduced absorption. Major offenders are antacids vitamins containing calcium and iron can also be problematic. All fluoroquinolones interact with warfarin, didanosine (ddi), and phenytoin, resulting in decreased absorption or metabolism. Ciprofloxacin and other second-generation drugs interact with theophylline by decreasing its clearance, which leads to theophylline toxicity. 

Geriatric Considerations - Summary Primidone is poorly tolerated in older adults avoid use if possible. Dosage adjustments are required in renal impairment. Numerous drug interactions with primidone exist. Primidone may reduce bone mineral den-sitybyinterferingwith vitamin D catabolism. Calcium and vitamin D supplementation and monitoring of bone mineral density are recommended for older adults taking this drug. 

Isoniazid causes peripheral neuropathy and liver damage (centrilobular necrosis). The liver damage is caused by a metabolite, acetylhydrazine whereas the peripheral neuropathy is caused by the parent drug interacting with pyridoxal phosphate and thereby interfering with the metabolism of vitamin B6. The genetic factor acetylator phenotype is important in both types of toxicity. Thus... 

Linnebank, M., Moskau, S., Semmler, A., Widman, G., Stoffel-Wagner, B., Weller, M., and Eiger, C.E., 2011. Antiepileptic drugs interact with folate and vitamin B12 serum levels. Annals of Neurology. 69 352-359. 

Levodopa interacts with many different drugs. When levodopa is used with phenytoin, reserpine, and papaverine, there is a decrease in response to levodopa The risk of a hypertensive crisis increases when levodopa is used with the monoamine oxidase inhibitors (see Chap. 31). Foods high in pyridoxine (vitamin B6) or vitamin B6 preparations reverse the effect of levodopa However, when carbidopa is used with levodopa, pyridoxine has no effect on the action of levodopa hi fact, when levodopa and carbidopa are given together, pyridoxine may be prescribed to decrease the adverse effects associated with levodopa... 

Vitamin B12 generally is well tolerated and exhibits minimal adverse effects. Injection-site pain, pruritus, rash, and diarrhea have been reported. Drug interactions have been observed with omeprazole and ascorbic acid that decrease oral absorption. 

Chemical drug interactions result when two administered substances combine with each other chemically Tetracyclines complex with Ca (in milk), with aluminum (Al) and magnesium (Mg) (often components of antacids), and with Fe (in some multiple vitamins) to reduce the absorption of the tetracycline antibiotic. 

Other potential adverse effects include impaired absorption of fat-soluble vitamins A, D, E, and K hypernatremia and hyperchloremia GI obstruction and reduced bioavailability of acidic drugs such as warfarin, nicotinic acid, thyroxine, acetaminophen, hydrocortisone, hydrochlorothiazide, loperamide, and possibly iron. Drug interactions may be avoided by alternating administration times with an interval of 6 hours or greater between the BAR and other drugs. 

PPIs are usually well tolerated. Potential adverse effects include headache, dizziness, somnolence, diarrhea, constipation, nausea, and vitamin B12 deficiency. All PPIs can decrease the absorption of drugs such as ketoco-nazole or itraconazole that require an acidic environment for absorption. Other drug interactions vary with each agent. 

Food can interact with drugs, but drugs can also interact with food. Examples of the latter are decreased absorption and elimination of vitamins and minerals, decreased motility, and also taste-, appetite- and vomiting problems (Box 8.4). 

Drugs that may interact with lepirudin and increase the risk of bleeding include thrombolytics (eg, tPA, streptokinase) and coumarin derivatives (vitamin K antagonists). 

Drugs that may interact with orlistat include cyclosporine, fat-soluble vitamins, pravastatin, and warfarin. 

Drugs that may interact with laxatives include mineral oil, milk or antacids, H2 antagonists, proton pump inhibitors, lipid soluble vitamins (A, D, E, and K), and tetracycline. 

Drug interactions No formal drug interaction studies have been carried out. Clinical trials have indicated that Pulmozyme can be effectively and safely used in conjunction with standard cystic hbrosis therapies including oral, inhaled, and/or parenteral antibiotics, bronchodila-tors, enzyme supplements, vitamins, oral or inhaled corticosteroids, and analgesics. 

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