Levodopa Foods

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... 

When taking levodopa, avoid vitamin B6 (pyridox-ine) because diis vitamin may interfere with the action of levodopa (see Home Care Checklist Avoiding Certain Foods While Taking Levodopa). 

AVOIDING CERTAIN FOODS WHILE TAKING LEVODOPA... 

FIGURE 29-2. Levodopa absorption and metabolism. Levodopa is absorbed in the small intestine and is distributed into the plasma and brain compartments by an active transport mechanism. Levodopa is metabolized by dopa decarboxylase, monoamine oxidase, and catechol-O-methyltransferase. Carbidopa does not cross the blood-brain barrier. Large, neutral amino acids in food compete with levodopa for intestinal absorption (transport across gut endothelium to plasma). They also compete for transport across the brain (plasma compartment to brain compartment). Food and anticholinergics delay gastric emptying resulting in levodopa degradation in the stomach and a decreased amount of levodopa absorbed. If the interaction becomes a problem, administer levodopa 30 minutes before or 60 minutes after meals. 

Levodopa, a dopamine precursor, is the most effective agent for PD. Patients experience a 40% to 50% improvement in motor function. It is absorbed in the small intestine and peaks in the plasma in 30 to 120 minutes. A stomach with excess acid, food, or anticholinergic medications will delay gastric emptying time and decrease the amount of levodopa absorbed. Antacids decrease stomach acidity and improve levodopa absorption. Levodopa requires active transport by a large, neutral amino acid transporter protein from the small intestine into the plasma and from the plasma across the blood-brain barrier into the brain (Fig. 29-2). Levodopa competes with other amino acids, such as those contained in food, for this transport mechanism. Thus, in advanced disease, adjusting the timing of protein-rich meals in relationship to levodopa doses may be helpful. Levodopa also binds to iron supplements and administration of these should be spaced by at least 2 hours from the levodopa dose.1,8,16,25... 

Drug/Food interactions Administration of a single dose of the extended-release form with food increased the extent of levodopa availability by 50% and increased peak levodopa concentrations by 25%. 

Tyramine-rich foods, sympathomimetics, dextromethorphan, anorectics, and other antidepressants should be avoided when treating with moclobemide. It also interacts with opioid analgesics, serotonin agonists, NSAIDs, levodopa, and cimetidine.140,141... 

Absorption and metabolism The drug is absorbed rapidly from the small intestine (when empty of food). Levodopa has an extremely short half-life (1 to 2 hours), which causes fluctuations in plasma concentration. This may produce fluctuations in motor response ( on-off phenomenon), which may cause the patient to suddenly lose normal mobility and experience tremors, cramps, and immobility. Ingestion of meals, particularly if high in protein content, interferes with the transport of levodopa into the CNS. Large, neutral amino acids (for example, leucine and isoleucine) compete with levodopa for absorption from the gut and for transport across the blood-brain barrier. Thus levodopa should be taken on an empty stomach, typically 45 minutes before a meal. Withdrawal from the drug must be gradual. 

Drugs that are considered to be absorbed to a lesser degree with food include antibiotics (ampicillin, penicillins G and VK, isoniazid, rifampicin, lincomycin, nafcillin, tetracyclines), methyldopa and levodopa (to be... 

Clinically important, potentially hazardous interactions with amitriptyline, amoxapine, amphetamines, bupropion, citalopram, clomipramine, cyproheptadine, desipramine, dextroamphetamine, dextromethorphan, diethylpropion, dopamine, doxepin, entacapone, ephedrine, epinephrine, fluoxetine, fluvoxamine, imipramine, levodopa, mazindol, meperidine, methamphetamine, nefazodone, nortriptyline, paroxetine, phendimetrazine, phentermine, phenylephrine, phenylpropanolamine, pizotifen, protriptyline, pseudoephedrine, rizatriptan, sertraline, sibutramine, sumatriptan, sympathomimetics, tramadol, tricyclic antidepressants, trimipramine, tryptophan, tyramine-containing foods, venlafaxine, zolmitriptan... 

Vitamin 65 interferes with the therapeutic effects of levodopa. Multivitamin supplements should not be taken together with levodopa and foods high in vitamin Be (for example liver, walnuts and bananas) should be limited during use of levodopa. 

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