Contraindications Precautions And Interactions

The dopaminergic drugs are contraindicated in patients with known hypersensitivity to the drugs. Levodopa is contraindicated in patients with narrow-angle glaucoma, those receiving a monoamine oxidase inhibitor (see

Chap. 31), and during lactation. Levodopa is used cautiously in patients with cardiovascular disease, bronchial asthma, emphysema, peptic ulcer disease, renal or hepatic disease, and psychosis. Levodopa and combination antiparkinsonism drugs (eg, carbidopa/levodopa) are classified as Pregnancy Category C and are used with caution during pregnancy and lactation.

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 lev-odopa 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, pyri-doxine has no effect on the action of levodopa. In fact, when levodopa and carbidopa are given together, pyri-doxine may be prescribed to decrease the adverse effects associated with levodopa.

Selegiline is used cautiously in patients with psychosis, dementia, or excessive tremor. When selegiline is administered with levodopa, the effectiveness of lev-odopa increases. This effect allows for a decrease in the dosage of levodopa. If selegiline is given in doses greater than 10 mg/d there is an increased risk of hypertension, particularly if tyramine-containing foods (eg, beer, wine, aged cheese, yeast products, chicken livers, and pickled herring) are ingested. A potentially serious reaction

(confusion, agitation, hypertension, and seizures) can occur when fluoxetine is administered with selegiline. Fluoxetine therapy is discontinued for a least 1 week before treatment with selegiline is initiated.

Amantadine is used cautiously in patients with seizure disorders, hepatic disease, psychosis, cardiac disease, and renal disease. The antihistamines, pheno-thiazines, disopyramide, and alcohol increase the risk of adverse reactions when administered with amantadine.

the muscles of the lower esophagus to relax causing difficulty swallowing), myasthenia gravis, and megacolon.

These drugs are used with caution in patients with tachycardia, cardiac arrhythmias, hypertension, hypotension, those with a tendency toward urinary retention, those with decreased liver or kidney function, and those with obstructive disease of the urinary system or gastrointestinal tract. The anticholinergic drugs are given with caution to the older adult.

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