<p>Caution should be exercised when the following drugs are administered concomitantly with Levodopa-Carbidopa prolonged-release tablet.<br />
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<strong>Antihypertensive agents</strong>: Symptomatic postural hypotension has occurred when levodopa/decarboxylase inhibitor combinations were added to the treatment of patients receiving some antihypertensive drugs. Therefore when therapy with Levodopa-Carbidopa prolonged-release tablet is started, dosage adjustment of the antihypertensive drug may be required.<br />
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<strong>Antidepressants</strong>: There have been rare reports of adverse reactions, including hypertension and dyskinesia, resulting from the concomitant use of tricyclic antidepressants and carbidopa-levodopa preparations.<br />
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<strong>Anticholinergics</strong>: Anticholinergics may affect the absorption and thus the patient&rsquo;s response.<br />
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<strong>Iron</strong>: Studies demonstrate a decrease in the bioavailability of carbidopa and/or levodopa when it is ingested with ferrous sulphate or ferrous gluconate.<br />
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<strong>Other drugs</strong>: Dopamine D2 receptor antagonists (e.g. phenothiazines, butyrophenones and risperidone) and isoniazid may reduce the therapeutic effects of levodopa. The beneficial effects of levodopa in Parkinson&rsquo;s disease have been reported to be reversed by phenytoin and papaverine. Patients taking these drugs with Levodopa-Carbidopa prolonged-release tablet should be observed carefully for loss of therapeutic response. Concomitant therapy with selegiline and carbidopa-levodopa may be associated with severe orthostatic hypotension not attributable to carbidopa-levodopa alone. Since levodopa competes with certain amino acids, the absorption of levodopa may be impaired in some patients on a high protein diet. The effect of simultaneous administration of antacids with Levodopa-Carbidopa prolonged-release tablet on the bioavailability of levodopa has not been studied.</p>