Sinemet‐ferrous sulphate interaction in patients with Parkinson's disease.

Abstract

1. This study examined the effects of administering ferrous sulphate 325 mg with Sinemet (100/25 tablet) on levodopa and carbidopa bioavailability and on signs of Parkinson's disease in nine patients. 2. Ferrous sulphate ingestion with Sinemet resulted in a decrease in levodopa area under the curve (AUC) of 30% (P less than 0.01) and a greater than 75% decrease in carbidopa AUC. Despite a strong relationship between reductions in levodopa AUC and reductions in Sinemet efficacy (r = 0.83, P less than 0.01), the average reduction in Sinemet's efficacy associated with ferrous sulphate did not achieve statistical significance (P = 0.055). 3. Chemical studies indicate that iron forms chemical complexes with carbidopa in a similar manner to levodopa and is a likely mechanism for the drug interactions. 4. AUC when a Sinemet tablet is taken concurrently with a ferrous sulphate tablet appears to be clinically significant in some but not all patients. The clinical significance of repeated ingestion of ferrous sulphate with Sinemet requires further studies. 1990 The British Pharmacological Society