Spiramycin Carbidopa

The plasma levels of levodopa (given with carbidopa) are reduced by spiramycin, thereby reducing its therapeutic effects. 

The observation of a patient with Parkinson s disease taking levodopa/car-bidopa whose condition became less well-controlled when treated with spiramycin, prompted further study. Levodopa/carbidopa 250/25 mg was given to 7 healthy subjects after they had taken spiramycin 1 g twice daily for 3 days. The spiramycin reduced the AUC of levodopa by 57%, and maximum plasma levels fell from 2162 to 1680 nanograms/niL (not significant). The relative bioavailability of levodopa was only 43%. The plasma levels of the carbidopa were barely detectable. ... 

Not fully established. In some way spiramycin markedly reduces the absorption of carbidopa, possibly by forming a non-absorbable complex in the gut or by accelerating its transit through the gut. As a result, not enough carbidopa is absorbed to inhibit the peripheral metabolism of the levodopa by dopa-decarboxylase, so that the effects of the levodopa are reduced. ... 

Brion N, Kollenbach K, Marion MH, Gregoire A, Advenier C, Pays M. Effect of a macrolide (spiramycin) on the pharmacokinetics of L-dopa and carbidopa in healdiy volunteers. Clin Neuropharmacol ( 992) 15, 229-35. 

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