Ferrous sulfate can reduce bioavailability of levodopa andcarbidopa, and may possibly reduce control of Parkinson’sdisease.
A study in 9 patients with Parkinson’s disease found that a single 325mg dose of ferrous sulfate reduced AUC of levodopa by 30 % and reduced AUC of carbidopa by more than 75%. There was a trend towards an increase in disability,suggesting a worsening of disease, but this did not reach statistical significance. Some, but not all of patients had some deterioration in control of their disease(See reference number 1)
In another study, 8 healthy subjects were given a single 250mg dose of levodopa, with and without a single 325mg dose of ferrous sulfate, and plasma levodopa levels were measured for following 6 hours. Peak plasma levodopa levels and levodopa AUC were reduced by 55 % and AUC was reduced by 51%. Those subjects who had highest peak levels and greatest absorption when given levodopa alone, showed greatest reductions when additionally given ferrous sulfate (See reference number 2).
Ferrous iron rapidly oxidises to ferric iron at pH values found in gastrointestinal tract
Information appears to be limited to these single-dose and in vitro studies. The importance of this interaction in patients taking both drugs long-term awaits further study but extent of reductions in absorption (30 to 50%), and hint of worsening control,(See reference number 1) suggests that this interaction may be of clinical importance. Be alert for any evidence of this. Separating administration of iron and levodopa as much as possible is likely to prove effective, as this appears to be an absorption interaction. More study is needed.
Campbell NRC,Rankine D, Goodridge AE, Hasinoff BB, Kara M. Sinemet-ferrous sulphateinteraction in patients with Parkinson’s disease. Br J Clin Pharmacol (1990) 30, 599–605.
Campbell NRC,Hasinoff B. Ferrous sulfate reduces levodopa bioavailability: chelation as apossible mechanism. Clin Pharmacol Ther (1989) 45, 220–5.
Campbell RRA,Hasinoff B, Chernenko G, Barrowman J, Campbell NRC. The effect of ferroussulfate and pH on L-dopa absorption. Can J Physiol Pharmacol (1990) 68, 603–7.
Greene RJ,Hall AD, Hider RC. The interaction of orally administered iron with levodopa andmethyldopa therapy. J Pharm Pharmacol (1990) 42, 502–4.