The first therapeutic use of levodopa for Parkinson disease (PD) was by the intravenous route \citep{13869404,18591089,21080185}. Oral administration is preferred clinically due to ease of use, although intravenous (i.v.) levodopa infusion has been favored in certain clinical circumstances \citep{7519334,4544184,11840662,19860235}.
The i.v. route has advantages for some research purposes as well \citep{Black_2004,Black_2010,Black_2015}. However, levodopa is approved by the U.S. Food and Drug Administration for treatment of PD and other parkinsonian conditions only in a tablet formulation. In the U.S., giving an approved drug by another route for research purposes may require an investigational new drug (IND) application if changing the route of administration “significantly increases the risks (or decreases the acceptability of the risks)” (§21 CFR 312.2(b)(iii)). Some have assumed that this might hold for i.v. compared to oral levodopa.
In fact, however, numerous studies have reported on brief (\(<\)24 hr) infusions or large single-dose i.v. boluses, and i.v. levodopa has been tolerated approximately as well as oral levodopa \citep{Abraham2006,Siddiqi2015}. One study even deliberately attempted to induce hallucinations by giving high-dose i.v. levodopa to patients at high risk, but produced no hallucinations \citep{9484386}. However, data on hemodynamic effects of i.v. levodopa have been limited over the past 20 years, and such results have not yet been quantitatively reported in the presence of a peripheral decarboxylase inhibitor \citep{Abraham2006,Siddiqi2015}.
Here we provide quantitative data, from a double-blind, random-allocation crossover study, on orthostatic blood pressure and pulse responses to i.v. levodopa in the presence of adequate carbidopa pretreatment.