Clinical pharmacokinetics of the norepinephrine precursor L-threo-DOPS in primary chronic autonomic failure.
BACKGROUND
Oral L-threo-3,4-dihydroxyphenylserine (L-DOPS), a synthetic catechol amino acid, increases standing blood pressure and improves standing ability in patients with neurogenic orthostatic hypotension, by conversion of L-DOPS to norepinephrine (NE) outside the brain. This study assessed the pharmacokinetics of L-DOPS, NE, and dihydroxyphenylglycol (DHPG), the main neuronal metabolite of NE, in patients with primary chronic autonomic failure from pure autonomic failure (PAF) or multiple system atrophy (MSA).


METHODS
In 5 MSA and 4 PAF patients, antecubital venous blood was drawn during supine rest and plasma levels of catechols measured at various times for 48 hours after a single oral dose of 400 mg of L-DOPS.


RESULTS
Plasma L-DOPS peaked at 1.9 microg/ml (9 micromol/L) about 3 hours after drug administration, followed by a monoexponential decline with a half-time of 2-3 hours in both patient groups. Plasma NE and DHPG also peaked at about 3 hours, but at much lower concentrations (4 and 42 nmol/L). Compared to the MSA group, the PAF group had a smaller calculated volume of distribution of L-DOPS and up to 10-fold lower plasma NE levels at all time points. Plasma NE was above baseline in MSA even at 48 hours after L-DOPS.


CONCLUSIONS
The relatively long half-time for disappearance of L-DOPS compared to that of NE explains their very different attained plasma concentrations. The similar NE and DHPG responses in PAF and MSA suggests production of NE from LDOPS mainly in non-neuronal cells. Persistent elevation of plasma NE in MSA suggests residual release of NE from sympathetic nerves.
Goldstein
David S
DS
Clinical Neurocardiology Section, National Institute of Neurological Disorders and Stroke National Institutes of Health, Bethesda, MD 20892-1620, USA. goldsteind@ninds.nih.gov
Holmes
Courtney
C
Kaufmann
Horacio
H
Freeman
Roy
R
D000368:Aged; D000978:Antiparkinson Agents / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D001342:Autonomic Nervous System Diseases / Q000188:drug therapy*; D001794:Blood Pressure / Q000187:drug effects; D002395:Catecholamines / Q000097:blood; D002908:Chronic Disease; D004032:Diet; D015103:Droxidopa / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D005260:Female; D006207:Half-Life; D006801:Humans; D008297:Male; D008734:Methoxyhydroxyphenylglycol / Q000031:analogs & derivatives* / Q000097:blood; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood*
D000978:Antiparkinson Agents; D002395:Catecholamines; D008734:Methoxyhydroxyphenylglycol; D015103:Droxidopa; C010117:3,4-dihydroxyphenylglycol; D009638:Norepinephrine