Carbidopa for Afferent Baroreflex Failure in Familial Dysautonomia: A Double-Blind Randomized Crossover Clinical Trial.

Afferent lesions of the arterial baroreflex occur in familial dysautonomia. This leads to excessive blood pressure variability with falls and frequent surges that damage the organs. These hypertensive surges are the result of excess peripheral catecholamine release and have no adequate treatment. Carbidopa is a selective DOPA-decarboxylase inhibitor that suppresses catecholamines production outside the brain. To learn whether carbidopa can inhibit catecholamine-induced hypertensive surges in patients with severe afferent baroreflex failure, we conducted a double-blind randomized crossover trial in which patients with familial dysautonomia received high dose carbidopa (600 mg/day), low-dose carbidopa (300 mg/day), or matching placebo in 3 4-week treatment periods. Among the 22 patients enrolled (13 females/8 males), the median age was 26 (range, 12-59 years). At enrollment, patients had hypertensive peaks to 164/116 (range, 144/92 to 213/150 mm Hg). Twenty-four hour urinary norepinephrine excretion, a marker of peripheral catecholamine release, was significantly suppressed on both high dose and low dose carbidopa, compared with placebo (P=0.0075). The 2 co-primary end points of the trial were met. The SD of systolic BP variability was reduced at both carbidopa doses (low dose: 17±4; high dose: 18±5 mm Hg) compared with placebo (23±7 mm Hg; P=0.0013), and there was a significant reduction in the systolic BP peaks on active treatment (P=0.0015). High- and low-dose carbidopa were similarly effective and well tolerated. This study provides class Ib evidence that carbidopa can reduce blood pressure variability in patients with congenital afferent baroreflex failure. Similar beneficial effects are observed in patients with acquired baroreflex lesions.

Subcutaneous Administration of Carbidopa Enhances Oral Levodopa Pharmacokinetics: A Series of Studies Conducted in Pigs, Mice, and Healthy Volunteers.

OBJECTIVES: Although commercially available levodopa (LD) formulations include carbidopa (CD) or benserazide for gastrointestinal L-aromatic amino acid decarboxylase inhibition, little is known how manipulating CD delivery affects the pharmacokinetics of LD. Our research systematically evaluated the peripheral and central pharmacokinetics of LD during continuous subcutaneous CD delivery. METHODS: We conducted pharmacokinetic experiments in pigs, mice, and humans to characterize effects of continuous subcutaneous CD delivery co-administered with LD as compared with oral LD/CD administration on LD pharmacokinetics. The porcine and human studies compared peripheral LD pharmacokinetic parameters (area under the curves [AUCs], peak plasma concentrations [Cmax], and plasma elimination half-life [t1/2]) and the mouse studies compared brain LD and dopamine concentrations. RESULTS: In the pig, supplementary subcutaneous CD delivery significantly increased the LD t1/2 and AUC versus LD/CD alone and versus additional oral CD administration. In mice, administration of supplementary subcutaneous CD substantially increased mean plasma concentrations of both LD and CD versus oral LD/CD alone at all time points. These increases were mirrored by increased brain dopamine levels for at least the 7 hours of study. In healthy human subjects, continuous subcutaneous CD administration, 3.33 mg/h x24h, increased the plasma LD t1/2, Cmax, and AUC by 17.4%, 40.5%, and 22.3%, respectively (P < 0.003). CONCLUSIONS: This series of studies demonstrates that small continuous dosing of subcutaneous CD has an unexpected effect on LD pharmacokinetics greater than the extent of decarboxylase inhibition achieved by additional oral CD administration.

Opicapone: A Review in Parkinson's Disease.

Oral opicapone (Ongentys(®)), a potent, third-generation, long-acting, peripheral catechol-O-methyltransferase (COMT) inhibitor, is approved as adjunctive treatment to levodopa (L-Dopa)/dopa-decarboxylase inhibitor (DDCI) therapy in adults with Parkinson's disease (PD) and end-of-dose motor fluctuations who cannot be stabilized on those combinations. In 14- to 15-week, double-blind, multinational trials and in 1-year, open-label extension studies in this patient population, opicapone was an effective and generally well tolerated adjunctive therapy to L-Dopa plus a DDCI and other PD therapy. During the double-blind phase, adjunctive opicapone 50 mg once daily provided significantly greater improvements in motor fluctuations than placebo, with these improvements noninferior to those with entacapone. These beneficial improvements in motor fluctuations with opicapone were maintained in patients who continued adjunctive opicapone during the extension studies, with patients who switched from placebo or entacapone to opicapone experiencing significant improvements in motor fluctuations during this year. No new unexpected safety concerns were identified after ≈1.4 years' treatment with opicapone, with no serious cases of hepatotoxicity reported in clinical trials. With its convenient once-daily regimen, oral opicapone is an emerging COMT inhibitor option for use as adjunctive therapy to L-Dopa/DDCI therapy in adults with PD and end-of dose motor fluctuations who cannot be stabilized on those combinations.