Barnidipine

C - Cardiovascular system；C08 - Calcium channel blockers；C08C - Selective calcium channel blockers with mainly vascular effects；C08CA - Dihydropyridine derivatives；C08CA12 - Barnidipine

QC - Cardiovascular system；QC08 - Calcium channel blockers；QC08C - Selective calcium channel blockers with mainly vascular effects；QC08CA - Dihydropyridine derivatives；QC08CA12 - Barnidipine

In vitro binding of barnidipine with plasma proteins was between 92.4 and 98.9%, and was mainly with albumin. Barnidipine binds at the rate of 26-32% to human erythrocytes. In addition to serum albumin, barnidipine also binds to α1 acid glycoprotein and high density lipoproteins. To a much lesser extent, binding to γ-globulin takes place.

Barnidipine reduces peripheral resistance and lowers blood pressure. The chronic use of the drug is not reported to lead to an increase in basic heart frequency. The antihypertensive effects of barnidipine are reported to remain during the entire 24-hour dose interval. Barnidipine does not exert any negative effect on serum lipids profile, glucose level or blood electrolytes.

Barnidipine is a lipophilic 1,4-dihydropyridine calcium antagonist that is characterized by a slow onset of action and a strong and long-lasting binding to the L-type calcium channels. It displays high affinity for the channels expressed in the smooth muscle cells in the vascular wall. Its main mechanism of action arises from the reduction of peripheral vascular resistance secondary to its vasodilatory actions. Calcium ion influx via L-subtype ‘voltage-operated’ channels in the excitable membranes of the smooth muscle cells promotes the formation of calcium-dependent formation of cross-bridges between myosin and actin which are the two major contractile proteins that drive contraction. By blocking the L-type 'voltage-dependent' calcium channels, barnidipine selectively blocks the calcium ion influx in the smooth muscle cells and inhibits the activation of contractile proteins. It is suggested that barnidipine displays a high affinity to the inactivated state of the channel. Like other dihydropyridine calcium antagonists, barnidipine is predicted to interact with the alpha 1-C subunit of the L-type calcium channels. Alpha 1-C subunit of the channel is predicted to reside within the bilayer or channel pore at a location closer to the extracellular rather than the intracellular face of the membrane. Its lipophilicity is likely a reason why barnidipine displays a slow onset and long duration of action. Being a highly lipophilic molecule with an octanol/water partition coefficient of 2000, barnidipine is expected to accumulate in the cell membrane and consequently, gains access to its target receptor in a slow manner.

Barnidipine is expected to undergo hepatic metabolism. The primary metabolism of barnidipine involves the oxidation of the 1,4-dihydropyridine ring and hydrolysis of the methyl ester. Secondary metabolism involves N-debenzylization of the side chain, hydrolysis of the N-benzylpyrrolidine ester, and reduction of the nitro group. Both the primary and secondary metabolic pathways are mediated by the CYP3A isoenzyme family and the metabolites formed are pharmacologically inactive.

Barnidipine has known human metabolites that include 3-O-methyl 5-O-pyrrolidin-3-yl 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate, 3-O-(1-Benzylpyrrolidin-3-yl) 5-O-methyl 2,6-dimethyl-4-(3-nitrophenyl)pyridine-3,5-dicarboxylate, and 5-methoxycarbonyl-2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3-carboxylic acid.

Following a single, modified-release dose of 10mg barnidipine, the peak plasma concentration was approximately 0.48 µg/L and the area under the curve (AUC) was 2.85 µg/Lxh. The peak plasma concentrations are reached within 5 to 6 hours after oral administration of 20mg barnidipine. While the plasma concentrations of the drug may vary between individuals, the absolute bioavailability of the barnidipine is approximately 1.1% due to extensive first-pass hepatic metabolism. After repeated administration of 20mg barnidipine to healthy individuals, the concomitant intake of food did not have a statistically significant effect on the AUC, Cmax or half-life of the drug.

Barnidipine and its metabolites are metabolized into feces (60%), urine (40%) and breath (1%). Following a single dose administration of barnidipine ranging from 5 to 20mg in healthy volunteers, urinary excretion of unchanged drug was negligible (≤0.003% of an administered dose).

After administration of single oral doses of radiolabelled barnidipine in rats, levels of radioactivity were found to be higher in the kidney, liver and gastrointestinal tract than in plasma, whereas the brain showed the lowest level of radioactivity. The drug was also detectable in the breast milk.