Levocet Mechanism of Action

Pharmacotherapeutic group: Antihistamines for systemic use, piperazine derivatives. ATC Code: R06AE09.
Pharmacology: Pharmacodynamics: Mechanism of action: Levocetirizine, the (R) enantiomer of cetirizine, is a potent and selective antagonist of peripheral H1-receptors.
Binding studies revealed that levocetirizine has high affinity for human H1-receptors (Ki = 3.2 nmol/l). Levocetirizine has an affinity 2-fold higher than that of cetirizine (Ki = 6.3 nmol/l).
Levocetirizine dissociates from H1-receptors with a half-life of 115 ± 38 min.
After single administration, levocetirizine shows a receptor occupancy of 90% at 4 hours and 57% at 24 hours.
Pharmacokinetics: Absorption: Levocetirizine is rapidly and extensively absorbed following oral administration. ln adults, peak plasma concentrations are achieved 0.9 h after dosing. Steady state is achieved after two days.
Peak concentrations are typically 270 ng/ml and 308 ng/ml following a single and a repeated 5 mg o.d. dose, respectively. The extent of absorption is dose-independent and is not altered by food, but the peak concentration is reduced and delayed.
Distribution: No tissue distribution data are available in humans, neither concerning the passage of levocetirizine through the blood-brain-barrier. In rats and dogs, the highest tissue levels are found in liver and kidneys, the lowest in the CNS compartment.
In humans, levocetirizine is 90% bound to plasma proteins. The distribution of levocetirizine is restrictive, as the volume of distribution is 0.4 l/kg.
Biotransformation: The extent of metabolism of levocetirizine in humans is less than 14% of the dose and therefore differences resulting from genetic polymorphism or concomitant intake of enzyme inhibitors are expected to be negligible. Metabolic pathways include aromatic oxidation, N- and O-dealkylation and taurine conjugation. Dealkylation pathways are primarily mediated by CYP 3A4 while aromatic oxidation involved multiple and/or unidentified CYP isoforms. Levocetirizine had no effect on the activities of CYP isoenzymes 1A2, 2C9, 2C19, 2D6, 2El and 3A4 at concentrations well above peak concentrations achieved following a 5 mg oral dose.
Due to its low metabolism and absence of metabolic inhibition potential, the interaction of levocetirizine with other substances, or vice-versa, is unlikely.
Elimination: The plasma half-life in adults is 7.9 ± 1.9 hours. The half-life is shorter in small children.
The mean apparent total body clearance in adults is 0.63 ml/min/kg. The major route of excretion of levocetirizine and metabolites is via urine, accounting for a mean of 85.4% of the dose.
Excretion via feces accounts for only 12.9% of the dose. Levocetirizine is excreted both by glomerular filtration and active tubular secretion.
Special population: Renal impairment: The apparent body clearance of levocetirizine is correlated to the creatinine clearance. It is therefore recommended to adjust the dosing intervals of levocetirizine, based on creatinine clearance in patients with moderate and severe renal impairment The amount of levocetirizine removed during a standard 4-hour hemodialysis procedure was < 10%.
Pediatric population: The paediatric patient with oral administration of a single dose of 5 mg Levocetirizine in 14 children age 6 to 11 years with body weight ranging between 20 and 40 kg show that Cmax and AUC values are about 2-fold greater in paediatric population than in healthy adult. The mean Cmax was 450 ng/ml, occurring at a mean time of 1.2 hours, weight-normalized, total body clearance was 30% greater, and the elimination half-life 24% shorter in this paediatric population than in adults.
Elderly: The total body clearance on elderly was approximately 33% lower compared to that in younger adults. The disposition of racemic cetirizine is dependent on renal function rather than on age.
This was also applicable to levocetirizine and cetirizine which are both predominantly excreted in urine. Therefore, the levocetirizine dose should be adjusted in accordance with renal function in elderly patients.
Gender: The half-life was slightly shorter in women than in men, however the body weight-adjusted oral clearance in women appears to be comparable to that in men. The same daily doses and dosing intervals are applicable for men and women with normal renal function.
Race: As levocetirizine is primarily renal excreted, and there are no important racial differences in creatinine clearance, pharmacokinetic characteristics of levocetirizine are not expected to be different across races. No race-related differences in the kinetics of racemic cetirizine have been observed.
Hepatic impairment: Patients with chronic liver diseases (hepatocellular, cholestatic, and biliary cirrhosis) given 10 or 20 mg of the racemic compound cetirizine as a single dose had a 50% increase in half-life along with a 40% decrease in clearance compared to healthy person.
Pharmacokinetic/pharmacodynamic relationship: The action on histamine-induced skin reactions is out of phase with the plasma concentrations.