Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1 Pharmacodynamic properties
Pharmacotherapeutic group: Beta-Blocking agent, non-selective, ATC code: C07AA05 
Mechanism of action
Potential mechanisms of action of propranolol in proliferating infantile haemangioma described in the literature could include various mechanisms all in close relationship:
•     a local haemodynamic effect (vasoconstriction which is a classical consequence of beta- adrenergic blockade and a decrease of infantile haemangioma lesion perfusion);
•     an antiangiogenic effect (decrease of vascular endothelial cells proliferation, reduction of the neovascularization and formation of vascular tubules, reduction of the secretion of Matrix Metalloproteinase 9);
•     an apoptosis-triggering effect on capillary endothelial cells;
•     a reduction of both VEGF and bFGF signalling pathways and subsequent angiogenesis / proliferation.

Pharmacodynamic effects
Propranolol is a beta-blocker that is characterised by three pharmacological properties:
•    the absence of cardioselective beta-1 beta-blocking activity, •    an antiarrhythmic effect,
•    lack of partial agonist activity (or intrinsic sympathomimetic activity).

Clinical efficacy and safety in the paediatric population
The efficacy of propranolol in infants (aged 5 weeks to 5 months at treatment initiation) with proliferating infantile haemangioma requiring systemic therapy has been demonstrated in a pivotal randomised, controlled, multicentre, multidose, adaptive phase II/III study aimed to compare four regimens of propranolol (1 or 3 mg/kg/day for 3 or 6 months) to placebo (double blind).

Treatment was administered to 456 subjects (401 Propranolol at a dose of 1 or 3 mg/kg/day for 3 or 6 months; 55 Placebo), including a titration phase over 3 weeks. Patients (71.3% female; 37% aged 35-90 days old and 63% aged 91-150 days old) presented a target haemangioma on the head in 70% and majority of the infantile haemangiomas were localized (89%).

Treatment success was defined as a complete or nearly complete resolution of the target haemangioma, which was evaluated by blinded centralized independent assessments made on photographs at Week 24, in the absence of premature treatment discontinuation.

The regimen 3 mg/kg/day during 6 months (selected at the end of the phase II part of the study) presented 60.4% of success versus 3.6% in the placebo arm (p value < 0.0001). Age (35-90 days / 91-150 days), gender and haemangioma location (head / body) subgroups did not identify differences in response to propranolol. Improvement of haemangioma was observed at 5 weeks of treatment by propranolol in 88% of patients. 11.4% of patients needed to be re- treated after treatment discontinuation.
For ethical reasons related to the use of placebo, the demonstration of the efficacy was not established in patients with high-risk haemangioma. Evidence of the efficacy of propranolol in patients with high-risk haemangioma is available both in literature and in a specific compassionate use program performed with Hemangiol.

Based on a retrospective study, a minority of patients (12%) required a re-initiation of systemic treatment. When treatment was re-initiated, a satisfactory response was observed in a large majority of patients.

Pharmacokinetic Properties

5.2 Pharmacokinetic properties
Adults
Absorption and distribution:
Propranolol is almost completely absorbed after oral administration. However, it undergoes an extensive first-pass metabolism by the liver and on average only about 25% of propranolol reaches the systemic circulation. Peak plasma concentrations occur about 1 to 4 hours after an oral dose. Administration of protein-rich foods increases the bioavailability of propranolol by about 50% with no change in time to peak concentration.

Propranolol is a substrate for the intestinal efflux transporter, P-glycoprotein (P-gp). However, studies suggest that P-gp is not dose-limiting for intestinal absorption of propranolol in the usual therapeutic dose range.

Approximately 90% of circulating propranolol is bound to plasma proteins (albumin and alpha1 acid glycoprotein). The volume of distribution of propranolol is approximately 4 L/kg. Propranolol crosses the blood-brain barrier and the placenta, and is distributed into breast milk.

Biotransformation and elimination:
Propranolol is metabolized through three primary routes: aromatic hydroxylation (mainly 4- hydroxylation), N-dealkylation followed by further side-chain oxidation, and direct glucuronidation. The percentage contributions of these routes to total metabolism are 42%, 41% and 17%, respectively, but with considerable variability between individuals. The four major final metabolites are propranolol glucuronide, naphthyloxylactic acid and glucuronic acid, and sulfate conjugates of 4-hydroxy propranolol. In vitro studies indicated that CYP2D6 (aromatic hydroxylation), CYP1A2 (chain oxidation) and to a less extent CYP2C19 were involved in propranolol metabolism.

In healthy subjects, no difference was observed between CYP2D6 extensive metabolizers and poor metabolizers with respect to oral clearance or elimination half-life.
The plasma half-life of propranolol ranges from 3 to 6 hours. Less than 1% of a dose is excreted as unchanged drug in the urine.

Paediatric population
The pharmacokinetics of repeated administrations of Hemangiol at 3 mg/kg/day given in 2 intakes has been investigated in 19 infants aged 35 to 150 days at the beginning of treatment.
The pharmacokinetic evaluation was performed at steady-state, after 1 or 3 months of treatment.

Propranolol was rapidly absorbed, the maximum plasma concentration generally occurring 2 hours after administration with a corresponding mean value around 79 ng/mL whatever the infant age.
Mean apparent oral clearance was 2.71 L/h/kg in infants aged 65- 120 days and 3.27 L/h/kg in infant aged 181- 240 days. Once corrected by the body weight, primary pharmacokinetic parameters for propranolol (such as plasma clearance) determined in infants were similar to those reported in the literature for adults.
The 4-hydroxy-propranolol metabolite was quantified, its plasma exposure accounting for less than 7% of the parent drug exposure.

During this pharmacokinetic study including infants with function-threatening haemangioma, haemangioma in certain anatomic locations that often leave permanent scars or deformity, large facial haemangioma, smaller haemangioma in exposed areas, severe ulcerated haemangioma, pedunculated haemangioma, efficacy was also studied as a secondary evaluation criteria.
Treatment with propranolol resulted in a rapid improvement (within 7-14 days) in all patients and resolution of the target haemangioma was observed in 36.4% of patients by 3 months.