Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1         Pharmacodynamic properties
Pharmaco-therapeutic group: selective beta2-agonist, terbutaline,
ATC code: R03A C03.

Terbutaline is a selective beta2-adrenergic stimulant, having the following pharmacological effects:-
 i)   In the lung: bronchodilation; increase in mucociliary clearance; suppression of oedema and anti-allergic effects.
 ii) In skeletal muscle: stimulates Na+/K+ transport and also causes depression of subtetanic contractions in slow-contracting muscle.
iii) In uterine muscle: Inhibition of uterine contractions.
iv) In the C.N.S: Low penetration into the blood-brain barrier at therapeutic doses, due to the highly hydrophilic nature of the molecule.
v) In the C.V.S.: Administration of terbutaline results in cardiovascular effects mediated through beta2-receptors in the peripheral arteries and in the heart e.g. in healthy subjects, 0.25 - 0.5 mg injected s.c., is associated with an increase in cardiac output (up to 85% over controls) due to an increase in heart rate and a larger stroke volume. The increase in heart rate is probably due to a combination of a reflex tachycardia, via a fall in peripheral resistance, and a direct positive chronotropic effect of the drug.
BRICALIN                                       1. 1.   2015, RH                    Page 6 of 8 

Pharmacokinetic Properties

5.2        Pharmacokinetic properties
Basic parameters have been evaluated in man after i.v. and oral administration of therapeutic doses, e.g.
I.V. single dose
Volume distribution (VSS) - 114L
Total body clearance (CL) - 213 ml/min.
Mean residence time (MRT) - 9.0 h.
Renal clearance (CLR) - 149 ml/min.(males)

Oral dose
Renal clearance (CLR) - 1.925 ml/min. (males)
Renal clearance (CLR) - 2.32 ml/min. (females)

The plasma concentration/time curve after i.v. administration is characterised by a fast distribution phase, an intermediate elimination phase and a late elimination phase.
Terminal half-life t½ has been determined after single and multiple dosing (mean values varied between 16-20 h.).

Bioavailability
Food reduces bioavailability following oral dosing (10% on average) fasting values of 14- 15% have been obtained.
Metabolism
The main metabolite after oral dosing is the sulphate conjugate and also some glucoronide conjugate can be found in the urine.