Source: Υπουργείο Υγείας (CY) Revision Year: 2017 Publisher: MEDOCHEMIE LTD, 1-10 Constantinoupoleos street, 3011 Limassol, Cyprus
Pharmacotherapeutic group: selective β2-agonist, terbutaline
ATC code: R03CC03
Terbutaline is a selective β2-adrenergic stimulant having the following pharmacological effects:
In the lung: bronchodilation; increased mucociliary clearance; suppression of oedema and anti-allergic effects.
In skeletal muscle: stimulates Na+/K+ transport and also causes depression of subtetanic contractions in slow-contracting muscle.
In uterine muscle: inhibition of uterine contractions.
In the CNS: low penetration of the blood-brain barrier at therapeutic doses, due to the highly hydrophilic nature of the molecule.
In the CVS: administration of terbutaline results in cardiovascular effects mediated through β2-receptors in the peripheral arteries and in the heart e.g. in healthy subjects, 0.25-0.5mg 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.
Tablet/Syrup: The bronchodilating effect has in clinical trials been shown to have duration for up to 8 hours.
There is a considerable first–pass metabolism in the intestinal wall and in the liver. The bioavailability is about 10% and increases to about 15% if terbutaline is taken on an empty stomach. Maximum plasma concentration of terbutaline is reached within 3 hours.
Terbutaline is metabolized mainly by conjugation with sulfuric acid and excreted as the sulfate conjugate. No active metabolites are formed. Terbutaline crosses the placenta. After single dose IV administration of terbutaline to 22 women in late pregnancy who were delivered by elective Caesarean section due to clinical reasons, umbilical blood levels of terbutaline were found to range from 11 to 48% of the maternal blood levels.
Basic parameters have been evaluated in man after i.v. and oral administration of therapeutic doses, e.g. i.v. single dose.
| Volume of distribution (VSS) | 114L |
| Total body clearance (CL) | 213ml/min |
| Mean residence time (MRT) | 9.0h |
| Renal clearance (CLR) | 149 ml/min (males) |
Oral dose:
| Renal clearance (CLR) | 1.925ml/min (males) |
| Renal clearance (CLR) | 2.32ml/min (females) |
The plasma concentration/time curve after i.v. administration is characterized by a fast distribution phase, an intermediate elimination phase and a late elimination phase.
Terminal half-life T1/2 has been determined after single and multiple dosing (mean values varied between 16-20h).
Food reduces bioavailability following oral dosing (10% on average).
Fasting values of 14-15% have been obtained.
The main metabolite after oral dosing is the sulphate conjugate and also some glucoronide conjugate can be found in the urine.
The major toxic effect of terbutaline, observed in toxicological studies in rats and dogs at exposures in excess of maximum human exposure, is focal myocardial necrosis. This type of cardiotoxicity is a well known pharmacological manifestation seen after the administration of high doses of β2-agonists.
In rats, an increase in the incidence of benign uterine leiomyomas has been observed. This effect is looked upon as a class-effect observed in rodents after long term exposure to high doses of β2-agonists.
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