Terbutaline, uterine selectivity

Terbutaline (Brethine, Bricanyl) is a relatively specific P2-adrenoceptor agonist (see Chapters 10 and 39). Terbutaline can prevent premature labor, especially in individuals who are more than 20 weeks into gestation and have no indication of ruptured fetal membranes or in whom labor is not far advanced. Its effectiveness in premature labor after 33 weeks of gestation is much less clear. Terbutaline can decrease the frequency, intensity, and duration of uterine contractions through its ability to directly stimulate Pj-adrenoceptors. While it appears to be especially selective for P2-receptor activation, terbutaUne does have some Pi activity as well. 

Terbutaline [ter BYOO te leen] is a p2 agonist with more selective properties than metaproterenol and a longer duration of action. Terbutaline can be administered either orally or subcutaneously. It is used as a bronchodilator and to reduce uterine contractions in premature labor. 

Salbutamol, fenoterol, rimiterol, reproterol, pir-buterol, salmeterol, ritodrine and terbutaline are P-adrenoceptor agonists that are relatively selective for p2-receptors, so that cardiac (chiefly p -receptor) effects are less prominent. Tachycardia still occurs because of atrial (sinus node) p -receptor stimulation the P2-adrenoceptors are less numerous in the ventricle and there is probably less risk of serious ventricular arrhythmias than with the use of nonselective catecholamines. The synthetic agonists are also longer-acting than isoprenaline because they are not substrates for catechol-O-methyltransferase, which methylates catecholamines in the liver. They are used principally in asthma, and to reduce uterine contractions in premature labour. 

The responses of uterine muscle to Epi vary with phase of the sexual cycle, state of gestation, and dose. During the last month of pregnancy and at parturition, Epi inhibits uterine tone and contractions. fi -Selective agonists (e.g., ritodrine or terbutaline) can delay premature labor, although... 

J -selective (intermediate- acting) Albuterol Bitolterol Fenoterol Isoetharine Metaproterenol Procaterol Terbutaline Ritodrine Relaxation of bronchial smooth muscle Relaxation of uterine smooth muscle Activation of other receptors after systemic administration Bronchodilators for treatment of asthma and COPD Short/intermediate-acting drugs for acute bronchospasm Skeletal muscle tremor Tachycardia and other cardiac effects seen after systemic administration (much less with inhalational use) Use with caution in patients with CV disease (reduced by inhalational administration) Minimal side effects... 

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