Ambroxol 30 mg, Guaifenesin 50 mg, Terbutaline 1.25 mg / 5 ml Syrup

In vitro and in vivo pharmacologic studies have demonstrated that terbutaline exerts a preferential effect on beta 2-adrenergic receptors. While it is recognized that beta2-adrenergic receptors are the predominant receptors in bronchial smooth muscle, data indicate that there is a population of beta2-receptors in the human heart, existing in a concentration between 10% to 50%. The precise function of these receptors has not been established [see WARNINGS ]. In controlled clinical studies in patients given terbutaline sulfate orally, proportionally greater changes occurred in pulmonary function parameters than in heart rate or blood pressure. While this suggests a relative preference for the beta 2-receptors in man, the usual cardiovascular effects commonly associated with other sympathomimetic agents were also observed with terbutaline sulfate.

The pharmacologic effects of beta-adrenergic agonists, including terbutaline, are at least in part attributable to stimulation through beta-adrenergic receptors of intracellular adenyl cyclase, the enzyme which catalyzes the conversion of adenosine triphosphate (ATP) to cyclic 3’, 5’-adenosine monophosphate (cAMP). Increased cAMP levels are associated with relaxation of bronchial smooth muscle and inhibition of release of mediators of immediate hypersensitivity from cells, especially from mast cells.

Pharmacokinetics — Oral administration of 5-mg terbutaline sulfate tablets or 5 mg terbutaline sulfate in solution in 17 healthy, adult, male subjects, resulted in mean (SD) peak plasma terbutaline concentration of 8.3 (3.9) and 8.6 (3.6) ng/mL, which were observed at median (range) times of 2 (1 to 3) and 1.5 (0.5 to 3.0) hours after dosing. The mean (SD) AUC (0-48) values were 54.6 (26.8) and 53.1 (23.5) hr•ng/mL, and corresponded to a bioavailability of 103% for the tablet relative to the solution.

After oral administration of terbutaline, 51 to 62 mcg/kg of body weight, to 3 healthy male subjects, peak serum levels of 3.1 to 6.2 ng/mL were observed 1 to 3 hours later. In the same study, after 3 days only 30% to 50% of the dose was recovered from urine and the remainder from the feces, which may indicate poor absorption.

After an oral dose to asthmatic patients, the elimination half-life of terbutaline was approximately 3.4 hours.

There are no reports of any clinical pharmacokinetic studies investigating dose proportionality, effect of food, or special population studies with terbutaline.

Ambroxol is a bromhexine metabolite with secretolytic and secretomotor activity described in the oral-solution product information. Its full mechanism is not completely established. The separate HPRA lozenge reference also describes sodium-channel blockade in laboratory studies, a mechanism related to local anesthetic activity.

The oral-reference studies summarized by HPRA report peak plasma levels after approximately 1–2.5 hours for immediate-release ambroxol, protein binding of about 90% and a terminal half-life of about 10 hours. Metabolism occurs mainly in the liver, including glucuronidation and CYP3A4-mediated pathways. Lozenge, syrup and modified-release formulations can produce different exposure.

The proposed expectorant mechanism involves gastric receptor stimulation and a reflex increase in respiratory fluid secretion, reducing mucus viscosity. The source presents this mechanism as a proposed explanation.

The cited product information reports oral absorption but limited pharmacokinetic evidence. A 600 mg study in healthy adults found a plasma peak near 15 minutes. In three healthy men given 600 mg, the estimated half-life was about 1 hour. Distribution data and specific studies in renal or hepatic impairment were unavailable in this reference.