Actions of Terbutaline Sulphate in details
Pharmacology: Pharmacotherapeutic Group: Selective β2-agonist. ATC Code: R03AC03.
Pharmacodynamics: Terbutaline Sulphate is an adrenergic agonist which predominantly stimulates β2-receptors, thus, producing relaxation of bronchial smooth muscle, inhibition of the release of endogenous spasmogens, inhibition of edema caused by endogenous mediators, increased mucociliary clearance and relaxation of the uterine muscle.
The tertiary butyl group attached to the terminal nitrogen of the Terbutaline Sulphate molecule is thought to confer selective stimulation of the pulmonary β2-receptors and only relatively minor stimulation of cardiac β1-receptors. The presence of the 2 phenolic hydroxyl groups in the meta positions confers resistance to metabolism by the enzyme catechol-o-methyl transferase.
The active drug is released gradually from Terbutaline Sulphate prolonged-release tablets, leading to a prolonged bronchodilatation which in clinical trials has been demonstrated for up to 12 hrs.
The potent bronchospasmolytic effect is rapid in onset and reaches a maximum about 30 min after SC injection, 1 hr after aerosol and 2-3 hrs after oral administration. The duration of action is between 4 and 5 hrs.
Inhaled Terbutaline Sulphate acts within a few minutes and has a duration for up to 6 hrs.
Pharmacokinetics: There is a considerable first-pass metabolism in the intestinal wall and in the liver. The bioavailability is around 10%. Maximum plasma concentration of Terbutaline Sulphate is reached within 2-6 hrs, somewhat later after dosing in the evening.
About 20-30% of the metered-dose is deposited in the lungs at a normal inhalation flow rate.
Terbutaline Sulphate is metabolised mainly by conjugation with sulfuric acid and excreted as the sulphate conjugate. No active metabolites are formed.
Metabolism of Terbutaline Sulphate sulphate which is ingested orally or swallowed following inhalation is principally by conjugation in the GI mucosa. The drug is absorbed unchanged from the respiratory tract and is excreted mainly eg, in the urine. Practically all of an administered dose of Terbutaline Sulphate is eliminated after 72 hrs.
How should I take Terbutaline Sulphate?
A nurse or other trained health professional will give you Terbutaline Sulphate. Terbutaline Sulphate is given as a shot under your skin (usually into the shoulder area).
Terbutaline Sulphate may sometimes be given at home to patients who do not need to be in a hospital or clinic. If you are using Terbutaline Sulphate at home, your doctor will teach you or someone who cares for you how to prepare and inject the medicine. Be sure that you understand exactly how the medicine is prepared and injected.
Use Terbutaline Sulphate only as directed. Do not use more of it and do not use it more often than your doctor ordered. To do so may increase the chance of side effects.
If you are using Terbutaline Sulphate for asthma, you should use another medicine that works faster for an asthma attack that has already started. If you do not have another medicine to use for an acute attack or if you have any questions about this, check with your doctor.
Dosing
The dose of Terbutaline Sulphate will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of Terbutaline Sulphate. If your dose is different, do not change it unless your doctor tells you to do so.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.
- For injection dosage form:
- For prevention of bronchospasm:
- Adults and teenagers—0.25 milligrams (mg) injected under your skin. Your doctor may increase your dose as needed. However, the dose is usually not more than 0.5 mg within 4 hours.
- Children younger than 12 years of age—Use is not recommended.
- For prevention of bronchospasm:
Missed Dose
If you miss a dose of Terbutaline Sulphate, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.
Storage
Store unopened vials of Terbutaline Sulphate at room temperature, away from heat and direct light. Do not freeze. An open vial of medicine must be used right away.
Keep out of the reach of children.
Do not keep outdated medicine or medicine no longer needed.
Ask your healthcare professional how you should dispose of any medicine you do not use.
Throw away used needles in a hard, closed container that the needles cannot poke through. Keep this container away from children and pets.
Terbutaline Sulphate administration
IV: Use infusion pump.
Oral: Administer around-the-clock to promote less variation in peak and trough serum levels
Inhalation: Terbutaline Sulphate Turbuhaler [Canadian product]: After removing lid, patient should hold inhaler upright and turn blue grip as far as it will go in one direction then turn it back to original position. Clicking sound indicates that inhaler is ready for use. Patient should exhale fully but not into the inhaler and then place mouthpiece gently between teeth, close lips around inhaler and inhale deeply. Inhaler should be removed from mouth prior to exhaling. Instruct patients to rinse mouth with water after each inhalation as some medication may stick to the inside of the mouth and throat. If inhaler is dropped or shaken, or if patient exhales into the inhaler after a dose is loaded, the dose will be lost and a new dose should be loaded and inhaled. Outside of mouthpiece should be cleaned once weekly with a dry tissue. Instruct patient to keep inhaler dry. First appearance of red mark in dose indicator (window underneath mouthpiece) indicates that 20 doses remain. When red mark reaches bottom of dose indicator no doses remain and Turbuhaler should be discarded.
SubQ: Extravasation management, sympathomimetic vasopressors (off-label use): Stop vesicant infusion immediately and disconnect IV line (leave needle/cannula in place); gently aspirate extravasated solution from the IV line (do NOT flush the line); remove needle/cannula; elevate extremity. Infiltrate extravasation area with Terbutaline Sulphate solution 1 mg diluted with 10 mL (large extravasation site) or 1 mg diluted in 1 mL (small/distal extravasation site) of 0.9% sodium chloride into extravasation site (Stier 1999).
Terbutaline Sulphate pharmacology
In vitro and in vivo pharmacologic studies have demonstrated that Terbutaline Sulphate exerts a preferential effect on beta2-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. In controlled clinical studies in patients given Terbutaline Sulphate 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 beta2-receptors in man, the usual cardiovascular effects commonly associated with other sympathomimetic agents were also observed with Terbutaline Sulphate sulfate.
The pharmacologic effects of beta-adrenergic agonists, including Terbutaline Sulphate, 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.
Controlled clinical studies have shown that Terbutaline Sulphate sulfate relieves bronchospasm in chronic obstructive pulmonary disease by significantly increasing pulmonary function (e.g., an increase of 15% or more in FEV1 and in FEF25%-75%). After administration of Terbutaline Sulphate sulfate tablets, a measurable change in flow rate usually occurs within 30 minutes, and a clinically significant improvement in pulmonary function occurs within 60 to 120 minutes. The maximum effect usually occurs within 120 to 180 minutes. Terbutaline Sulphate sulfate also produces a clinically significant decrease in airway and pulmonary resistance, which persists for 4 hours or longer. Significant bronchodilator action (as measured by airway resistance, FEF25%-75% or PEFR) has also been demonstrated for up to 8 hours in some studies.
In studies comparing the effectiveness of Terbutaline Sulphate sulfate with that of ephedrine for up to 3 months, both drugs maintained a significant improvement in pulmonary function throughout this period of treatment.
Preclinical
Studies in laboratory animals (minipigs, rodents, and dogs) have demonstrated the occurrence of cardiac arrhythmias and sudden death (with histologic evidence of myocardial necrosis) when beta-agonists and methylxanthines were administered concurrently. The clinical significance of these findings is unknown.
Pharmacokinetics
Oral administration of 5-mg Terbutaline Sulphate sulfate tablets or 5 mg Terbutaline Sulphate sulfate in solution in 17 healthy, adult, male subjects, resulted in mean (SD) peak plasma Terbutaline Sulphate 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 Sulphate, 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 Sulphate was approximately 3.4 hours.
In comparison to oral dosing, subcutaneous administration of 0.5 mg of Terbutaline Sulphate sulfate to 17 healthy, adult, male subjects resulted in a mean (SD) peak plasma Terbutaline Sulphate concentration of 9.6 (3.6) ng/mL, which was observed at a median (range) time of 0.5 (0.08 to 1.0) hours after dosing. The mean (SD) AUC(0-48) and total body clearance values were 29.4 (14.2) hr•ng/mL, and 311 (112) mL/min, respectively. The terminal half-life was determined in 9 of the 17 subjects and had a mean (SD) of 5.7 (2.0) hours.
About 90% of the drug was excreted in the urine at 96 hours after subcutaneous administration, with about 60% of this being unchanged drug. The sulfate conjugate is a major metabolite of Terbutaline Sulphate, and urinary excretion is the primary route of elimination.
There are no reports of any clinical pharmacokinetic studies investigating dose proportionality, effect of food, or special population studies with Terbutaline Sulphate.
References
- DailyMed. "TERBUTALINE SULFATE: DailyMed provides trustworthy information about marketed drugs in the United States. DailyMed is the official provider of FDA label information (package inserts).". https://dailymed.nlm.nih.gov/dailyme... (accessed September 17, 2018).
- NCIt. "Terbutaline Sulfate: NCI Thesaurus (NCIt) provides reference terminology for many systems. It covers vocabulary for clinical care, translational and basic research, and public information and administrative activities.". https://ncit.nci.nih.gov/ncitbrowser... (accessed September 17, 2018).
- EPA DSStox. "Terbutaline: DSSTox provides a high quality public chemistry resource for supporting improved predictive toxicology.". https://comptox.epa.gov/dashboard/ds... (accessed September 17, 2018).
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Information checked by Dr. Sachin Kumar, MD Pharmacology
