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Common name
Salbutamol
Synonyms: salbutamol, ventolin, albuterol
Description
Adrenergic bronchodilators are medicines that are used to open up the bronchial tubes (air passages) of the lungs. Some of these medicines are used to treat the symptoms of asthma, chronic bronchitis, emphysema, and other lung diseases, while others are used to prevent the symptoms.
Salbutamol relaxes the smooth muscle in the lungs and opens airways to improve breathing. It is used to treat asthma, chronic bronchitis, emphysema and to prevent exercise-related asthma.
The drug is also a good means of prevention and treatment of
overweight. It depresses the appetite, which leads to weight loss. In
addition, the combination of ephedrine and caffeine gives thermogenic
effect (metaphorically speaking, this is the "browning" of fat cells to
their total destruction).
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Active Ingredients:
salbutamol
Therapeutic actions:
Several studies have suggested an association between Beta agonist use and an increased risk of death from asthma. Proposed mechanisms include increased bronchial hyperresponsiveness, drug tolerance or an underlying increased severity of disease. The resulting controversy has stimulated multiple studies. Such analyses support the continued use of salbutamol as a first-line therapy for the treatment of asthma. This apparent controvosy appears to be due to the two different isomers have opposing effects. R-salbutamol causes smooth muscle to relax whereas S-salbutamol causes smooth muscle to contract. The two isomers act on different receptors and thus on different pathways resulting in the opposing effects.
R-Salbutamol:
R-Salbutamol acts on Beta 2 Adrenergic Receptors (three dimensional structure). These receptors are found on the smooth muscle lining airways of the lungs. The binding or R-salbutamol to this receptor causes a conformational change in the protein. Beta 2 adrenergic receptors are an example of a G linked protein, the receptor has seven trans membrane domains and is associated in the membrane with a G protein. The G protein has three sub units (an alpha sub unit and a tightly associated beta and gamma sub units).
The conformational change in the beta 2 receptor causes the beta 2 receptor to bind to a G protein and this in tern causes a conformation change in the G protein. A GDP (guanosine 5'-diphosphate) group associated with the G protein becomes dissociated and is then replaced with a GTP (guanosine 5'-triphosphate) group. This in turn causes the alpha sub unit to dissociate from the G complex. The dissociated alpha sub unit is then free to move in the membrane and has a binding site for the enzyme adenylyl cyclase. It binds to an adenylyl cyclase (three dimensional structure) and activates it. This enzyme catalyses the conversion of ATP to cAMP (adenosine 5'-triphosphate to adenosine 3',5'-monophosphate):
cAMP levels in the cell therefore increase due to the additional adenylyl cyclase produced by the binding of R-salbutamol. cAMP activates protein kinase A (a cyclic AMP dependent protein kinase). Protein kinase A transfers the terminal phosphate group of an ATP to several target proteins within the cell which leads to muscle relaxation.
The phosphorylation process leads to muscle relaxation by several processes including
* active removal of Ca2+ ions from the cell and into intracellular stores, thus lowering intracellular Ca2+ ion concentration. Ca2+
* inhibition of phosphoinositide hydrolysis
* direct inhibition of of myosin light chain kinase
* opening of calcium activated potassium channels that repolarises smooth muscle cells.
Muscle concentration is initiated by a sudden rise in cytosolic Ca2+ ions concentration and reduced cytosolic Ca2+ ion concentration will cause muscle relaxation.
Thus R-salbutamol can cause muscle relaxation irrespective of the method of initiation of the muscle contraction (the contractile agent, be it neural or mediated). As asthma is caused by many different contributions leading to muscle contraction and makes salbutamol a suitable drug for its treatment.
R salbutamol also has several other beneficial effects on the lungs (other than smooth muscle relaxation):
* Inhibition of mast cell mediator release
* Increases mucous secretion
* Increased clearing of the mucus by the action of cilia
But R-salbutamol has no effect on chronic inflammation but the inhibition of mast cell mediator release is anti-inflammatory and thus salbutamol can to an extent also modify acute inflammation, another symptom of asthma..
S-Salbutamol:
S-salbutamol is now thought to be the main cause of bronchial hyper responsiveness in the treatment of asthma with salbutamol.
S-salbutamol acts on muscarinic receptor receptors. These are also G linked proteins and also have seven trans membrane domains.
Being a G linked protein the conformational changes and the dissociation of the alpha sub unit is identical to that of the beta two receptor. However the alpha sub unit activates a different enzyme in this pathway. In this pathway the alpha sub unit activates phospholipase C. This enzyme catalyses the phosphorylation of phosphatidylinositol 4,5-bisphosphate (PIP2) to inositol 1,4,5-triphosphate (IP3) on the inside of the membrane. Phosphatidylinositol 4,5-bisphosphate (PIP2) is a membrane bound structure:
The PIP2 is then hydrolysed by phospholipase C to inositol 1,4,5-triphosphate (IP3).
This small molecule (IP3) is no longer bound to the membrane and leaves the plasma membrane and diffuses through the cytosol. In the cytosol it releases Ca2+ from the endoplasmic reticulum (ER) by binding to IP3 gated Ca2+ release channels in the ER membrane or ryanodine receptors in the sarcoplasmic reticulum of muscle cells. This initiates a positive feedback system as the Ca2+ released can bind back to the channels releasing more Ca2+. Thus S-salbutamol initiates a sudden increase of Ca2+ ions which initiates muscle contraction.
What is it used for?: (Indications:)
Bronchial asthma
Bronchial obstruction at exercise
Emphysema
Bronchitis
Other lung related problems
Contraindications and cautions:
Tell your doctor your medical history, especially of: an overactive thyroid, heart disease, high blood pressure, epilepsy, diabetes, drug allergies. This medication should be used only when clearly needed during pregnancy. Discuss the risk and benefits with your doctor. This drug may be excreted into breast milk. Consult your doctor before breast-feeding.
Side effects:
Dry mouth, irritated throat, dizziness, headache, lightheadedness, heartburn, loss of appetite, altered taste sensation, restlessness, anxiety, nervousness, trembling, and sweating may occur but should subside as your body adjusts to the medication. If these symptoms persist or worsen, inform your doctor. To relieve dry mouth, suck on (sugarless) hard candy or ice chips, chew (sugarless) gum, drink water or use saliva substitute. Inform your doctor if you experience: chest pain, pounding heartbeat, breathing difficulties. In the unlikely event you have a serious allergic reaction to this drug, seek medical attention immediately. Symptoms of a serious allergic reaction include: rash, itching, swelling, severe dizziness, trouble breathing. If you notice other effects not listed above, contact your doctor or pharmacist.
More common side effects include: Aggression, agitation, cough, diarrhoea, dizziness, excitement, general bodily discomfort, headache, heartburn, increased appetite, increased blood pressure, indigestion, irritability, laboured breathing, light-headedness, muscle cramps, nausea, nervousness, nightmares, nosebleed, over activity, palpitations, rapid heartbeat, rash, ringing in the ears, shakiness, sleeplessness, stomach ache, stuffy nose, throat irritation, tooth discoloration, tremors, vomiting, wheezing, worsening bronchospasm.
Less common side effects include: Chest pain or discomfort, difficulty urinating, drowsiness, dry mouth and throat, flushing, high blood pressure, muscle spasm, restlessness, sweating, unusual taste, vertigo, weakness.
Rare side effects following the use of inhaled salbutamol include: Hoarseness, skin rash or hives, hypokalemia, myocardial insufficiency, heart failure, angina-pectoris, hypertension, severe cardiovascular disease, diabetes-mellitus, maternal-thyrotoxicosis.
Interactions:
Tell your doctor of all prescription and nonprescription medications you use, including: beta-blockers (e.g., propranolol, timolol), all asthma medications, ephedrine, epinephrine, pseudoephedrine, antidepressants, MAO inhibitors (e.g., furazolidone, linezolid, phenelzine, selegiline, tranylcypromine), diuretics (e.g., hydrochlorothiazide). It is important to read the labels carefully on all over-the-counter medications, especially those used for colds, allergies, asthma or diets as they may contain ingredients mentioned above. Do not start or stop any medicine without doctor or pharmacist approval.
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