Pirbuterol

Pirbuterol belongs to the pharmacological class of Beta 2 adrenergic agonists. Pirbuterol appears to have bronchodilating effects.

Pirbuterol has been approved for relieving symptoms as well as for the treatment and maintenance of episodes of asthma.

Pirbuterol exhibits low systemic absorption. When it is administered as a 2% ophthalmic solution in adult human volunteers, less than 4% of the total dose is found to be systemically absorbed following multiple dosing. Absorption is mainly through the nasolacrimal duct rather than through the conjunctiva. Pirbuterol is not metabolized and is found to be eliminated primarily in the unchanged form in the urine, about 70%, and in the feces, about 30%.

The common side effects associated with Pirbuterol are headache, nausea, insomnia, vomiting, tremor, cough, diarrhea, muscle pain, etc.

Pirbuterol is found to be available in the form of oral Inhalation.

Pirbuterol is available in Canada, E.U., U.A.E., India, Australia, and Japan.

Pirbuterol belongs to the pharmacological class of Beta 2 adrenergic agonists. Pirbuterol appears to have bronchodilating effects.

The pharmacologic effects of the beta-adrenergic agonist drugs, including pirbuterol, are at least in proof attributable to stimulation through beta-adrenergic receptors of intracellular adenyl cyclase, the enzyme which catalyzes the conversion of adenosine triphosphate (AlP) to cyclic-3†,5†-adenosine monophosphate (c-AMP). Increased c-AMP levels are associated with the relaxation of bronchial smooth muscle and inhibition of the release of mediators of immediate hypersensitivity from cells, especially from mast cells.

Pirbuterol has been approved for relieving symptoms as well as also for the treatment and maintenance of episodes of asthma.

The onset of Pirbuterol is said to be within 5 minutes, and the duration of action is about 1-4 hours.

Pirbuterol is available in inhalation dosage form (aerosol):

For prevention of bronchospasm:

Adults as well as children 12 years of age and older—2 puffs every 4 to 6 hours as needed, up to a total of 12 puffs per day. Each puff contains 200 micrograms (mcg) of pirbuterol.

Pirbuterol can be used in the treatment of the following conditions:

• Asthma maintenance

Pirbuterol can help to relieve symptoms and also for the treatment and maintenance of asthma.

Pirbuterol is approved for use in the following clinical indications/conditions:

• Asthma maintenance

Inhalation

1. Hold the inhaler in an upright position.
2. Cover the mouthpiece of the inhaler.
3. Shake the inhaler three or four times
4. Now breathe out all the air from the lungs.
5. Now breathe in the puff through the mouthpiece
6. Hold your breath for a second and breathe out.

Oral Inhalation:

200mcg per actuation (14g canister with 400 actuation)

Oral Inhalation.

Smoking cessation and maintaining health are a must.

Caffeine should be avoided or limited to use as it might lead to the risk of nausea, palpitations, nervousness, rapid heartbeat, etc.

Alcohol intake should be avoided in patients, especially those with an underlying liver disorder or liver dysfunction.

A diet containing food with a high sugar content as well as carbohydrates should be restricted. This includes jams, candies, chips, pies, cakes, honey, cookies, and bread. It is also advised to limit or reduce the intake of cholesterol and saturated fat and instead choose poultry, lean meat, or fish.

The dietary restrictions should be individualized as per the patient's requirements.

Pirbuterol may be contraindicated under the following conditions:

• Hypersensitivity to the ingredients of the medication.

The treating physician should closely monitor the patients and keep pharmacovigilance as follows:

Cardiovascular

Pirbuterol like other inhaled beta-adrenergic agonists, has the ability tp produce a clinically significant cardiovascular effect in some patients, as measured by the pulse rate, blood pressure, and/or symptoms. Although such effects are uncommon after the administration of Pirbuterol at recommended doses, if they occur, the drug might need to be discontinued. In addition to that beta-agonists has been reported to produce ECG changes, such as flattening of the T wave, prolongation of the QTc interval, as well as ST segment depression. The clinical significance of these findings is found to be unknown. Therefore, Pirbuterol, like all sympathomimetic amines, should be used cautiously in patients with cardiovascular disorders, especially coronary insufficiency, cardiac arrhythmias, and hypertension.

Paradoxical Bronchospasm

Pirbuterol can produce paradoxical bronchospasm, which can be life-threatening. If paradoxical bronchospasm occurs, Pirbuterol should be discontinued immediately and also alternative therapy should be instituted. It should be recognized that the paradoxical bronchospasm, when associated with the inhaled formulations, frequently occurs when first used with a new canister or vial.

Use of Anti-Inflammatory Agents

The use of beta-adrenergic agonist bronchodilators alone might not be adequate to control asthma in alot of patients. Early consideration should be given to adding of anti-inflammatory agents,such as corticosteroids.

Deterioration of Asthma

Asthma might deteriorate acutely over a period of hours or it might deteriorate chronically over several days or longer. If the patient needs more doses of Pirbuterol than usual, this might be a marker for the destabilization of asthma and requires reevaluation of the patient as well as the treatment regimen, giving special consideration to the possible need for the anti-inflammatory treatment,such as corticosteroids.

Avoid alcohol usage while on Pirbuterol medication, as alcohol can worsen the effects of any underlying disease condition, including conditions such as dizziness, blurred vision, etc.

It is not known whether the drug pirbuterol is excreted in human milk. Therefore, Pirbuterol should be used during nursing only when the potential benefits justifies the possible risk to the newborn.

Pregnancy Category C

Pirbuterol was not found to be teratogenic in rats administered oral doses of about 30, 100, and 300 mg/kg which is approximately 100, 340, and 1000 times the MRDID for adults on an mg/m2 basis. Pirbuterol was not found to be teratogenic in rabbits administered oral doses of about 30 and 100 mg/kg which is approximately 200 and 680 times the MRDID for adults on an mg/m2 basis. However, pirbuterol at an oral dose of about 300 mg/kg which is approximately 2000 times the MRDID in adults on an mg/m2 basis caused abortions and fetal death.

No sufficient scientific evidence is traceable regarding the use and safety of Pirbuterol in concurrent use with any particular food.

The adverse reactions related to Pirbuterol can be categorized as follows:

• Vomiting
• Diarrhea
• Sweating
• Nausea
• Tremor
• Cough
• Hoarseness
• Sore throat
• Dry mouth or throat
• Insomnia
• Headache
• Dizziness
• Lightheadedness
• Insomnia
• Nervousness
• Runny or stuffy nose
• Muscle pain

The clinically relevant drug interactions of Pirbuterol are briefly summarized here:

Another short-acting beta-adrenergic aerosol bronchodilator should not be used concomitantly with Maxair Autohaler because it might have additive effects.

• Monoamine Oxidase Inhibitors or Tricyclic Antidepressants

Pirbuterol should be administered with an extreme caution to patients who are being treated with monoamine oxidase inhibitors or tricyclic antidepressants or within the 2 weeks of discontinuation of such agents because the action of pirbuterol on the vascular system might be potentiated.

• Beta Blockers

Beta-adrenergic receptor blocking agents are said to not only block the pulmonary effect of the beta-agonists, such as Pirbuterol but might produce severe bronchospasm in patients with asthma. Therefore, patients who are suffering from asthma should not normally be treated with the beta-blockers. However, under certain circumstances, such as prophylaxis after the myocardial infarction, there might be no acceptable alternatives to the use of the beta-adrenergic blocking agents in patients with asthma. In this setting, cardioselective beta-blockers can be considered, although they should be administered cautiously.

• Diuretics

The ECG changes and/or hypokalemia that might result from the administration of non-potassium sparing diuretics such as loop or thiazide diuretics ,can be acutely worsened by the beta-agonists, especially when the recommended dose of the beta-agonist has been exceeded. Although the clinical significance of these effects has not been known, caution is advised in the coadministration of the beta-agonists with the non-potassium-sparing diuretics.

The common side effects of Pirbuterol include the following:

• Vomiting
• Diarrhea
• Sweating
• Nausea
• Tremor
• Cough
• Hoarseness
• Sore throat
• Dry mouth or throat
• Insomnia
• Headache
• Dizziness
• Lightheadedness
• Insomnia
• Nervousness
• Runny or stuffy nose
• Muscle pain

Pregnancy

Pregnancy Category C

Pirbuterol was not found to be teratogenic in rats administered oral doses of about 30, 100, and 300 mg/kg which is approximately 100, 340, and 1000 times the MRDID for adults on an mg/m2 basis. Pirbuterol was not found to be teratogenic in rabbits administered oral doses of about 30 and 100 mg/kg which is approximately 200 and 680 times the MRDID for adults on an mg/m2 basis. However, pirbuterol at an oral dose of about 300 mg/kg which is approximately 2000 times the MRDID in adults on an mg/m2 basis caused abortions and fetal death.

• Nursing Mothers

It is not known whether the drug pirbuterol is excreted in human milk. Therefore, Pirbuterol should be used during nursing only when the potential benefits justifies the possible risk to the newborn.

• Pediatric Use

Pirbuterol is not recommended for patients under the aged 12 years because of insufficient clinical data to establish safety and effectiveness.

• Geriatric Use

There is no overall difference in the efficacy and safety that has been observed between the older and the younger patients.

Pharmacodynamics

Pirbuterol is a beta-2 adrenergic bronchodilator. In vitro studies and in vivo pharmacologic studies had demonstrated that the pirbuterol had a preferential effect on the beta-2 adrenergic receptors. While it is recognized that the beta-2 adrenergic receptors are the predominant receptors found in the bronchial smooth muscle, the data indicates that there is a population of the beta-2 receptors found in the human heart, which is existing in a concentration between 10-50%.

Pharmacokinetics

As expected by the extrapolation from the oral data, the systemic blood levels of the drug pirbuterol are below the limit of assay sensitivity i.e.2–5 ng/ml, followed by the inhalation of doses up to 800 mcg i.e.twice the maximum recommended dose. A mean of 51% of the dose of Pirbuterol is recovered in urine as pirbuterol plus its sulfate conjugate following administration by aerosol. Pirbuterol is not metabolized by catechol-O-methyltransferase.

The percent of the administered dose recovered as the pirbuterol plus its sulfate conjugate does not change significantly over the dosage range of 400 mcg to 800 mcg of Pirbuterol and is not significantly different from that after the oral administration of pirbuterol. The plasma half-life measured after oral administration is around 2 hours.

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