Theophylline and guaifenesin

Uses

Guaifenesin is an expectorant commonly found in OTC products for the symptomatic relief from congested chests and coughs associated with cold, bronchitis, and/or other breathing illnesses.

Guaifenesin is an expectorant that is indicated for providing temporary symptomatic relief from congested chests and coughs which may be due to a cold, bronchitis, and/or other breathing illnesses .

This is used for the symptomatic treatment of reversible bronchoconstriction associated with bronchial asthma, chronic obstructive pulmonary emphysema, chronic bronchitis and related bronchospastic disorders.

Theophylline and guaifenesin is also used to associated treatment for these conditions: Allergic Reaction, Asthma, Asthma, Allergic, Bronchial Asthma, Bronchitis, Bronchospasm, Chronic Bronchitis, Chronic Obstructive Respiratory Diseases, Common Cold, Cough, Cough caused by Common Cold, Coughing caused by Allergies, Coughing caused by Flu caused by Influenza, Drug Allergy, Emphysema, Fever, Flu caused by Influenza, Food Allergy, Headache, House dust allergy, Irritative cough, Laryngitis, Nasal Congestion, Nasal Congestion caused by Common Cold, Phlegm, Pollen Allergy, Productive cough, Rash, Rhinorrhoea, Sneezing, Sore Throat, Tracheitis, Urticaria, Whooping Cough, Acute Rhinitis, Chest congestion, Chills occurring with fever, Dry cough, Excess mucus or phlegm, Mild to moderate pain, Minor aches and pains, Airway secretion clearance therapy, ExpectorantAsthma, Bronchitis, Bronchoconstriction, Bronchospasm, Chronic Obstructive Pulmonary Disease (COPD), Chronic bronchial inflammation, Airway secretion clearance therapy, Bronchodilation

How Theophylline and guaifenesin works

Although the exact mechanism of action of guaifenesin may not yet be formally or totally elucidated, it is believed that expectorants like guaifenesin function by increasing mucus secretion . Moreover, it is also further proposed that such expectorants may also act as an irritant to gastric vagal receptors, and recruit efferent parasympathetic reflexes that can elicit glandular exocytosis that is comprised of a less viscous mucus mixture . Subsequently, these actions may provoke coughing that can ultimately flush difficult to access, congealed mucopurulent material from obstructed small airways to facilitate a temporary improvement for the individual .

Consequently, while it is generally proposed that guaifenesin functions as an expectorant by helping to loosen phlegm (mucus) and thin bronchial secretions to rid the bronchial passageways of bothersome mucus and make coughs more productive, there has also been research to suggest that guaifenesin possesses and is capable of demonstrating anticonvulsant and muscle relaxant effects to some degree possibly by acting as an NMDA receptor antagonist .

Theophylline relaxes the smooth muscle of the bronchial airways and pulmonary blood vessels and reduces airway responsiveness to histamine, methacholine, adenosine, and allergen. Theophylline competitively inhibits type III and type IV phosphodiesterase (PDE), the enzyme responsible for breaking down cyclic AMP in smooth muscle cells, possibly resulting in bronchodilation. Theophylline also binds to the adenosine A2B receptor and blocks adenosine mediated bronchoconstriction. In inflammatory states, theophylline activates histone deacetylase to prevent transcription of inflammatory genes that require the acetylation of histones for transcription to begin.

Dosage

Theophylline and guaifenesin dosage

Dosages are adjusted to maintain serum theophylline concentrations that provide optimal relief of symptoms with minimal side effects. Most of the controlled release preparations may be administered every 12 hours in adults while administration every 8 hours may be necessary in some children with markedly rapid hepatic metabolism of theophylline. The recommended dosages for achieving serum theophylline concentrations within the accepted therapeutic range is as follow:

• 1-6 months: 10mg/Kg/day
• 6 months-1 year: 15mg/Kg/day
• 1-9 years: 24mg/Kg/day
• 10-16 years: 18mg/Kg/day
• Adults: 10-15mg/Kg/day

Side Effects

The following side effects have been observed:

Gastrointestinal: Nausea, vomiting, epigastric pain and diarrhoea.

Central nervous system: Headache, irritability, restlessness, insomnia, muscles twitching.

Cardiovascular: Palpitation, tachycardia, hypotension. circulatory failure.

Respiratory: Tachypnoea.Renal: Potentiation of diuresis.

Others: Alopecia, hyperglycemia, rash etc.

Toxicity

The most prevalent signs and symptoms associated with an overdose of guaifenesin have been nausea and vomiting .

Although adequate and well-controlled studies in pregnant women have not been performed, the Collaborative Perinatal Project monitored 197 mother-child pairs exposed to guaifenesin during the first trimester . An increased occurrence of inguinal hernias was found in the neonates . However, congenital defects were not strongly associated with guaifenesin use during pregnancy in 2 large groups of mother-child pairs .

Moreover, guaifenesin is excreted in breast milk in small quantities . Subsequently, caution should be exercised by balancing the potential benefit of treatment against any possible risks .

Additionally, an LD₅₀ value of 1510 mg/kg (rat, oral) has been reported for guaifenesin .

Symptoms of overdose include seizures, arrhythmias, and GI effects.

Precaution

Careful consideration is needed for various interacting drugs and physiologic conditions that can alter Theophylline clearance. Dosage adjustment is required prior to initiation of Theophylline therapy, prior to increases in Theophylline dose, and during follow up. The dose of Theophylline selected for initiation of therapy should be low and, if tolerated, increased slowly over a period of time.

Interaction

Allopurinol, cimetidine, norfloxacin, ciprofloxacin, erythromycin, oral contraceptives and propranolol increase serum theophylline levels. Phenytoin, methotrexate and rifampicin lead to decreased serum theophylline levels

Volume of Distribution

The geometric mean apparent volume of distribution of guaifenesin determined in healthy adult subjects is 116L (CV=45.7%) .

• 0.3 to 0.7 L/kg

Elimination Route

Studies have shown that guaifenesin is well absorbed from and along the gastrointestinal tract after oral administration .

Theophylline is rapidly and completely absorbed after oral administration in solution or immediate-release solid oral dosage form.

Half Life

The half-life in plasma observed for guaifenesin is approximately one hour .

8 hours

Clearance

The mean clearance recorded for guaifenesin is about 94.8 L/hr (CV=51.4%) .

• 0.29 mL/kg/min [Premature neonates, postnatal age 3-15 days]
• 0.64 mL/kg/min [Premature neonates, postnatal age 25-57 days]
• 1.7 mL/kg/min [Children 1-4 years]
• 1.6 mL/kg/min [Children 4-12 years]
• 0.9 mL/kg/min [Children 13-15 years]
• 1.4 mL/kg/min [Children 16-17 years]
• 0.65 mL/kg/min [Adults (16-60 years), otherwise healthy non-smoking asthmatics]
• 0.41 mL/kg/min [Elderly (>60 years), non-smokers with normal cardiac, liver, and renal function]
• 0.33 mL/kg/min [Acute pulmonary edema]
• 0.54 mL/kg/min [COPD >60 years, stable, non-smoker >1 year]
• 0.48 mL/kg/min [COPD with cor pulmonale]
• 1.25 mL/kg/min [Cystic fibrosis (14-28 years)]
• 0.31 mL/kg/min [Liver disease cirrhosis]
• 0.35 mL/kg/min [acute hepatitis]
• 0.65 mL/kg/min [cholestasis]
• 0.47 mL/kg/min [Sepsis with multi-organ failure]
• 0.38 mL/kg/min [hypothyroid]
• 0.8 mL/kg/min [hyperthyroid]

Elimination Route

After administration, guaifenesin is metabolized and then largely excreted in the urine .

Theophylline does not undergo any appreciable pre-systemic elimination, distributes freely into fat-free tissues and is extensively metabolized in the liver. Renal excretion of unchanged theophylline in neonates amounts to about 50% of the dose, compared to about 10% in children older than three months and in adults.

Pregnancy & Breastfeeding use

Pregnancy: It is not known whether Theophylline can cause foetal harm when administered to pregnant woman.Xanthines should be given to a pregnant woman only if clearly needed.

Nursing mother: Theophylline is excreted into breast milk and may cause irritability or other signs of mild toxicity in nursing human infants. Serious adverse effects in the infant are unlikely unless the mother has toxic serum Theophylline concentrations.

Contraindication

Hypersensitivity to xanthine derivatives. It is also contraindicated in patients with active peptic ulcer disease and in individuals with underlying seizure disorders (unless receiving appropriate anti-convulsing medication).

Theophylline should not be administered concurrently with other xanthine. Use with caution in patients with hypoxemia, hypertension, or those with history of peptic ulcer. Do not attempt to maintain any dose that is not tolerated.

Acute Overdose

Symptoms may include nausea, vomiting, gastrointestinal irritation, cramps, convulsions, tachycardia & hypotension. The stomach contents should be emptied & supportive measures employed to maintain circulation, respiration & fluid & electrolyte balance. Electrocardiographic monitoring should be carried out & in severe poisoning charcoal haemoperfusion should be used.

Storage Condition

Store in a cool and dry place, protect from light and moisture. Keep out of the reach of children

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