Theovent SR

Uses

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

Theovent SR is also used to associated treatment for these conditions: Asthma, Bronchitis, Bronchoconstriction, Bronchospasm, Chronic Obstructive Pulmonary Disease (COPD), Chronic bronchial inflammation, Airway secretion clearance therapy, Bronchodilation

How Theovent SR works

Theovent SR relaxes the smooth muscle of the bronchial airways and pulmonary blood vessels and reduces airway responsiveness to histamine, methacholine, adenosine, and allergen. Theovent SR 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. Theovent SR 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

Theovent SR 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

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

Precaution

Careful consideration is needed for various interacting drugs and physiologic conditions that can alter Theovent SR clearance. Dosage adjustment is required prior to initiation of Theovent SR therapy, prior to increases in Theovent SR dose, and during follow up. The dose of Theovent SR 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

Food Interaction

• Avoid excessive or chronic alcohol consumption. Ingesting alcohol may reduce the clearance, and therefore increase the serum concentrations of theophylline.
• Avoid St. John's Wort.
• Take with or without food. Take consistently with regard to food.

[Moderate] GENERALLY AVOID: Coadministration with caffeine may increase the serum concentrations of theophylline.

The proposed mechanism involves competitive inhibition of theophylline metabolism via CYP450 1A2, as well as metabolic conversion of caffeine to theophylline in vivo and saturation of theophylline metabolism at higher serum concentrations.

In six healthy male volunteers (all smokers), serum concentrations of theophylline (administered as aminophylline 400 mg single oral dose) were significantly higher following consumption of caffeine (2 to 7 cups of instant coffee over 24 hours, equivalent to approximately 120 to 630 mg of caffeine) than after caffeine deprivation for 48 hours.

Caffeine consumption also increased the apparent elimination half-life of theophylline by an average of 32% and reduced its total body clearance by 23%.

In another study, steady-state concentration and area under the concentration-time curve of theophylline (1200 mg intravenously over 24 hours) increased by 23% and 40%, respectively, in eight healthy volunteers following administration of caffeine (300 mg orally three times a day).

MANAGEMENT: Given the narrow therapeutic index of theophylline, patients should limit or avoid significant fluctuations in their intake of pharmacologic as well as dietary caffeine.

ADJUST DOSING INTERVAL: Administration of theophylline with continuous enteral nutrition may reduce the serum levels or the rate of absorption of theophylline.

The mechanism has not been reported.

In one case, theophylline levels decreased by 53% in a patient receiving continuous nasogastric tube feedings and occurred with both theophylline tablet and liquid formulations, but not with intravenous aminophylline.

MANAGEMENT: When administered to patients receiving continuous enteral nutrition , some experts recommend that the tube feeding should be interrupted for at least 1 hour before and 1 hour after the dose of theophylline is given; rapid-release formulations are preferable, and theophylline levels should be monitored.

Theovent SR Hypertension interaction

[Moderate] The use of theophyllines is associated with an increase in heart rate which may progress to supraventricular tachycardia or ventricular arrhythmia at high serum drug concentrations.

Appearance of cardiac adverse effects is generally an indication of theophylline toxicity, although patients with a history of tachyarrhythmias may be more susceptible to the chronotropic effect of these drugs.

Therapy with theophyllines should be administered cautiously in such patients.

Caution is also advised in patients with hypertension, hyperthyroidism, angina pectoris, or recent myocardial infarction, since high dosages of the drugs are associated with positive inotropic as well as chronotropic effects.

Clinical monitoring of serum drug concentrations is recommended to prevent toxicity.

Theovent SR Drug Interaction

Moderate: fluticasone / salmeterol, albuterol / ipratropium, albuterol / ipratropium, esomeprazole, albuterol, budesonide / formoterol, albuterolMinor: furosemide, alprazolam, cetirizineUnknown: aspirin, duloxetine, pregabalin, guaifenesin, acetaminophen, clopidogrel, montelukast, tiotropium, cyanocobalamin, cholecalciferol

Theovent SR Disease Interaction

Major: PUD, renal dysfunction, seizure disordersModerate: GERD, hemodialysis, reduced clearance, tachyarrhythmias

Volume of Distribution

• 0.3 to 0.7 L/kg

Elimination Route

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

Half Life

8 hours

Clearance

• 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

Theovent SR 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 Theovent SR can cause foetal harm when administered to pregnant woman.Xanthines should be given to a pregnant woman only if clearly needed.

Nursing mother: Theovent SR 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 Theovent SR 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).

Theovent SR 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

Innovators Monograph

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