Lecture 1 anti-asthmatics drugs Part-1

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Pharmacology of Respiratory system-Part 1

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Anti-Asthmatics Ms. Seema Thakur Associate Professor Faculty of Pharmaceutical Sciences PCTE Group of Institutes

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Content • Definition • Aim of treatment • Classification • Bronchodilators – β 2 Sympathomimetics: – Methlyxanthines – Anticholinergics • Leukotriene antagonist • Mast cell stabilizers • Corticosteroids – Systemic – Inhalational

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Bronchial asthma is characterized by hyperresponsiveness of the tracheobronchial smooth muscle to variety of stimuli resulting in • Narrowing of air tubes • ↑ secretion • Mucosal oedema • Mucus plugging Symptoms • Dyspnoea • Wheezing • Cough • May be limitation of activity

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Allergen IgE Mast cells on the mucosal surface sensitise Histamine LTs PGs PAF chemotactic factors for eosinophils and neutrophils Degranulate and Release bronchoconstriction oedema Mucus hypersecretion Accumulation of eosinophils and neutrophils

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Approaches of treatment • Prevention of AG:AB reaction • Neutralization of IgE: Omalizumab • Suppression of inflammation and bronchial hyperreactivity: Corticosteroids • Prevention of release of mediators : Mast cell stabilizers • Antagonism of released mediators: Leukotriene antagonists antihistaminic PAF antagonists • Blockade of constrictor neurotransmitter: Anticholinergics • Mimicking dilator neurotransmitter: Sympathomimetics • Directly acting bronchodilators-Methylxanthines

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Classification • Bronchodilators – β 2 Sympathomimetics: Salbutamol terbutaline bambuterol salmeterol formeterol – Methlyxanthines: Theophylline aminophylline choline theophyllinate hydroxyethyl theophylline doxophylline – Anticholinergics: Ipratropium bromide tiotropium bromide • Leukotriene antagonist: Montelukast zafirlukast • Mast cell stabilizers: Sodium cromoglycate ketotifen • Corticosteroids – Systemic: Hydrocortisone prednisolone – Inhalational: Beclomethasone dipropionate budesonide fluticasone propionate flunisolide ciclesonide • Anti-IgE antibody: Omalizumab

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SYMAPATHOMIMETICS • Adrenergic drugs cause bronchodilatation through β receptor stimulation → increased cAMP formation in bronchial muscle cell → relaxation • Also ↑ cAMP in mast cell ↓ AG-AB reaction induced mediator release should be used cautiously used in hypertensives heart patients and in those receiving digitalis • Are fastest acting bronchodilators when inhaled

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SALBUTAMOL Albuterol • Highly selective β2 agonist • Cardiac side-effects are less prominent • Inhalation selectively increase drug selectivity • Causes dose-related muscle tremor • Also cause palpitations restlessness nervousness throat irritation ankle edema • Undergo presystemic metabolism oral bioavailability ≈ 50

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METHYL XANTHINES • Caffeine theophylline theobromine PHARMACOLOGICAL ACTIONS 1. CNS Caffeine and theophylline are CNS stimulants - primarily affect higher centres - about 150-250 mg produces sense of well being alertness beats boredom allays fatigue thinking becomes clearer improve performance increase alertness - caffeine is more active than theophylline - higher doses causes nervousness restlessness panic insomnia and excitement theophylline produce side-effects by greater propensity

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• Also stimulate medullary vagal respiratory and vasomotor centres • V omiting at higher doses is due to both gastric irritation and CTZ stimulation CVS • Methylxanthines directly stimulate the heart and increase force of myocardial contractions • Tend to increase heart rate by direct action but decrease it by causing vagal stimulation → variable effect • Tachycardia is more common with theophylline caffeine decreases heart rate • Action is more marked in CHF patients increase cardiac work at higher doses produces cardiac arrythmias

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• Methyl xanthines esp. theophylline dilate systemic blood vessels including coronaries by direct action reduce peripheral resistance • cranial blood vessels are constricted esp. by caffeine → therefore used in migraine • Effects on BP is variable and unpredictable: - vasomotor centre and direct cardiac stimulation → ↑ BP - vagal stimulation and direct vasodilatation → ↓ BP - usually rise in systolic and fall in diastolic BP is observed

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SMOOTH MUSCLES • All smooth muscles are relaxed • prominent effect on bronchi esp. in asthmatics • Theophylline is more potent produces consistent vasodilatation • Increase vital capacity • Action may be direct as well as due to release of adrenergic transmitter • Caffeine has minimal action • Negligible effect on intestines and urinary tract

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SKELETAL MUSCLES • Caffeine increases contractile power of skeletal muscles • At higher concentrations it increases calcium release from sarcoplasmic reticulum by direct action • At low doses twitch response to nerve stimulation is augmented at toxic doses contracture is produced • Facilitates neuromuscular transmission by increasing Ach release • Central action relieves fatigue and increases muscular work

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STOMACH • Methylxanthines increase acid and pepsin secretion in stomach • Are also gastric irritants • Theophylline more potent than caffeine

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MECHANISM OF ACTION 1. Release of calcium from sarcoplasmic reticulum in cardiac and skeletal muscles 2. Inhibition of phosphodiesterase which degrade cyclic nucleotides intracellurly ATP cAMP 5-AMP or GTP cGMP 5-GMP → Concentration of cyclic nucleotides is increased → Bronchodilatation cardiac stimulation and vasodilatation occur when cAMP level rise in concerned cells Adenylyl cyclase Guanylyl cyclase phosphodiesterase theophylline -

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BRONCHODILATATION Therapeutic range Plasma concentration TOXICITY Convulsions shock arrythmias Delirium worsening CV status Increased muscle tone extrasystoles light flashes seen Agitation tachapnoea flushing hypotension Restlessness tremors vomiting palpitations diuresis Dyspepsia headache nervousness insomnia Minimal side effects death ADVERSE EFFECTS

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USES • Bronchial asthma and COPD • Apnoea in premature infants

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