Adrenergic Drugs - Therapeutic Uses

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Chapter: Essential pharmacology : Adrenergic System and Drugs

Hypotensive states (shock, spinal anaesthesia, hypotensive drugs) One of the pressor agents can be used along with volume replacement for neurogenic and haemorrhagic shock; also as an expedient measure.....


THERAPEUTIC USES

 

1. Vascular Uses

 

Hypotensive states (shock, spinal anaesthesia, hypotensive drugs) One of the pressor agents can be used along with volume replacement for neurogenic and haemorrhagic shock; also as an expedient measure to maintain cerebral circulation for other varieties of shock. They should not be used in secondary shock when reflex vasoconstriction is already marked. Use in cardiogenic shock is tricky, because attempts to raise BP may also increase cardiac work. Slow i.v. infusion of dopamine/dobutamine is more appropriate in this situation; use of NA is practically obsolete. Adr 0.5 mg injected promptly i.m. is the drug of choice in anaphylactic shock (see p. 82). It not only raises BP, but counteracts bronchospasm/ laryngeal edema that may accompany. Because of the rapidity and profile of action Adr is the only life saving measure. Oral ephedrine has been used to treat postural hypotension due to autonomic neuropathy (diabetes, parkinsonism, idiopathic) or advanced age. However, it is not satisfactory because it cannot mimic selective NA release that occurs only on standing. Elastic stockings and use of fludrocortisone to expand plasma volume are more helpful.

 

Along with local anaesthetics Adr 1 in 200,000 to 1 in 100,000 for infiltration, nerve block and spinal anaesthesia. Duration of anaesthesia is prolonged and systemic toxicity of local anaesthetic is reduced. Local bleeding is minimised.

 

Control of local bleeding From skin and mucous membranes, e.g. epistaxis : compresses of Adr 1 in 10,000, phenylephrine/ephedrine 1% soaked in cotton can control arteriolar and capillary bleeding. NA 8 mg in 100–200 ml saline put in stomach through a tube can control bleeding from gastric erosions and stress ulcers.

 

Nasal decongestant In colds, rhinitis, sinusitis, blocked nose or eustachian tube—one of the αagonists is used as nasal drops. Shrinkage of mucosa provides relief, but aftercongestion, atrophy of mucosa on prolonged use are still a problem. The imidazolines should be used in lower concentrations in infants and young children, because they are more sensitive to central effects of these drugs. Nasal decongestants should be used very cautiously in hypertensive patients and in elderly males.

 

Pseudoephedrine, PPA, and phenylephrine have been used orally as decongestants, but effective doses will constrict other blood vessels as well and cause rise in BP. However, they do not produce aftercongestion.

 

Peripheral vascular diseases like Buerger’s disease, Raynaud’s phenomena, diabetic vascular insufficiency, gangrene, frost bite, ischaemic ulcers, night leg cramps, cerebral vascular inadequacy : vasodilators including isoxsuprine have been used, but are far from satisfactory in most cases, because often the capacity of the affected vessels to dilate is severely limited, and ischaemia itself is a potent vasodilator.

 

2.  Cardiac Uses

 

Cardiac arrest (drowning, electrocution, StokesAdams syndrome and other causes) Adr may be used to stimulate the heart; i.v. administration is justified in this setting with external cardiac massage.

 

Partial or complete AV block Isoprenaline may be used as temporary measure to maintain sufficient ventricular rate.

 

Congestive heart failure (CHF) Adrenergic inotropic drugs are not useful in the routine treatment of CHF. However, controlled short term i.v. infusion of DA/dobutamine can tide over acute cardiac decompensation during myocardial infarction, cardiac surgery and in resistant CHF.

 

3. Bronchial Asthma

 

Adrenergic drugs, especially β2 stimulants are the primary drugs for relief of reversible airway obstruction.

 

4. Allergic Disorders

 

Adr is a physiological antagonist of histamine which is an important mediator of many acute hypersensitivity reactions. It affords quick relief in urticaria, angioedema; is life saving in laryngeal edema and anaphylaxis. It is ineffective in delayed, retarded and other types of allergies, because histamine is not involved.

 

5. Mydriatic

 

Phenylephrine is used to facilitate fundus examination; cycloplegia is not required. It tends to reduce intraocular tension in wide angle glaucoma. The ester prodrug of Adr dipivefrine is a second choice/adjuvant drug for open angle glaucoma.

 

6. Central Uses

 

Hyperkinetic children (minimal brain dysfunction, attention deficit hyperkinetic disorder): Amphetamines have an apparently paradoxical effect to calm down hyperkinetic children. This disorder is recognized as the mildest grade of mental retardation or a reduction in the ability to concentrate, i.e. the span of time for which attention can be focused on a subject is abbreviated. Amphetamines by increasing attention span improve behaviour and performance in studies ; tolerance to this effect does not develop. However, growth retardation may occur due to reduction in appetite. The riskbenefit ratio of such therapy needs to be considered in individual patients.

 

Narcolepsy  Narcolepsy is sleep occurring in fits and is adequately controlled by amphetamines. Development of tolerance, abuse and behavioural abnormalities are the calculated risks of such therapy. Imipramine like drugs are generally tried first.

 

Epilepsy Amphetamines are occasionally used as adjuvants and to counteract sedation caused by antiepileptics.

 

Parkinsonism Amphetamines improve mood and reduce rigidity (slightly) but do not benefit tremor. They are occasionally used as adjuvants in parkinsonism.

 

Obesity  The anorectic drugs can help the obese to tolerate a reducing diet for short periods, but do not improve the longterm outlook. Their use (for 2–3 months) may be considered in severe obesity, but not for cosmetic reasons in mild to moderate obesity. In the absence of dietary restriction none of them has any significant weight reducing effect, and lifestyle modification is required to maintain weight loss. Tolerance develops to the anorectic action of all available drugs. Most subjects tend to regain weight after the slimming regimen is over. Currently, sibutramine is being used, though its longterm safety is not established.

 

The newer approaches being developed for control of obesity are:

 

Orlistat An inhibitor of gastric and pancreatic lipase; it interferes with digestion and absorption of dietary triglycerides. Absorption of cholesterol and fat soluble vitamins is also impaired. It has facilitated weight loss in clinical trials. Fluid motions, steatorrhoea, abdominal pain, nausea, flatulence and vitamin deficiency are the side effects.

 

Olestra is a sucrose polyester which can be used as a cooking medium in place of fat but is neither digested nor absorbed. Its acceptability is inconsistent.

 

Leptin (the endogenous slimming peptide) analogues, neuropeptide Y antagonists and β3 adrenergic agonists are under investigation as antiobesity drugs.

 

Rimonabant A selective cannabinoid (CB1) receptor antagonist that blocks hunger promoting action of cannabis has been found in clinical trials to decrease appetite and help weight reduction by the obese. Neusea is a side effect. Rimonabant has also been tried to help smoking cessation.

 

7. Nocturnal Enuresis In Children And Urinary Incontinence

 

Amphetamine affords benefit both by its central action as well as by increasing tone of vesical sphincter.

 

8.   Uterine Relaxant

 

Isoxsuprine has been used in threatened abortion and dysmenorrhoea, but efficacy is doubtful. Selective β2 stimulants, specially ritodrine, infused i.v. have been successfully used to postpone labour but maternal morbidity and mortality may be increased due to their cardiac and metabolic actions and incidents of pulmonary edema.

 

9.     Insulin Hypoglycaemia

 

Adr may be used as an expedient measure, but glucose should be given as soon as possible.

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