Pharmacology for Midwifery PDF

Pharmacology for Midwifery Dr. Shereen Arabiyat  Chapter 4-2: Drugs affecting the autonomic nervous system (ANS) Fundamentals of Pharmacology: An Applied Approach for Nursing and Health 2nd Edition by Alan Galbraith (Author), Shane Bullock (Author), Elizabeth Manias (Aut...

Pharmacology for Midwifery Dr. Shereen Arabiyat  Chapter 4-2: Drugs affecting the autonomic nervous system (ANS) Fundamentals of Pharmacology: An Applied Approach for Nursing and Health 2nd Edition by Alan Galbraith (Author), Shane Bullock (Author), Elizabeth Manias (Author), Barry Hunt (Author), Ann Richards (Author) Cholinergic division Like adrenergic receptors, two main subtypes of cholinergic receptor have been identified. One group of receptors responds to stimulation by nicotine; these are termed nicotinic receptors. The other group responds to a chemical, muscarine, extracted from Amanita muscaria; these are termed muscarinic receptors. Both subtypes can be activated by acetylcholine but bear structural differences to develop cholinergic agents specific to one subtype of receptor. Nicotinic receptors Nicotinic receptors are located centrally, in autonomic ganglia and in the neuromuscular junction of skeletal muscles. The effects of stimulating these receptors are as follows: behavioral changes, including feelings of relaxation and wellbeing an increase in autonomic tone above the resting state of activity of both parasympathetic and sympathetic effectors release of adrenaline and noradrenaline from the adrenal medulla. an increase in skeletal muscle tone. COMMON ADVERSE EFFECTS Essentially, at the doses absorbed during smoking, nicotine is a stimulant in which many of the peripheral effects (particularly cardiovascular) are brought about via an increase in autonomic tone. Nicotine treatment for people trying to quit cigarette smoking mimics these effects. Adverse effects include cardiovascular stimulation, headache, nausea and insomnia. Nicotine patches can cause skin reactions such as itching, burning and redness. Nicotine therapy is contraindicated in pregnancy and lactation, in patients with known hypersensitivity and in patients with serious cardiovascular conditions, e.g., acute myocardial infarction, unstable angina, recent cerebrovascular accident or dysrhythmia Muscarinic receptors Muscarinic receptors are located both centrally and peripherally. Peripheral muscarinic receptors are found on the surfaces of effectors stimulated by cholinergic nerves – that is, all parasympathetic and some sympathetic effectors. More specifically, these receptors are found on the following peripheral tissues: iris, sweat glands, lacrimal glands, digestive glands, myocardium, bronchioles, gastrointestinal tract, urinary tract, liver and sex organs, and blood vessels of the skin, genitalia and skeletal muscle. MECHANISM OF ACTION Five distinct functional subtypes of muscarinic receptors have been identified, known as M1 , M2 , M3 , M4 and M5 receptors. The physiological roles of M4 and M5 receptors remain unclear. muscarinic receptors are associated predominantly with the brain and mediate higher cerebral function; reduction in receptor numbers within the cerebral cortex has been linked to dementias such as Alzheimer’s disease Interestingly, all five subtypes have been found in the brain. M1 receptors are also found peripherally on the parietal cells of the stomach and stimulate increased acid secretion and on postganglionic neurons at autonomic ganglia.  M2 receptors are located on the myocardium and when stimulated trigger a decrease in the rate and force of contraction of the heart  M3 muscarinic receptors are associated with visceral smooth muscle and exocrine glands. Stimulation of these receptors causes the following parasympathetic-like effects: pupil constriction (miosis) and increased rate of drainage of aqueous humor from the anterior cavity of the eye; relaxation of gastrointestinal sphincters, increased gastrointestinal motility and increased secretion of digestive juices (saliva, pancreatic juice, bile); promotion of micturition and defecation; promotion of glycogenesis and gluconeogenesis – increases insulin secretion; promotion of lacrimal secretion (tears); bronchoconstriction and increased bronchial mucus secretion. COMMON ADVERSE EFFECTS Common adverse include bradycardia, hypotension, pupil constriction, sweating, bronchoconstriction, drooling and diarrhea. Contraindications include intestinal and urinary obstruction. CHOLINERGIC AGONISTS 1) DIRECT ACTING 2)A INDIRECT ACTING …. STIMULATE ACETYLCHOLINE RELEASE Acetylcholine, bethanechol, carbachol and pilocarpine are 1) direct- acting muscarinic agonists. Cisapride is an 2)A… indirect-acting cholinergic agent that stimulates the release of acetylcholine from the myenteric plexus. The release of endogenous transmitter from this plexus stimulates gastrointestinal motility. Clinical applications for these agents include the treatment of mydriasis, glaucoma, constipation and other gastrointestinal conditions characterized by diminished motility, urinary retention and tachycardia. 2)B … ANTICHOLINESTERASES… INHIBITS ACETYLCHOLINE METABOLISM MECHANISM OF ACTION Muscarinic agonist drugs specifically stimulate muscarinic receptors and therefore mimic the effects of acetylcholine at these receptors, but there is another important group of cholinergic stimulants that reversibly inactivate the cholinesterase enzymes responsible for the degradation of acetylcholine. As a result, the action of acetylcholine in the synapse and in other tissues is prolonged. These indirect-acting drugs are called the anticholinesterases (not to be confused with the anticholinergic (antimuscarinic) agents, (which are antagonists) and will enhance the action of endogenous acetylcholine at both nicotinic and muscarinic receptors. COMMON ADVERSE EFFECTS pupil constriction, hypotension, bradycardia, diarrhea, muscle twitching, bronchoconstriction, increased lacrimation and sweating.  Anticholinesterases include donepezil, galantamine, pyridostigmine, neostigmine and physostigmine. Edrophonium is a very short-acting anticholinesterase with a duration of action of about 10 minutes. When giving anticholinesterases to reverse the effects of neuromuscular blocking agents, atropine or propantheline is also necessary in order to minimize the muscarinic adverse effects.  Medications used for myasthenia gravis should be taken early in the day because it is during this time that muscle weakness and fatigue are most severe. Overdose with an anticholinesterase may lead to a cholinergic crisis, as demonstrated by excessive sweating, defecation, urination, miosis, salivation, bradycardia and muscle weakness.  d ation. m m o p ai re d acco and im r y rete ntion o t i l i t y, urina m