4. Antimuscarinic drugs and Ganglionic

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antimuscarinic and ganglionics

List antimuscarinic Drugs

tertiary amines - atropine, scopolamine, homatropine, tolterodine, trihexyphenidyl. Quaternary ammonium compounds - glycopyrrolate, Ipratropium

Muscarinic drugs mechanism of action

competitively block muscarinic receptors. Atropine and scopolamine block all M receptors. Other antimuscarinic drugs are selective. Tertiary antimuscarinics don't block Nn. Quarernary block muscarinic but also Nn.

Effects of antimuscarinic mnemonic

mad as hatter, blind as bat, red as beat, dry as bone, bloated as toad, hot as hell.

Antimuscarinics on CNS intermediate dose

mild vagal stimulation. Fatigue, sedation, drowsiness, depression of vestibular, reduction in parkinsonian tremor and rigidity

Antimuscarinic on CNS high dose

amnesia, malaise, restlessness, irritability, disorientation, halluciations, delirium. Coma.

Antimuscarinics on heart low dose

decrease in heart rates (due to blockade of M2 presynaptic autoreceptors and to central vagal stimulation.

Antimuscarinics on heart intermediate dose

tachycardia. Many types of reflex vagal cardiac slowing can be abolished. Atria - increase in automaticity and contractility. AV node - increase in conduction and automaticity, decrease in refractoriness. Ventricles - minimal direct effect.

Antimuscarinics on Cardiovascular vessels therapeutic dose

negligible effects (but vasodilation and hypotension caused by choline esters are antagonized)

Antimuscarinics on CV vessels after high dose

dilation of cutaneous blood vessels (unknown mechanism) in children can cause atropine flush.

Antimuscarinics on GI

decreased gastric secretion, decreased tone, contractions, peristaltic activity. Relaxation of LES, gallbladder, bile ducts

Antimuscarinics on Genitourinary system

relaxation of pelves, calyces, ureters. Decreases peristalsis, relaxation of detrusor muscle (increased capacity)

Antimuscarinics on respiratory system

bronchial relaxation, decreased secretions, decreased mucociliary clearance (except ipratropium)

Antimuscarinics on eyes

relaxation of sphincter of iris (mydriasis), relaxation of ciliary muscle (cycloplegia, accommodation is lost) hinders outflow of aqueous humor thru schlemm's canal. When atropine is given locally, these effects last for 3 days. Decreased lacrimal gland secretion

Antimuscarinics on skin

decreased sweat. Raises body temperature. Infants and children are prone to atropine fever.

Antimuscarinic absorption

oral biovaliability = atropine = 70%, scopolamine = 30%, ipratropium >1%

Antimuscarinic distribution

tertiary amines all tissues, quaternary derivatives don't enter cns

Atropine excretion

60% excreted by kidney

Atropine and scopolamine half life

3 hours

Glycopyrrolate halflife

10 hours

Antimuscarinic toxicity

skin rashes, urticarial, fever. Therapeutic index >100 adults, but a dose of 5mg can be lethal to children. Serious atropine poisoning appears in 30 minutes, lasts for 2-7 days. Death due to respiratory failure may follow coma and collapse.

Diagnosis of antimuscarinic poisoning

IM injection of physostigmine. If signs of muscarinic activation do not occur, poisoning with antimuscarinic drug is almost always certain.

Antimuscarinic treatment

maintenance of vital signs, alleviation of convulsion with diazepam, temp control with icebag and alcohol sponges.

Poisoning by antimuscarinics

mydriasis, blurring of vision, dryness conjunctiva, difficulty speaking, dyspnea, respiratory depression, dry hot red skin, dryness of mouth, difficulty swallonging, no bowel sounds, difficulty in micturition, tachycardia, arrhythmias, fatigue, ataxia, restlessness, delirium, hallucinations, coma

Contraindications of antimuscarinics

glaucoma, prostatic hypertrophy, urinary tract obstruction, GI tract obstruction, adynamic ileus, gastric ulcer, infectious diareah, UC, chron's disease, tachyarrhythmias, coronary artery disease, hyperthyroidism, children, elderly

Therapeutic uses of antimuscarinics

funduscopic exam (mydriasis), measurements of refractive errors, iritis, chroiditis. IBS diahrea, renal colic, enuresis, urinary incontinence (to reduce frequency), preoperative lung surgery to reduce secretions, bronchial asthma and copd (ipratropium), cardio resuscitation (when vagal hyperactivity is the cause of cardiac arrest), sinus or nodal bradycardia, AV block due to increased vagal tone. CNS - prevention of motion sickness (scopolamine), parkinsons (triexyphenidyl). To counteract parasympathomimetic effects of neostigmine in myasthenic patients. Poisoning by AchE inhibitors or mushrooms containing muscarine.

Atropine

visceral hypermotility and spasms, excessive salivation, cardio disorders, cholinesterase inhibitor overdose, ophthalmology, preanesthetic medication

Scopolamine

motion sickness, ophthalmology, preanesthetic medication

Homatropine

ophthalmology

Tolterodine

neurogenic bladder, urinary urge incontinence

Trihexyphenidyl

parkinsons

Glycopyrrolate

vvisceral hypermotility and spasms, cardiovascular disorders, preanesthetic medication

Ipratropium

bronchospastic disorders

Ganglionic stimulating drugs

nicotine, tetramethylammonium (carbachol, cholinesterase inhibitors, succinylcholine less used)

Ganglionic blocking drugs

hexamethonium, mecamylamine (glycopyrrolate, ipratropium, tubocurarine less used)

Nicotine pharm

natural alkaloid. Basic amine 8.5 pka. Mechanism of action - low doses activate nicotinic receptors at autonomic ganglia, nm junction, presynaptic nerve terminals, adrenal medulla, cns. Large doses - depolarization blockade (prolonged depolarization of post junctional membrane hinders neuronal transmission.

Nicotine pharm effects cns

stimulation of renshaw cels (interneurons in ventral horn of spinal), stimulation of RF (low doses), depression of RF (high doses). Reflex stimulation of emetic (vomit), direct stimulation of chemoreceptor trigger zone, stimulation of ADH secretion.

Nicotine effects CV

increased CO and HR. constriction of skin and splancnic. Dilation of muscular vessels. Increased BP. After toxic doses- CV collapse.

Nicotine effects GI

anorexia, nausea, vomiting, stimulation of peristalsis. Toxic doses - paralytic ileus.

Nicotine effects

Respiratory - stimulation of respiration, bronchoconstriction and increased secretions. Toxic - apnea due to central depression and block of diaphragm and intercostals.

Nicotine effects urinary

decreases diuresis (due to ADH release). Contraction of detrusor, relaxation of trigone and internal sphincter of urethra

Nicotine general effects

stimulation of sweat glands, miosis (activation of nn receptors of ciliary ganglion), rate of metabolism of many drugs increases, loss of body weight, increased hand tremors, paralysis of skeletal muscles with toxic doses

Nicotine tolerance and dependence

nausea vomiting, dizziness, headache, dysphoria and effects to peripheral ganglionic stimulation undergo tachyphylaxis. Rapid tolerance is lost overnight.

Nicotine bioavailability

oral 30%, smoking 90%, transdermal 89-90%. Distributed in all tissues (smoked reaches brain faster than IV). Most biotransformed by liver, kidney, lung. Half life = 2 hours

Nicotine poisoning

salivation, nausea, vomiting, abdominal pain, loss of urine and feces, cold sweat, tachypnea, tachycardia, disturbed hearing and vision, headache, dizziness, confusion, marked weakness. Then symptoms progress to faintness, falling of BP, weak irregular rapid pulse, difficulty breathing, tremors, convulsions. Death in a few minutes from respiratory failure

Ganglionic blocker on heart effect

tachycardia (M2)

Ganglionic blocker arterioles

vasodilation, orthostatic hypotension

Ganglionic blocker veins

vasodilation, venous pooling, decreased cardiac output

Ganglionic blocker iris

mydriasis

Ganglionic blocker ciliary muscle

cycloplegia

Ganglionic blocker GI tract

decreased motility and tone, constipation

Ganglionic blocker urinary bladder

urine retention

Ganglionic blocker exocrine glands

reduced secretion

Ganglionic blocker sweat glands

reduced secretion (anhydriosis)

Ganglionic blocker sex organs

impaired erection, impaired ejaculation

Mechanism of action of ganglionic blockers

competitive blockade of Nn receptors in autonomic ganglia, adrenal medulla, presynaptic nerve terminals, CNS (mecamylamine)

Only ganglionic blocker available

mecamylamine

Ganglionic blockers CV

moderate HR increase, decreased CO (b/c of peripheral venous pooling decreases preload), marked decrease in venous tone and peripheral resistance (hypotension in upright position), skin blood flow is decreased, spanchnic and renal blood flow are decreased.

Pharmacokinetics of ganglionic blocker s

hexamethonoium is quaternary ammonium, mecamyalamine is secondary amine (active by oral and enters CNS)

Therapeutic uses of ganglionic blockers

mecamylamine treats neurological disseases, ie tourettes. Also may be used for nicotine and cocaine dependence.

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