The primary effect of phenylephrine is peripheral vasoconstriction with a concomitant rise in systemic vascular resistance and arterial blood pressure. Clonidine seems to decrease anesthetic and analgesic requirements and to provide sedation and anxiolysis. It has sedative, analgesic, and sympatholytic effects that blunt many of the cardiovascular responses seen during the perioperative period. Long-term use of these agents, particularly clonidine and dexmedetomidine, leads to supersensitization and up-regulation of receptors; with abrupt discontinuation of either drug, an acute withdrawal syndrome manifested by a hypertensive crisis can occur.
Ephedrine is commonly used as a vasopressor during anesthesia. As such, its administration should be viewed as a temporizing measure while the cause of hypotension is determined and remedied. Stimulation of these nonadrenergic receptors specifically, DA 1 receptors vasodilates the renal vasculature and promotes diuresis.
Favorable effects on myocardial oxygen balance are believed to make dobutamine a good choice for patients with the combination of congestive heart failure and coronary artery disease, particularly if peripheral vascular resistance is elevated. There are some recent debates regarding this beneficial effect. Adrenergic agonists and antagonists produce their clinical effects by interacting with the adrenergic receptors ie, adrenoceptors.
The clinical effects of these drugs can be deduced from an understanding of the adrenoceptor physiology and a knowledge of which receptors each drug activates or blocks. With the exception of eccrine sweat glands and some blood vessels, norepinephrine is released by postganglionic sympathetic fibers at end-organ tissues Figure In contrast, acetylcholine is released by preganglionic sympathetic fibers and all parasympathetic fibers. The sympathetic nervous system. Organ innervation, receptor type, and response to stimulation.
The origin of the sympathetic chain is the thoracoabdominal T1-L3 spinal cord, in contrast to the craniosacral distribution of the parasympathetic nervous system. Another anatomic difference is the greater distance from the sympathetic ganglion to the visceral structures. Norepinephrine is synthesized in the cytoplasm of sympathetic postganglionic nerve endings and stored in the vesicles Figure After release by a Your MyAccess profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'.
Airways dysfunction; bronchial asthma, chronic bronchitis, emphysema In airways dysfunction, beta 2 selective agonists relax airways thus decreasing airways resistance.
Premature labor In premature labor, the beta 2 selective agonists relax uterine smooth muscle. Drugs that relax uterine smooth muscle are referred to as tocolytic agents. Side effects related to dental practice 1. Xerostomia, with inhaler usage. These structural modifications of the parent catecholamine nucleus result in drugs that are orally active and have longer plasma half-lives.
However, these same modifications result in lower affinity for the receptor than do the endogenous agonists epinephrine or norepinephrine. There are two structural classes of alpha 1 agonists phenethylamines which are closely aligned in structure to epinephrine and the imidazolines, compounds structurally unrelated to epinephrine.
Levonordeferin is a phenyethylamine that has been used in dental practice in combination with local anesthetics. Hypotension-to increase blood pressure during a surgical procedure where a general anesthetic has induced hypotension 2.
Ophthalmic preparations-to induce mydrasis also in topical preparations for symptomatic release of eye irritation. Cough and cold preparations-Induces constriction of nasal mucosa decreases resistance to air flow. Indirect Acting Sympathomimetics These agents require the presence of endogenous catecholamines to produce their effects.
They have little activity if catecholamines are depleted. Cocaine: Blocks reuptake of monoamines into nerve endings.
Cocaine also has local anesthetic activity. Amphetamine: Promotes the release of NE from nerve endings. Amphetamine can also block the reuptake of norepinephrine. Amphetamine-like compounds 1. Methylphenidate A major site action of cocaine, amphetamine and amphetamine-like agents is in the CNS. These drugs produce a feeling of well being and euphoria. As a result the drugs carry a significant abuse liability. Both cocaine and amphetamine are on the FDA schedule 2.
Uses of Cocaine 1 below , Amphetamine and Amphetamine-like agents below 1. Cocaine has limited use as a local anesthesic and vasoconstrictor in surgical procedures involving oral, laryngeal or nasal cavities. Appetite suppression 3. Hyperactivity in children 4.
Recall that epinephrine can be absorbed systemically after intraoral administration. This epinephrine can be taken up by nerve terminals and this uptake contributes to the the termination of the actions of epinephrine.
Thus, the risk of hypertension and other problems associated with systemic absorption of epinephrine will be greater in patients taking cocaine or amphetamine-like drugs. Methamphetamine can be produced from over the counter cough and cold medications such as pseudoephedrine. Lithium, muriatic acid, sulfuric acid, red phosphorus and lye are used in this preparation.
When smoked these highly corrosive agents are vaporized resulting in significant damage to teeth and gums. Sympatholytics: synthetic analogs which bind to beta or alpha receptors or act through other mechanisms to block the actions of endogenous neurotransmitters or other sympathomimetics.
Review the pharmacodynamic properties and characteristics of antagonists. Understand the pharmacologic properties and therapeutic uses of clonidine, prazosin analogs, the beta blockers and MAO-inhibitors.
Understand the special precautions that exist for sympatholytic drugs in dental practice. This drug stimulates alpha 2 receptors in the nucleus tractus solitarius NTS to decrease sympathetic outflow to the heart and blood vessels. The decrease in sympathetic tone results in a decrease in peripheral vascular resistance. Clonidine is used in dental practice in the management of chronic pain. It can be given orally or in patch form. Clonidine is a second-line antihypertensive that has many other uses including opiate withdrawal, nicotine withdrawal, vascular headaches, diabetic diarrhea, glaucoma, ulcerative colitis and Tourette's syndrome.
Side Effects The use of clonidine may result in clinical symptoms related to dry mouth, such as difficulty in swallowing and speech. Chronic use of xerostomia-producing drugs is associated with a higher incidence of oral candidiasis and dental caries. E ffects on the Cardiovascular System: 1. Relaxes arterial and venous smooth muscle as well as nonvascular smooth muscle. Decreases peripheral vascular resistance and venous return with a resultant decrease in systemic arterial blood pressure.
Hypertension 2. Benign prostatic hypertrophy Tamsulosin specifically blocks the alpha 1 -receptor associated with the prostate and is used to treat benign prostatic hypertropy. The Relevance of Orthostatic Hypotension to Dental Practice Orthostatic hypotension is a problem with prazosin analogs and to a lesser extent tamsulosin.
However, the increase in total peripheral resistance produced by epinephrine administration is only modest. Systemic epinephrine is often administered prior to cardiopulmonary resuscitation when bradycardia is present; cardiac arrest or in patients with anaphylactic shock. It can also be used in patients with ventricular fibrillation. Both of these drugs have chronotropic and inotropic effects, but norepinephrine elicits a much larger increase in total peripheral resistance.
Since afterload increases precipitously following norepinephrine administration, increases in cardiac output can be limited despite the stimulatory effects of the drug on the heart. Because norepinephrine causes sharp increases in blood pressure, its administration activates the baroreceptor reflex. This diminishes the effects of the drug on the heart, so chronotropic effects are attenuated and the drug tends not to induce tachycardia.
Systemic norepinephrine is used to treat profound hypotension. Although dopamine is usually considered a neurotransmitter of the central nervous system, dopamine is also produced and secreted by some renal cells. The pharmacology of systemically administered dopamine is complex. At low does, the drug mainly binds to D1 receptors in the kidney, resulting in renal vasodilation and a decrease in total peripheral resistance. Increased renal blood flow will result in increased urine output and decreased fluid retention and decreased edema.
Dopamine has been used to treat heart failure patients, as it stimulates cardiac function while producing renal effects that aid to clearing the fluid accumulation resulting from the pumping mismatch between the left and right ventricles. Isoproterenol is thus an ideal drug to treat patients with poor myocardial contractility and low heart rate, but high peripheral resistance. Clinically, it is used most often for its chronotropic effects. Dobutamine was developed as a structural analogue of isoproterenol.
Thus, dobutamine increases heart rate and contractility, while producing less changes in peripheral resistance than isoproterenol. Dobutamine is a useful drug to treat patients with low cardiac contractility due to organic disease or surgical procedures. Dobutamine is also commonly used in the hospital setting as a pharmacologic stress testing agent to identify coronary artery disease.
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