By I. Sugut. University of Northern Iowa. 2018.
Higher concentrations of quinidine have a direct that is cheap nimotop 30mg with visa, an extension of refractoriness beyond the recov- effect of depressing the rate of spontaneous diastolic ery of the resting membrane potential buy nimotop 30 mg. The maximum rate of phase 0 depolariza- Serum K concentrations have a major inﬂuence on tion and the amplitude of phase 0 are depressed equally the activity of quinidine on cardiac tissue order nimotop 30mg overnight delivery. Quinidine also decreases lular K concentrations antagonize the depressant ef- atrial muscle excitability in such a way that a larger cur- fects of quinidine on membrane responsiveness, rent stimulus is needed for initiation of an active re- whereas high extracellular K concentrations increase sponse. This dependency may explain why hypokalemic patients are often unresponsive to the antiarrhythmic A-V Node effects of quinidine and are prone to develop cardiac Both the direct and indirect actions of quinidine are rhythm disorders. The indirect (anticholinergic) properties of Electrocardiographic Changes quinidine prevent both vagally mediated prolongation At normal therapeutic plasma concentrations, quinidine of the A-V node refractory period and depression of prolongs the PR, the QRS, and the QT intervals. QRS conduction velocity; these effects lead to enhancement and QT prolongations are more pronounced with quini- of A-V transmission. The logical actions on the A-V node are to decrease con- magnitude of these changes is related directly to the duction velocity and increase the ERP. His-Purkinje System and Ventricular Muscle Hemodynamic Effects Quinidine can depress the automaticity of ventricu- lar pacemakers by depressing the slope of phase 4 de- Although myocardial depression is not a problem in pa- polarization. Depression of pacemakers in the His- tients with normal cardiac function, in patients with Purkinje system is more pronounced than depression of compromised myocardial function, quinidine may de- sinoatrial node pacemaker cells. The These adverse effects are generally dose related and re- depressant effects of quinidine on the cardiovascular versible with cessation of therapy. In some patients, system are most likely to occur after IV administration, quinidine administration may bring on thrombocytope- and therefore, quinidine should not be employed rou- nia due to the formation of a plasma protein–quinidine tinely in the emergency treatment of arrhythmias. Although platelet counts re- myocardial contractility and to decrease peripheral vas- turn to normal on cessation of therapy, administration cular resistance, parenteral administration of quinidine of quinidine or quinine at a later date can cause the is seldom indicated. The cardiac toxicity of quinidine includes A-V and Pharmacokinetics intraventricular block, ventricular tachyarrhythmias, and depression of myocardial contractility. Ventricular The pharmacokinetic characteristics of quinidine: arrhythmia induced by quinidine leading to a loss of consciousness has been referred to as quinidine syn- Oral bioavailability Almost complete absorption cope. This devastating side effect is more common in Onset of action 1–3 hours women than in men and may occur at therapeutic or Peak response 1–2 hours subtherapeutic plasma concentrations. Duration of action 6–8 hours Large doses of quinidine can produce a syndrome Plasma half-life 6 hours known as cinchonism, which is characterized by ringing Primary route of Hepatic; active metabolite in the ears, headache, nausea, visual disturbances or metabolism blurred vision, disturbed auditory acuity, and vertigo. Primary route of 10–50% renal (unchanged) Larger doses can produce confusion, delirium, hallucina- excretion tions, or psychoses. Quinidine can decrease blood glucose Therapeutic serum 2–4 g /mL concentrations, possibly by inducing insulin secretion. For this reason, digitalis should be used before quinidine when one is attempting Drug Interactions to convert atrial ﬂutter or atrial ﬁbrillation to normal si- Quinidine can increase the plasma concentrations of nus rhythm. Gastrointestinal, central nervous system Adverse Effects (CNS), or cardiac toxicity associated with elevated The most common adverse effects associated with digoxin concentrations may occur. Quinidine and digoxin quinidine administration are diarrhea (35%), upper can be administered concurrently; however, a downward gastrointestinal distress (25%), and light-headedness adjustment in the digoxin dose may be required. Cimetidine Procainamide can decrease the occurrence of all inhibits the hepatic metabolism of quinidine. Phenytoin, types of active ventricular dysrhythmias in patients with rifampin, and barbiturates increase the hepatic metabo- acute myocardial infarction who are free from A-V dis- lism of quinidine and reduce its plasma concentrations. About 90% of patients with ventricular prema- Procainamide ture contractions and 80% of patients with ventricular tachycardia respond to procainamide administration. Procainamide (Pronestyl, Procan SR) is a derivative of Although the spectrum of action and electrophysio- the local anesthetic agent procaine. Procainamide has a logical effects of quinidine and procainamide are simi- longer half-life, does not cause CNS toxicity at thera- lar, the relatively short duration of action of pro- peutic plasma concentrations, and is effective orally. Adverse Effects Electrophysiological Actions Acute cardiovascular reactions to procainamide admin- istration include hypotension, A-V block, intraventricu- Table 16.
Reflex Activities Although reflex pathways may be quite complex buy discount nimotop 30mg, a simple reflex is a rapid buy cheap nimotop 30 mg, uncompli- cated purchase 30 mg nimotop otc, and automatic response involv- ing very few neurons. Reflexes are spe- cific; a given stimulus always produces the same response. When you fling out an arm or leg to catch your balance, withdraw from a painful stimulus, or blink to avoid an object approaching your eyes, you are experiencing reflex Figure 9-13 Typical reflex arc. Contraction of the biceps brachii results in flexion of the arm at the elbow. Central nervous system—where im- pulses are coordinated and a response is organized. One or more interneu- Table 9•2 Components of a Reflex Arc rons may carry impulses to and from the brain, may function within the COMPONENT FUNCTION brain, or may distribute impulses to Receptor End of a dendrite or specialized cell that responds to different regions of the spinal cord. Motor neuron, or efferent neuron— system response; usually requires interneurons a cell that carries impulses away Motor neuron Carries impulses away from the CNS toward the from the CNS. Motor impulses leave effector, a muscle, or a gland Effector A muscle or gland outside the CNS that carries out a the cord through the ventral horn of response the spinal cord gray matter. Injection of anesthetic into the epidural space in the lumbar region of the spine (an “epidural”) is 2 Sensory often used during labor and childbirth. This process of demyelination (quadriceps muscle) slows the speed of nerve impulse conduction and disrupts nervous system communication. Genetic makeup, in combination with environmental fac- tors, may trigger MS. Some research suggests that a prior viral or bacterial infection, even one that occurred many Figure 9-14 The patellar (knee-jerk) reflex. ZOOMING IN How many MS is the most common chronic CNS disease of young total neurons are involved in this spinal reflex? The disease affects women transmitter is released at the synapse shown by number 5? MS progresses at different rates depending on the contracting, is one example of a spinal reflex. If you tap individual, and it may be marked by episodes of relapse the tendon below the kneecap (the patellar tendon), the and remission. At this point, no cure has been found for muscle of the anterior thigh (quadriceps femoris) con- MS, but drugs that stop the autoimmune response and tracts, eliciting the knee-jerk reflex (Fig. Such stretch reflexes may be evoked by appropriate tap- Amyotrophic (ah-mi-o-TROF-ik) lateral sclerosis is a ping of most large muscles (such as the triceps brachii in the disorder of the nervous system in which motor neurons arm and the gastrocnemius in the calf of the leg). The progressive destruction causes muscle flexes are simple and predictable, they are used in physical atrophy and loss of motor control until finally the affected examinations to test the condition of the nervous system. Poliomyelitis (po-le-o-mi-eh-LI-tis) (“polio”) is a Medical Procedures Involving the viral disease of the nervous system that occurs most com- Spinal Cord monly in children. Polio is spread by ingestion of water contaminated with feces containing the virus. It is sometimes necessary to remove the gastrointestinal tract leads to passage of the virus into a small amount of cerebrospinal fluid (CSF) from the the blood, from which it spreads to the CNS. CSF is the fluid that circu- tends to multiply in motor neurons in the spinal cord, lates in and around the brain and spinal cord. This fluid leading to paralysis, including paralysis of the breathing is taken from the space below the spinal cord to avoid muscles. Because the spinal cord is Polio has been virtually eliminated in many countries only about 18 inches long and ends above the level of through the use of vaccines against the disease—first the the hip line, a lumbar puncture or spinal tap is usually injected Salk vaccine developed in 1954, followed by the done between the third and fourth lumbar vertebrae, at Sabin oral vaccine. A goal of the World Health Organiza- about the level of the top of the hipbone. The sample tion (WHO) is the total eradication of polio by worldwide that is removed can then be studied in the laboratory vaccination programs.
In con- pressed into a tablet or the drug is incor- trast to solutions discount nimotop 30mg line, which permit direct porated into a matrix-type tablet generic nimotop 30mg with mastercard. Con- absorption of drug (A nimotop 30mg with visa, track 3), the use trary to timed-release capsules (Span- of solid dosage forms initially requires sules®), slow-release tablets have the ad- tablets to break up and capsules to open vantage of being dividable ad libitum; (disintegration) before the drug can be thus, fractions of the dose contained dissolved (dissolution) and pass within the entire tablet may be admin- through the gastrointestinal mucosal istered. Because disintegra- This kind of retarded drug release tion of the tablet and dissolution of the is employed when a rapid rise in blood drug take time, absorption will occur level of drug is undesirable, or when ab- mainly in the intestine (A, track 2). In sorption is being slowed in order to pro- the case of a solution, absorption starts long the action of drugs that have a in the stomach (A, track 3). For acid-labile drugs, a coating of wax or of a cellulose acetate polymer is used to prevent disintegration of solid dosage forms in the stomach. Accord- ingly, disintegration and dissolution will take place in the duodenum at nor- mal speed (A, track 1) and drug libera- tion per se is not retarded. The liberation of drug, hence the site and time-course of absorption, are subject to modification by appropriate production methods for matrix-type tablets, coated tablets, and capsules. In the case of the matrix tablet, the drug is incorporated into a lattice from which it can be slowly leached out by gastroin- testinal fluids. As the matrix tablet undergoes enteral transit, drug libera- tion and absorption proceed en route (A, track 4). In the case of coated tablets, coat thickness can be designed such that release and absorption of drug occur ei- ther in the proximal (A, track 1) or distal (A, track 5) bowel. Thus, by matching dissolution time with small-bowel tran- Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Drug Administration 11 Administration in form of Enteric- Tablet, Drops, Matrix Coated coated capsule mixture, tablet tablet with tablet effervescent delayed solution release 1 2 3 4 5 A. Oral administration: drug release and absorption Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. The resulting oily Pulmonary (2), Rectal or Vaginal (3), film spreads over the mucosa and en- and Cutaneous Application ables the drug to pass into the mucosa. For intravenous, intramuscular, or Transdermal drug delivery subcutaneous injections, drugs are of- systems are pasted to the epidermis. An injectable solu- tage that a drug depot is attached non- tion must be free of infectious agents, invasively to the body, enabling the pyrogens, or suspended matter. It drug to be administered in a manner should have the same osmotic pressure similar to an infusion. Drugs amenable and pH as body fluids in order to avoid to this type of delivery must: (1) be ca- tissue damage at the site of injection. From ampules for multiple or sin- (3) possess a wide therapeutic margin gle use, the solution is aspirated via a (dosage not adjustable). The cartridge am- pule is fitted into a special injector that enables its contents to be emptied via a needle. An infusion refers to a solution being administered over an extended period of time. Drugs can be sprayed in aerosol form onto mucosal surfaces of body cav- ities accessible from the outside (e. An aerosol results when a drug solution or micronized powder is reduced to a spray on being driven through the nozzle of a pressur- ized container. Mucosal application of drug via the rectal or vaginal route is achieved by means of suppositories and vaginal tablets, respectively. On rectal applica- tion, absorption into the systemic circu- lation may be intended. With vaginal tablets, the effect is generally confined to the site of application. Usually the drug is incorporated into a fat that solid- ifies at room temperature, but melts in Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Drug Administration 13 Sterile, iso-osmolar Ampule Cartridge Propellant gas 1 – 20 ml ampule 2 ml Drug solution With and without Often with fracture ring preservative Jet nebulizer 2 35 ºC Vaginal tablet Suppository Multiple-dose Infusion vial 50 – 100 ml, solution always with 500 – 1000 ml preservative 1 35 ºC Melting point 3 Backing layer Drug reservoir Adhesive coat Paste Ointment Transdermal delivery system (TDS) Drug release Powder Ointment TDS Time 12 24 h 4 A. Preparations for parenteral (1), inhalational (2), rectal or vaginal (3), and percutaneous (4) application Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved.
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