Tachycardia, caffeine

Adenosine is produced by many tissues, mainly as a byproduct of ATP breakdown. It is released from neurons, glia and other cells, possibly through the operation of the membrane transport system. Its rate of production varies with the functional state of the tissue and it may play a role as an autocrine or paracrine mediator (e.g. controlling blood flow). The uptake of adenosine is blocked by dipyridamole, which has vasodilatory effects. The effects of adenosine are mediated by a group of G protein-coupled receptors (the Gi/o-coupled Ai- and A3 receptors, and the Gs-coupled A2a-/A2B receptors). Ai receptors can mediate vasoconstriction, block of cardiac atrioventricular conduction and reduction of force of contraction, bronchoconstriction, and inhibition of neurotransmitter release. A2 receptors mediate vasodilatation and are involved in the stimulation of nociceptive afferent neurons. A3 receptors mediate the release of mediators from mast cells. Methylxanthines (e.g. caffeine) function as antagonists of Ai and A2 receptors. Adenosine itself is used to terminate supraventricular tachycardia by intravenous bolus injection. 

Caffeine is a mild to potent CNS stimulant, with the degree of its stimulating effect dependent on the dose administered. Caffeine stimulates the CNS at all levels, including the cerebral cortex, die medulla, and the spinal cord. Caffeine has mild analeptic (respiratory stimulating) activity. Other actions include cardiac stimulation (which may produce tachycardia), dilatation of coronary and peripheral blood vessels, constriction of cerebral blood vessels, and skeletal muscle stimulation. Caffeine also has mild diuretic activity. 

A cnp of coffee can contain 50-150 mg of caffeine, and cola drinks can have 35-55 mg. Theophiline,l,3-dimethylxanthine, a principal, characteristic alkaloid of tea, and theobromine, 3,7-dimethylxanthine (23.3.19), a principal alkaloid of cocoa, are among a number of methylxanthines. In small doses, caffeine is a relatively weak psychostimulant and is used for increasing awareness as well as for relieving headaches associated with blood flow disorders of the brain. Caffeine has a stimulatory effect on the respiratory and vasomotor centers, and it stimnlates centers of the vagus nerve. It has a direct stimulatory effect on the myocardium, and in large doses can cause tachycardia and arrhythmia. 

Patients with cardiovascular disease (including hypertension), diabetes (risk of hyperglycemia), pregnancy (uterine contractions), prostatism, and anxiety disorders are among those who should not take ma huang at any dose. Drug-herb interactions occur with MAOIs (hypertensive crisis), phenoth-iazines (tachycardia, hypotension), (3-blockers (hypertension) and theophylline (increased CNS effects). Of course, caffeine and other stimulants have an additive effect. 

At high doses, caffeine can cause arrhythmias, palpitations, and tachycardia. 

Adenosine is a nucleoside that occurs naturally throughout the body. Its half-life in the blood is less than 10 seconds. Its mechanism of action involves activation of an inward rectifier K+ current and inhibition of calcium current. The results of these actions are marked hyperpolarization and suppression of calcium-dependent action potentials. When given as a bolus dose, adenosine directly inhibits atrioventricular nodal conduction and increases the atrioventricular nodal refractory period but has lesser effects on the sinoatrial node. Adenosine is currently the drug of choice for prompt conversion of paroxysmal supraventricular tachycardia to sinus rhythm because of its high efficacy (90-95%) and very short duration of action. It is usually given in a bolus dose of 6 mg followed, if necessary, by a dose of 12 mg. An uncommon variant of ventricular tachycardia is adenosine-sensitive. The drug is less effective in the presence of adenosine receptor blockers such as theophylline or caffeine, and its effects are potentiated by adenosine uptake inhibitors such as dipyridamole. 

Esmolol Theophylline, caffeine, metaproterenol Short-acting 13-blocker reverses Bi-induced tachycardia and (possibly) -induced vasodilation. Infuse 25-50 vg/kg/min IV. 

Toxicants may have three effects on pulse rate bradycardia (decreased rate), tachycardia (increased rate), and arrhythmia (irregular pulse). Alcohols may cause either bradycardia or tachycardia. Amphetamines, belladonna alkaloids, cocaine, and tricyclic antidepressants (see imi-primine hydrochloride in Figure 6.12) may cause either tachycardia or arrhythmia. Toxic doses of digitalis may result in bradycardia or arrhythmia. The pulse rate is decreased by toxic exposure to carbamates, organophosphates, local anesthetics, barbiturates, clonidine, muscaric mushroom toxins, and opiates. In addition to the substances mentioned above, those that cause arrhythmia are arsenic, caffeine, belladonna alkaloids, phenothizine, theophylline, and some kinds of solvents. 

Cardiovascular system. Both caffeine and theophylline directly stimulate the myocardium and cause increased cardiac output, tachycardia and sometimes ectopic beats and palpitations. This effect occurs almost at once after i.v. injection and lasts half an hour. Theophylline contributes usefuUy to the relief of acute left ventricular failure. There is peripheral (but not cerebral) vasodilatation due to a direct action of the drugs on the blood vessels, but stimulation of the vasomotor centre tends to counter this. Changes in the blood pressure are therefore somewhat unpredictable, but caffeine 250 mg (single dose) usually causes a transient rise of blood pressure of about 14/10 mmHg in occasional coffee drinkers (but has no additional effect in habitual drinkers) this effect can be used advantageously in patients with autonomic nervous system failure who experience postprandial hypotension (2 cups of coffee with breakfast may suffice for the day). In occasional coffee drinkers 2 cups of coffee (about 160 mg caffeine) per day raise blood pressure by 5/4 mmHg. Increased coronary artery blood flow may occur but increased cardiac work counterbalances this in angina pectoris. 

Insomnia, anxiety, tachycardia, and tremor are among the symptoms most commonly reported with caffeine (11). Tenseness and irritability also occur and, with high intake, symptoms resembhng those of anxiety neurosis (12). A case of caffeine psychosis has also been reported (13). Dose-response associations have not been particularly well studied, but some are known (SEDA-7, 6). Paradoxically, six cases have been reported of pathological sleepiness induced by caffeine (14). Tonic-clonic seizures occurred postpartum in a woman who had... 

Xanthines have been given to infants at the risk of sudden infant death sjmdrome or idiopathic apnea of prematurity (see monograph on Theophylline). About 50% of 30 infants treated with caffeine (and 12 of 18 infants treated with theophylline) had significant increases in episodes of gastroesophageal reflux (36). The authors stressed that screening for reflux should precede the administration of caffeine (and theophylline) to infants at the risk of sudden infant death syndrome. As expected, the frequency of adverse effects such as tachycardia and gastroesophageal reflux is lower with lower doses of caffeine for example 2.5 mg/kg qds (SEDA-17,1). 

Mexiletine reduces the clearance of theophylline, and this combination has been reported to cause ventricular tachycardia (52). A similar interaction tvith caffeine has been reported (53). 

An article in the Canadian Adverse Reaction Newsletter published their reporting of adverse effects caused by products containing C. aurantium from January 1, 1998 to February 28, 2004 (46). The article lists 16 reports of synephrine associated with cardiovascular events including tachycardia, cardiac arrest, ventricular fibrillation, transient collapse, and blackout. In one case, bitter orange was the sole suspected culprit. In seven others the products also contained caffeine, and in eight cases the product contained both caffeine and ephedrine. Health Canada has issued an advisory stating that synephrine may have effects similar to ephedrine and caution should be used if taking it (47). 

Cuffeine is extracted from tea dust and during coffee roasting, caffeine sublimes. Caffeine has above all a centrally stimulant (analeptic) effect on the cerebrum, produces tachycardia and has a diuretic effect. 

Sinus tachycardia Increased SA automaticity results in a sinus rhythm in excess of 100 beats per minute. Sinus tachycardia is usually not pathological and is caused by simple anxiety or stimulants (caffeine, amphetamines). 

Caffeine Neonatal respiratory distress syndrome Dizziness, insomnia, tachycardia... 

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