Beta blockers clinical effects

For some of these diseases, such as hypertension and heart disease, drugs such as ACE inhibitors and beta-blockers are available for treatment. For some other diseases, such as Alzheimer s disease, more effective drugs have yet to be discovered. For stroke, two late stage (Phase III) trials of NXY-059 and desmoteplase failed to meet the trial criteria. Other clinical trials in progress for ischemic stroke are presented in Table 11.1. 

In vitro, diphenhydramine inhibits CYP2D6 and therefore may interact with beta-blockers, some antidepressants such as desipramine, and antipsychotics such as promethazine. In a study by Hamelin et al. (2000), diphenhydramine was found to inhibit the metabolism of metoprolol in phenotypically extensive metabolizers, but not in poor metabolizers. The effects where observed clinically as well as pharma-cokinetically. 

Beta blockers without intrinsic sympathomimetic activity (eg, metoprolol, propranolol, atenolol) are effective therapeutic adjuncts in the management of thyrotoxicosis since many of these symptoms mimic those associated with sympathetic stimulation. Propranolol has been the 3 blocker most widely studied and used in the therapy of thyrotoxicosis. Beta blockers cause clinical improvement of hyperthyroid symptoms but do not typically alter thyroid hormone levels. Propranolol at doses greater than 160 mg/d may also reduce T3 levels approximately 20% by inhibiting the peripheral conversion of T4 to T3. 

Beta-blockers have various effects on glucose metabolism, but these are usually too small to be of clinical significance (288,289). However, beta-blockers can block the adrenergic symptoms of hypoglycemia. 

Beta antagonists are generally administered for their effect on the beta-1 receptors that are located on the heart.31 When stimulated, these receptors mediate an increase in cardiac contractility and rate of contraction. By blocking these receptors, beta antagonists reduce the rate and force of myocardial contractions. Consequently, beta antagonists are frequently used to decrease cardiac workload in conditions such as hypertension and certain types of angina pectoris. Beta blockers may also be used to normalize heart rate in certain forms of cardiac arrhythmias. Specific clinical applications of individual beta blockers are summarized in Table 20-2. 

Currently, a number of beta blockers are used clinically the selection of a specific agent depends on factors such as cardioselectivity, duration of action (half-life), and several other ancillary properties of each drug.110 Certain beta blockers, for instance, produce added effects such as mild peripheral vasodilation or stabilization of cardiac membranes that can be beneficial in treating certain cardiovascular condi-... 

Alpha-adrenergic antagonists are used primarily as antihypertensive drugs because of their ability to block vascular alpha-1 receptors. Beta-adrenergic antagonists (beta blockers) are administered primarily for their inhibitory effects on myocardial function and are used in the prevention and treatment of hypertension, angina pectoris, arrhythmias, and myocardial reinfarction. Many of the drugs introduced in this chapter are discussed further in chapters that deal with the specific clinical conditions (e.g., hypertension, asthma, and other disorders). 

Kawakami, K., Nagatomo, T., Abe, H., Kikuchi, K., Takemasa, H., Anson, B.D., Delisle, B.P., January, C.T., Nakashima, Y. Comparison of HERG channel blocking effects of various beta-blockers -implication for clinical strategy. Br J Pharmacol 147 (2006) 642-652. 

BETA-BLOCKERS CYTOTOXICS Imatinib may cause an t in plasma concentrations of metoprolol, propanolol and timolol, with a risk of toxic effects Imatinib is a potent inhibitor of CYP2D6 isoenzymes, which metabolize beta-blockers Monitor for clinical efficacy and toxicity of beta-adrenergic blockers... 

ACEBUTOLOL, ATENOLOL, BETAXOLOL, BISOPROLOL, METOPROLOL, PROPANOLOL CICLOSPORIN t risk of hyperkalaemia Beta-blockers cause an efflux of potassium from cells, and side-effect has been observed during cidosporin therapy Monitor serum potassium levels during co-administration > For signs and symptoms of hyperkalaemia, see Clinical Features of Some Adverse Drug Interactions, Hyperkalaemia... 

Systemic beta-blockers are used extensively far the treatment of hypertension and other cardiovascular disorders. Of the available oral beta-blockers, atenolol, metoprolol, nadolol, pindolol, propranolol, and timolol have been documented to produce a dose-dependent reduction in lOP. The ocular hypotensive effect associated with systemically administered beta-blockers can be compared with that achieved with topically applied beta-blockers such as timolol. Although specific studies have not been conducted with most of the remaining systemic beta-blockers, these agents might also be expected to reduce lOP at clinically useful doses. 

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