Beta blockade and chest pain in acute myocardial infarction

Aspects on the intensity and the relief of pain in the prehospital phase of acute coronary syndrome: experiences from a randomized clinical trial

The primary aim of this study was to evaluate the pain relief and tolerability of two pain-relieving strategies in the prehospital phase of presumed acute coronary syndrome (ACS), and the secondary aim was to assess the relationship between the intensity and relief of pain and heart rate, blood pressure, and ST deviation. Patients with chest pain judged as caused by ACS were randomized (open) to either metoprolol 5 mg intravenously (i.v.) three times at 2-min intervals (n = 84; metoprolol group) or morphine 5 mg i.v. followed by metoprolol 5 mg three times i.v (n = 80; morphine group). Pain was assessed on a 10-grade scale before randomization and 10, 20, and 30 min thereafter. The mean pain score decreased from 6.5 at randomization to 2.8 30 min later, with no significant difference between groups. The percentages with complete pain relief (pain score < or = 1) after 10, 20, and 30 min were 11, 16, and 21%, respectively, with no difference between groups. Hypotension was less frequent in the metoprolol group compared with the morphine group (0 vs. 6.3%; P=0.03), as was nausea/vomiting (7.2 vs. 24.0%; P=0.004). At randomization intensity of pain was associated with degree of ST elevation (P=0.009). The degree of pain relief over 30 min was associated with decrease in heart rate (P=0.03) and decrease in ST elevation (P=0.01).In conclusion, in the prehospital phase of presumed ACS, neither a pain-relieving strategy including an anti-ischemic agent alone nor an analgesic plus anti-ischemic strategy in combination resulted in complete pain relief. Fewer side effects were found with the former strategy. Other pain-relieving strategies need to be evaluated.

The pharmacokinetics of lignocaine and beta-adrenoceptor antagonists in patients with acute myocardial infarction

Lignocaine (lidocaine) and beta-adrenoceptor antagonists are widely used after acute myocardial infarction. The therapeutic value of these agents depends on the achievement and maintenance of safe and effective plasma concentrations. Lignocaine pharmacokinetics after acute myocardial infarction (MI) are controlled by a number of variables. The single most important is left ventricular function, which affects both volume of distribution and plasma clearance. Other major factors include bodyweight, age, hepatic function, the presence of obesity, and concomitant drug therapy. Lignocaine is extensively bound to alpha 1-acid glycoprotein, a plasma protein which is also an acute phase reactant. Increases in alpha 1-acid glycoprotein concentration occur after an acute MI, decreasing the free fraction of lignocaine in the plasma and consequently decreasing total plasma lignocaine clearance without altering the clearance of non-protein-bound lignocaine. Complex changes in lignocaine disposition occur with long term infusions, and therefore early discontinuation of lignocaine infusions (within 24 hours) should be undertaken whenever possible. Because the risk of ventricular tachyarrhythmia declines rapidly after the onset of an acute MI, lignocaine therapy can be rationally discontinued within 24 hours in most patients. Lignocaine has a narrow toxic/therapeutic index, so that pharmacokinetic factors are critical in dose selection. In contrast, beta-adrenoceptor antagonists' adverse effects are more related to the presence of predisposing conditions (such as asthma, heart failure, bradyarrhythmias, etc.) than to plasma concentration. The pharmacokinetics of beta-adrenoceptor antagonists are important to help assure therapeutic efficacy, to provide information about the anticipated time course of drug action, and to predict the possible role of ancillary drug effects (such as direct membrane action) and loss of cardioselectivity. Lipid solubility is the main determinant of the pharmacokinetic properties of a beta-adrenoceptor antagonist. Lipid-soluble agents like propranolol and metoprolol are well absorbed orally, and undergo rapid hepatic metabolism, with important presystemic clearance and a short plasma half-life. Water-soluble drugs like sotalol, atenolol, and nadolol are less well absorbed, and are eliminated more slowly by renal excretion. Clinical assessment of beta-adrenoceptor antagonism is more valuable than plasma concentration determinations in evaluating the adequacy of the dose of a particular beta-adrenoceptor antagonist.(ABSTRACT TRUNCATED AT 400 WORDS)