Myocardial infarction after propranolol withdrawal

Alterations in vascular sensitivity to vasoactive agents after discontinuation of propranolol in SHR

Spontaneously hypertensive rats (SHR) were treated with propranolol (P) (70 mg/kg) daily for 2 or 4 weeks and then the effects of vasoactive substances on blood pressure were studied 10 or 36 hours after the last dose of P. At 10 hours after the last dose of P, vascular hyperresponsiveness to norepinephrine (NE) and angiotensin II (AII) had largely disappeared, but the hypotensive action of isoproterenol and prostacyclin was still blocked in P-treated SHR. An increase of cyclic AMP (cAMP) in response to isoproterenol was blocked in the thoracic aorta. Similarly, an increase of circulating cAMP and blood glucose in response to epinephrine (E) was depressed. At 36 hours after the last dose of P, an elevation of blood pressure in response to NE and AII was significantly reduced in P-treated SHR. Although basal blood pressure with or without anesthesia was the same in P-treated SHR and control SHR, a decrease of blood pressure in response to isoproterenol and prostacyclin was augmented significantly in P-treated SHR. This was also true in normal rats similarly treated. In addition, an increase of cAMP in the thoracic aorta in response to isoproterenol and prostacyclin was augmented significantly in P-treated SHR. An increase in blood glucose in response to E was not blocked, but an increase of circulating cAMP in response to E was blocked. These data suggest that cAMP synthesis in the vessels is somehow related to the production of peculiar vascular responses during escape from P action.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha- and beta-adrenergic receptor subtypes properties, distribution and regulation

The effects of catecholamines in the central and peripheral nervous systems appear to be mediated through interactions with 2 major classes of receptor: alpha-adrenoceptors and beta-adrenoceptors. Subtypes of both alpha- and beta-adrenoceptors exist. In the periphery, alpha 1-receptors are located postsynaptically, mediating the excitatory effects of catecholamines at alpha-receptors. alpha 2-Adrenoceptors, on the other hand, are autoreceptors involved in the regulation of noradrenaline (norepinephrine) release. In the central nervous system, both alpha 1- and alpha 2-receptors exist on postsynaptic cells; there are also 2 principal subtypes of beta-adrenoceptors. beta 1-Receptors have a high affinity for both noradrenaline and adrenaline (epinephrine) and are found in the heart, brain, and adipose tissue. beta 2-Receptors have a low affinity for noradrenaline and are involved in mediation of relaxation of vascular and other smooth muscles and in many of the metabolic effects of catecholamines. A variety of effector systems have been implicated in the actions of catecholamines. Most, though not all, of the effects of catecholamines at beta-receptors are mediated through activation of adenyl cyclase and increases in cyclic AMP accumulation. The effects of catecholamines at alpha-receptors generally involve other second messenger systems. Thus, in at least some systems, stimulation of alpha 1-adrenoceptors mediates increases in phosphoinositide breakdown, while alpha 2-adrenoceptors appear to act through inhibition of adenyl cyclase activity. The pharmacological effects of alpha- and beta-adrenoceptors were initially characterised by measuring responses observed in intact preparations. The advent of the use of radioligand binding techniques has allowed direct approaches to the characterisation of receptor properties. The use of radioligands makes it possible to determine the affinities of receptors for specific ligands, and it is possible to determine the density of receptors in a tissue. Finally, in vitro assays serve as a means through which receptors can be followed during solubilisation, isolation, and reconstitution. Several ligands are now available for the study of alpha- and beta-adrenoceptors. In general, relatively selective radioligands are available for the study of alpha-receptors. Thus, 3H-WB 4101 and 3H-prazosin are selective ligands for alpha 1-receptors; the ligand 125I-IBE 2254 also shows high selectivity for alpha 1-receptors. 3H-Yohimbine and 3H-rauwolscine are selective antagonists for the labelling of alpha 2-receptors and 3H-clonidine is a selective agonist used for studying alpha 2-receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Withdrawal of beta-blocking drugs

Our early observations indicated that when treatment was changed from propranolol to placebo, anginal patients experienced a higher incidence of chest pain during the first week of placebo treatment compared to the second week. Since then, there have been several reports of myocardial infarction and sudden death occurring when propranolol therapy has been stopped. However, more formal hospital studies have indicated that ischemia from propranolol withdrawal is relatively infrequent. Studies in normal subjects and hypertensive patients have shown an increase in beta-receptor sensitivity as suggested by increased responsiveness to isoprenaline after propranolol withdrawal. Some investigators have found an increase in free triiodothyronine levels. Catecholamine levels do not appear to be raised. Other relevant factors in ischemic patients might be a reversal of the favorable rightward shift of the oxyhemoglobin dissociation curve or a reversal of reduced platelet aggregation produced by propranolol. Last, propranolol withdrawal in patients who have received the drug for a considerable period might unmask a withdrawal in patients who have received the drug for a considerable period might unmask a progression of the disease process, so that in the absence of beta blockade oxygen supply is inadequate to meet the requirements of relatively ischemic areas even at rest. Whether all beta blockers are similar to propranolol in this regard is unknown. We are examining, in normal volunteers, the sensitivity of the beta receptor after the withdrawal of atenolol, pindolol, or propranolol, administered for at least 2 weeks after final dose adjustment to levels sufficient to produce maximum inhibition of exercise tachycardia. The sensitivity of the beta receptor is being assessed by the response of bolus injections of isoprenaline and the response to exercise tachycardia.

High-dose analgesic anesthesia with morphine or sufentanil in propranolol-treated dogs

In propranolol-pretreated dogs (2 mg . kg -1) the immediate cardiovascular effects of sufentanil (0.01 mg . kg -1) or morphine (4 mg . kg -1) were compared. Besides a 40% decrease in cardiac index (CI), sufentanil and morphine initiated quite different hemodynamic changes. Sufentanil did not significantly change mean arterial pressure (MAP), central venous pressure (CVP) and mean pulmonary artery pressure (MPAP), while the pulmonary capillary wedge pressure (PCWP) increased by 50%. After morphine, MAP declined significantly by about 65%, and significant decreases in MPAP (14%) and PCWP (33%) were also observed. Propranolol reduced heart rate by 16%, and morphine caused no further reduction in HR. A significant decrease of about 30% was seen in HR after sufentanil. Sufentanil significantly raised systemic vascular resistance index (SVRI) by 15%, whereas morphine decreased it by 32%. Pulmonary vascular resistance index (PVRI) was unchanged after sufentanil, but significantly increased after morphine. Right ventricular stroke work index (RVSWI) was unaffected by both analgesics, and morphine decreased left ventricular work index (LVSWI) significantly by 80%. Oxygen transport index declined significantly after both analgesics. Sufentanil reduced oxygen consumption by 20%, while morphine left this parameter unaffected. We conclude that the administration of high-dose sufentanil leads to a stable circulation, even when a total beta-blockade exists.

Adverse effects of sudden withdrawal of antihypertensive medication

The withdrawal syndrome following abrupt discontinuation of antihypertensive medication may consist of symptoms of sympathetic overactivity alone or in association with a rapid increase in blood pressure. The phenomenon may occur after discontinuation of any of a variety of drugs. Although the exact incidence of the syndrome is not known, it appears to be rare, at least in patients receiving standard doses of antihypertensive medications. The best treatment is prevention. However, if the syndrome does occur, reinstitution of the previously discontinued medication usually is successful in controlling the withdrawal events.

Elevation of beta-adrenergic receptor density in human lymphocytes after propranolol administration

Abrupt withdrawal after the chronic administration of propranolol has resulted in clinical syndromes that suggest adrenergic hypersensitivity. The effect of propranolol administration and withdrawal on beta-adrenergic receptors was studied in human lymphocyte membranes. Receptor density was quantitated by direct binding assays with the radioligand [125I]iodohydroxybenzylpindolol. Administration of propranolol (160 mg/d) for 8 d resulted in trough plasma levels of approximately 35 ng/ml. By day 5 of propranolol administration the density of beta-adrenergic receptors had increased 43 +/- 4% (P less than 0.01) above pretreatment levels. Abrupt withdrawal of propranolol was followed by the disappearance of propranolol from the plasma within 24 h. The density of beta-adrenergic receptors did not return to pretreatment level for several days. Physiologic supersensitivity of beta-adrenergic receptor-mediated responses was suggested by the appearance of significant increases in the orthostatic change in heart rate (P less than 0.05) and the orthostatic change in the heart rate-systolic blood pressure product (P less than 0.01) during the first 48 h after propranolol withdrawal. These data show that propranolol administration leads to an increase in the density of beta-adrenergic receptors in human tissue. The results are consistent with the hypothesis that some of the untoward effects observed after abrupt discontinuation of propranolol are caused by beta-receptor-mediated adrenergic hypersensitivity.

Timolol eye drops: bradycardia or tachycardia?

26 eyes of 14 patients--8 with primary open angle glaucoma, 6 glaucoma suspects--were treated for at least 6 months with either twice daily timolol 0.25% in both eyes or twice daily timolol 0.50% in one eye. None of the patients received concomitant local or oral drugs. Special attention was paid to tachyphylaxis and to blood pressure and pulse rate. We could detect a slight although not significant tendency to tachyphylaxis (1-2 mm Hg) after 1 week of timolol treatment. It takes at least 1-2 weeks to reach the initial I.O.P. level after withdrawal of timolol therapy. Blood pressure did not change significantly. The pulse rate showed a slight although not significant tendency to decrease (a few beats/minute), but we detected a reflex tachycardia (10 beats/minute) after withdrawal of timolol therapy which was very significant. This rebound phenomenon has not been referred to in the literature. It seems reasonable to conclude that one should take care in treating glaucoma patients with concomitant arrhythmias with timolol eye drops.

The abrupt discontinuation of antihypertensive treatment

Although deleterious events following abrupt withdrawal of antihypertensive treatment are relatively uncommon, considerable attention has recently been focused on this problem. A withdrawal syndrome may occur after termination of almost all types of antihypertensive drugs, but most experience has been with the centrally acting agents and with beta-adrenoreceptor blockers. Abrupt discontinuation of high doses of centrally acting drugs such as alpha-methyldopa, clonidine, and guanabenz can produce a syndrome of sympathetic overactivity that includes agitation, headache, sweating, and nausea and less commonly can provoke rapid upswings in blood pressure. If beta blockers are suddenly stopped, a similar pattern can occur that may be related to excessive activity of thyroid hormones as well as sympathetic factors. Additionally, patients with ischemic heart disease may be susceptible to an acute exacerbation of their cardiac disease when beta-blocker treatment is stopped. It seems likely that discontinuation events can be particularly severe when combinations of different types of antihypertensive medications are sud-disease when betablocker treatment is denly stopped. This problem can be dealt with by educating patients to avoid sudden drug cessation and when elective discontinuation is planned, by gradual dose reduction.

Acute central chest pain in the elderly. A review of 296 consecutive hospital admissions during 1976 with particular reference to the possible role of beta-adrenergic blocking agents in inducing substernal pain

Two hundred and ninety-six patients were admitted to geriatric medical beds in Cardiff in 1976 with acute central chest pain. One hundred and eighty-six (63 per cent) had a confirmed acute myocardial infarction. Of the 37 per cent without evidence of cardiac infarction, 32 per cent were on beta-blocking drugs. The possible role of adrenergic blocking agents in producing acute central chest pain is discussed.

Hemodynamic and metabolic response after abrupt uithdrawal of long-term propranolol

Because the mechanism of adverse reactions to abrupt withdrawal of propranolol in patients with coronary disease is an enigma, we studied the effect of cessation of propranolol on beta receptor reactivity to catecholamine stimulation. Heart rate and maximum rate of rise of left ventricular pressur (dP/dt max) during isoproterenol infusions and plasma free fatty acids (FFAs) after epinephrine infusions were measured in six conscious dogs before, during and after four weeks of oral propranolol (40 mg p.o. q8h). Rises in heart rate, dP/dt max and FFAs were blocked during propanolol administration. Twenty-four hours after withdrawal from propranolol, heart rate and dP/dt max responses remained significantly attenuated, although FFA responses were at premedication levels. The 72-hour, 96-hour and one week postmedication responses did not differ from premedication values. Thus, partial beta blockade of the heart was still present at 24 hours and no evidence of heightened beta receptor sensitivity was detected on repeated study one week after withdrawal from a long-term, high dose propranolol regimen.

Propranolol rebound--a retrospective study

To assess the effects of sudden withdrawal of propranolol on inpatients with coronary artery disease, 102 patients admitted for cardiac catheterization were evaluated. Criteria for inclusion in the study were angiographically documented coronary artery disease, propranolol therapy at a mean daily dose of at least 80 mg and abrupt discontinuation of propranolol therapy before catheterization. There were 55 patients (mean age 52.5) who discontinued propranolol therapy (mean daily dose 127 mg) and a control group of 47 patients (mean age 53) who continued to receive propranolol (mean daily dose 143 mg). The criteria for morbidity were death, myocardial infarction or change in pain pattern. In the withdrawal group there were no deaths, one myocardial infarction judged to be related to catheterization and only one instance of a change in pain pattern. Thus, propranolol rebound appears to occur infrequently among hospitalized patients with reduced activity.

Myocardial revascularization in patients receiving long-term propranolol therapy

Twenty-seven patients receiving long-term propranolol therapy underwent myocardial revascularization to relieve stable or unstable angina. The patients were randomly divided into two groups, one (Group 1) in which propranolol was discontinued 48 hours prior to operation and one (Group 2) in which patients received a final dose of propranolol 1 to 2 hours prior to operation. Several physiological variables were compared, and there was no statistically significant difference between the groups except for a slower pulse rate in Group 2 patients. Although the patients in Group 1 showed a greater frequency of hypertension before bypass, the incidence of postoperative complications and perioperative myocardial infarction was the same for both groups. The findings of this study indicate that myocardial revascularization is safe even if propranolol is administered up to 1 or 2 hours before operation.

Propranolol therapy in patients undergoing myocardial revascularization

The records of 185 consecutive patients having myocardial revascularization were reviewed with regard to preoperative administration of propranolol and intraoperative or postoperative complications. Tachycardia and hypertension before cardiopulmonary bypass were slightly more common in patients never taking propranolol or those who had discontinued it for more than 48 hours before operation. There was no statistically significant difference in the incidence of postbypass hypotension among patients who took propranolol within 24 hours of operation, those who discontinued it more than 24 hours before operation, and those who never took the drug. Operative mortality was not significantly different among patients who received propranolol within 48 hours of operation (3%), those who never took it and those who discontinued it more than 48 hours before operation (4%). Early in the series, five patients had an acute myocardial infarction within 48 hours after routine preoperative withdrawal of propranolol. Because complete withdrawal of propranolol in patients with unstable angina pectoris may lead to acute myocardial infarction, we recommend gradual withdrawal of the drug during 48 hours before operation. If this is not possible because anginal pain recurs or intensifies, then reduced doses may be given safely up to 10 hours before revascularization, provided that the patient is a satisfactory candidate for bypass and that adequate myocardial revascularization can be accomplished.

Pharmacologic therapy of ventricular arrhythmias

To treat patients with ventricular arrhythmias properly, one must characterize the arrhythmia, define the underlying heart disease and look for and treat reversible causes. When arrhythmias are suitable for pharmacologic suppression, it is necessary to predefine therapeutic goals, then carefully document that the drug accomplishes these goals. Knowledge of a drug's metabolism, excretion, active metabolites and plasma protein binding is often required for full understanding of its clinical effect. Pharmacokinetic principles require that antiarrhythmic drugs be given on a rigid schedule and that plasma drug levels be frequently determined. Use of compartment models and the principle of superposition can enable one to achieve and maintain therapeutic drug concentrations while avoiding toxic side effects. The drugs commonly used to treat arrhythmias, lidocaine, propranolol, procainamide, diphenylhydantoin and quinidine, as well as some newer agents, have specific pharmacokinetics and toxic effects that must be understood.