Nadolol in thyrotoxicosis

Effect of propranolol on heart rate variability in hyperthyroidism

Objectives

We aimed to determine the effect of propanolol on heart rate variability (HRV) in hyperthyroidism before antithyroid treatment. This was a before and after study, on ten patients presenting overt hyperthyroidism naïve to treatment. In each patient, a resting electrocardiogram was done followed by estimation of cardiac autonomic dysfunction during five maneuvers (Ewing battery tests). Long term HRV measurement was done using 24 h ambulatory electrocardiographic recording. This automatically provided estimation of HRV using SDNN and RMSSD index, LF, HF, and HF/LF ratio. After baseline investigations, 40 mg of propanolol was given twice a day for 3 days and same parameters were measured after 72 h of treatment.

Results

Our patients were aged 40 ± 10 years. Propanolol significantly reduced RR and HR interval (669 ms vs 763 ms and 91 vs 79 bpm; p < 0.01). QT and PR space were significantly extended (360 vs 384 ms and 133 vs 172 ms; p = 0.01). It increases QRS complex and blood pressure response to sustained handgrip but failed to modify previously decreased heart response to deep breathing. HRV parameters such as SDNN, RMSSD, LF, HF and sympathovagal balance estimate by HF/LF ratio remained unchanged. Although a significant reduction in heart excitability, propanolol failed to restore a good sympathovagal balance in hyperthyroidism.

Trial registration NCT03393728 “Retrospectively registered”

Serum phosphate increase during short-term beta-adrenoceptor blockade in thyrotoxicosis

We studied the changes in blood plasma electrolytes during acute and short-term treatment with four different beta-adrenergic-blocking agents in 31 patients with hyperthyroidism. Serum phosphate increased during the first four hours and remained elevated after one week both after cardioselective (acebutolol) and non-cardioselective (oxprenolol, pindolol and timolol) beta-blockade (p less than 0.05). Albumin decreased after four hours but no change was found after one week. Serum creatinine increased after one week in the acebutolol-treated group, while sodium, potassium and albumin-corrected calcium in serum did not change. The hyperphosphatemic effect may be due to blockade of beta 1-adrenoceptors, since the effect of the cardioselective acebutolol was no less than that of the non-cardioselective beta-adrenoceptor blockers.

The management of hyperthyroidism

Although effective treatments for hyperthyroidism are available, none is perfect. Particularly with respect to Graves' disease, what is needed is a therapy directed at modulating the disease process itself rather than merely reducing the synthesis and secretion of thyroid hormones in the hope that the underlying Graves' disease will remit. Greater understanding of the pathogenesis of Graves' disease, resulting from cloning of the thyrotropin receptor and better knowledge of the interactions between these receptors or other thyroid antigens and the immune system, may lead to such treatment. Broad-spectrum immunosuppression, with all its side effects, is not the answer; more focused therapies to inhibit the immune response to specific thyroid antigens may represent the treatment of the future. Meanwhile, radioiodine therapy is the most effective and convenient method of achieving long-term control of hyperthyroidism, although at the cost of hypothyroidism in many patients.

Beta-adrenergic blockade for the treatment of hyperthyroidism

PURPOSE

To review the clinical and biochemical effects of beta-adrenergic blocking drugs on hyperthyroidism.

MATERIALS AND METHODS

Studies published since 1972 were identified through a computerized search of MEDLINE and extensive searching of the bibliographies of the articles identified. Based on an understanding of the differences in beta-blocker metabolism in euthyroid and hyperthyroid patients, we reviewed the differences in pharmacokinetics and metabolic and clinical outcomes during their use in hyperthyroidism, as reported in the articles reviewed.

RESULTS

beta Blockers have been used to modify the severity of the hyperadrenergic symptoms of hyperthyroidism for the past 20 years. The clinical efficacy of these agents is affected by hyperthyroid-induced alterations in their gastrointestinal absorption, hepatic metabolism, and renal excretion. The mechanisms whereby these clinical changes are effected is unknown. The agents differ in their beta 1 cardioselectivity, membrane-stabilizing activity, intrinsic sympathomimetic activity, and lipid solubility. They do not appear to alter synthesis or secretion of thyroid hormone by the thyroid gland. Their effects on thyroxine metabolism are contradictory. Decreased thyroxine to triiodothyronine conversion is caused by some, but not all, beta blockers, and this appears to correlate with membrane-stabilizing activity. There does not appear to be any alteration in catecholamine sensitivity during beta-adrenergic blockade.

CONCLUSIONS

The principal mechanism of action of beta blockers in hyperthyroidism is to antagonize beta-receptor-mediated effects of catecholamines. beta Blockers are effective in treating hypermetabolic symptoms in a variety of hyperthyroid states. Used alone, they offer significant symptomatic relief. They are also useful adjuvants to antithyroid medications, surgery, and radioactive iodide treatment in patients with Graves' disease and toxic nodular goiters.

Propranolol and thyroid hormone metabolism

Propranolol decreases plasma T3 and increases plasma rT3 in a dose-dependent manner due to a decreased production rate of T3 and a decreased metabolic clearance rate of rT3, respectively, caused by inhibition of the conversion of T4 into T3 and of rT3 into 3,3'-T2. This inhibition of 5'-deiodination is not secondary to inhibition of thyroid hormone transport across the plasma membrane. Propranolol and its major metabolite, 4-hydroxypropranolol, are not directly responsible for these effects, but an unidentified metabolite of propranolol might be involved. beta-blockers ameliorate clinical symptoms and signs of thyrotoxicosis independent of the decrease of plasma 13, that is confined to beta-blockers with membrane-stabilizing activity, such as propranolol and alprenolol. The decrease of plasma T3, however, appears responsible for some of the metabolic responses to beta-blockers.

Changes in serum phosphate during beta-blockade in healthy men are not due to changes in the renal handling of phosphate

Serum parathyroid hormone (PTH), phosphate, ionized calcium, magnesium, alkaline phosphatase and creatinine and the urinary excretion of phosphate and creatinine were studied after 1 and 3 weeks beta-blockade in 32 young healthy men given either atenolol at 50 mg, metoprolol at 100 mg, propranolol at 80 mg or placebo twice a day. After 1 week treatment serum phosphate (mean (range] increased in the propranolol-treated subjects (1.17 (0.99-1.30) to 1.32 (1.08-1.71) mmol l-1 (P = 0.03), minor changes were found in the atenolol and the metoprolol-treated subjects but not in the placebo group. Serum phosphate was unchanged compared to pretreatment values after 3 weeks. Renal clearance and urinary excretion of phosphate and creatinine was unchanged after both 1 and 3-weeks treatment. Serum PTH, ionized calcium, magnesium and alkaline phosphatase were unchanged in all groups, whereas serum urate and creatinine increased in the metoprolol-treated subjects after both 1 and 3 weeks.

Beta-adrenergic blockers

beta-Adrenergic blocking drugs have been available for several years to treat ischemic heart disease and other cardiovascular and noncardiovascular disorders. There are multiple drugs in this class with various pharmacodynamic and pharmacokinetic properties that may be important in specific clinical situations and in avoiding certain adverse reactions. These drugs have been shown to be efficacious in relieving anginal symptoms and prolonging exercise tolerance, in reducing high blood pressure, for treating various arrhythmias, in therapy of hypertrophic cardiomyopathy, and for prolonging life in many survivors of acute myocardial infarction.

A comparison of propranolol and nadolol pharmacokinetics and clinical effects in thyrotoxicosis

For a comparison of propranolol and nadolol pharmacokinetics and clinical effects, 20 newly diagnosed patients with thyrotoxicosis were randomly selected to receive as sole therapy, either propranolol, 40 mg every 6 hours for 14 days, or nadolol, 80 mg each morning for 14 days. The study was repeated when the patients were in the euthyroid state. There was a similar and highly significant degree of beta blockade and amelioration of symptoms of thyrotoxicosis at the end of the dosage interval (trough), i.e., 24 hours after nadolol or 6 to 8 hours after propranolol. Trough and peak serum levels of propranolol were significantly lower when the patients were in a thyrotoxic state than when they were in a euthyroid state, whereas the pharmacokinetics of nadolol were not appreciably altered by thyrotoxicosis. In thyrotoxicosis, trough levels of propranolol and nadolol were significantly inversely correlated with derived creatinine clearance values. In the symptomatic treatment of thyrotoxicosis, nadolol, a once-daily nonmetabolized beta blocker, has certain advantages compared with propranolol. It is preferred by patients, is more convenient, and probably aids compliance.

Use of beta-adrenoceptor blocking drugs in hyperthyroidism

There is an increasing use and variety of beta-adrenoceptor blocking agents (beta-blockers) available for the treatment of hyperthyroidism. Recent comparative studies suggest that atenolol (200mg daily), metoprolol (200mg daily); acebutolol (400mg daily), oxprenolol ( 160mg daily), nadolol ( 80mg daily) and timolol (20mg daily) produce a beneficial clinical response equal to that seen with propranolol ( 160mg daily). Most beta-blockers reduce resting heart rate by approximately 25 to 30 beats/min, although a lesser reduction is seen with those possessing intrinsic sympathomimetic activity such as oxprenolol and pindolol. While earlier studies employing large doses of intravenous propranolol concluded that beta-blockade reduced myocardial contractility, more recent non-invasive studies suggest that the predominant cardiac effect is on heart rate. In patients with cardiac failure, beta-blockers may, however, produce a profound fall in cardiac output. Nevertheless, in combination with digoxin they may be useful in controlling the atrial fibrillation of thyrocardiac disease. beta-Blockers improve nervousness and tremor (although to a lesser extent with cardioselective agents) and severe myopathy, and they also reduce the frequency of paralysis in patients with thyrotoxic periodic paralysis. There is often subjective improvement in sweating but usually no major effect on eye signs. Recent studies show a 10% reduction in oxygen consumption/basal metabolic rate with long term oral use of selective or nonselective beta-blockers. In addition, many agents (propranolol, metoprolol, nadolol and sotalol but not acebutolol, atenolol or oxprenolol) reduce circulating tri-iodothyronine (T3) concentration by between 10 and 40%, although the clinical significance of this effect (if any) is not established. beta-Blockers may also have endocrinological effects on gastrin, cyclic AMP, catecholamines and other hormone levels. Given in adequate dosage, propranolol has been shown to control thyrotoxic hypercalcaemia. Minor side effects (nausea, headaches, tiredness, etc.) are quite common but overall beta-blockers are well tolerated by the thyrotoxic patient. The major use of these drugs is in symptomatic control while awaiting definitive diagnosis or treatment. As an adjunct to antithyroid drugs or radioactive iodine, beta-blockers will produce a satisfactory clinical response in the weeks to months before these forms of therapy produce a euthyroid state. beta-Blockers are more convenient than antithyroid drugs in the control of patients receiving therapeutic radioiodine, in that continuous therapy and assessment of biochemical response is possible.(ABSTRACT TRUNCATED AT 400 WORDS)

Beta-adrenoceptor blockade and anaesthesia for thyroidectomy

The administration of beta-adrenoceptor blocking drugs in the pre-operative preparation and operative management of thyrotoxic patients undergoing subtotal thyroidectomy is reviewed. Particular reference is made to some of the recent advances and it is emphasised that there has been a considerable reduction in the incidence of problems following judicious use of these drugs. The choice of anaesthetic technique employed for thyroidectomy is less important than the degree of control of thyrotoxicosis by the beta-adrenoceptor blocking drug. Propranolol has proved safe and effective for the majority of patients. The longer acting agent nadolol is easier to administer, particularly in the peri-operative period. Patients are rendered less thyrotoxic and safety thereby enhanced by adding potassium iodide for 10 days preoperatively. The combination of nadolol and potassium iodide offers real advantages in the preparation of the thyrotoxic patient for surgery.

Nadolol and potassium iodide in combination in the surgical treatment of thyrotoxicosis

With the two aims of rapidly reducing circulating thyroid hormone levels and controlling the symptoms of thyrotoxicosis, we have prepared 17 thyrotoxic patients for subtotal thyroidectomy, using a combination of potassium iodide administered for 10 days and the long acting beta-adrenoceptor antagonist nadolol. All 17 patients had normal serum thyroxine levels after 10 days of such treatment although 10 still showed elevation of serum tri-iodothyronine and considerable elevation in the most severely toxic patient. All patients were, however, clinically euthyroid preoperatively. Nadolol was administered once daily, hence avoiding the problems of drug administration in the immediate postoperative period, and plasma nadolol concentrations were high throughout the perioperative period. Serum thyroxine and tri-iodothyronine levels were significantly lower and reverse tri-iodothyronine levels higher 24 h postoperatively than before operation. All patients remained stable throughout the perioperative period. We conclude that this regimen has a number of advantages in the preparation of patients for thyroidectomy, in reducing the degree of thyrotoxicosis, in convenience of drug administration and in ensuring adequate circulating concentrations of beta-adrenoceptor antagonist whilst still retaining a relatively short preoperative phase of drug treatment.