Tolerance and cardiovascular effects of single dose felodipine/beta-blocker combinations in healthy subjects

The effects of single oral doses of 10 mg felodipine and four beta-blockers (100 mg metoprolol, 5 mg pindolol, 80 mg propranolol, and 10 mg timolol) were evaluated alone and in combination in a 10-way crossover, double-blind, placebo-controlled trial in 10 healthy male volunteers randomized to the medication sequence according to a latin square design. Adverse effects were recorded from spontaneous complaints and investigator observations. Heart rate (HR), PR interval, systolic blood pressure (SBP), and diastolic blood pressure (DBP) were measured supine, standing, and after treadmill exercise, before and 2 h after drug administration. The adverse effects experienced with felodipine were as expected for a vasodilator. Seven subjects mentioned complaints voluntarily on the combinations while three experienced side effects receiving felodipine or beta-blocker alone. Felodipine increased resting HR significantly. Timolol produced a greater depression of exercise heart rate than the other beta-blockers, indicating that the dose given was not equivalent to that of the other beta-blockers. Pindolol was ineffective in preventing the increase in supine HR produced by felodipine. Felodipine did not alter PR interval at any level of activity, but rate-corrected supine PR interval was prolonged slightly by felodipine. Metoprolol and timolol significantly prolonged standing PR interval. All beta-blockers prolonged exercise PR interval. Felodipine/beta-blocker combinations did not prolong PR interval more than beta-blockers alone. Prolonged PR interval was the result of reduced HR and direct inhibition of atrioventricular (AV) conduction. Only timolol and the timolol/felodipine combination lowered supine systolic blood pressure significantly. Timolol and all beta-blocker/felodipine combinations reduced exercise SBP significantly.

The influence of age on dorsal hand vein responsiveness to norepinephrine

The influence of age on the responsiveness of dorsal hand vein alpha-receptors to local infusions of norepinephrine was investigated by the use of a novel technique, the linear variable differential transformer. Studies were conducted in two groups of healthy subjects, 26 elderly individuals (14 men and 12 women) 60 to 78 years old and 32 young individuals (24 men and eight women) 16 to 29 years old. There was wide interindividual variation in responsiveness to norepinephrine within both groups of subjects. The dose of norepinephrine required to produce 50% venoconstriction in the elderly ranged from 1.5 to 300 ng/min (geometric mean 24.0 ng/min). The dose required to produce 50% venoconstriction in younger individuals ranged from 1.6 to 360 ng/min (geometric mean 23.8 ng/min). These results suggest that there is no systematic influence of age on dorsal hand vein alpha-receptor responsiveness. A power calculation demonstrates a very small likelihood of a type II error.

Simplified liquid-chromatographic assay of amiodarone and desethylamiodarone after solid-phase extraction

We describe a rapid, simplified isocratic "high-performance" liquid-chromatographic method for simultaneous measurement of the antiarrhythmic drug amiodarone and its major metabolite, desethylamiodarone, in small volumes of sera (100 microL). Compared with liquid-liquid extraction, the solid-phase method of extraction saves time and glassware and improves reproducibility for small sample volumes. Amiodarone and desethylamiodarone could be measured at concentrations as low as 250 micrograms/L. Standard curves for the drug and metabolite are linear over the range of concentrations found in our patients. Within-run CVs (n = 6) ranged from 2.7% to 4.5% for amiodarone and from 4.0% to 5.7% for desethylamiodarone over the range of 250 to 4000 micrograms/L. Between-run CVs (n = 12) were 8.3% and 5.7% for amiodarone and desethylamiodarone, respectively. Commonly used cardiovascular medications do not interfere with the assay.

Simplified liquid-chromatographic assay of amiodarone and desethylamiodarone after solid-phase extraction

We describe a rapid, simplified isocratic "high-performance" liquid-chromatographic method for simultaneous measurement of the antiarrhythmic drug amiodarone and its major metabolite, desethylamiodarone, in small volumes of sera (100 microL). Compared with liquid-liquid extraction, the solid-phase method of extraction saves time and glassware and improves reproducibility for small sample volumes. Amiodarone and desethylamiodarone could be measured at concentrations as low as 250 micrograms/L. Standard curves for the drug and metabolite are linear over the range of concentrations found in our patients. Within-run CVs (n = 6) ranged from 2.7% to 4.5% for amiodarone and from 4.0% to 5.7% for desethylamiodarone over the range of 250 to 4000 micrograms/L. Between-run CVs (n = 12) were 8.3% and 5.7% for amiodarone and desethylamiodarone, respectively. Commonly used cardiovascular medications do not interfere with the assay.

Gastric emptying before and after transverse gastroplasty for morbid obesity

Twenty-three morbidly obese patients underwent gastric emptying studies (Tc-99m egg salad sandwich--a semisolid meal) preoperatively, and at three months and 12 months postoperatively to evaluate the effect of transverse gastroplasty on gastric emptying and to determine the predictive value of this study for weight loss. At three months pouch emptying was variable with nine of 23 patients having prolonged half-times, and 14 shortened half-times compared with preoperative values, despite both groups having identical weight loss. At 12 months pouch half-times returned to baseline. The data suggests that this type of gastroplasty causes weight loss solely by reducing the gastric volume resulting in reduced meal volume. Weight loss is not related to impaired pouch emptying, which might result in a prolonged feeling of fullness. Gastric emptying studies neither preoperatively nor postoperatively have weight loss predictive value for this particular operation.

Respiratory and cardiac effects of metoprolol and bevantolol in patients with asthma

The effects on standing heart rate and respiratory function of two relatively selective beta 1-adrenoceptor antagonists, metoprolol and bevantolol, were compared in a double-blind, randomized, crossover study of 16 patients with asthma. After control observations on 2 separate days, the patients received approximately equivalent cardiac beta-adrenoceptor antagonist doses of metoprolol, 12.5, 25, 50, and 100 mg, and bevantolol, 18.75, 37.5, 75 and 150 mg, at intervals of 2 hours. Dosing was stopped if symptoms warranted or if there was a fall of greater than or equal to 20% in the forced expiratory volume in 1 second. In general, the cumulative dosing regimen proved a safe and effective means of assessing bronchial responsiveness to these beta-blockers in asthma, but one patient had to be dropped from the study because of severe bronchoconstriction after the first dose. Of the 15 patients studied who were taking both drugs, seven patients were withdrawn prematurely. In these seven patients, the average maximum tolerated cumulative doses were 45.5 mg bevantolol and 26.8 mg metoprolol, doses that are much lower than those usually required for therapeutic activity. The respiratory response to either drug could not be predicted.

Evaluation of once daily endralazine in hypertension

Endralazine, a novel vasodilator related to hydralazine, exhibits a longer half-life and is only minimally influenced by acetylator status. The antihypertensive action of once daily endralazine has been studied in 17 patients previously controlled with an antihypertensive regimen which included hydralazine and a beta-blocker. Hydralazine was discontinued but other medications were unchanged. Pre-study dosage of hydralazine ranged from 25 mg b.i.d. to 50 mg g.i.d., mean daily dose 126.5 mg. Endralazine was started at a dose of 10 mg o.d. and increased by 10 mg to a maximum of 40 mg o.d. until seated DBP was controlled below 95 mmHg. All 17 patients completed the study. Seated BP significantly decreased from 147.5/99.7 to 133.8/83.9 and standing BP from 145.8/99.2 to 133.6/87.3 mmHg. Ten patients (59%) were successfully controlled with endralazine once daily but 7 patients required twice daily dosage schedules because of lack of BP control at 24 h after dosing or excessive hypotension shortly after dosing. Other adverse effects were headache, palpitations and fatigue. There was a statistically insignificant average weight gain of 1 kg but pedal edema was not observed. Endralazine is an effective antihypertensive agent with adverse symptoms similar to those experienced with hydralazine.

Evaluation and application of the linear variable differential transformer technique for the assessment of human dorsal hand vein alpha-receptor activity

Diurnal, day-to-day, intrasubject, and intersubject variability of responsiveness of dorsal hand veins to norepinephrine has been investigated in healthy young subjects through the use of a novel technique in which a linear variable differential transformer (LVDT) is placed directly over the vein. Under constant operating conditions, control vein diameter remained consistent. There is a log dose responsiveness to norepinephrine infused directly into the hand vein. There was little diurnal, day-to-day, or intrasubject variability in the dose of norepinephrine required to induce 50% constriction of hand vein diameter. The responsiveness to norepinephrine of different veins in either hand was also consistent. However, there was wide intersubject variability, apparently unrelated to age, gender, or other subject characteristics. We conclude that the LVDT method is reproducible and reliable and offers a relatively noninvasive means of assessing the effects of disease and drugs on the human dorsal hand vein in vivo. The LVDT technique has been applied to study the rate of onset, magnitude of effect, dose responsiveness, and duration of action of intravenous dihydroergotamine, 0.1, 0.2, and 0.4 mg, on human dorsal hand veins. Despite systemic intravenous administration, there was an average delay in maximum response of 30 minutes to 1 hour. Venoconstriction was incomplete, with a maximum reduction of approximately 50% of vein diameter after each of the larger doses. There was no significant difference between the effects produced by 0.2 or 0.4 mg, which persisted for 6 hours after dosing.

Contrasts between pindolol and propranolol concentration-response relationships

The plasma concentration-response relationships of oral and intravenous pindolol and propranolol have been studied in a group of eight healthy male subjects who received each dosage form in a randomized single-blind cross-over manner. Despite similar elimination half-lives, the duration of action of pindolol was longer than that of propranolol. This longer duration of action was associated with a flatter concentration-response curve for pindolol and may be related to the partial agonist activity of pindolol. Propranolol concentration-response curves were dependent on the route of drug administration whereas pindolol curves were similar following oral and intravenous routes of administration.

A secondary prevention, randomized trial of suloctidil in patients with a recent history of thromboembolic stroke

Four hundred and thirty-eight patients who had suffered a thromboembolic stroke not less than two weeks or more than four months previously, were entered into a placebo-controlled randomized clinical trial to determine whether suloctidil (200 mg t.i.d.) would influence the subsequent recurrence of stroke, the occurrence of myocardial infarction, or cardiovascular death. The two treatment groups were comparable at baseline with respect to important prognostic variables and there was good adherence to the study protocol during an average follow-up of 20 months. Significantly more patients complained of side-effects in the suloctidil group and more hepatotoxicity was also reported in the suloctidil group. Four cases of clinical hepatitis were suspected to be due to suloctidil, each of which was reversible on termination of study treatment; relative increases in SGOT and SGPT at three months in the suloctidil group were found to be mild and transient. The primary analysis of efficacy was based on the incidence of the first event of stroke, myocardial infarction or cardiovascular death, but excluding events that occurred more than 28 days after complete withdrawal from study medication for whatever reason. Thus, the primary analysis included 38 events in the suloctidil group and 47 in the placebo group (p = 0.17) representing a risk reduction of 24%. If total mortality is substituted for cardiovascular death, the corresponding figures are 47 in the suloctidil group and 58 in the placebo group (p = 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of cyclosporin-phenytoin interaction with observations on cyclosporin metabolites

We have observed that patients on concurrent cyclosporin and phenytoin therapy required increased doses of cyclosporin to maintain therapeutic concentrations of this novel immunosuppressive drug. We have, therefore, studied the influence of phenytoin on the pharmacokinetics of oral cyclosporin in six healthy male subjects. Cyclosporin concentrations in serum and whole blood were measured by high pressure liquid chromatography (h.p.l.c.) and radioimmunoassay (RIA). Concentrations of cyclosporin in whole blood were consistently higher than corresponding values in serum. Concentrations of cyclosporin determined by RIA were also consistently higher than those determined by h.p.l.c. Irrespective of the biological fluid (serum or whole blood) or the type of drug analysis (h.p.l.c. or RIA), changes in cyclosporin kinetics following phenytoin administration exhibited similar patterns. Phenytoin significantly reduced the maximum concentration and the area under the concentration-time curve and significantly increased total body clearance of cyclosporin. There was a statistically significant reduction of cyclosporin half-life (t 1/2) in whole blood using h.p.l.c. analysis. However, there was no significant change in cyclosporin t 1/2 in serum following phenytoin administration, using either form of drug analysis. Cyclosporin metabolites 17 and 18 were measured by h.p.l.c. in whole blood samples only, since these metabolites were found almost entirely in red blood cells. Phenytoin significantly reduced the Cmax and AUC of both metabolites, but no significant change was observed in the t 1/2 of either. Phenytoin enhanced the metabolism of antipyrine which was co-administered with cyclosporin to assess oxidative enzyme activity. We conclude that patients undergoing organ transplantation should be carefully monitored if they require phenytoin or other drugs known to accelerate oxidative metabolism.

Verapamil in chronic atrial fibrillation: variable patterns of response in ventricular rate

We determined the effects of single intravenous (10 mg) and oral (80, 160 mg) doses of verapamil in 8 digitalized patients with chronic atrial fibrillation. The time course of drug effect was analyzed with computer assistance by considering several measures in atrial fibrillation, including average R-R interval (ARR), shortest R-R interval (SRR), longest R-R interval (LRR), and variability of R-R intervals. Peak plasma concentrations of verapamil were observed immediately after intravenous verapamil (mean elimination half-life of 3.3 h) and 1 hour after oral verapamil (mean elimination half-life 3.4 h, 80 mg; 3.1 h, 160 mg). In contrast to previous studies, we observed the maximum bradycardic effect of intravenous verapamil to occur at one-half to 1 h, and this effect lasted for 2-4 h. Following oral verapamil the peak effect occurred at 3-4 h and lasted for 5-8 h. Analysis of the time course of changes in APR, SRR, LRR, and variability of R-R revealed two distinct "patterns" of ventricular response. In one group (4 of 8 patients), verapamil caused an increase in SRR but a decrease in LRR. R-R intervals "regularized" in this group. In the remaining patients, verapamil increased the SRR but did not change or increase the LRR. This enhanced the observed increase in ARR intervals. We postulate that the decrease in LRR intervals after verapamil is due to reflex adrenergic discharge as a result of the vasodilator effect of the drug while the increase in SRR is a direct effect. These two opposing effects result in regularization of R-R intervals in many patients. Patients demonstrating an increase in LRR intervals after verapamil may not get reflex adrenergic discharge or may be incapable of responding to the latter due to conduction disease; these patients may experience bradycardic complications after verapamil.

Influence of cardioselectivity and respiratory disease on pulmonary responsiveness to beta-blockade

The effects on ventilation of the non-selective beta-blocker propranolol, and the relatively cardioselective beta-blocker, metoprolol, were compared in a randomized single-blind crossover study in 16 patients with asthma, bronchitis and emphysema (American Thoracic Society criteria). Group I had "fixed" airways disease with less than 20% improvement in FEV1 following inhaled salbutamol 5 mg by nebuliser. Group II had "reversible" obstruction, greater than 20% improvement. Bronchodilator therapy was withheld for 24 h with the exception of aerosols which were permitted until 12 h before study. After control observations on each of 2 study days, each patient received cumulative doses of propranolol (maximum 170 mg) and metoprolol (maximum 187.5 mg). Ventilatory function (FEV1, FVC, FEV1%) was assessed at 0, 2, 4, 6 and 8 h. In Group I, 2 patients were unable to complete the study. One patient became dizzy with propranolol 70 mg but tolerated metoprolol 187.5 mg. One patient developed wheeze with propranolol 15 mg but tolerated metoprolol 187.5 mg. Metoprolol was tolerated in all 8 patients with "fixed" disease, although FEV1 was reduced by more than 30% in 1 patient. Three patients in Group II did not complete the study because of wheezing following propranolol 10 mg, metoprolol 37.5 mg; propranolol 17.5 mg, metoprolol 37.5 mg; propranolol 45 mg, tolerated metoprolol 187.5 mg respectively. Wheezing responded in all cases to inhaled isoprenaline. The response to either propranolol or metoprolol was unpredictable in patients with "reversible" disease. When wheezing occurred in this group, it developed following small, potentially subtherapeutic doses of each drug. Although metoprolol was better tolerated, the practical benefit of cardioselectivity in those patients with reversible airways disease was negligible.

An audit of requests for therapeutic drug monitoring of digoxin: problems and pitfalls

The use of serum digoxin measurements in a teaching hospital was audited. The reason for test requisition, the timing of blood samples, the recognition of results, and the action taken by house staff were assessed using formal criteria. In 200 consecutive requests for serum digoxin measurements, the reason for requesting the test could not be determined in 165 (82.5%). The timing of plasma samples with respect to duration of therapy and time since last dose was usually satisfactory. However, only 73 (36.5%) of results appear to have been adequately recognized, and approximately 1 result in 4 was followed by an inappropriate decision. High plasma concentrations were usually dealt with more promptly and more appropriately than low plasma concentrations, possibly because the biochemistry laboratory informed physicians directly of the high results. There is a clear need for physicians to better identify the reasons for measuring plasma concentrations of digoxin and to request serum digoxin measurements only when there is a pertinent problem. Indiscriminate requests for serum digoxin measurements are associated with apparent disregard for the results and a high likelihood of making an inappropriate decision regarding further digoxin prescription.

Pindolol and propranolol in patients with angina pectoris and normal or near-normal ventricular function. Lack of influence of intrinsic sympathomimetic activity on global and segmental left ventricular function assessed by radionuclide ventriculography

To investigate the role of intrinsic sympathomimetic activity on left ventricular (LV) function during antianginal therapy with beta-adrenoreceptor antagonists, 23 patients with chronic, exercise-induced angina pectoris and normal or near normal LV function underwent radionuclide ventriculography at rest and during exercise, during 3 randomly allocated periods: (a) treatment with oral propranolol, a drug without intrinsic sympathomimetic activity, 40 to 80 mg 4 times a day; (2) treatment with pindolol, a drug with marked intrinsic sympathomimetic activity, 5 to 10 mg 2 times a day; and (3) a control period. During the control period, the LV ejection fraction decreased from rest (58.9 +/- 8.2%) to exercise (54.3 +/- 10.7%), and the wall motion score decreased from 0.57 +/- 1.08 at rest to 2.39 +/- 2.10 during exercise, p less than 0.001. After propranolol, the ejection fraction did not change significantly at rest (57.2 +/- 8.1%) but improved during exercise (56.8 +/- 11.8%), compared with control values. After pindolol, the ejection fraction did not change at rest (57.9 +/- 8.6%) but improved during exercise (56.9 +/- 8.1%), compared with control values. Similarly, the wall motion score after administration of both agents did not change significantly at rest, but improved during exercise (p less than 0.001). The number of anginal episodes, nitroglycerin tablets consumed, and magnitude of S-T segment depression decreased significantly with both pindolol and propranolol. With both drugs, a similar improvement in exercise tolerance and a similar decrease in exercise heart rate and blood pressure were obtained. It is concluded that pindolol and propranolol, beta-adrenoreceptor antagonists with and without intrinsic sympathomimetic activity, respectively, have similar effects on global and regional LV function in patients with angina pectoris, at doses producing equal suppression of exercise heart rate and similar antianginal effect.

Simplified liquid-chromotographic analysis for cyclosporin A, and comparison with radioimmunoassay

We describe a simplified isocratic "high-performance" liquid-chromatographic method for measuring a new immunosuppressive drug, cyclosporin A, in biological fluids with use of its analogs cyclosporin C and cyclosporin D as internal standards. The method is reproducible and accurate and appears to be specific for cyclosporin A; the detection limit is 31 micrograms/L. The chromatographic measurements of the concentration of cyclosporin A in serum of patients receiving the drug were invariably lower than those by radioimmunoassay and the difference became more pronounced the greater the period of time after dosing. Because measurements of cyclosporin A in serum standards were almost identical with both techniques, the differences between the two sets of results for patients' samples suggests that the radioimmunoassay is nonspecific and measures metabolites of cyclosporin A.

Simplified liquid-chromotographic analysis for cyclosporin A, and comparison with radioimmunoassay

We describe a simplified isocratic "high-performance" liquid-chromatographic method for measuring a new immunosuppressive drug, cyclosporin A, in biological fluids with use of its analogs cyclosporin C and cyclosporin D as internal standards. The method is reproducible and accurate and appears to be specific for cyclosporin A; the detection limit is 31 micrograms/L. The chromatographic measurements of the concentration of cyclosporin A in serum of patients receiving the drug were invariably lower than those by radioimmunoassay and the difference became more pronounced the greater the period of time after dosing. Because measurements of cyclosporin A in serum standards were almost identical with both techniques, the differences between the two sets of results for patients' samples suggests that the radioimmunoassay is nonspecific and measures metabolites of cyclosporin A.

Ineffectiveness of beta-adrenergic blockers on ventilatory response to carbon dioxide

The effects of the beta-adrenoceptor blockers atenolol, metoprolol, pindolol, and propranolol on the ventilatory response to carbon dioxide rebreathing have been determined in a double-blind randomized manner. Eight healthy, male, nonsmoking subjects received cumulative doses of each drug over a 10-hr period. The effects of each drug on heart rate and carbon dioxide sensitivity were determined at intervals of 2 hr and were related to plasma concentrations of each drug. Maximum reduction of exercise heart rate was achieved with all four beta blockers and plasma concentrations were in the usual therapeutic range for these drugs. There was considerable intersubject and within-subject variability in ventilatory responsiveness to inhaled carbon dioxide, but we were not able to discern any alteration in central sensitivity to increasing carbon dioxide concentrations.

Acceleration of the ventricular response during atrial fibrillation in the Wolff-Parkinson-White syndrome after verapamil

We examined the electrophysiologic effects of verapamil in eight patients with the Wolff-Parkinson-White syndrome. Verapamil shortened the antegrade effective refractory period of the accessory pathway in three patients and abbreviated the shortest cycle length with 1:1 conduction over the accessory pathway in two patients. More significantly, verapamil decreased the shortest RR interval between preexcited ventricular complexes during atrial fibrillation (279 +/- 20 msec vs 236 +/- 18 msec, mean +/- SEM; p less than 0.01). After verapamil, two patients required cardioversion for hemodynamic deterioration after acceleration of the ventricular response during atrial fibrillation. In the four patients with predominantly preexcited ventricular complexes during atrial fibrillation the ventricular rate accelerated after verapamil, whereas in patients with predominantly normal ventricular complexes, the average ventricular rate decreased or did not change after verapamil. Verapamil may result in significant acceleration of ventricular response during atrial fibrillation in the Wolff-Parkinson-White syndrome. The safety of verapamil in individual patients with the Wolff-Parkinson-White syndrome should be established by electrophysiologic testing before its use.

Comparison of the electrophysiologic effects of intravenous and oral verapamil in patients with paroxysmal supraventricular tachycardia

The electrophysiologic effects of intravenous verapamil (a bolus dose of 0.15 mg/kg body weight followed by infusion of 0.005 mg/kg per min) were compared with those of oral verapamil (80 mg every 6 hours for 48 hours) in eight patients who had paroxysmal supraventricular tachycardia. The mechanism of tachycardia was atrioventricular (A-V) nodal reentry in four patients and A-V reentry utilizing an accessory pathway for retrograde conduction in the remaining four. The electrophysiologic effects of oral and intravenous verapamil were similar. Both preparations significantly prolonged anterograde effective and functional refractory periods of the A-V node (p less than 0.001). Both significantly increased the shortest pacing cycle length maintaining 1:1 anterograde conduction over the A-V node (p less than 0.001). Retrograde conduction over the A-V node was greatly prolonged with verapamil in one patient but was unaffected in the others. There was no significant effect on sinoatrial conduction time, sinus nodal recovery time or atrial or ventricular refractoriness. Both preparations prevented induction of tachycardia in six patients none of whom had recurrence of sustained tachycardia while receiving long-term oral therapy (5 to 10 months). Neither preparation had a significant effect in two patients and this predicted failure of long-term oral therapy in one of these patients. The results of acute drug testing with intravenous verapamil can be extrapolated to predict the electrophysiologic results and response to long-term therapy with oral verapamil.

Cardiac dose-response relationships of oral and intravenous pindolol

1 The dose-response curve of pindolol on exercise heart rate has been constructed from observations in healthy male subjects studied 2 h after oral doses of pindolol 0.25 mg, 0.5 mg, 1 mg, 2.5 mg, 5 mg, 10 mg and 20 mg. This dose-response curve has been compared with historical controls who received atenolol, oxprenolol, practolol, propranolol and sotalol.

2 The dose-response curves differ in the relative potency of the drug, the maximum reduction of heart rate and possibly in the slope of the curves. Pindolol is extremely potent. At doses which produce 15% reduction of exercise heart rate, the relative potencies of the drugs were: pindolol (1), atenolol (1:21) oxprenolol (1:19), practolol (1:44), propranolol (1:25) and sotalolol (1:160). The maximum effects produced by pindolol, oxprenolol and practolol were less than those of the other β-adrenoceptor blocking drugs, an effect which is probably the result of their partial agonist activity.

3 Following intravenous pindolol 0.005, 0.01, 0.02 and 0.045 mg/kg the reduction of exercise heart rate and duration of action were dose-dependent.

4 The effects of pindolol 0.045 mg/kg i.v. (mean total dose 3.5 mg), pindolol 5 mg p.o., propranolol 0.3 mg/kg i.v. (mean total dose 25.1 mg) and propranolol 80 mg p.o. were assessed on resting, standing and exercise heart rates. Neither drug reduced resting heart rate but propranolol reduced standing heart rate from 98.8 to 80.3 beats/min. The effects of all four preparations on exercise heart rate were similar.

5 Oral pindolol is approximately 16-20 times as potent as oral propranolol.

6 Intravenous pindolol is approximately 6-8 times as potent as intravenous propranolol.

Measurement of partial agonist activity of pindolol

The partial agonist activity of pindolol was assessed by examining the action of cumulative doses on the heart rate of resting, standing, and exercising healthy men and by studying the interaction of pindolol with metoprolol, a beta blocker devoid of partial agonist activity. Pindolol did not affect resting or standing heart rates (RHR, SHR) but reduced the heart rate after vigorous exercise by approximately 25%. The flatter dose-response curve of pindolol for exercise heart rate (EHR) has been reported from practolol and oxprenolol, which also exert partial agonist activity. After extremely large doses of pindolol there was no evidence of enhancement of agonist activity on RHR, nor was there any evidence of dominance of agonist activity over antagonist activity on EHR. Metoprolol did not alter RHR but reduced SHR by approximately 20% and EHR by approximately 31%. The effects of pindolol on SHRs and EHRs were not enhanced by metoprolol, even though the drug itself induced greater reductions of both. The reduction of SHR by metoprolol was reversed by pindolol. Pindolol appears to have greater affinity than metoprolol for atrial beta adrenoceptors in man.

Duration of drug action

Duration of drug action depends on several factors: the absolute amount of drug given; the pharmaceutical preparation; the reversibility of drug action; the half-life of the drug; the slope of the concentration-response curve; the activity of metabolites, and the influence of disease on drug elimination. The duration of action of a drug with more than one effect may differ, depending on which effect is followed. Drugs with a prolonged therapeutic effect should be given once or twice daily. Drugs with a short duration of therapeutic effect are best given at regular intervals rather than by t.i.d. or q.i.d. regimens.

Cholestyramine and spironolactone and their combination in digitoxin elimination

The effects of oral cholestyramine 4 gm 8 times daily and spironolactone 300 mg daily, given independently and in combination, on the elimination rate of digitoxin were studied in 6 healthy subjects pretreated with 0.1 or 0.15 mg oral digitoxin daily for 30 days before each intervention. The mean pretreatment digitoxin concentrations for the group ranged from 21 +/- 2.9 (SD) ng/ml to 28.5 +/- 6.9 ng/ml. The mean control digitoxin half-life (t 1/2) was reduced from 141.6 to 84.4 by treatment with cholestyramine alone. Treatment with spironolactone alone prolonged the mean digitoxin t 1/2 to 192.2 hr. The mean digitoxin t 1/2 after both active drugs was intermediate at 102.9 hr. Spironolactone did not fulfill the expectation from animal studies that it would enhance the clearance of digitoxin by cholestyramine. The prolongation of digitoxin elimination after spironolactone may contraindicate this drug in digitoxin intoxication.

Kinetics of pamatolol, a cardioselective beta adrenoreceptor blocker

The systemic bioavailability, elimination half-life (t1/2), and plasma concentration--response relationships of pamatolol, a relatively cardioselective beta adrenoceptor blocker, have been measured in healthy subjects. Pamatolol is rapidly and completely absorbed after oral dosing. Elimination t1/2 ranged from 2.9 to 4.6 hr after oral doses and from 2.2 to 5.6 hr after intravenous doses. There was a clear relationship between log plasma pamatolol concentration and sympathetic blockade assessed by reduction of exercise heart rate. Concentration-response curves were essentially identical after oral and intravenous doses. There is no evidence of a first-pass effect, nor is there any evidence of metabolite activity.

Pamatolol: phase I evaluation of the pharmacodynamics of a cardioselective beta adrenoceptor blocking drug

A Phase I evaluation of a new adrenoceptor blocker, pamatolol, was performed in 10 healthy male volunteers. Minor reductions in standing and exercise and isoproterenol-induced increases in heart rate were observed with the 10-mg oral dose and appeared maximal with the 400-600 mg dose. The rate of decline of effect averaged 1.5% of the exercise heart rate/hr. Neither resting systolic time intervals nor post-exercise pulmonary function was affected by this dose range of pamatolol. Based on the latter responses and the isoproterenol dose response curve, we tentatively conclude that pamatolol is relatively cardioselective in man.

Correlation between plasma diphenhydramine level and sedative and antihistamine effects

The sedative and antihistamine effects of diphenhydramine were assessed in relation to plasma concentration after placebo, diphenhydramine 50 mg intravenously, and diphenhydramine 50 mg orally to each of 6 healthy volunteers on three separate occasions. Diphenhydramine plasma elimination t1/2 was 3.0 to 4.3 hr, volume of distribution was 188 to 336 L, and clearance was 637 to 1,014 ml/min. Systemic bioavailability of the oral preparation ranged from 0.26 to 0.60. The sedative effect of intravenous diphenhydramine differed from that of placebo only during the first 3 hr. Antihistamine effect, as measured by reduction of histamine provoked skin wheal diameter, was significantly different from that of placebo for at least 8 hr. There was a positive correlation between plasma diphenhydramine level and sedative and antihistamine effects, but wide variation in the extent and rate of change of these effects were observed between the subject. There appears to be a concentration range of 25 to 50 ng/ml, within which there is significant antihistamine effect without significant sedation.

Influence of intrinsic sympathomimetic activity and cardioselectivity on beta adrenoceptor blockade

Dose-response curves for propranolol and oxprenolol were studied in healthy volunteers, with a standardized excercise test and percentage reduction in excercise heart rate (EHR) as the index of drug effect. The dose-response curves obtained were compared with similar curves previously reported for sotalol, practolol, and atenolol with identical experimental methods. Two distinct types of response were identified: in the first, shown by propranolol and sotalol, increasing doses of the beta adrenoceptor-blocking drug continued to produce increasing effects to the limits of the dose levels examined; with the second (oxprenolol and practolol), increasing the dose initially resulted in substantial increase in effect but subsequently larger doses produced almost no increase in effect. Consideration of the additional properties of these beta adrenoceptor-blocking drugs revealed that both practolol and oxprenolol have intrinsic sympathomimetric activity (ISA), whereas propranolol and sotalol do not. In addition, practolol is cardioselective. Further investigation of the possible influence of ISA or cardioselectivity on beta adrenoceptor-blocking activity was undertaken by studying the effects of combinations of drugs on EHR. Sotalol produced greater effect when given 2 hr after sotalol, oxprenolol, practolol, or atenolol. When oxprenolol was given after sotalol or oxprenolol, or practolol was given after sotalol or practolol, there was no further increase in percentage reduction in EHR. When atenolol was given, the combinations of sotalol and atenolol together with two doses either of sotalol or atenolol all induced increases and similar final percentage reductions in EHR. Thus atenolol induces effects like those of sotalol, which are quite different from those of oxprenolol or practolol. The presence or absence of ISA would appear to be the important difference between these two groups of drugs: ISA would, therefore, appear to be demonstrated in man by flattening of the dose-response curves with exercise.

Biliary excretion and enterohepatic recirculation of practolol in man

The elimination of practolol in bile was studied in six patients who received a single oral dose of 400 mg within six days of undergoing biliary surgery. Bile collections were made from a T-tube drain left in the common bile duct after removal of multiple biliary calculi. There was wide variation in the concentration of practolol in bile and in the total amount of practolol excreted in bile during the 48 hour period after dosage. Two patients excreted 23 per cent and 41 per cent of the 400 mg dose in bile, whereas the excretion in the other four patients was only one per cent to four per cent of the oral dose. The mean urinary excretion of practolol in 48 hours was 74.2±S.E. 8.4 per cent of the ingested dose, and the total elimination (biliary plus urinary) was 86.5±S.E. 7.6 per cent. The total elimination ranged from 92 per cent to 105 per cent in four of the patients. The mean elimination half-life of practolol in blood was 6.4±S.E. 0.5 hours. This was significantly less than the half-life in normal subjects receiving the same practolol dose. Since complete or near-complete urinary excretion of practolol is found in normal subjects, the presence of large amounts of drug in the bile suggests that enterohepatic recirculation of the drug occurred in some of the patients at least. This is a possible explanation of the shortened half-life in these patients in whom drug was being removed with bile. The four patients with low excretion of practolol in bile were receiving other drugs at the time of the study. These included nitrazepam, diazepam and tetracycline which are known to have substantial biliary elimination either in animals or man. It is suggested that competition for biliary excretion may have occurred and this may represent a drug interaction of possible clinical significance.

Clinical pharmacologic observations on atenolol, a beta-adrenoceptor blocker

The effects of oral and intravenous administration of atenolol were studied in healthy volunteers. The oral administration of a series of single doses of atenolol reduced an exercise tachycardia. After a 200-mg dose, the effect on an exercise tachycardia was maximal at 3 hr and declined linearly with time at a rate of approximately 10% per 24 hr. The peak plasma atenolol concentration occurred at 3 hr and thereafter declined exponentially with time with an elimination half-life of 6.36 +/- 0.55 hr: 43 +/- 3.9% of the dose was excreted in the urine within 72 hr. There was a correlation between the reduction in an exercise tachycardia and the logarithm of the corresponding plasma concentration. The intravenous administration of atenolol reduced exercise tachycardia with a significant correlation between effect and plasma concentration. After 50 mg intravenously, 100% of the dose was recovered from the urine, and the clearance was 97.3 ml/min. Comparison of AUC O leads to chi after oral and intravenous administration of 50 mg showed the bioavailability to be 63% after oral drug. Repeated oral administration of atenolol 200 mg daily either as a single dose or in divided 12 hourly doses for 8 days maintained reduction of an exercise tachycardia of at least 24% during the period of drug administration. The plasma elimination half-life, area under the plasma concentration-time curve, and peak plasma concentration after 200 mg atenolol were not changed by chronic dosing for 8 days.

Observations on the efficacy and pharmacokinetics of sotalol after oral administration

The effects of sotalol after oral administration were measured on the tachycardia induced by strenuous exercise in normal subjects. Plasma sotalol levels were also determined. The oral administration of sotalol (50, 100, 200 and 400 mg) to 6 subjects produced a progressive reduction in the tachycardia induced by severe exercise. This was similar to the effects of 25, 50, 100, 200, 400 and 800 mg given to different subjects. Each increase in sotalol dose produced a successively greater reduction in exercise tachycardia. This did not appear to be maximum even with 800 mg. Oral sotalol was rapidly absorbed and produced peak blood levels in 2 - 3 hours. The plasma levels of sotalol measured 2 hours after the oral administration of 25 to 800 mg showed never more than a six-fold variation between different subject. The half-life of sotalol in plasma was 12.7 +/- SE 1.6 hours. There was a significant correlation between the logarithm of the plasma sotalol concentration and the percentage reduction of exercise heart rate. It is concluded that the oral administration of sotalol either once or twice daily (depending on dose level) will provide satisfactory 24-hour blockade of beta-adrenoceptors.

Plasma and tissue digoxin concentrations in patients undergoing cardiopulmonary bypass

Plasma myocardial, and skeletal muscle digoxin concentrations were measured in 32 patients undergoing cardiopulmonary bypass who were on long-term treatment with digoxin. The patients were divided into 4 groups according to the daily digoxin dose and the interval between discontinuation of the drug and operation. Before bypass, the mean digoxin concentrations were 1.58 nmol/l (1.24 ng/ml) in plasma 65.2 nmol/kg (50.9 ng/g) in the atria, 121.4 nmol/kg (94.98 ng/g) in 11 papillary muscles, and 16.6 nmol/kg (13.0 ng/g) in skeletal muscle. Mean atrial digoxin concentrations were significantly lower tham mean papillary muscle concentrations in 11 patients. Ratios of plasma of myocardial or skeletal muscle digoxin concentrations were very variable. Generally digoxin concentrations were higher in patients on the larger digoxin dose and with the shorter discontinuation time before surgery. These differences attained significance only with plasma digoxin concentrations. There was a slight fall in plasma digoxin concentration during cardiopulmonary bypass but no significant differences were observed between plasma, atrial, or skeletal muscle digoxin concentrations before and at the end of bypass. No clear relation was seen between plasma or atrial digoxin concentrations and postoperative cardiotoxicity. Stopping digoxin 48 hours before operation appeared to account for pre- or post-bypass plasma digoxin concentrations of less than 1.0 nmol/l (0.8 ng/ml) in most of the instances encountered, whereas the 3 patients who developed pulsus bigeminus postoperatively had received 0.5 mg digoxin only 24 hours before operation.