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  • 1
    ISSN: 1432-1041
    Keywords: digoxin ; nomogram ; prescribing aid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary We have designed a simple nomogram for predicting digoxin dosage and have tested it prospectively in two consecutive studies. These were both conducted in hospital inpatients who were not already taking digoxin but who required drug therapy for atrial tachyarrhythmias and/or cardiac failure. Study I. Sixty-seven patients received digoxin according to the nomogram and 50 completed the ten day course of the study. Fortyone of these patients were eligible for the final analysis. On the tenth day of treatment, 28 patients were within the therapeutic range for plasma digoxin (0.8 to 2.0 ng·ml−1), 12 were subtherapeutic (〈0.8 ng·ml) and one was potentially toxic (〉2.0 ng·ml−1). Study II. Thirty patients completed the second study. Digoxin was prescribed according to the nomogram with the addition of a dosage correction based on the plasma digoxin level on Day 3. On the tenth day of treatment, 24 patients were within the therapeutic range, one in the subtherapeutic and 5 in the potentially toxic. This simple digoxin nomogram, with or without the Day 3 dosage correction, should prove to be a useful aid to prescribing in patients who do not require rapid digitalisation. It is particularly relevant to elderly inpatients with atrial tachyarrhythmias and/or cardiac failure.
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  • 2
    ISSN: 1432-1041
    Keywords: salbutamol ; asthma ; controlled-release formulation ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Fifteen patients with asthma were given salbutamol controlled-release (SCR) 4 mg or 8 mg twice daily for seven days, in a randomised double-blind cross-over design. Plasma salbutamol levels were measured after the first and fifteenth doses for a 12 h period following drug ingestion. At steady-state the geometric mean values for Cmax were 8.2 ng/ml for 4 mg, and 16.1 ng/ml for 8 mg. Median tmax values were 300 and 240 min respectively. The geometric mean AUC (0–12) were 4507 ng·min·ml−1 and 8980 ng·min/ml. Peak to trough fluctuation ratios were 0.577 and 0.572. There were no significant differences between 4 mg or 8 mg formulations, for any of the parameters measured, after appropriate corrections for dose. The concentration-time profiles at steady-state showed little fluctuation in plasma salbutamol levels over the twelve hour dosing interval. These results show that 4 mg and 8 mg formulations of SCR provide smooth plasma profiles at steady-state with a twice daily dosing regime.
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  • 3
    ISSN: 1432-1041
    Keywords: magnesium ; ventral ectopy ; atrial fibrillation ; digitalised patients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary We have examined the effects of magnesium replacement therapy upon post-exercise heart rate and incidence of ventricular premature beats (VPB) in digitalised patients with AF. In 11 such patients, all of whom had serum magnesium concentrations of less than 0.85 mmol/l, treatment with magnesium glycerophosphate was associated with a significant reduction in number of VPBs (982 v. 416 VPB/24 h). Five patients had a high prevalence of ventricular ectopy (〉300 VPB/24 h) and these subjects showed particularly marked decreases in VPBs during magnesium treatment (1998 v. 690 VPB/24 h). Three patients had slightly increased QTc intervals but these did not change during magnesium replacement. No significant changes were seen in the mean post-exercise heart rate although 2 subjects did show falls of 25% of more during magnesium replacement. We conclude that treatment with magnesium glycerophosphate may be associated with a decreased prevalence of ventricular ectopy in some digitalised patients with chronic AF and mild-moderate hypomagnesaemia.
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  • 4
    ISSN: 1432-1041
    Keywords: Asthma ; Salbutamol ; Tachyphylaxis ; Beta-adrenoceptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Tremor (Tr), chronotropic (HR) and metabolic (K, Glu) responses to cumulative doses of inhaled salbutamol (100 μg to 4000 μg) were compared in an age and sex matched group of 7 normal (N) and asthmatic (A) subjects. Comparison of regression lines between groups showed differences in HR and K. This was also reflected in attenuation of maximum responses in group A, for HR and K. These results show subsensitivity of chronotropic and hypokalaemic responses in patients with asthma, which may reflect tachyphylaxis from the effects of long term inhaled salbutamol therapy.
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  • 5
    ISSN: 1432-1041
    Keywords: Atenolol ; bisoprolol ; β-adrenoceptor ; cardioselectivity ; healthy volunteers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary A dose-ranging study was performed to compare the β1-adrenoceptor selectivity of bisoprolol with that of atenolol and nadolol. Seven normal subjects (mean age 26 y) were given single oral doses of bisoprolol 5 mg (B5), 10 mg (B10), 20 mg (B20); atenolol 50 mg (A50), 100 mg (A100); nadolol 40 mg (N40); and placebo (PL), in a single blind randomised cross-over design. β2-adrenoceptor responses were assessed by attenuation of finger tremor and cardiovascular responses to graded isoprenaline infusions. Dose-response curves were constructed, and doses of isoprenaline required to increase finger tremor by 100% (IT100), heart rate by 25 beats/min (IH25), SBP by 25 mm Hg (IS25), cardiac output by 35% (IC35), and decrease DBP by 10 mm Hg (ID10), after each treatment were calculated. These indices were compared with placebo response and expressed as dose-ratios. Exercise heart rate (EHR) was used to assess β1-adrenoceptor blockade. There were dose-related increases in plasma concentrations of bisoprolol and atenolol. Reduction of EHR was significantly less with B5 (16.8%) in comparison with all other treatments: B10 21.9%, B20 23.1%; A50 22.5%, A100 22.6%; N40 22.9%. There were small but significant reductions in isoprenaline-induced tachycardia with bisoprolol and atenolol, although mean dose-ratios were considerably less in comparison with N40 (IH25 dose-ratios): B5 2.55, B10 3.18, B20 3.93, A50 2.91, A100 4.89, N40 17.23. There were similar patterns for the other isoprenaline responses. These results show that conventional doses of bisoprolol (10 mg) and atenolol (50 mg) produced equal antagonism of β1 and β2-adrenoceptors, and therefore possess equal degrees of β1-adrenoceptor selectivity. Increasing doses of bisoprolol and atenolol were associated with partial loss of selective β1-adrenoceptor blockade, although antagonism of β2-adrenoceptors was significantly less compared with the effects of nadolol.
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  • 6
    ISSN: 1432-1041
    Keywords: Microcrystalline theophylline ; chronic obstructive airways disease ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Plasma theophylline concentrations have been measured in 9 patients with chronic obstructive airways disease following the oral administration of a microcrystalline theophylline preparation. Some measurements of FEV1 were also made. Four patients were given 375 mg as a single dose and then subsequently 375 mg stat and 125 mg 4 times daily for 3 days, (Group I). A further 5 patients took 250 mg as a single dose and then 250 mg 4 times daily for 3 days, (Group II). In both groups, following the single dose and again after the last dose of chronic administration, blood samples were obtained at frequent intervals up to 24 h for plasma drug estimation. During the 3-day course, blood samples were drawn before and 2 h after each morning dose. In Group I patients, substantial plasma theophylline concentrations were seen only after the loading dose. Thereafter, the mean concentrations before or 2 h after the morning doese were always less than 4.0 µg/ml. Trough concentrations were usually below 2.0 µg/ml. In contrast patients in Group II achieved substantially higher plasma theophylline concentrations, with mean peak concentrations always 10 µg/ml or greater, and trough concentrations greater than 5 µg/ml on at least one occasion in every subject. The elimination half-lives after chronic administration in both groups were not significantly different from those obtained after single doses. Mean drug accumulation, measured as AUCss/AUC1, was 0.87±0.07 in Group I and 0.72±0.14 in Group II, indicating that accumulation had not occurred with either regimen. The mean increase in FEV1 2 h after the administration of a single dose was 19.2% after 375 mg and 16.7% after 250 mg. These results indicate that the recommended dosage regimen for microcrystalline theophylline preparation (375 mg stat and 125 mg 4 times daily) produces inadequate plasma theophylline concentrations: 250 mg 4 times daily would appear to be likely to result in satisfactory theophylline levels in more patients.
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  • 7
    ISSN: 1432-1041
    Keywords: digoxin ; therapeutic range ; intuitive prescribing ; prescribing aid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary 37 patients on maintenance digoxin therapy were observed in hospital over an 8 day period. From day 1 to day 8 measurements of plasma digoxin and serum creatinine indicated that these patients were in the equilibrium state with regard to digoxin levels and renal function. Assuming a linear relationship between dose and plasma concentration, it was possible to calculate the doses which would have produced plasma concentrations of 1.5 ng/ml, and at the limits of the ‘usual therapeutic range’, 0.8 and 2.0 ng/ml. Doses obtained from six prescribing aids and those prescribed intuitively by the doctor were then compared. None of the methods used would have resulted in plasma digoxin concentrations within the ‘usual therapeutic range’ in more than 57% of the patients. The physicians' intuitive choice appeared to be better than the doses estimated from prescribing aids, in that they were correct as often as any assisted method, and when wrong tended to prescribe ‘too low’ rather than ‘too high’. The prescribing aids tended to overestimate dosage in many patients, as high as 65% with one. Plasma digoxin concentration measurement would appear to be the only way to ensure adequate therapeutic efficacy and avoid toxicity in patients receiving maintenance digoxin.
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  • 8
    ISSN: 1432-1041
    Keywords: Theophylline ; sustained-release ; microcrystalline ; plasma concentrations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Plasma theophylline concentrations have been measured in 14 normal subjects following the oral administration of a microcrystalline theophylline preparation (MT) 187.5 mg every 6 h and a sustained-release theophylline preparation (SRT) 375 mg every 12 h for 5 days. During the 5 days, blood samples were drawn before and 2 h after each morning dose with MT, and before and 4.5 h after each morning dose of SRT. On days 1 and 5, more frequent samples were taken during the dose interval. With both preparations, steady-state plasma concentrations were achieved by the third day. The trough levels were significantly higher with SRT than with MT on days 3 and 4, and the levels at 4.5 h after SRT were significantly higher than those measured 2 h after MT on days 3, 4 and 5. Over the terminal 3 days of the study, mean theophylline concentrations with SRT ranged between 11.2 and 15.5 µg/ml at measured trough and peak times, whereas the mean trough levels with MT were always below 10 µg/ml. With adjustment for the dosage differences, the mean ratio of the areas under the plasma concentration/time curves for the final dosage interval for the two formulations (AUCSRT/AUCMT) was 1.29±0.56, suggesting that the SRT preparation was well absorbed. The “mean” steady-state plasma theophylline concentrations (AUC/dose interval) on day 5 were 11.5±4.7 µg/ml with MT and 13.7±5.7 µg/ml with SRT. Nine subjects experienced a total of 35 side-effects whilst taking MT, compared with 10 subjects complaining of 23 side-effects on SRT. These results indicate that, in normal subjects, SRT 375 mg every 12 h exhibited satisfactory sustained-release properties and achieved adequate mean plasma theophylline concentrations during chronic administration. It produced higher plasma levels and a lower incidence of side-effects than the same daily dose of MT.
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  • 9
    ISSN: 1432-1041
    Keywords: hypertension ; hypertensive therapy ; drug utilization ; therapeutic traditions ; international differences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary A questionnaire survey based on hypertension case histories was performed among a representative sample of 400 GP's and hospital doctors in Northern Ireland, Norway and Sweden, countries having markedly different utilization of antihypertensive drugs. We found a greater propensity to start antihypertensive drug treatment in Northern Ireland than in Norway and Sweden. This was true both in mild diastolic and isolated systolic hypertension. Yet the utilization of antihypertensive drugs in Sweden is about 60% higher than in Northern Ireland and 30% higher than in Norway. Swedish physicians preferred beta-blockers as their first choice to a greater extent than physicians in Northern Ireland and Norway who selected thiazides more often. In general, the choice of drugs agreed with the sales and prescribing patterns in the three countries. Besides providing more insight in therapeutic traditions the study indicates that the lower prescribing of antihypertensive drugs in Northern Ireland, and to some extent in Norway, compared to Sweden, might be due to differences in true or apparent morbidity.
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  • 10
    ISSN: 1432-1041
    Keywords: beta-adrenoceptor ; salbutamol ; airways response ; tremor ; haemodynamic response ; metabolic response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The aim of the present study was to quantify and compare the airways and systemic beta-adrenoceptor responses to inhaled salbutamol in normal subjects. Seven non-atopic, normal subjects were given cumulative doubling doses of inhaled salbutamol (100 µg to 4000 µg) or placebo in a single-blind cross-over design. Airways (sGaw, FEF 50%, FEF 25%), tremor, haemodynamic and metabolic responses were measured at each dose increment. There were dose-related changes in sGaw, FEF 50% and FEF 25% up to a plateau at 1.0 mg. Analysis of individual responses showed that most subjects required either 1.0 or 2.0 mg for maximum bronchodilatation, independent of the parameter of airflow. There was no correlation between maximum response and baseline airway calibre. In contrast to airways effects, systemic beta-adrenoceptor responses did not occur until 500 µg, and a ceiling in the dose-response curve was not reached. Therer were significant correlations between air-ways, tremor and haemodynamic responses, and between different metabolic variables. The intraindividual variability was greatest for tremor and sGaw, although this was small in comparison to the size of maximum change with salbutamol. The converse applied to the hypomagnesaemic response.
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