[Cardiac failure in the geriatric patient]

Cardiac insufficiency is a disease of old age. Analyses of subgroups have showed that old patients benefit to a particular extent from therapeutic measures the effectiveness of which has been confirmed in numerous studies. In the light of this knowledge, it is all the more difficult to understand why this group of patients are still not receiving effective treatment. In this area, there is an urgent need for improvement. Also difficult to understand is the fact that the guidelines for the treatment of chronic cardiac failure issued by the German Cardiology Society pay so little attention to cardiovascular research of cardiac insufficiency in old age, and thus bear indirect responsibility for the less than optimal treatment of this condition, which can be so severe in the old patient. These guidelines should contain a section on the peculiarities of cardiac insufficiency in high old age.

A NOVEL INEXPENSIVE MURINE MODEL OF ORAL CHRONIC DIGITALIZATION

A novel inexpensive murine model of oral administration of digitoxin (100 micro g/kg per day) added to routine chow is described. Serum digitoxin levels achieved after oral (n = 5; 116 +/- 14 ng/mL) and subcutaneous (n = 5; 124 +/- 11 ng/mL) administration were similar. A significant increase in the maximal left ventricular pressure rise of treated (n = 9) compared with control (n = 6) rats (dP/dt: 8956 +/- 233 vs 7980 +/- 234 mmHg/s, respectively; P = 0.01) characterized the positive inotropic action of digitoxin. In addition, no differences were observed in treated compared with control rats with regard to the electrocardiogram and systolic and diastolic left ventricular pressures.

Digitoxin medication and cancer; case control and internal dose-response studies

BACKGROUND

Digitoxin induces apoptosis in different human malignant cell lines in vitro. In this paper we investigated if patients taking digitoxin for cardiac disease have a different cancer incidence compared to the general population.

METHODS

Computer stored data on digitoxin concentrations in plasma from 9271 patients with cardiac disease were used to define a user population. Age and sex matched controls from the Norwegian Cancer Registry were used to calculate the number of expected cancer cases.

RESULTS

The population on digitoxin showed a higher incidence of cancer compared to the control population. However, an additional analysis showed that the population on digitoxin had a general increased risk of cancer already, before the start on digitoxin. Leukemia/lymphoma were the cancer types which stood out with the highest risk in the digitoxin population before starting on digitoxin. This indicates that yet unknown risk factors exist for cardiovascular disease and lymphoproliferative cancer. An internal dose-response analysis revealed a relationship between high plasma concentration of digitoxin and a lower risk for leukemia/lymphoma and for cancer of the kidney/urinary tract.

CONCLUSION

Morbidity and mortality are high in the population on digitoxin, due to high age and cardiac disease. These factors disturb efforts to isolate an eventual anticancer effect of digitoxin in this setting. Still, the results may indicate an anticancer effect of digitoxin for leukemia/lymphoma and kidney/urinary tract cancers. Prospective clinical cancer trials have to be done to find out if digitoxin and other cardiac glycosides are useful as anticancer agents.

Effects of digoxin and digitoxin on circadian blood pressure profile in healthy volunteers

BACKGROUND

The aim of the study was to investigate the potential effects of chronic digoxin or digitoxin treatment or circadian blood pressure profile in normotensive subjects.

METHODS

In two randomized double-blind, placebo-controlled cross-over protocols, 22 healthy normotensive subjects were enrolled, 12 subjects in either study. After adequate loading doses, digoxin 0.25 mg twice daily or digitoxin 0.1 mg daily was given for a total of 10 days. Automatic 24-h ambulatory blood pressure measurements were carried out at days 4 and 10 of either glycoside or placebo.

RESULTS

Digoxin treatment significantly decreased heart rate (HR) and diastolic blood pressure (DBP) during the overnight sleeping phase of day 10 compared with placebo (HR, 4 beats min-1; DBP, 8 mmHg; P < 0.05). Digitoxin treatment significantly decreased heart rate and diastolic blood pressure during the overnight sleeping phase of day 4 (HR, 8 beats min-1; DBP, 7 mmHg) and day 10 (HR, 7 beats min-1; DBP, 5 mmHg) compared with placebo (P < 0.05). Neither digoxin nor digitoxin significantly affected systolic blood pressure.

CONCLUSIONS

Both digoxin and digitoxin, within therapeutic steady-state plasma concentrations, reduced diastolic blood pressure and heart rate during overnight sleep, presumably because of increased parasympathetic activity or decreased sympathetic activity.

Prolonged digitoxin half-life in very elderly patients

The digitoxin half-life in elderly patients in the eight and ninth decade was more prolonged (mean +/- SD: 25 +/- 9 days) than in younger people (6.7 +/- 1.7). These elderly patients accumulated digitoxin even on a dose of 0.05 mg/ day. The symptoms of digitoxin intoxication disappeared on discontinuation of medication. When digitoxin is used in the treatment for heart failure in the very elderly patients, one should be aware of the possibility of digitoxin intoxication, even on a low dose.

[Serum digitoxin in concomitant use of antiepileptics in routine therapy]

Concomitant use of digitoxin and enzyme-inducing antiepileptics may lower serum levels, and accordingly the effect of digitoxin, unless the higher metabolic clearance is compensated for by higher dosage. Use of digitoxin is almost always guided by serum concentration measurements. Information on a possible enzyme-inducing effect of phenobarbital, phenytoin and carbamazepine is easily accessible. Compilation of serum level measurements for digitoxin showed that serum levels shifted towards lower values during concomitant use of phenytoin or carbamazepine than when digitoxin was used alone. As a consequence, the fraction of patients with serum levels below the therapeutic range was doubled. Concomitant use of phenobarbital did not cause a shift in the levels of digitoxin. In fact, in this group, a larger fraction of the serum level measurements were within the therapeutic range. Thus, the dosage of digitoxin appears to be fully compensated during concomitant use of phenobarbital, but obviously deserves attention during concomitant use of phenytoin or carbamazepine.

Involvement of a peripheral mechanism in the emesis induced by cardiac glycosides in Suncus murinus

The ability of three cardiac glycosides, ouabain, digitonin and digitoxin, to induce emesis and their mechanism(s) of action were investigated in Suncus murinus. The intraperitoneal injection of ouabain but not digitonin nor digitoxin caused vomiting in a dose-dependent manner. However, the administration of ouabain into the cerebroventricle did not cause emesis. Ouabain-induced emesis was partly prevented by surgical abdominal vagotomy. Pretreatment with tropisetron, a selective 5-HT3 (5-hydroxytriptamine) receptor antagonist, did not affect the emetic response evoked by ouabain. These results suggest that ouabain exerts emetic effects via peripheral mechanism(s), but 5-HT3 receptors are not involved in the pathway.

[Thrombocytopenia caused by digitoxin overdose]

The authors report a new case of digitoxin-related thrombocytopenia. It involved a patient hospitalised for torsades de pointe in whom blood digitoxin was 85 micromols/l on admission. This rare complication progressed to a satisfactory conclusion in seven days. The mechanism is immuno-allergic and/or toxic since thrombocytopenia occurs only following therapeutic overdose. The prognosis is determined by the cardiac arrhythmia rather than the hemostasis abnormality. Treatment is symptomatic and should include the withdrawal of digitoxin which can be replaced by digoxin. Oral activated charcoal decreases the plasma half-life by blocking the enterohepatic cycle and is hence recommended in this situation.

Lack of a pharmacokinetic interaction between carvedilol and digitoxin or phenprocoumon

The possibility of a pharmacokinetic interaction between carvedilol and digitoxin (Study I) or phenprocoumon (Study II) has been evaluated in groups of 12 healthy volunteers. The bioavailability (Cmax, tmax, AUC) of digitoxin and phenprocoumon were assessed after a single dose, given once alone and once on day 6 of treatment with carvedilol 25 mg o.d. Cmax, tmax, AUC and Ut of carvedilol and desmethylcarvedilol were also investigated after the fifth dose of carvedilol and after the sixth dose given concomitantly with digitoxin or phenprocoumon. In Study I, the 95% confidence intervals of the ratio test versus the reference findings were; digitoxin Cmax 0.80-1.20, tmax 0.56-1.14, AUC 0.97-1.33, and for carvedilol Cmax 0.81-1.22; tmax 0.66-1.23; AUC 0.91-1.17. Formation of the active metabolite desmethylcarvedilol and the urinary recovery of carvedilol and desmethylcarvedilol were not influenced by digitoxin. In Study II Cmax and AUC of phenprocoumon were not changed after carvedilol. Cmax of carvedilol was decreased after phenprocoumon. The kinetic parameters of phenprocoumon were Cmax 0.80-1.05, tmax 0.47-2.00, AUC 0.78-1.05, and for carvedilol Cmax 0.59-1.06, tmax 0.71-1.73; AUC 0.80-1.08, respectively. The plasma levels of desmethylcarvedilol and the urinary recovery of carvedilol and desmethylcarvedilol were not influenced by phenprocoumon. The blood pressure and heart rate after carvedilol alone were not affected by concomitant administration of digitoxin or phenprocoumon.

Captopril does not interact with the pharmacodynamics and pharmacokinetics of digitoxin in healthy man

The chronic oral administration of 0.07 mg digitoxin o.d. for up to 58 days to 12 healthy volunteers caused a small drop in mean heart rate HR (95% CI: -7.9 to -1.6 beats.min-1), in mean diastolic blood pressure (95% CI: -8.3 to -0.4 mmHg), shortening of the QTc-interval (95% CI: -42 to -19 ms), shortening of the HR-corrected pre-ejection period PEPc (95% CI: -16 to -1 ms) and electromechanical systole QS2c (95% CI: -25 to -1 ms), and an increase in the impedance cardiographic Heather index (dZ/dtmax/RZ, 95% CI: 0.3 to 4.3) relative to the baseline measurements before digitalisation. The concomitant administration of 25 mg oral captopril b.d. did not significantly alter these responses relative to the concomitant double-blind administration of placebo, nor did it alter the pharmacokinetic characteristics of plasma digitoxin at steady state. Thus, no relevant change in the pharmacokinetic and pharmacodynamic characteristics of chronically administered digitoxin were induced by concomitant treatment with captopril.

Influence of induced cholestasis on pharmacokinetics of digoxin and digitoxin in dogs

Dogs with ligated common bile ducts were used to determine effects of cholestasis on pharmacokinetics of digoxin and digitoxin. Forty-three dogs were assigned to: group 1--sham-operated controls (n = 13); group 2--dogs with ligated common bile duct (n = 17); group 3--dogs given phenobarbital for 2 weeks before common bile duct was ligated (n = 11); or group 4--dogs with an induced biliary fistula (n = 2). Digoxin (group A) or digitoxin (group B) was given as single IV injections, and digitalis concentration in plasma was measured by radioimmunoassay. In 18 dogs given digoxin, differences in plasma digoxin concentrations among groups 1A to 3A were not significant (P greater than 0.1). Plasma elimination rate of digoxin was delayed in group 2A. Group-3A dogs had a shortened beta phase half-life (t1/2 (beta] and a decreased distribution volume. In 25 dogs given digitoxin, group-2B dogs maintained a significantly higher plasma digitoxin concentration (P less than 0.01) and had a significantly longer t1/2 (beta] than did dogs in groups 1B and 3B (P less than 0.05). In group-3B dogs, plasma digitoxin concentration was decreased and t1/2 (beta] of digitoxin was shortened. In 10 group-B dogs given 3H-digitoxin (groups 1B, 2B, and 4B), the excretion of total radioactivity in urine and bile was 15 to 20 and 7% of the dose, respectively in the first 24 hours. Most radioactivity in urine and bile was a dichloromethane-unextractable fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

[Therapeutic drug monitoring of digitoxin--results of 3 years' experience]

Between 1986 and 1988 within our therapeutic drug monitoring plasma concentrations were estimated in 1,442 plasma samples by radioimmunoassay. Plasma levels between 0 and 84.2 ng.ml-1 with a mean of 20.8 ng.ml-1 were measured. If the maintenance dose was reduced from 0.1 to 0.07 mg the frequency distribution of the plasma samples was shifted to the left, and the mean value decreased by 5.8 ng.ml-1 (23.5 vs. 17.7 ng.ml-1). The physician's assumptions underdosage?, optimum dosage schedule? or overdosage? were confirmed by the laboratory results in 22.3, 63.6, or 23.0% of the requests, respectively. In 61.2% of all plasma samples were digitoxin concentrations in the range between 10 and 30 ng.ml-1, i.e. in the optimum therapeutic range. Main reasons for the divergent results are non-compliance of the patients and inter-individual differences in the pharmacokinetics of digitoxin. Furthermore, incomplete filling of the forms by the physicians aggravates the assessment of the results. Therefore, a permanent dialogue between clinician and clinical pharmacologist is necessary for an improvement of digitalis therapy.

[Dosage adjustment of drugs during continuous hemofiltration. Results and practical consequences of a prospective clinical study]

In 43 ICU patients undergoing continuous volume constant hemofiltration (CVHF), the pharmacokinetics of 12 drugs were investigated to ensure correct dosage adjustments. Under conditions of CVHF, maximum doses were defined for cefotaxime, ceftazidime, digoxin, digitoxin, imipenem, metronidazole++, netilmicin, phenobarbital, phenytoin, theophylline, tobramycin, and vancomycin. For the estimation of sufficient doses without blood level measurements, sieving coefficients (S) were calculated by a new method. In addition, S was integrated as a CVHF-specific factor into a common equation for drug dose adjustment in patients with renal insufficiency. The regression of dosage received from kinetics on blood-level-independent equation adjustment was r = 0.9923. Since the volumes of distribution in ICU patients are variable, it is suggested that further drug monitoring is necessary for toxic drugs.

Digitoxin in patients with hepatorenal insufficiency after repeated oral administration

Following chronic oral administration of digitoxin 0.1 mg day-1 the pharmacokinetics of this glycoside were studied in seven patients with hepatorenal insufficiency and were compared with those of seven healthy volunteers. Liver cirrhosis of the patients was confirmed by liver biopsy. Mean creatinine clearance of the healthy subjects was 129.7 +/- 3.3 ml min-1 (mean +/- SEM), that of the patients was 25.6 +/- 20.4 ml min-1. Mean antipyrine clearance (parameter of oxidative liver function) was 49.7 +/- 6.0 ml min-1 in the volunteers and 22.0 +/- 2.9 ml min-1 in the patients. Plasma protein binding of digitoxin (PPB) was 95.0 +/- 1.1% in the patients and 96.7 +/- 0.6% in the healthy subjects (n.s.). Total body clearance of digitoxin (Cltot) was 0.0728 +/- 0.0120 ml min-1 kg-1 in the patients and 0.0615 +/- 0.0027 ml min-1 kg-1 in normals (n.s.]. Mean steady state plasma levels (Css) of the patients were 18.3 +/- 4.7 ng ml-1 and 15.8 +/- 1.3 ng ml-1 in the normals (n.s.). Our data obtained from chronic oral administration do not indicate a reduced total body clearance of digitoxin in patients with hepatorenal insufficiency.

Combined intoxication with digitoxin and verapamil. The possible inhibition of sensitisation to digitalis-specific antiserum by toxic drug concentrations

The clinical course in a patient with a combined intoxication with digitoxin (maximal serum level 357 nmol/l) and verapamil is described. The patient received two injections of digitalis-specific antiserum. No adverse reactions to the therapy was seen, and the antiserum markedly shortened the plasma half-life of digitoxin. In vitro studies indicate that digitoxin in concentrations seen during the intoxication may have an immunosuppressive effect, thereby reducing the risk of sensitisation to the antiserum.

[Digitalis therapy in chronic heart failure. Digitoxin in patients in sinus rhythm pretreated with diuretics]

Eight patients in sinus rhythm with chronic heart failure were studied. After individually adjusted six-week treatment with diuretics (hydrochlorothiazide-triamtere and/or frusemide) all patients were clearly improved symptomatically. Subsequently they additionally received digitoxin for six weeks, 0.07-0.1 mg daily. Before and at the end of the digitoxin period cardiac volume was determined radiologically, echocardiography was performed and haemodynamic parameters determined at rest and on exercise via indwelling catheters. During digitoxin administration there was a slight increase in cardiac output from 4.63 +/- 0.82 to 5.05 +/- 0.98 l/min (P less than 0.1) at rest and from 7.22 +/- 1.94 to 7.79 +/- 2.59 l/min at rest. The mean values of all other haemodynamic parameters remained unchanged. These results suggest that in patients with chronic heart failure and sinus rhythm any clinical or haemodynamic improvement achieved will not be significantly bettered by digitoxin.

Quinidine syncope in children

Quinidine syncope and factors associated with it are well known among adult patients treated for cardiac arrhythmias. To define factors that may influence the occurrence of syncope in children taking quinidine, the clinical, anatomic, electrocardiographic, roentgenographic and pharmacologic data were compared in six patients with syncope (Group A) and 22 patients without syncope (Group B). There was a significant (chi-square = 10.2, p = 0.001) relation between heart disease and quinidine syncope: all six Group A (syncopal) patients had heart disease whereas 15 of the 22 Group B (non-syncopal) patients had no structural heart disease. In contrast, no significant difference was noted between Group A and Group B patients in mean age (11.4 versus 11.4 years), mean quinidine serum concentration (2.9 versus 2.3 micrograms/ml), mean corrected QT interval before quinidine (0.43 versus 0.40 second) or mean corrected QT interval during quinidine therapy (0.46 versus 0.46 second) or between those taking digitalis and those not. Two of the six Group A (syncopal) patients died during therapy, one 6 days after initiating therapy and one suddenly at home 6 months after beginning quinidine. Another two of the six Group A patients exhibited hypokalemia (both 2.9 mEq/liter) at the time of syncope, 2 weeks and 6 months, respectively, after initiation of quinidine therapy; both survived. Syncope occurred within 8 days of initiation of quinidine therapy in three of the six patients. Sustained ventricular tachycardia was observed during quinidine associated arrhythmia in three of six patients with syncope; nonsustained ventricular tachycardia or complex ventricular ectopic activity while on this therapy was observed before syncope in the other three patients in Group A.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of verapamil on pharmacokinetics and pharmacodynamics of digitoxin in patients

Investigations by various teams have shown that combined treatment with verapamil and digoxin may result in a marked increase in digoxin plasma concentrations, necessitating a reduction in the dose of digoxin. This is mainly due to an impairment of the renal digoxin excretion. Unlike digoxin, the excretion of digitoxin is independent of renal function. A prospective clinical study was therefore planned to investigate the influence of a daily dose of 240 mg of verapamil on pharmacokinetics and the cardiac effect of digitoxin after a single dose (n = 3) and under steady-state conditions (n = 10). While pretreatment with verapamil did not alter pharmacokinetics of digitoxin in the single-dose study, there was a slight rise of digitoxin plasma concentrations (an average of 35% in 8 out of 10 patients) following administration of verapamil for a period of 4 to 6 weeks. Renal excretion of digitoxin, however, was not changed significantly. Simultaneous with a rise of digitoxin plasma concentrations and until a new steady state was reached, PQ interval was prolonged and T wave flattening intensified. On the other hand, the antagonistic effect on contractility which was initially observed after verapamil administration was diminished. Based on these observations, it can be concluded that the risk of digitalis overdose after combined treatment with verapamil and digitoxin may be less pronounced than after digoxin, and that this glycoside can prove a valuable alternative.

Effects of digitoxin and hypokalaemia on pancreatic NaHCO3 secretion and pancreatic Na,K-ATPase activity

To study the role played by Na,K-ATPase in the pancreatic secretion of NaHCO3, experiments were performed in 20 anaesthetized, secretin-infused pigs (3.0 clinical units X kg b. wt. X h-I). The relationship between pancreatic NaHCO3 secretion and arterial pH was obtained before and during Na,K-ATPase inhibition by digitoxin and hypokalaemia. Na,K-ATPase activity in pancreatic tissue homogenate averaged 5.45 (5.02-6.68) mumol Pi X mg X protein X h-I. Retrograde injection of 0.5 ml 1.4 X 10(-4) mol X l-I digitoxin into pancreatic ducts reduced pancreatic Na,K-ATPase activity by 3I(I8-47)%, while intra-arterial injection of 0.2 mg X kg b. wt-I digitoxin reduced pancreatic Na,K-ATPase activity by 50(45-56)%. Digitoxin and hypokalaemia reduced the rate of pancreatic NaHCO3 and shifted the normal, proportional relationship between NaHCO3 secretion and arterial pH towards higher pH. Hypokalaemia reduced Na,K-ATPase activity and NaHCO3 secretion in proportion. These effects indicate that Na,K-ATPase helps to sustain the requisite electrochemical potential gradients for driving H+ ions, and hence HCO-3 ions, out of secretory cells.

Effect of intravenous digitoxin on inotropy, haemodynamics and P-Q interval in ischaemic heart disease

The haemodynamic and electrophysiologic responses to rapid intravenous injection of digitoxin (0.6 mg over 5 min) were measured in 6 patients with chronic coronary heart disease without clinical heart failure. Two minutes after end of injection peripheral resistance increased and stroke volume fell, while peak dP/dt in the right ventricle showed minimal increase. AV nodal conduction velocity decreased markedly. Thereafter, the peripheral resistance remained unchanged, stroke volume and peak dP/dt in the right ventricle increased slightly, while AV conduction remained stable. In 2 control patients stable values were found during 60 min. We conclude that digitoxin given intravenously as a single bolus injection induces an abrupt slight increase in peripheral resistance. Thereafter, a gradual increase in inotropy is found. The effect on the AV node appears rapidly and remains stable.

[Epidemiology of digitalis medication. Results of the Munich blood-pressure study]

As part of a blood-pressure survey in Munich, some of its inhabitants aged 30-69 years were asked by questionnaire about any digitalis medication. Chemically defined glycosides were taken by 127 of 1827 persons (7%), two-thirds of them older than 60 years, for clinically compensated chronic heart failure. Using the equation of Cockcroft and Gault to calculate creatinine clearance, it was below 80 ml/min and thus indicative of early impairment of renal function in more than 50%. In 44% the prescribed daily dose of glycoside corresponded to the calculated maintenance dose, 29% had less and 27% had taken more. None had clinical signs of digitalis intoxication. ECG changes possibly due to digitalis were much less common than had been expected. Sinus rhythm was present in 93%. More than 50% did not know why they were taking digitalis and 80% were taking two or more drugs at the same time. Since more than half had signs of early renal function impairment, creatinine clearance should be taken into account when determining the dosage of a digoxin preparation especially in elderly patients; alternatively, digitoxin should be prescribed. The survey also showed that a large number of persons on glycoside medication did not take the drug regularly.

[Trial for digitalis withdrawal in hemodialysis patients]

The indication for digitalis treatment was investigated in a controlled and prospective study lasting 12 months in 110 patients on long-term haemodialysis. In ten patients, digitalis was needed because of tachyarrhythmia due to atrial fibrillation and in five because of recurrent pulmonary edema. In 57 patients receiving digitoxin, therapy was discontinued for 4 to 6 weeks, whereas 13 patients not yet treated with digitalis, received digitoxin for 4 weeks. Without digitoxin, trial fibrillation occurred in 4 patients, while no patient experienced atrial fibrillation with digitoxin (P = 0.002). In 13 patients, radiological findings (heart enlargement, pulmonary congestion) were better with digitoxin than without. Thus digitoxin appeared to be clearly indicated in 29% of the haemodialysed patients. Additionally, digitalis was indicated in 31 patients because of heart enlargement, pulmonary congestion and (or) previous pulmonary edema. Initially, 76% of the patients were receiving digitoxin, whereas, after the investigation, the rate was only 57% (P less than 0.001). The prospective frequency of clinically apparent digitoxin intoxication was low (3%) and so were the overall toxic plasma digitoxin levels (5%). Digitalis should be given deliberately but not restrictively to haemodialysis patients, since atrial fibrillation (13%) and heart failure (50%) are frequent and often concealed.

[Digitoxin blood picture and renal elimination in long-term therapy with aluminum-magnesium hydroxide gel]

In ten patients in heart failure for which they were on long-term administration of digitoxin, the influence of aluminium-magnesium hydroxide gel (Maaloxan) on steady-state digitoxin plasma concentration and renal glycoside excretion was studied. Compared with control values before antacid medication (13.6 +/- 4.4 ng/ml), the administration of 20 ml aluminium-magnesium hydroxide gel three or four times daily for several weeks caused no significant change in digitoxin plasma levels (15.1 +/- 4.9 ng/ml). Daily renal glycoside excretion, as a further measure of bioavailability of digitoxin, was also unchanged by the antacid. Therapeutic plasma concentrations of digitoxin are not influenced by antacids which contain aluminium-magnesium hydroxide, at least not if the antacid is taken 1-2 hours after the digitoxin dose.

Digitoxin kinetics and renal excretion in children

Digitoxin kinetics were investigated in 11 children, three girls and eight boys, with a mean age of 7.1 yr (5.9 to 9.2). Five children received digitoxin, 17.5 to 20 micrograms/kg IV, and six other children received 20 micrograms/kg as an oral solution. Digitoxin was given as a single dose 24 to 48 hr after cardiac surgery, and patients were monitored in an intensive care unit for 24 hr. Serum and urine digitoxin concentrations were determined by radioimmunoassay. Children had larger apparent volumes of distribution (1 l/kg) than adults (0.57 l/kg). Mean serum elimination t 1/2 was 6.4 days in children (3 to 11.2) and 8.2 days in adults (5.9 to 11.3). Total body clearance was much greater in children (0.085 ml X min-1 X kg-1) than in adults (0.036 ml X min-1 X kg-1). This was because of an increase in metabolic clearance, although there was no difference in renal clearance in children and adults. Absolute oral bioavailability, measured by comparing serum AUCs after intravenous and oral doses, was complete. Peak serum concentrations of 23 to 50 ng/ml developed 90 to 120 min after the oral dose. A single digitalization dose of 20 micrograms/kg was well tolerated and did not induce arrhythmias.

Digitoxin intoxication with severe thrombocytopenia: reversal by digoxin-specific antibodies

As a result of overdosage a 77-year-old patient with heart disease developed digitoxin intoxication, associated with arrhythmias, extracardiac symptoms of intoxication and severe thrombocytopenia. Treatment with digoxin-specific antibody fragments relieved the signs and symptoms of intoxication within a few hours. The rise in platelet count from the pretreatment value of 26 000/mm3 to 47 000 within 12 h and to over 60 000/mm3 within 16 h of starting the antibody infusion may also be attributed to the treatment with antibodies. Such a rapid recovery from digitoxin-induced thrombocytopenia has not hitherto been described. Digoxin-specific antibodies, obtained by immunization of sheep with a digoxin-albumin conjugate, were used to treat intoxication with digitoxin, since cross-reaction had been demonstrated in vitro and in animal experiments. The present paper briefly discusses the mode of action and the general problems relating to the antibody therapy of digitalis poisoning.

Effects of arrhythmia-producing concentrations of digitoxin on mechanical performance of cat myocardium

Digitalis toxicity in vivo generally is recognized by the appearance of cardiac arrhythmias but in vitro by a decline in myocardial performance. To determine whether concentrations of digitoxin producing cardiac arrhythmias in intact animals also produce a decline in myocardial performance directly, three groups of adult cats were studied. One received digitoxin daily until arrhythmias developed (toxic group), the second sufficient digitoxin to produce an inotropic effect without arrhythmias (nontoxic group), and the third was untreated. Peak isometric force and maximal dF/dt of isolated right ventricular papillary muscles were significantly greater in nontoxic muscles (3.9 +/- 0.4 gm/mm2 and 21.3 +/- 1.7 gm/mm2 . sec-1). Values in toxic muscles were similar to untreated ones (2.8 +/- -.6 gm/mm2 and 19.0 +/- 3.2 gm/mm2 . sec-1). Acetylstrophanthidin (2 X 10(-8) M) resulted in an increase in peak force and max dF/dt in nontoxic muscles, whereas myocardial performance changed minimally in untreated muscles and declined in 8 of 10 toxic muscles. We conclude that electrical and mechanical toxicity induced by digitoxin frequently coexist.

Digitoxin accumulation

1 Nine healthy volunteers received single 1 mg intravenous doses of digitoxin, following which serum digitoxin concentrations were measured at multiple points in time over the next 14 days. 2 Mean kinetic variables for digitoxin were: volume of distribution, 0.76 l/kg; elimination half-life, 8 days; total clearance, 0.049 ml min-1 kg-1. 3 After a drug-free interval of at least 4 months, subjects took 0.07 mg of oral digitoxin daily for 28 consecutive days. Serum digitoxin concentrations were measured during the period of dosage and in the 21 day post-dosage washout. 4 Digitoxin accumulation was slow, proceeding with a mean half-life (7.9 days) that was nearly identical to the single-dose half-life. However, the two were not significantly correlated. 5 Mean observed steady-state serum concentrations (15.4 ng/ml) also were nearly identical to those predicted from the single-dose study (15.3 ng/ml), but again the two were not significantly correlated. 6 Steady state is very slowly attained after initiation of maintenance therapy with digitoxin. The kinetic data suggest that a loading dose on the average should be 12 times the maintenance dose.

[Characteristics of the effect of drug combinations on the development of immediate hypersensitivity]

As compared to the action of the drugs given alone, the combinations of antiallergic drugs and cardiac glycosides had different effects on the nature and intensity of the processes inherent in allergy. These differences correlated to a certain degree with the mechanism of a reaction which experienced the action of the drug combination. Within the frames of synergoantagonism interplay, the drug combination produced on some of the reactions an effect which was similar to that exerted by one of the components. Meanwhile the magnitude of the effect produced by the same drug combination on the other reactions was half as that manifested by the components administered alone. Sometimes in the combinations of the drugs, the effects of the constituent parts were perversed in the course of action on some of the processes. In individual cases the combined drugs had remarkable effects on a reaction, while the individual components did not change it. Strophanthine given in the combinations tested, almost never displayed its specific action on the reactions inherent in sensitization. Combined diphenhydramine affected, as a rule, the sensitization and altered the effect of other substances.

Digitalis therapy in renal failure with special regard to digitoxin

When prescribing cardiac glycosides for patients with renal failure, one should consider the different pharmacokinetics of the two most important glycosides, digoxin and digitoxin. Whereas steady state plasma concentrations of digoxin are altered proportionally to renal clearance of creatinine, those of digitoxin remain the same throughout a wide range of renal impairment. The steady state level of both glycosides is partly determined by several clinical factors such as dose, body weight, height, age and serum potassium. However, it is thought that bioavailability, volume of distribution, biotransformation, and total body clearance have the greatest importance for the variability of the plasma glycoside concentrations in patients with normal and with impaired renal function. The bioavailability and biotransformation of digoxin do not vary between healthy subjects and patients with renal insufficiency. As the volume of distribution is smaller in patients with severe renal failure that in normal subjects, the loading dose has to be altered. With decreasing creatinine clearance the total body clearance as well as the renal clearance of digoxin is reduced. On the basis of this assumption maintenance dosage regiments must be adjusted. For digitoxin, the four above-mentioned pharmacokinetic parameters are not altered in patients with renal failure compared to healthy subjects. Moreover, investigations dealing with this problem have suggested an altered protein binding of digitoxin and its metabolites as a possible factor in avoiding accumulation of the drug. However, it is one of the aims of this article to show that a decreased urinary excretion of digitoxin and metabolites is compensated by an increased excretion via the feces. Loading dose and maintenance dose of digitoxin do not have to be adjusted in patients with renal failure.