Multiple-dose pharmacokinetics of epirubicin at four different dose levels: studies in patients with metastatic breast cancer.

Pharmacokinetic analysis of epirubicin and its metabolites epirubicinol and 7-deoxy-13-dihydro-epirubicinol aglycone during the first and the fourth courses of treatment was performed in 78 patients with metastatic breast cancer. The patients were treated every 3 weeks with epirubicin given as 10-min i.v. infusions at four different dose levels: 40, 60, 90 and 135 mg/m2. In most cases (76 of 78 cases), plasma concentration-time curves fitted to a three-compartmental pharmacokinetic model. The terminal half-life of epirubicin was independent of dose and duration of treatment. Large interindividual differences were demonstrated (mean t1/2 gamma, 21.6 +/- 7.9 h; range, 10.6-69 h; n = 110). In two subjects, extremely long half-lives and high serum bilirubin concentrations indicated impaired liver function. No correlation was found between the half-life and levels of liver alanine aminotransferase (ALAT) or serum creatinine. The metabolite epirubicinol appeared quickly after epirubicin administration and its half-lives were shorter than that of the parent compound (mean t1/2 gamma, 18.1 +/- 4.8 h; range, 8.2-38.4 h; n = 105). Formation of the aglycone metabolite was delayed and the half-life of this metabolite was shorter than that of epirubicin (mean t1/2 gamma, 13 +/- 4.6 h; range, 2.7-29 h; n = 104). The AUC of epirubicin and the total AUC (drug and metabolites) were linearly proportional to the dose, with the former value constituting two-thirds of the latter. A correlation was found between AUC and the plasma concentration of epirubicin at two time points (2 and 24 h after administration). The proposed model was AUC = 9.44 x c2 + 62.5 x c24 + 157.7 (r = 0.953).

Furosemide kinetics and dynamics in rats and humans.

1. Increasing doses of furosemide (F) were given intravenously to rats and humans and initial pharmacokinetics and pharmacodynamics were compared. 2. Weight-related initial renal excretion rate of F was twice as high in rats and serum concentration at 30 min was twice as high in humans (P less than 0.01). 3. Volume of distribution for F was 44% larger in rats (P less than 0.01). 4. Maximal weight-related diuretic and natriuretic responses were, like the theoretical maximal efficiency, 5-6 times higher in the rat. The potency was 230 times lower in the rats. 5. On a molecular basis species differences in kinetics disappeared when standardization was based on ERPF and species differences in dynamics disappeared when standardization was based on GFR.

Effects of long-term coenzyme Q10 and captopril treatment on survival and functional capacity in rats with experimentally induced heart infarction.

The effects of coenzyme Q10 (CoQ) and captopril on functional capacity, hemodynamics and survival were studied in 154 rats that recovered after experimental myocardial infarction. Rats were randomized into four groups receiving either CoQ, captopril, a combination of the two drugs or 1 ml of tap water once daily for 12 weeks from the day of coronary artery ligation. CoQ as well as captopril and the combined treatment significantly improved exercise capacity as evaluated by lactate production during a standardized treadmill exercise test. No significant changes in heart rate or mean blood pressure were observed during the study in the captopril-treated group. CoQ treatment increased the maximum heart rate significantly, whereas no effect on mean blood pressure was observed. Both captopril and CoQ decreased pulmonary congestion. Furthermore, the data may suggest that captopril prevents right ventricular hypertrophy seen in placebo-treated rats with large infarcts. This was not observed after CoQ treatment. Captopril treatment improved 3-month probability of survival (93%) as compared with placebo (74%) (P less than .05). CoQ and the combined treatment tended to improve survival, but this was, however, not statistically significant.

Bumetanide-induced natriuresis and antinatriuresis in the proximal and distal parts of the human nephron. Investigations in acute and chronic bumetanide treatment.

In the present study we used the Li clearance technique to evaluate the effects of submaximal bumetanide infusion on proximal and distal Na reabsorption in healthy volunteers with and without volume and Na replacement. These effects were studied both in chronic bumetanide-treated and in previous nontreated subjects. Li was given as Li carbonate p.o. Glomerular filtration was evaluated by creatinine clearance. Infusion of bumetanide increased fractional Na excretion and fractional Li excretion in the volume-replaced subject. Without volume-replacement bumetanide infusion increased these excretion rates to a significantly lower level. These results suggest that in humans acute submaximal doses of bumetanide cause inhibition of both proximal and distal tubular reabsorption of Na. Along with diuretic-induced volume contraction the natriuretic response is diminished perhaps due to a secondary increase in fractional Na reabsorption which occurs only in the proximal tubular portions of the nephron. In chronic bumetanide-pretreated subjects, however, the fractional Na and Li excretion increased significantly more than in the previous nontreated subjects. Compared to these ion excretions in diuretic-induced Na and volume-depleted subjects the results suggest that a secondary increase in fractional Na reabsorption is developed rapidly during submaximal bumetanide infusion in chronic bumetanide-treated subjects. In the distal part of the nephron, however, the bumetanide-induced increase in Na excretion is much less in the chronic bumetanide-treated subjects than in previous nontreated. Because of these results it is suggested that simple dose-effect relationship for loop-diuretics will be difficult to describe.

Time course of functional deterioration after coronary artery ligation in rats.

The aim of this study was to investigate the time course of deterioration of functional capacity in the rat after ligation of the left coronary artery. Functional capacity was evaluated from the increase in blood lactate concentrations in 109 rats during a standardised treadmill test. Animals with myocardial infarction were compared with sham operated and normal controls. Functional capacity was followed during a 13 week period and estimations of the functional capacity were performed 1, 3, 7, 9 and 13 weeks after infarction. Coronary artery ligation produced a significant reduction in functional capacity, averaging 47% (p less than 0.01) over the first 3 weeks after myocardial infarction, irrespective of infarct size. In rats with large infarcts, functional capacity remained essentially unchanged throughout the observation period, but rats with small infarcts improved gradually until their measured exercise response was completely normal at the end of the 13 week period.

Isolation of cardiac ventricular myocytes from newborn rats by use of fractional elutriation centrifugation.

Isolation of cardiac ventricular myocytes from newborn rats (0-4 days old) by use of elutriation centrifugation is described. By the use of fractional centrifugation, a homogeneous myocyte population with high purity was obtained without any further procedures, yielding about 10(6) myocytes/rat. When 48-hr monolayer cultures were established, the cells showed normal pulsatory contractions. A morphological evaluation of such cultures is given.

Pharmacokinetics of oral idarubicin in breast cancer patients with reference to antitumor activity and side effects.

The pharmacokinetics of orally administered idarubicin (22.5 mg/m2/week) and idarubicinol were studied for 12 weeks in 14 patients with breast cancer. Plasma concentrations were monitored for 72 hours after the first, fourth, and twelfth doses and trough concentrations after 1, 2, 3, 4, 5, 7, 11, and 12 weeks of treatment. The half-lives of idarubicin and idarubicinol were 19 and 60 hours, respectively. No time-dependent changes or cumulation were observed. The metabolic ratio showed little variation. The plasma AUCs of idarubicin and idarubicinol varied between patients but were fairly constant in individual patients. The sum of the plasma AUCs was lower in patients with rapid progression than in patients who responded to treatment. A correlation between this parameter and the relative decrease in the leukocyte counts was demonstrated (p less than 0.05). No correlation was found between the pharmacokinetic parameters and the time to final progression.

Dose dependency of furosemide-induced sodium excretion.

Intravenous furosemide doses ranging from 5 to 120 mg were given to healthy young volunteers with and without individualized active rehydration with a sodium chloride solution. Sodium excretion rates and fractional sodium excretions (FENa) percentages were correlated significantly with dose and with urinary excretion rates of furosemide. The ED50 was below 5 mg and no additional natriuretic effect was seen above 40 mg. The efficiency (FENa percentage per microgram of furosemide excreted per minute during a certain clearance period) was dependent on hydration and on time. For the period 15 to 30 min a significant linear relationship between furosemide dose and the reciprocal of the efficiency indicated a higher efficiency for lower doses and a theoretical maximal value of FENa of 0.4% per micrograms of furosemide excreted per minute. A relative value for a dose-dependent efficiency reduction was calculated for each dose. The ED50 for dose-dependent efficiency reduction was about 12 mg i.v. Simultaneous measurements of lithium clearance indicated a proximal site of action for furosemide which was saturated at furosemide excretion rates above 50 micrograms/minute. For the major, distal, site of action no maximal value was demonstrated. It is concluded that a wanted balance between a strong natriuretic effect and weak sodium retaining mechanism not necessarily is achieved by a high dose and that information concerning that problem must be obtained from studies in relevant patient groups.

Atrial content and plasma levels of atrial natriuretic peptides in rats with chronic renal failure.

The possible role of atrial natriuretic peptides (ANP) for the adaptive changes in renal Na excretion during chronic renal failure was studied in 5/6 nephrectomized (NX) rats maintained on a normal (100 mmol/kg) and a high (800 mmol/kg) Na diet. Atrial content of natriuretic substances was determined by bioassay and plasma ANP by radioimmunoassay. Nephrectomized rats showed a twofold increase in plasma ANP irrespective of their Na intake. Atrial ANP content was increased by high Na diet but unchanged by NX. Nephrectomized rats maintained on high Na diet showed partial depletion of atrial ANP stores. There were no significant changes in the volume fraction of atrial granules determined. The results suggest that ANP is involved in the regulation of renal Na excretion during chronic renal failure and acute Na loading; other mechanisms are probably involved in the adaption to chronic Na loading.

Beta 2-mediated changes in central haemodynamics, coronary circulation and myocardial metabolism in canine.

The combined effect of terbutaline on systemic and coronary circulation was investigated in dogs to clarify its influence on myocardial oxygen supply and lactate balance. The dogs were anaesthetized and the chest opened. Coronary sinus blood flow and cardiac output were monitored by thermodilution, aortic pressure was measured by tip-transducer and heart rate by RR-interval on ECG, coronary sinus blood were analyzed for lactate, oxygen and carbon dioxide. Terbutaline caused a substantial systemic vasodilation and an increased heart rate, the total external cardiac work increased to a minor degree. Terbutaline increased arterial lactate concentration. Coronary vascular resistance was reduced after terbutaline. Even if myocardial perfusion pressure was reduced and an increased external cardiac work was present, no signs of myocardial distress was observed in lactate metabolism or coronary sinus oxygen content. In fact a tendency to increased myocardial aerobic metabolism was observed, as myocardial lactate consumption increased after terbutaline. Terbutaline seems to be a coronary vasodilator in dogs. However, the demand for oxygen secondary to both an increase in cardiac work and aerobic metabolism can be hazardous to the potentially ischaemic myocardium.

Dose dependence of proximal and distal tubular effects of furosemide in conscious rats.

The dose-response relationship for the diuretic effect of furosemide, given as i.v. bolus injections (0.1-480 mg/kg) was investigated by clearance technique in conscious rats. By measuring the renal Li clearance, the effects on proximal and distal nephron segments were separated, and peak responses were correlated to the maximal excretion rate of furosemide in the urine. At the highest dose of furosemide, fractional Na excretion was increased from 1 to 19%, due to inhibition of fractional proximal Na reabsorption from 65 to 40% and fractional distal Na reabsorption from 97 to 57%. Furosemide inhibition of fractional proximal Na reabsorption showed a maximum at intermediate doses (7.5 mg/kg), whereas there was no maximum for the inhibition of distal fractional Na reabsorption. The natriuretic response was shorter than expected from the decline in furosemide excretion due to an abrupt fall in glomerular filtration rate and a rapid normalization of proximal fractional Na reabsorption. It is suggested that the maintenance of a normal delivery of tubular fluid to the distal nephron during furosemide-induced volume contraction may be due to inhibition of proximal tubular reabsorption.

Evaluation of increased serum creatine kinase as an indicator of irreversible myocardial damage in dogs.

To evaluate the relationship between creatine kinase (CK) elevation and irreversible myocardial damage, a coronary artery branch was occluded for periods of 5 to 40 min in ten dogs. In five other dogs the coronary vessel was occluded for 480 min, and five dogs underwent the same operative procedure but without occlusion of the artery. The serum CK was monitored for 8 hours postoperatively in all dogs. Elevation of the CK levels occurred in all groups, but the area under the time-enzyme activity curve showed no statistically significant difference between the group with 480-min occlusion, in which transmural myocardial infarction occurred in all dogs, and the group with temporary occlusion, in which no infarction could be histologically or histochemically demonstrated. Contrastingly, a statistically significant difference was found between the group with temporary occlusion and the control group with no occlusion. The results suggest that CK elevation is of no value as an indicator of irreversible myocardial damage during heart surgery that involves temporary myocardial ischaemia.

Tubular sites of furosemide natriuresis in volume-replaced and volume-depleted conscious rats.

There is accumulating evidence that the renal Li clearance reflects the delivery of Na and volume out of the proximal tubules. In the present study we used the Li clearance technique to evaluate the effects of submaximal furosemide (Fur) infusion (7.5 mg/kg/hr) on proximal and distal Na reabsorption in conscious rats with and without volume replacement with saline. Li was given as an p.o. test dose (0.5 mmol/kg) and [3H]inulin was infused in saline to measure the glomerular filtration rate (GFR). In control rats not infused with F, fractional Na excretion was about 1% and fractional Li excretion was about 30 to 35%. Infusion of F with constant rate and volume replacement increased fractional Na excretion to 22% and fractional Li excretion to 57% associated with a small decrease of the GFR. Without volume replacement F infusion caused a smaller and temporary diuretic and natriuretic response (maximum fractional Na excretion = 7.5%) followed by a decrease of urine flow and Na excretion almost to control levels, despite continued high excretion rates of F. The GFR decreased by 25% and fractional Li excretion showed an initial increase followed by return to baseline levels. The results suggest that in conscious rats submaximal doses of F cause major inhibition of proximal tubular Na reabsorption, which effect contributes substantially to the initial natriuresis. Along with diuretic-induced volume contraction, the natriuretic response is abolished due to a fall in GFR and particularly due to a secondary increase in fractional Na reabsorption, which occurs both in proximal distal tubular nephron segments.

Positive inotropic drugs--digitalis.

Digitalis glycosides inhibit Na+K+-ATPase in the cells and have been used for scientific studies of cation transport over cell membranes. Furthermore, digitalis has a positive inotropic and antiarrhythmogenic effect. Specific binding sites for digitalis glycosides have been observed in erythrocytes, the myocardium and the central nervous system. Transcellular transport of digoxin has been found in the kidney, since digoxin is excreted by tubular secretion. Recent studies have discovered an endogenous digitalis-like substance both inhibiting Na-K-ATPase and displacing digoxin from specific binding sites at the erythrocytes. The concentration of this component in plasma seems to be higher in hypertension than in normotension. Future studies will have to disclose other effects of this substance in order to evaluate whether it can be used as a drug in heart failure.

Doxorubicin binds in a cooperative manner to myocardial cells. Two binding sites.

Experimental evidence indicates that the anthracycline antibiotic doxorubicin (adriamycin) localizes mainly in cell nuclei of cardiac cells and has a high affinity to several cellular constituents in addition to DNA. In the present study the cellular kinetics of doxorubicin in cultured rat myocardial cells were determined by measuring its uptake, its binding pattern over a concentration range of 0.1 mM to 80 microM, and the cellular release by means of [14-14C]doxorubicin. The binding kinetics of doxorubicin were compared with the doxorubicin-induced inhibition of [methyl-3H]thymidine incorporation into DNA. It is demonstrated that at micromolar concentrations doxorubicin is readily taken up by myocardial cells and that myocardial cells have the ability to bind doxorubicin at two specific binding sites and that a noncooperative high-affinity/low-capacity type and a positive cooperative type of binding are involved, as indicated by the positive slope in the initial region of the binding isotherm (Scatchard plot). A dose-dependent inhibition of [methyl-3H]thymidine incorporation into DNA is demonstrated. It is suggested that this is associated with the positive cooperative binding of doxorubicin. The cellular release of doxorubicin appeared to be biphasic, with estimated half-lives of about 5-6 h for the initial phase and 50-60 h for the terminal phase. The results of this study indicate that doxorubicin preferably binds to sites within myocardial cells and that the positive cooperative binding pattern is due to DNA as one of the binding sites. A relationship between the noncooperative high-affinity/low capacity binding and the pharmacological activity has yet to be determined.

Aprotinin does not add protective effect to cold cardioplegia during coronary artery bypass surgery.

The effect of aprotinin on intraoperative and postoperative CK-MB and left ventricular contractility in terms of dp/dt response to atrial pacing up to 150 beats/min was studied in 20 patients randomized before aortocoronary bypass surgery to either aprotinin or placebo administration. Cold cardioplegia and topical deep hypothermia were used in both groups. No difference could be demonstrated between the aprotinin and the placebo group, and the authors therefore concluded that aprotinin does not add substantially to the protective effect of cold cardioplegia and deep topical hypothermia during aortocoronary bypass surgery.

Similar changes in cardiac morphology and DNA synthesis induced by doxorubicin and 4'-epi-doxorubicin.

Doxorubicin is an antineoplastic agent whose clinical administration is limited by dose-dependent irreversible cardiomyopathy. Doxorubicin inhibits the rate of DNA synthesis in cultured rat myocardial cells after 1 h incubation with 16 microM, as is demonstrated by a decreased incorporation of [methyl-3H]thymidine. An analogue of doxorubicin, 4'-epi-doxorubicin, also inhibits the rate of DNA synthesis within 1 h after treatment with 16 microM, to the same extent as doxorubicin-treatment of myocardial cells. Furthermore, similarity between doxorubicin and 4'-epi-doxorubicin in their effect on the myocardial thymidylate pool was also demonstrated by a significantly decreased incorporation of total [methyl-3H]thymidine. The effect of doxorubicin on the rate of DNA synthesis in cultured rat skeletal muscle cells treated for 1 h with 16 microM was quantitatively the same as in myocardial cells. Light microscopy of doxorubicin- and 4'-epi-doxorubicin-treated myocardial cells and doxorubicin-treated skeletal muscle cells showed distinct nucleolar fragmentation and revealed no differences between the two drugs in their effect on either myocardial or skeletal muscle cells. Electron microscopy of myocardial cells following doxorubicin treatment showed increased nuclear pleomorphism and invaginations, along with a striking and distinctive clumping of nuclear chromatin. Furthermore, an apparent high density of the mitochondria due to an increased matrix volume and a concomitant decrease in the intermembrane compartment were observed. The results of this study indicate that doxorubicin-induced inhibition of cardiac DNA synthesis in cultured myocardial cells is nonpredictive of cardiotoxicity. The mechanism is at least bimodal, and the apparent minor toxicity of 4'-epi-doxorubicin compared with that of doxorubicin in clinical trials cannot be distinguished by a difference in the inhibition of DNA synthesis in the rat heart.