Pharmacokinetic profile of recombinant human N-acetylgalactosamine 4-sulphatase enzyme replacement therapy in patients with mucopolysaccharidosis VI (Maroteaux-Lamy syndrome): a phase I/II study.

AIM: Mucopolysaccharidosis VI (Maroteaux-Lamy syndrome) is a lysosomal storage disease caused by a deficiency of the enzyme-N-acetylgalactosamine 4-sulphatase (ASB). Enzyme replacement therapy with recombinant human ASB (rhASB) has been studied in a randomized, double-blind, two-dose (0.2 and 1.0 mg/kg/week) phase I/II study (n = 7) followed by an open-label single dose (1.0 mg/kg/week) extension study. We report the pharmacokinetic profile of rhASB and the impact of antibody development. METHODS: Pharmacokinetic analysis was performed at weeks 1, 2, 12, 24, 83, 84 and 96. Infusions were administered over 4 hours using a ramp-up protocol. Plasma ASB and rhASB antibody concentrations and urine glycosaminoglycan (GAG) concentrations were determined. RESULTS: The area under the plasma concentration-time curve (AUC(0-t)) for the high-dose group increased from week 1 to week 2, but remained unchanged at weeks 12 and 24. A large difference in mean AUC(0-t) was observed between the low- and high-dose groups. Pharmacokinetic results at weeks 83, 84 and 96 were similar to those at week 24. Six patients developed antibodies to rhASB. One patient developed high antibody levels in combination with a high ASB concentration, while a second patient also developed high antibody levels with undetectable ASB concentrations. Antibodies from the second patient blocked detection of ASB. By week 72, antibody levels had decreased in all patients. The high-dose rhASB produced a more rapid and greater percentage reduction in urinary GAG concentrations than the lower dose (70% versus 55% at 24 weeks). Antibody levels did not appear to influence urinary GAG concentrations. CONCLUSION: Pharmacokinetic parameters appear to be independent of the duration of treatment and are not linear between the 0.2 and 1.0 mg/kg/week doses. Antibodies to rhASB develop in most patients, but their concentration decreases over time. Antibody formation may influence pharmacokinetic parameters during the early phases of treatment, although it appears to have limited impact on biochemical efficacy.

Median effect analysis of efficacy versus adverse effects of immunosuppressants.

BACKGROUND: A rigorous model to describe concentration-effect relations-the median effect analysis-was applied to quantitate immunosuppressive versus adverse effects in human renal transplantation. METHODS: The median effect equation was used to analyze data collected from three clinical studies, including the two phase III blinded, placebo-controlled trials (n = 1295 patients) of sirolimus versus azathioprine or placebo treatment added to a cyclosporine (INN, ciclosporin)/prednisone regimen and a sirolimus/azathioprine/prednisone (in the absence of cyclosporine) phase II cohort (n = 41 patients). RESULTS: The clinical effects correlated with drug concentrations as expressed by the median effect equation. Sirolimus or cyclosporine alone permitted drug concentrations that were 5-fold and 2.2-fold lower, respectively, to render 90% of patients rejection-free, suggesting a synergistic interaction between the two drugs. Further, the sirolimus concentrations to render 50% of patients rejection-free were about 200-fold and 60-fold less, respectively, than the concentration that caused 50% of patients to experience thrombocytopenia or hypertriglyceridemia. The correlation coefficient of the median effect analysis for the occurrence of hypercholesterolemia was more robust for sirolimus than for cyclosporine. Although the concentrations for 50% of patients rendered rejection-free versus 50% affected by hypercholesterolemia were similar, a 7-fold difference was calculated between the concentrations at which 90% of patients were free of rejection versus patients who were affected by hypercholesterolemia. CONCLUSION: The median effect analysis proffers a useful tool to assess both drug interactions and the windows between therapeutic versus toxic effects of immunosuppressive agents. The current analysis suggests a synergistic interaction between sirolimus and cyclosporine.

Effect of cardiopulmonary bypass on fentanyl distribution and elimination.

Fentanyl kinetics was studied in two groups of six patients, one group undergoing surgery with and one without cardiopulmonary bypass; the latter served as the controls. Plasma fentanyl concentrations declined biexponentially in the control patients with an average half-life (t1/2 beta) of 3.3 +/- 1.1 hr, total plasma clearance of 11.2 +/- 3.4 ml/min/kg, and volume of distribution (Vd beta) of 3.2 +/- 1.5 l/kg. The plasma concentration/time curves were severely disrupted during cardiopulmonary bypass but appeared to regain a log-linear decay once bypass was complete. This elimination phase had a t1/2 of 5.2 +/- 2.7 hr, longer than that in the control patients. Since fentanyl is eliminated primarily by hepatic metabolism, decreased liver plasma flow observed during and after bypass, as evidenced by a 30% decrease in indocyanine green clearance, may contribute to the extended t1/2. The prolonged t1/2 had clinical importance because of potentially prolonged effects and their relation to other drugs and the clinical management of the patient.

The pharmacodynamics of torsemide in patients with congestive heart failure.

The pharmacodynamics of torsemide (a new loop diuretic of the pyridine sulfonylurea class) was studied in 16 subjects who had compensated congestive heart failure and had been receiving stable diuretic therapy. Oral doses of 50, 100, and 200 mg were studied by use of a randomized crossover design. The results of this study show that the pharmacokinetics of torsemide is linear up to at least a dose of 200 mg in patients with congestive heart failure. Approximately 20% of each of the three doses was excreted unchanged, consistent with previous findings in healthy volunteers. A hyperbolic relationship between diuretic effect and drug excretion rate was defined. The maximum urinary sodium excretion rate attained was about 0.6 mEq/min, which is about 20% of that in healthy subjects, indicating diuretic resistance in these patients. Although there was no saturation of the urinary excretory pathway with doses as high as 200 mg, the upper plateau of the dose-response curve was reached with doses of 50 mg, indicating that this dose represents a ceiling dose in patients with New York Heart Association class II and III congestive heart failure.

Bioavailability, pharmacokinetics, and pharmacodynamics of torsemide in patients with cirrhosis.

The bioavailability, pharmacokinetics, and pharmacodynamics of torsemide (10 mg orally and intravenously) were determined in a randomized crossover clinical trial with 12 patients with ascites caused by cirrhosis. Torsemide was rapidly absorbed with a bioavailability of 96.3% (confidence interval, 84% to 109%). Compared with healthy subjects, patients with cirrhosis exhibit a decrease in nonrenal clearance and increases in bioavailability, volume of distribution, renal clearance, elimination half-life, and percentage of the dose excreted into the urine. A greater proportion of the dose is delivered to the site of action over a more prolonged period of time. In spite of a shift of the pharmacodynamic curve to the right in patients with cirrhosis, there was no significant difference in natriuresis. Pharmacokinetic changes of torsemide in cirrhosis therefore compensate for the pharmacodynamic abnormality.

Multiple-dose amikacin kinetics in pediatric oncology patients.

Amikacin kinetics was studied in 8 pediatric oncology patients who received the drug by intravenous infusion over 30 or 60 min at a dose of 5 mg/kg every 6 or 8 hr. This regimen is recommended but, due to patient variability, patients should be monitored. Dosing intervals during 1 or 2 and 3 or 4 days of therapy were studied with serum samples collected before and at the end of the infusion and serially to the end of the dosing interval. The data appeared consistent with and were analyzed according to 1-compartment model. An equation describing serum concentration with time for the multiple-dose case was fit to each patient's multiple-interval data with nonlinear regression. Half-life averaged 1.2 hr. volume of distribution 0.24 l/kg, and total body clearance 109 ml/min/1.73 m2 or 2.51 ml/min/kg. The volume of distribution and the clearance are greater than reported for adults and probably account for the larger dose needed to achieve and maintain therapeutic levels. Although the total daily dose was greater than previously reported, there were no signs of toxicity, although therapuetic concentrations were maintained.

The pharmacokinetics of intravenous and oral torsemide in patients with chronic renal insufficiency.

Torsemide is a diuretic that acts in the thick ascending limb of the loop of Henle. Unlike furosemide, it undergoes substantial hepatic elimination and should not accumulate in patients with renal insufficiency. Therefore the pharmacokinetics of intravenous and oral torsemide and its metabolites were investigated in patients with chronic renal insufficiency. Two groups of 24 patients stratified by creatinine clearance (30 to 60 ml/min and < 30 ml/min) were studied in two separate randomized dose escalating crossover studies, one using intravenous torsemide and the other using oral torsemide. The pharmacokinetics of both intravenous and oral torsemide were linear over the dosage range studied. Absolute bioavailability was essentially 100%. Renal clearance was greatly diminished and correlated with renal function. Total plasma clearance and half-life were not related to renal function and were found to be similar to those of healthy subjects. The substantial nonrenal clearance of torsemide prevents accumulation in patients with chronic renal insufficiency.

The pharmacodynamics of intravenous and oral torsemide in patients with chronic renal insufficiency.

The pharmacodynamics of intravenous and oral torsemide were determined in two randomized cross-over clinical trials in patients with chronic renal insufficiency. There was no significant difference in the rate or magnitude of the diuretic response between oral and intravenous administration. As has been shown with other loop diuretics, patients with chronic renal insufficiency have a reduced diuretic response compared with healthy subjects. This diuretic resistance is primarily related to a diminished delivery of drug to the urinary site of action. The response of torsemide at the tubular level is not different from that seen in subjects with normal renal function. Metabolites of torsemide do not appear to contribute to the diuretic response. A dose of 50 to 100 mg dependent on renal function is required to obtain a maximal response. A ceiling dose of approximately 100 mg in patients with chronic renal insufficiency is therefore recommended.

Pharmacokinetics and pharmacodynamics of dilevalol.

The pharmacokinetics and pharmacodynamics of dilevalol, the R,R stereoisomer of labetalol, were evaluated in nine subjects. Dilevalol was given as a single 50 mg intravenous dose and as a 400 mg daily oral dose for 7 days. To study the effects of hepatic enzyme inhibition, each subject received dilevalol in the presence of and absence of cimetidine. Cardiac beta-blockade was assessed by use of standardized treadmill tests for 48 hours after oral dilevalol. The three-compartment model analysis showed that systemic clearance (29.8 +/- 5.7 ml/min/kg), volume of distribution (16.6 +/- 4.1 L/kg), and terminal half-life (11.7 +/- 2.7 hours) were not altered by cimetidine. However, there was a 20% increase in the area under the curve (p less than 0.05) and an 11% increase in systemic bioavailability (p less than 0.05) after oral administration. Dilevalol caused significant cardiac beta-blockade for more than 24 hours, but these effects were not altered by cimetidine. The pharmacokinetic changes are consistent with a decrease in first-pass extraction of a high clearance drug.

Bioavailability, pharmacokinetics, and pharmacodynamics of torsemide and furosemide in patients with congestive heart failure.

The bioavailability, pharmacokinetics, and pharmacodynamics of torsemide (10 mg orally and intravenously) and furosemide (40 mg orally and 20 mg intravenously) were determined in a randomized crossover clinical trial in 16 patients with compensated congestive heart failure. Torsemide (time to reach maximum concentration [tmax], 1.1 +/- 0.9 hour) was more rapidly absorbed than furosemide (tmax, 2.4 +/- 2.5 hours), the absorption of which was delayed compared with that in healthy volunteers. Bioavailability of torsemide was also greater and less variable than that of furosemide. All four treatments yielded comparable changes from baseline in 24-hour electrolyte excretion. Based on the relationships between sodium excretion rate and fractional sodium and urinary drug excretion rate, response to both diuretic agents at the level of the nephron was decreased compared with previous studies with healthy subjects. Assessment of the clinical relevance, if any, of the difference in the variability of absorption warrants further study.

The effects of diuresis on the pharmacokinetics of the loop diuretics furosemide and torsemide in patients with heart failure.

PURPOSE: To evaluate the pharmacokinetics of furosemide and torsemide before and after diuresis in patients presenting with marked fluid overload. SUBJECTS AND METHODS: We studied 44 patients with New York Heart Association class III or IV heart failure, ejection fraction < or =40%, and an estimated excess fluid body weight > or =6.8 kg. Oral furosemide or torsemide was administered before and after diuresis. Pharmacokinetic parameters were assessed before and after diuresis. RESULTS: Following diuresis, maximum plasma concentration increased from 11.0+/-5.0 microg/mL to 13.9+/-6.8 with torsemide (P <0.05) and from 3.1< or =1.5 to 3.9+/-1.9 with furosemide (P=0.16). Maximum concentration increased by more than 30% in only one third of the patients. Total absorption (by area under the curve method) increased 6% among patients on torsemide (P=0.38) and 7% among patients on furosemide (P=0.63) and increased >30% in only 1 torsemide and 2 furosemide patients. The time to maximum concentration decreased from 1.40+/-.82 h to 0.81+/-0.36 with torsemide (P <0.01). There were no differences between furosemide and torsemide in the effects of edema on absorption. CONCLUSION: Marked diuresis altered the pharmacokinetics of both furosemide and torsemide in only a small percentage of patients. The use of adequate doses of oral diuretics in edematous patients may be successful, thereby permitting home treatment with oral diuretics and avoiding the cost of hospitalizations or home intravenous administration services.

Demographic factors affecting the pharmacokinetics of cyclosporine estimated by radioimmunoassay.

In order to assess the impact of demographic factors on serum levels of cyclosporine (CsA) estimated by radioimmunoassay (RIA) in renal allograft recipients, 493 pharmacokinetic studies were performed in 212 patients. Neither the presence of diabetes mellitus nor the CsA dosing frequency affected the measured pharmacokinetic parameters. Age over 45 years led to slower CsA clearance with resultant increase in maximum serum concentration (Cmax) per administered milligram, and increased volume of distribution. Female patients showed more rapid drug clearance, but greater volume of distribution. Concomitant hepatic impairment reduced drug clearance, increasing the area under the curve (AUC) per administered milligram of drug, and the Cmax. Patients treated with a rapid steroid taper showed a shorter half-life and lower Cmax than those receiving a slow steroid taper. Nephrotoxicity was associated with increased AUC per administered mg, while patients with acute tubular necrosis requiring dialysis showed poorer drug absorption, lower Cmax, and longer time to peak. The only effect of cimetidine administration was a slightly shortened time to peak. Serial analyses posttransplant in 17 patients suggested a tendency toward improved drug absorption with no effect on other parameters. These studies demonstrating the significant impact of demographic factors thus afford a basis on which to predict the trend of anticipated CsA levels as measured by RIA in renal allograft recipients.

Pharmacokinetics of dilevalol in normotensive and hypertensive volunteers.

Dilevalol is a novel antihypertensive agent combining vasodilation due to selective beta 2-adrenergic receptor agonism with nonspecific antagonism of beta 1- and beta 2-adrenergic receptors. Studies of dilevalol's pharmacokinetics in normotensive and hypertensive volunteers have demonstrated that (1) it is rapidly and well absorbed; (2) because of extensive first-pass metabolism its absolute oral bioavailability is about 12%; (3) its mean elimination half-life is 8 to 12 hours after administration of single oral or intravenous doses to normal volunteers, a value consistent with once-daily dosing; and (4) food does not appear to alter its bioavailability or pharmacokinetics.

Antihypertensive effect of dilevalol is directly related to dose and plasma concentrations.

Dilevalol is a novel antihypertensive agent combining vasodilation due to selective beta 2-adrenergic receptor agonism with nonspecific beta antagonism. To determine the relation of dilevalol dose and plasma concentration to antihypertensive effect, dilevalol (n = 15) or placebo (n = 3) was administered to 18 hypertensive subjects. The study was performed under blinded conditions during a 21-day hospitalization after a 3-week drug-free outpatient phase. In the 15 hypertensive patients receiving dilevalol orally in single morning doses of 200, 400 and 800 mg each for 5 days, the drug was shown to reduce blood pressure effectively for 24 hours at all doses. The antihypertensive effect was significantly related to dose administered and to the concentration of unchanged dilevalol measured in plasma. Dilevalol did not cause excessive changes in heart rate at rest and did not produce postural hypotension. The antihypertensive effectiveness of dilevalol was essentially the same after the first and fifth (steady state) doses at each dose level. Finally, no tendency toward rebound hypertension or tachycardia was observed after the abrupt discontinuation of dilevalol in these patients.

Absorption of isosorbide-5-mononitrate at specific sites in the gastrointestinal tract.

As part of a development program for controlled- and extended-release formulations of isosorbide-5-mononitrate (ISMN), the rate and extent of drug absorption was evaluated after site-specific delivery in the gastrointestinal (GI) tract. Seven healthy male subjects received, on separate occasions, 20 mg of ISMN solution orally and via nasogastric tube to the jejunum, terminal ileum, and ascending colon. Compared with oral administration (AUC 2,963 hr x ng/mL, Cmax 442 ng/mL, Tmax 0.81 hr), placement of drug directly into the jejunum did not change the extent (AUC 2,844 hr x ng/mL) but increased the rate of absorption (Cmax 630 ng/mL, Tmax 0.28 hr) due to direct placement of drug into the intestine. Administration to the terminal ileum resulted in a rate of absorption comparable to that from the jejunum (Tmax 0.28 hr) but a reduction in extent (mean AUC 2,377 hr x ng/mL). Delivery to the ascending colon resulted in a further decrease in the extent (AUC 2,017 hr x ng/mL) and a "slowing" of the rate of absorption compared with the two intestinal sites (Cmax 392 ng/mL, Tmax 0.68 hr). Overall, bioavailability throughout the GI tract was sufficient to support development of controlled- and extended-release formulations.

The effect of obesity on acetaminophen pharmacokinetics in man.

This study examined the absorption and disposition of orally administered acetaminophen in morbidly obese patients as compared to subjects of normal weight, and possible changes in disposition as the patients underwent weight reduction through dietary modification. The overall disposition of acetaminophen was not affected by a weight loss of 8 to 30 kg; elimination half-life, time to reach the peak, and peak plasma concentration varied within each subject but not in a systematic way. The half-life was the same in the obese patients (2.6 +/- 0.85 hours) and normal subjects (2.6 +/- 0.12 hours). However, maximum plasma concentrations were reached at a significantly later time and were significantly lower in the obese patients as compared to the normals, implying an apparently lower absorption rate. The area under the plasma concentration-time curve for the obese patients when normalized to ideal body weight was more consistent with that in the normal subjects than when normalized to total body weight. Administration of a normal dose of acetaminophen to an obese patient should yield plasma levels in the same range as persons of normal weight. As total weight may exceed 200 per cent of the ideal weight in this patient group, dosing according to total rather than ideal weight could lead to toxic or lethal effects when using the 10 mg/kg dosing recommendation.

Pharmacokinetics and bioavailability of dilevalol in normotensive volunteers.

The bioavailability and pharmacokinetics of dilevalol following oral and intravenous administration were investigated in 12 healthy male volunteers. Dilevalol HCl was administered as a 200-mg oral tablet and a 50-mg intravenous infusion using a randomized cross-over design. Blood and urine samples were collected over 60 hours and analyzed for unchanged and total (unchanged plus Glusulase-released) dilevalol using a high performance liquid chromatography (HPLC) assay. After intravenous administration, total body clearance and volume of distribution of unchanged dilevalol were determined to be 23.2 mL/min/kg and 24.6 L/kg, respectively. After oral administration, a mean maximum concentration of 62 ng/mL was reached at an average peak time of 1.4 hours. Drug was eliminated with a half-life of 8.3 hours after oral administration and 12 hours after intravenous administration. Based on plasma levels and urinary excretion of total dilevalol, the drug was completely absorbed; however, due to first-pass metabolism, the absolute bioavailability of unchanged drug was 11 to 14%.

The pharmacokinetics of bleomycin in man.

A series of studies were carried out to investigate the pharmacokinetics of the antineoplastic antibiotic bleomycin in patients with neoplastic disorders. Drug was administered by long (four to five days) and short (10 minutes) zero-order infusions, and serial plasma and urine samples were collected. Serum and urine bleomycin concentrations were determined by radioimmunoassay. The disposition of bleomycin after the 10-minute infusion was described by a two-compartment open model. However, following multiple-day infusion estimates were obtained that were inconsistent with those from the short infusion. Parameters from the long infusions agreed with those from the short infusion when terminal plasma bleomycin levels less than 10 microunits/ml were excluded. The time to reach steady state following the long infusion (ca. 12 hours) was consistent with the half-life (3 hours) predicted by the short infusion and the long infusion excluding levels less than 10 microunits/ml. Possible explanations include assay interference by an unknown metabolite or strong binding of drug to tissues with release at a rate much less than the apparent rate of elimination of drug from the body.

Comparative bioavailability of intravenous and oral chloramphenicol in adults.

The comparative bioavailability of chloramphenicol from intravenous succinate, oral palmitate, and oral base preparations was studied in a crossover manner in 12 adult patients. Chloramphenicol was administered at a dose of 1 Gm every 6 hours, and blood samples were collected at steady state. For the succinate study, total urine output was also collected. The bioavailability of active chloramphenicol from the succinate preparation averaged 85.8 +/- 42.3 and 78.8 +/- 50.1 per cent of the free base and palmitate forms, respectively. This lower availability appeared to be due to variable excretion of unchanged succinate in the urine, averaging 27 +/- 11 per cent of the dose. Regardless of dosage form or route of administration, plasma chloramphenicol concentrations remained in the therapeutic range (5 to 25 mg/liter) for the entire dosage interval, implying that no change needs to be made when changing dosage form or route of administration. The interpatient variability, however, supports the need for monitoring of plasma chloramphenicol concentrations, especially in newborn infants, persons with liver disease, or those receiving other medications that alter chloramphenicol metabolism.

Pharmacokinetics of torsemide in patients with decompensated and compensated congestive heart failure.

Plasma pharmacokinetics of oral furosemide have been shown to be influenced by degree of decompensation in patients with congestive heart failure (CHF). This open-label, sequential comparison trial was conducted to determine whether CHF decompensation also alters the pharmacokinetics and pharmacodynamics of torsemide. Twelve patients with CHF, defined by either hemodynamic parameters or clinical signs and symptoms, were enrolled. On admission for treatment of their CHF, the patients were given 100 mg oral torsemide (phase A). A second dose of oral torsemide 100 mg was administered after hemodynamic parameters and clinical signs and symptoms of decompensated CHF resolved (phase B). Plasma and urine samples were collected over a 24-hour period for determination of torsemide concentrations and urine sodium. Hemodynamic measurements and physical signs and symptoms also were evaluated. During phase A, patients had significantly greater urine output and fractional sodium excretion compared with phase B. A significant increase in the area under the plasma concentration-time curve (AUC) was observed during phase B compared with phase A. However, no significant differences in maximal excretion rate of torsemide were noted between phase A and phase B. Heart failure status slightly affects the plasma pharmacokinetics of torsemide; however, this does not significantly alter the maximal urinary excretion rate of torsemide.