Improved efficacy of ciprofloxacin administered in polyethylene glycol-coated liposomes for treatment of Klebsiella pneumoniae pneumonia in rats.

Animal and clinical data show that high ratios of the area under the concentration-time curve and the peak concentration in blood to the MIC of fluoroquinolones for a given pathogen are associated with a favorable outcome. The present study investigated whether improvement of the therapeutic potential of ciprofloxacin could be achieved by encapsulation in polyethylene glycol (PEG)-coated long-circulating sustained-release liposomes. In a rat model of unilateral Klebsiella pneumoniae pneumonia (MIC = 0.1 microg/ml), antibiotic was administered at 12- or 24-h intervals at twofold-increasing doses. A treatment period of 3 days was started 24 h after inoculation of the left lung, when the bacterial count had increased 1,000-fold and some rats had positive blood cultures. The infection was fatal within 5 days in untreated rats. Administration of ciprofloxacin in the liposomal form resulted in delayed ciprofloxacin clearance and increased and prolonged ciprofloxacin concentrations in blood and tissues. The ED(50) (dosage that results in 50% survival) of liposomal ciprofloxacin was 3.3 mg/kg of body weight/day given once daily, and that of free ciprofloxacin was 18.9 mg/kg/day once daily or 5.1 mg/kg/day twice daily. The ED(90) of liposomal ciprofloxacin was 15.0 mg/kg/day once daily compared with 36.0 mg/kg/day twice daily for free ciprofloxacin; 90% survival could not be achieved with free ciprofloxacin given once daily. In summary, the therapeutic efficacy of liposomal ciprofloxacin was superior to that of ciprofloxacin in the free form. PEG-coated liposomal ciprofloxacin was well tolerated in relatively high doses, permitting once daily administration with relatively low ciprofloxacin clearance and without compromising therapeutic efficacy.

Pharmacokinetics and tissue disposition in monkeys of an antisense oligonucleotide inhibitor of Ha-ras encapsulated in stealth liposomes.

PURPOSE: This study examined the pharmacokinetics and tissue distribution of an antisense oligonucleotide ISIS 2503, formulated in stealth (pegylated) liposomes (encapsulated) or in phosphate-buffered saline (unencapsulated). METHODS: Encapsulated or unencapsulated ISIS 2503 was administered to rhesus monkeys by intravenous infusion. The concentrations of ISIS 2503 and metabolites in blood, plasma, and tissue samples were determined by capillary gel electrophoresis. RESULTS: Plasma concentrations of encapsulated ISIS 2503 decreased mono-exponentially after infusion with a mean half-life of 57.8 hours. In contrast, the concentration of unencapsulated ISIS 2503 in plasma decreased rapidly with a mean half-life of 1.07 hours. Both encapsulated and unencapsulated ISIS 2503 distributed widely into tissues. Encapsulated ISIS 2503 distributed primarily to the reticulo-endothelial system and there were few metabolites observed. In contrast, unencapsulated ISIS 2503 distributed rapidly to tissue with highest concentration seen in kidney and liver. Nuclease-mediated metabolism was extensive for unencapsulated oligonucleotide in plasma and tissues. CONCLUSIONS: The data suggest that stealth liposomes protect ISIS 2503 from nucleases in blood and tissues, slow tissue uptake, and slow the rate of clearance from the systemic circulation. These attributes may make these formulations attractive for delivering oligonucleotides to sites with increased vasculature permeability such as tumors or sites of inflammation.

Amphotericin B colloidal dispersion. Pre-clinical review.

Amphotericin B Colloidal Dispersion (ABCD, AmphocilTM), a noncovalent complex of amphotericin B and cholesteryl sulfate, is active in vitro and in vivo against a wide variety of fungal species; its activity is broadly comparable to the range of activity of conventionally formulated amphotericin B (CAB). The pharmacokinetics of ABCD and CAB differ. ABCD is more rapidly removed from circulation than CAB, with more than 99% clearance one hour after administration, but has a much more prolonged terminal elimination phase. Preclinical safety studies have shown that ABCD is significantly better tolerated and less nephrotoxic than CAB. ABCD does cause renal tubular damage after high doses, but only at doses five- to eight-fold higher than those of CAB. Preclinical studies suggest that the efficacy, but not the toxicity of ABCD and CAB will be identical. ABCD may thus provide a safer therapeutic alternative to CAB.

The population pharmacokinetics of amphotericin B colloidal dispersion in patients receiving bone marrow transplants.

The purpose of this study was to identify the pharmacokinetics of Amphotericin B Colloidal Dispersion in patients undergoing bone marrow transplantations with systemic fungal infections and to assess the influence of ABCD on renal function. Seventy-five patients (42 females, 33 males) with a median age of 34.5 years and median weight of 70.0 kg were enrolled in the study. The plasma concentration data was available in 51/75 patients and was best described by a two-compartment model; both plasma clearance and volume of distribution increased with escalating doses; the overall average terminal elimination half-life was 29 h. Serum creatinine values over the duration of therapy were available in 59/75 patients. Overall, there was no net change in renal function over the duration of therapy.

Reduction of the cardiotoxicity of doxorubicin in rabbits and dogs by encapsulation in long-circulating, pegylated liposomes.

The relative cardiotoxicity of pegylated (STEALTH) liposomal doxorubicin (PL-DOX; Doxil) was compared to nonliposomal doxorubicin (Adriamycin) in rabbits and dogs treated i.v. for up to 22 weeks. No histological evidence of cardiotoxicity was seen in dogs treated with placebo liposomes or PL-DOX every 3 weeks for a total of 10 doses (cumulative doxorubicin dose = 10 mg/kg) either 1 or 5 weeks post-treatment. All dogs treated with the same cumulative dose of free doxorubicin showed marked cardiotoxicity (vacuolization and myofibrillar loss in the myocardium) at both time points. In rabbits, progressive cardiomyopathy was seen in both treatment groups, but was more frequent and severe with free doxorubicin (67% of doxorubicin-treated rabbits, cumulative dose = 12 to 14 mg/kg versus 16% of PL-DOX-treated animals, cumulative dose = 14 to 21 mg/kg). Five doxorubicin-treated rabbits died of congestive heart failure or with histologic evidence of cardiotoxicity (median severity score = 6). No PL-DOX-treated rabbits died of congestive heart failure, although two animals that died early showed microscopic evidence of mild cardiotoxicity (median severity score = 2.5). Cardiotoxicity increased during the post-treatment period in both treatment groups. Rabbits received up to 50% more PL-DOX with no increase in cardiotoxicity. Thus, results in two species demonstrate that the cardiotoxicity of doxorubicin is significantly decreased when administered as PL-DOX. Significantly more PL-DOX can be given without incurring an increased risk of cardiomyopathy. Recent clinical studies have confirmed that PL-DOX is also less cardiotoxic than the same dose of unencapsulated doxorubicin in humans.

Relationship of dose intensity to the induction of palmar-plantar erythrodysesthia by pegylated liposomal doxorubicin in dogs.

The multiple dose pharmacokinetics of pegylated liposomal doxorubicin (PL-DOX), known as DOXIL (US) and CAELYX (EU), was characterized in dogs and a pharmacokinetic/pharmacodynamic model to identify a relationship between drug exposure and the probability of observing treatment-related palmar-plantar erythrodysesthesia (PPE) was developed. Twenty dogs were assigned to PL-DOX groups (2/sex/ group) that received intravenous PL-DOX doses of 0.5 mg/kg ql, 2, or 4 weeks; 1.0 mg/kg q2weeks; or 1.5 mg/kg q4weeks for 12 weeks. Blood was collected for HPLC analysis of doxorubicin concentration pre-dose and periodically up to 120 h after dosing three times during treatment. Plasma drug concentration was modeled using iterative 2-stage analysis. Dermal lesions (PPE) were scored twice weekly for six regions of each dog using a 0-6 severity scale; maximum severity was 36. PPE score data were modeled using an approach in which the % probability of PPE was related to a hypothetical effect site by a series of Hill-type functions. Pharmacokinetics were best modeled as a one-compartment open model. Vss (ml/kg), CLt (ml/hr/kg) and half-life (h) were 44.1, 1.39 and 23.1, respectively. Cmax increased linearly with dose. CLt decreased with repeated doses. 5 A two-compartment pharmacodynamic model, which correctly predicted 97% of the observed lesion severity, was developed to establish the relationship of lesion severity to dose intensity (a measure of drug exposure incorporating the effect of both dose level and dosing frequency, which can be expressed in units of mg/kg/week). The model demonstrated that maximal PPE was positively correlated with dose intensity, the major factor that affects the incidence and severity of dermal lesions. 6 The model can be used to predict acceptable dose intensities in humans utilizing body surface area conversion factors and comparative AUCs for dogs and humans. It predicts that a dose intensity of 10-12.5 mg/m2 of PL-DOX will be well tolerated in patients. The results of recent clinical studies are consistent with this prediction.

Therapy of a xenografted human colonic carcinoma using cisplatin or doxorubicin encapsulated in long-circulating pegylated stealth liposomes.

We compared the therapeutic effects of low doses of cisplatin and doxorubicin hydrochloride encapsulated in long-circulating liposomes composed of cholesterol/hydrogenated soy phosphatidylcholine-polyethylene glycol-distearoyl-phosphatidyl-ethanolamine. The encapsulation of cisplatin and doxorubicin in these liposomes made ineffectively low doses of the free drugs able to inhibit the growth of and affect cures of a human colonic carcinoma growing in nude mice. Liposome-encapsulated cisplatin had minor systemic toxic side effects indicated by an average 9% weight loss which was recovered 3-4 weeks after the last treatment. Toxicity was not observed in mice treated with liposome-encapsulated doxorubicin.

Comparative pharmacokinetics, tissue distribution, and therapeutic effectiveness of cisplatin encapsulated in long-circulating, pegylated liposomes (SPI-077) in tumor-bearing mice.

PURPOSE: The pharmacokinetics (PK), biodistribution and therapeutic efficacy of cisplatin encapsulated in long-circulating pegylated (Stealth) liposomes (SPI-077) were compared with those of nonliposomal cisplatin in two murine (C26 colon carcinoma and Lewis lung) tumor models. METHODS: In therapeutic effectiveness studies, mice bearing murine C26 or Lewis lung tumors received multiple intravenous doses of SPI-077 or cisplatin in a variety of treatment schedules and cumulative doses. In the PK and biodistribution study, mice received a single intravenous bolus injection of 3 mg/kg of either SPI-077 or cisplatin 14 days after inoculation with 10(6) C26 tumor cells. Plasma and tissues were analyzed for total platinum (Pt) content by graphite furnace (flameless) atomic absorption spectrophotometery (GF-AAS). RESULTS: Efficacy studies showed that SPI-077 had superior antitumor activity compared to the same cumulative dose of cisplatin. When lower doses of SPI-077 were compared to cisplatin at its maximally tolerated dose in Lewis lung tumors, equivalent SPI-077 antitumor activity was seen at only half the cisplatin dose. Higher cumulative doses of SPI-077 were well tolerated and had increased antitumor effect. SPI-077 PK were characterized by a one-compartment model with nonlinear (saturable) elimination, whereas cisplatin PK were described by a two-compartment model with linear elimination. SPI-077 had a 55-fold lower [corrected] volume of distribution, 3-fold higher peak plasma levels, and a 60-fold larger plasma AUC compared with cisplatin. In addition, SPI-077-treated animals displayed a 4-fold reduction in Pt delivered to the kidneys (primary target organ of toxicity) relative to cisplatin, but a 28-fold higher tumor AUC than cisplatin. CONCLUSIONS: Based on the results of our studies, encapsulation of cisplatin in long-circulating pegylated liposomes has overcome limitations experienced with other liposomal cisplatin formulations. SPI-077 has a prolonged circulation time and increased tumor Pt disposition, and its antitumor effect is significantly improved compared to cisplatin in murine colon and lung cancer models.

Antitumor activity of Herceptin in combination with STEALTH liposomal cisplatin or nonliposomal cisplatin in a HER2 positive human breast cancer model.

Single agent antitumor activity of Herceptin, a humanized monoclonal antibody directed against HER2, has been demonstrated in numerous preclinical and clinical studies. Additionally, combination therapy with Herceptin and chemotherapy (CRx) has demonstrated additive antitumor activity in both preclinical models and early clinical trials. STEALTH (pegylated) liposomal (PL) cisplatin, also known as SPI-077, is currently in clinical trials for a variety of solid tumors. The three studies reported here discuss the antitumor activity of the combination of Herceptin and nonliposomal cisplatin or PL-cisplatin in two xenograft tumor models, initiated from the cell lines, BT474 and MDA453, that overexpress the oncogene, HER2. Herceptin alone had significant antitumor activity in all three experiments (p < 0.0001). Nonliposomal cisplatin and PL-cisplatin were both effective antitumor agents but, at tolerable dose levels, PL-cisplatin was superior to nonliposomal cisplatin (p < 0.0003). The effect of combining Herceptin with the chemotherapeutic cisplatin or PL-cisplatin, was most significant at moderate doses of H (0.5 mg/kg, p < 0.0001), but tended to be greater than either agent alone in all experiments. The combination of PL-cisplatin with Herceptin had statistically similar antitumor activity to that of nonliposomal cisplatin with Herceptin in all experiments. We conclude that combination therapy with PL-cisplatin and Herceptin results in significant antitumor activity with the potential for reducing toxicity in metastatic breast cancer patients.

Sterically stabilized liposomes in cancer therapy and gene delivery.

The introduction of colloidally stable liposomes with low drug leakage rates resulted in a renaissance in liposome applications in cancer therapy. Furthermore, a platform of sterically stabilized liposomes also allows the construction of new generations of drug delivery vehicles. These include targeted liposomes and targeted nucleic acid delivery vehicles, based either on cationic sterically stabilized liposomes or pre-condensed DNA encapsulated in neutral or negatively charged liposomes.

Encapsulation of the topoisomerase I inhibitor GL147211C in pegylated (STEALTH) liposomes: pharmacokinetics and antitumor activity in HT29 colon tumor xenografts.

The topoisomerase I inhibitor GL147211C [7-[(4-methylpiperazino)methyl]-10,11-(ethylenedioxy)-(20S)-campto thecin trifluoroacetate], a camptothecin analogue, has significant activity in tumor cell cytotoxicity assays in vitro and antitumor activity in both animal tumor models and human patients. Its toxicity is significant, however, effectively limiting the amount of drug that can be administered and its clinical utility. To determine whether the therapeutic index of GL147211C could be improved, the drug was encapsulated in long-circulating, pegylated (STEALTH) liposomes (SPI-355). The pharmacokinetics and antitumor activity of SPI-355 were compared to those of nonliposomal GL147211C. The plasma pharmacokinetics of SPI-355 in rats were typical of those of other pegylated liposomal formulations, with significantly increased blood circulation time; the dose-corrected area under the curve and Cmax of SPI-355 (10 mg/kg) were 1250- and 35-fold higher, respectively, than those of nonliposomal GL14711C (8.72 mg/kg). The comparative antitumor activity of SPI-355 and nonliposomal GL1472211C was evaluated in nude mice implanted with HT29 colon carcinoma xenografts. SPI-355 was 20-fold more effective than GL147211C in inhibiting tumor growth (1 mg/kg SPI-355 and 20 mg/kg GL147211C) and produced durable complete remissions of tumors at well-tolerated dose levels that were >5-fold lower than the maximally tolerated dose of GL147211C, which induced no durable complete responses. Signs of toxicity were similar between the two drugs, but liposome encapsulation increased the toxicity of drug approximately 4-fold, with increased weight loss and several deaths with SPI-355 (5 mg/kg SPI-355 versus 20 mg/kg GL147211C). Despite the increased toxicity seen with SPI-355, the therapeutic index of the liposomal formulation was increased approximately 5-fold over that of nonliposomal GL147211C, suggesting that such a pegylated liposomal formulation could demonstrate increased therapeutic index in human patients.

Doxorubicin entrapped in sterically stabilized liposomes: effects on bacterial blood clearance capacity of the mononuclear phagocyte system.

The introduction of long-circulating liposomes sterically stabilized by surface coating with polyethylene glycol has expanded the potential for drug targeting to tumors. In recent clinical studies, evidence of significant antitumor activity has been obtained with the industrially prepared formulation of long-circulating polyethylene glycol-coated liposomes containing doxorubicin, referred to as DOXIL. Previous studies performed in rats showed that doxorubicin-containing liposomes can exert major toxic effects on the liver macrophage population for a considerable period of time; a strong impairment of phagocytic function and even a substantial depletion of the liver macrophage populations were observed. In the present study, the phagocytic function of the mononuclear phagocyte system (MPS) after administration of DOXIL at a clinically relevant dosage schedule was evaluated in rats. Phagocytic function of the MPS was assessed by determining bacterial blood clearance capacity. The observations reported herein show that DOXIL is fairly well tolerated regarding bacterial blood clearance capacity of the MPS when administered in a regimen that resembles the clinical setting closely. This outcome has important implications with regard to the clinical utility of the liposomal drug, especially in the restricted context of immunocompromised cancer patients who easily develop systemic infections and should not be confronted with a therapy-induced reduction of the bacterial blood clearance capacity of the MPS.

Inhibition of mouse mammary carcinoma development with doxorubicin in liposomes.

Monthly treatments with intravenous doxorubicin encapsulated in long circulating, sterically stabilized liposomes delayed the appearance of primary mammary carcinomas and reduced the final incidence from 49 in 50 untreated mice to 46 in 87 treated mice. No toxic side effects of the treatments were observed.

Comparative intravenous toxicity of cisplatin solution and cisplatin encapsulated in long-circulating, pegylated liposomes in cynomolgus monkeys.

The toxicity of cisplatin encapsulated in pegylated, long-circulating liposomes (SPI-077) was compared with nonliposomal cisplatin in male and female cynomolgus monkeys (n = 2-4 per sex per group) treated with intravenous infusions of 2.5 or 25 mg/kg SPI-077, 2.5 mg/kg cisplatin, placebo liposomes, or saline once every 3 weeks for total of five treatments. All animals survived until scheduled necropsy at 3 days after the final treatment or after a treatment-free 4-week recovery period. Emesis occurred after each treatment in all cisplatin-treated monkeys, but only once in one monkey treated with high-dose SPI-077. Dose-related mild decreases in red blood cell (RBC) count, hemoglobin, and hematocrit to or slightly below low normal range occurred in the high-dose SPI-077 and placebo liposome treatment groups after each treatment, with partial to complete recovery between treatments and no signs of correlating bone marrow toxicity. Decreases were similar in cisplatin-treated monkeys, but resolved only slightly between treatments and after the end of treatment (continuing to decrease in females) and were accompanied by bone marrow hypocellularity. Indirect, but not direct, bilirubin levels were cyclically elevated in the high-dose SPI-077 and placebo-treated animals, but not in the other treatment groups. Levels had either fully resolved or were near baseline and/or saline group values prior to the next treatment. Serum cholesterol levels were cyclically increased in SPI-077- and placebo liposome-treated animals, and minimally increased numbers of foam cells were seen in the liver, spleen, kidney, and other organs; both were considered related to the lipid dose administered. Cisplatin-treated monkeys exhibited sensory polyneuropathy and moderate irreversible toxic tubular nephrosis, but no neuropathy or nephrotoxicity was seen in either SPI-077 treatment group. Microscopically, treatment-related cell death was seen in dorsal root ganglia (DRG), affecting 15% of the cells in cisplatin-treated animals, compared to 8 and 12% in the low- and high-dose SPI-077 treatment groups. Neither drug was ototoxic. In summary, repeated administration of SPI-077 produced minimal, reversible effects related to the lipid dose administered, mostly limited to the 25 mg/kg dose group. The most notable effects in this group were cyclical decreases in hematology parameters thought to be related to increased recycling of a small fraction of RBCs and limited cell death in the DRG in the absence of any neurophysiological changes. Animals treated with a 10-fold lower dose of cisplatin (2.5 mg/kg), in contrast, exhibited myelo-, nephro-, and neurotoxicity, including sensory neuropathy, and were emetic after every dose. The SPI-077 liposomal formulation of cisplatin may provide a less toxic alternative to standard cisplatin solution.

Tumour uptake of doxorubicin in polyethylene glycol-coated liposomes and therapeutic effect against a xenografted human pancreatic carcinoma.

This study tested the therapeutic efficacy of doxorubicin hydrochloride in two formulations: free in saline suspension and encapsulated in polyethylene glycol-coated, long-circulating liposomes. The drug formulations at a dose level of 3 mg doxorubicin per kg body weight were injected intravenously to treat the human pancreatic carcinoma AsPC-1, implanted s.c. into nude Swiss mice. Liposome-encapsulated doxorubicin was significantly more effective in inhibiting tumour growth and in effecting cures, and had only minor systemic toxic side-effects, indicated by a transient weight loss. Confocal laser scanning microscopy was used to determine the tumour uptake and the clearance of doxorubicin in the free and in the liposomal forms. The liposome-encapsulated doxorubicin entered the tumour in greater quantity, and remained in the tumour longer, than the free drug. The liposome formulation produced a sixfold or greater increase in doxorubicin at the disease site. It is probable that increased penetration into the tumour, and long presence with slow drug release from liposomes in the tumour, account for the enhanced therapeutic effect when the drug was encapsulated in polyethylene glycol-coated liposomes.

Twelve-month evaluation of rhesus monkey dams and infants after relaxin (hRlx-2) infusion in late pregnancy.

Pregnant rhesus monkeys received daily i.v. infusions of chemically synthesized human relaxin (hRlx-2) (0.1 mg/kg/day N = 6, 2.0 mg/kg/day N = 6, vehicle control N = 7) from the onset of cervical softening to delivery (0 to 14 infusions) to simulate potential therapeutic use of this agent for cervical ripening. Reproductive fitness of dams was evaluated during the next breeding season, and infants were studied through 12 months of age. Birth weight and size, neonatal heart rate and body temperature and neurobehavioral status were not influenced by intrauterine relaxin exposure. Neonatal muscle tone was greater and responsiveness was lower in the hRlx-2 treated infants than in controls. No group differences were seen in infant postnatal growth, maturation or incidence of health problems. Maternal endpoints including uterine involution, resumption of menses, conception rate, and pregnancy outcome were similar across groups. Systemic exposure of rhesus monkeys to relatively high levels of hRlx-2 in late pregnancy did not have apparent long term effects for the measures evaluated under conditions of the experiment. Conclusions concerning adverse effects are limited by the small sample size.

Doxorubicin encapsulated in liposomes containing surface-bound polyethylene glycol: pharmacokinetics, tumor localization, and safety in patients with AIDS-related Kaposi's sarcoma.

A study of the plasma pharmacokinetics, tumor localization, and safety of a single dose of doxorubicin encapsulated in liposomes containing surface-bound polyethylene glycol (PEG-liposomal doxorubicin) was conducted in patients with Kaposi's sarcoma (KS) as a manifestation of acquired immune deficiency syndrome (AIDS). Eighteen patients with AIDS-KS diagnosed by examination of biopsy specimens were randomly assigned to receive either standard doxorubicin or PEG-liposomal doxorubicin. Consecutive participants were entered at three dose levels (10, 20, and 40 mg/m2) in ascending fashion. Clearance of PEG-liposomal doxorubicin was 0.034 L/h/m2 to 0.108 L/h/m2, volume of distribution (Vd) was 2.2 L/m2 to 4.4 L/m2, and half-lives (t1/2) of the initial decline in the plasma concentration-time curve and of the terminal decline were 3.77 hours and 41.3 hours, respectively. Seventy-two hours after administration, doxorubicin levels observed in lesions of patients receiving PEG-liposomal doxorubicin were 5.2 to 11.4 times greater than those found in patients given comparable doses of standard doxorubicin. PEG-liposomal doxorubicin and standard doxorubicin were roughly equipotent in producing toxicity. Encapsulation in liposomes containing surface-bound PEG significantly limits the distribution and elimination of doxorubicin, results in greater accumulation of the drug in KS lesions 72 hours after dosing than does standard doxorubicin, and may improve drug efficacy and therapeutic index in the treatment of AIDS-KS.

Prevention of metastasis from mouse mammary carcinomas with liposomes carrying doxorubicin.

Weekly treatments with doxorubicin encapsulated in long circulating, sterically stabilised liposomes (DOX-SL) reduced the incidence of metastases from primary mammary carcinoma from 24 of 47 untreated mice to 3 of 23 treated mice. Toxic side-effects were limited to minor, transient weight losses.

Population pharmacokinetics and renal function-sparing effects of amphotericin B colloidal dispersion in patients receiving bone marrow transplants.

The purpose of this study was to evaluate the pharmacokinetics of amphotericin B colloidal dispersion and its effect on creatinine clearance in bone marrow transplant patients with systemic fungal infections. Seventy-five patients (42 females and 33 males) with a median age of 34.5 years and a median weight of 70.0 kg were enrolled in the study. Patients received 1 of 15 dose levels (range, 0.5 to 8.0 mg/kg of body weight) daily for a mean duration of 28 days and a mean cumulative dose amount of 8 g. Plasma samples for amphotericin B determination (median number, 4; range, 2 to 30) and daily serum creatinine values were obtained for each patient. Iterative two-stage analysis, one of several approaches to population pharmacokinetic and pharmacodynamic modelling, was employed for the pharmacokinetic analysis. The plasma data were available for 51 of 75 patients and were best described by a two-compartment model. Both plasma clearance and volume of distribution increased with escalating doses; the overall average terminal elimination half-life was 29 h. Of the covariates studied, only body weight and dose size were significant. Serum creatinine values over the duration of therapy were available for 59 of 75 patients. Overall, there was no net change in renal function over the duration of therapy; 12 patients had > 30% increases in creatinine clearance, whereas 13 had > 30% decreases. No measure of amphotericin B colloidal dispersion exposure, demographic values, or concomitant treatment with other medications was related to changes in the creatinine clearance.