Administration Of Amphotericin B Research Articles

Amphotericin B: side effects and toxicity

Amphotericin B (AmB) is a crucial agent in the management of serious systemic fungal infections. In spite of its proven track record, its well-known side effects and toxicity will sometimes require discontinuation of therapy despite a life-threatening systemic fungal infection. The mechanism of action of AmB is based on the binding of the AmB molecule to the fungal cell membrane ergosterol, producing an aggregate that creates a transmembrane channel, allowing the cytoplasmic contents to leak out, leading to cell death. Most of the efforts at improving AmB have been focused on the preparation of AmB with a lipid conjugate. AmB administration is limited by infusion-related toxicity, an effect postulated to result from proinflammatory cytokine production. The principal acute toxicity of AmB deoxycholate includes nausea, vomiting, rigors, fever, hypertension or hypotension, and hypoxia. Its principal chronic adverse effect is nephrotoxicity. AmB probably produces renal injury by a variety of mechanisms. Risk factors for AmB nephrotoxicity include male gender, higher average daily dose of AmB (≥35 mg/day), diuretic use, body weight ≥90 kg, concomitant use of nephrotoxic drugs, and abnormal baseline renal function. Clinical manifestations of AmB nephrotoxicity include renal insufficiency, hypokalemia, hypomagnesemia, metabolic academia, and polyuria due to nephrogenic diabetes insipidus. Human studies show convincingly that sodium loading in excess of the usual dietary intake notably reduces the incidence and severity of AmB-induced nephrotoxicity.

A Review on the Clinical Use of Inhaled Amphotericin B

Despite the systemic toxicity of amphotericin B (AMB), it still has a place in treatment or prophylactic regimes of fungal infections. A strategy for minimizing the potential of systemic side effects is to bring it in direct contact with the body site most likely to be infected, such as the administration of AMB as an aerosol. Nebulized amphotericin has been used in humans since 1959. However, due to a lack of sufficient data regarding efficacy, its use is still not established. Little is known about the optimal dose, frequency, duration of administration, and the pharmacokinetics of inhaled AMB in humans. In this review, published data regarding inhaled AMB are summarized, including available descriptions regarding preparation, dose, efficacy, and toxicity, and its place in therapy is discussed. The results from the studies that were reviewed in this article indicate that inhaled AMB may have a place in the prophylactic regimens of patients with prolonged neutropenia and in lung transplant recipients. Furthermore, nebulized (liposomal) AMB may have a place in the treatment of allergic bronchopulmonary aspergillosis (ABPA) in patients with corticosteroid-dependent ABPA.

Pharmacokinetics and biodistribution of amphotericin B in rats following oral administration in a novel lipid-based formulation

To assess the pharmacokinetics and biodistribution of amphotericin B (AmB) following oral administration in a novel mono/diglyceride-phospholipid formulation and to compare with intravenous (iv) administrations using commercial formulations. Rats were allocated into the following treatment groups: oral gavage of AmB dispersed in mono/diglyceride-phospholipid formulation at doses of 4.5 and 10 mg/kg; iv bolus administration of 0.8 mg/kg Fungizone; iv bolus of 5 mg/kg Abelcet and iv bolus of 5 mg/kg AmBisome. Blood was sampled from jugular vein cannula at certain time points. The animals were sacrificed 72 h following administration of AmB and multiple tissues were harvested. The concentration of AmB in plasma and tissues was determined by means of HPLC. The plasma creatinine concentrations were determined using an enzymatic kit. The pharmacokinetics and tissue distribution of AmB following iv administrations of the commercial formulations were found to be highly formulation dependent. The terminal half-life and biodistribution of orally administered AmB in a mono/diglyceride-phospholipid formulation resembled those of Fungizone. The larger volume of the co-administered lipid-based formulation in the case of the higher dose of orally administered AmB resulted in flip-flop kinetics and in preferential distribution into the kidneys. No nephrotoxicity was detected for any formulation and route of administration. Oral administration of AmB in a mono/diglyceride-phospholipid formulation to rats resulted in significant intestinal absorption into the systemic circulation with pharmacokinetic and biodistribution properties similar to a micellar iv preparation.

Mechanism of decrease of oral bioavailability of cyclosporin A during immunotherapy upon coadministration of amphotericin B

The trough level of blood concentration of cyclosporin A (CyA) in a patient receiving immunotherapy was observed to decrease following coadministration of amphotericin B (AMB). This clinical observation was confirmed experimentally in Wistar rats intravenously given AMB (1.5 or 3.0 mg/kg) or saline (control) for 4 days, followed by CyA (10 mg/kg). The blood concentration of CyA after i.v. or p.o. administration in both AMB groups was significantly decreased compared with the control. The oral bioavailability of CyA after 1.5 or 3.0 mg/kg AMB treatment was decreased to 67% or 46%, respectively, of that of the control group. AMB treatment increased the expression levels of mdr1a and mdr1b mRNAs in the duodenum to about three times the control, and expression of CYP3A2 mRNA in the liver was increased to about twice the control. The P-gp and CYP3A2 proteins were increased significantly. These findings suggest that the oral bioavailability of CyA is reduced as a result of both increased efflux transport via P-glycoprotein in the duodenum and an increased first-pass effect of CYP3A2-mediated hepatic metabolic activity, induced by AMB. It is suggested that careful monitoring of CyA levels is necessary in the event of AMB administration to patients receiving immunotherapy with CyA.

A Randomized, Placebo-Controlled, Dose-Escalation, Phase 1 Study of the Safety and Pharmacokinetics of Amphotericin B Inhalation Powder in Healthy Subjects.

Nektar is developing Amphotericin B Inhalation Powder (ABIP; NKTR-024) to prevent invasive pulmonary fungal infections in immunocompromised patients. NKTR-024 is a proprietary dry-powder amphotericin B (AmB) formulation that is delivered to the patient's respiratory tract with a proprietary breath-actuated inhalation device (T-326). This study assessed 1) the safety and tolerability and 2) the pharmacokinetics (PK) of AmB in epithelial lining fluid (ELF) and plasma after a loading dose (LD) and 4 weekly maintenance doses (MD) of NKTR-024 in healthy subjects. Thirty-six (36) subjects enrolled in a single center in the US into 2 cohorts 2:1 to receive either NKTR-024 (n=12) or a matching (powder load) placebo inhalation powder (n=6), respectively. Subjects in Cohort 1 (Coh1) received a 25-mg LD and 4 weekly 5-mg MD (25/5) and subjects in Cohort 2 (Coh2) received a 50-mg LD and 4 weekly 10-mg MD (50/10) of NKTR-024 or placebo, respectively. PK assessments used blood [plasma] and bronchoalveolar lavage (BAL) [ELF] samples. Concomitant medications, adverse events (AEs) and other safety parameters were monitored for 17 wk (screening period of up to 28 d, a 4-wk treatment period, and a 9-wk post-treatment period). All 36 subjects received 1 LD and 4 MDs. Subjects were mostly male (n=24, 66.7%) and Caucasian (n=27, 75%). Mean age=28.1 yr, median height=175.3 cm and median weight=77.4 kg. PK data have been previously presented and will not serve as the focus of this abstract. Maximal plasma AmB concentrations occurred at ∼8–12 hr postdose following a ∼1 hr postdose lag. Plasma AmB concentrations (<54.6 ng/mL after the 50-mg NKTR-024 LD) remained well below those typically associated with renal toxicity (plasma AmB concentrations of ≥1000 ng/mL). Mean lung ELF AmB concentrations from the first BAL samples (∼4 hr) were 70.7 and 189 μg/mL for Coh1 and Coh2, respectively. These high lung ELF AmB concentrations show that a large fraction of the nominal NKTR-024 doses were delivered to the lung. Both the NKTR-024 regimens (25/5 and 50/10) were well-tolerated. AEs were mild or moderate. No serious AEs occurred. Most of the AEs across treatment groups were related to bronchoscopy or “other” reasons. Respiratory AEs were most common across treatment groups. Slightly more respiratory AEs (cough, productive cough, increased bronchial secretions, wheezing, dyspnea, and exertional dyspnea) occurred in the NKTR-024 groups versus the placebo groups. AEs were greatest on the day of dosing and for the first 2 days after dosing. Hematology, chemistry, and urinalysis showed no clinically concerning treatment-induced toxicity. No clinically significant abnormalities were noted on physical examination, vital signs, chest x-ray, or electrocardiogram. Spirometry (FVC and FEV1) remained virtually unchanged from predose to postdose at all scheduled visits except for 4 subjects who had transient declines in FVC or FEV1 >20% temporally related to bronchoscopy. Repeated administration of NKTR-024 resulted in high pulmonary and low systemic AmB exposure. Plasma AmB concentrations were well below those associated with renal toxicity; this observation supports an important potential benefit of the NKTR-024 investigational product. Constitutional symptoms and electrolyte abnormalities traditionally seen with systemic administration of AmB were essentially spared.

Endophthalmitis Due to Trichosporon beigelii in Acute Leukemia

We describe 2 patients with hematologic malignancy who developed endophthalmitis due to Trichosporon beigelii during the course of treatment with multiagent chemotherapy. Blood cultures revealed T beigelii for both patients. Although one of the patients was treated with fluconazole (FLCZ) and 5-fluorocytosine, the trichosporonous endophthalmitis was resistant to both drugs. This patient subsequently received amphotericin B (AMPH-B) therapy, and the eyes were treated with vitrectomy. The second patient also received AMPH-B for FLCZ-resistant trichosporonous chorioretinitis. In both patients, systemic treatment with AMPH-B successfully resolved the trichosporonous endophthalmitis that was resistant to multiple antifungal drugs. Endophthalmitis due to trichosporonosis is difficult to treat. The administration of AMPH-B is likely to be more effective in treating endophthalmitis due to trichosporonosis when the disease is at an early stage.

Measurement of Amphotericin B concentration by Resonant Raman Spectroscopy – a novel technique that may be useful for non-invasive monitoring

We wished to determine whether Resonant Raman Spectroscopy (RRS) could be used to measure Amphotericin B (AmB) at therapeutic and subtherapeutic concentrations in a model system mimicking the anterior chamber of the eye. The goal was to develop a technique for non-invasive measurement of AmB levels in the aqueous humor (AH) of the eye. A krypton-ion laser source (406.7 nm) was used for excitation and Resonant Raman Spectra were captured with a confocal system in an anterior chamber (AC) model. These spectra were used to develop a correlation curve for prediction of AmB levels. Subsequently, one rabbit was evaluated with this system after 5 days of intravenous AmB administration (1 mg/kg/day) and AmB concentrations measured by RRS were compared to those measured by high-performance liquid chromatography (HPLC). AmB exhibited a unique spectral peak at 1557 cm(-1). Integrated area of this peak linearly correlated with AmB concentration in our model AC. When integrated peak area from multiple in vivo measurements in one animal at steady-state was plotted on this correlation curve, we were able to predict AmB levels. These closely approximated those measured by HPLC. These measurements were not significantly affected by photobleaching or depth profile at acquisition. RRS at 406.7 nm is a method that may be useful for non-invasive monitoring of intraocular AmB levels. This instrument can help physicians decide when repeat, invasive delivery of this drug is warranted based on measurement of actual drug levels in the AH. Also, there is the potential to measure the ocular concentrations of other pharmaceutical agents with similar instruments.

Assessment of Effective Renal Plasma Flow, Enzymuria, and Cytokine Release in Healthy Volunteers Receiving a Single Dose of Amphotericin B Desoxycholate

The present study assessed potential subclinical markers of amphotericin B (AmB)-related nephrotoxicity and infusion-related reactions (IRR). Subjects were pretreated with diphenhydramine and acetaminophen and received a 500-ml bolus infusion of 0.9% sodium chloride prior to each effective renal plasma flow (ERPF) assessment. ERPF was measured before and after administration of a single 0.25-mg/kg intravenous AmB dose using technetium-99m mercaptoacetyltriglycine. Blood was collected before and 3 h after AmB infusion for tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta) plasma concentrations. Overnight 12-h urine collections were performed before administration of AmB and for 2 nights after administration of AmB and analyzed for alpha and pi glutathione-S-transferases (GSTalpha and GSTpi, respectively) and N-acetyl-beta-d-glucosaminidase (NAG). Six men and six women with mean +/- standard deviation (SD) ages of 24.8 +/- 5.3 and 28.0 +/- 8.5 years, respectively, were studied. Baseline serum creatinine values were within the normal range and were unaltered after administration of AmB. The mean +/- SD decrease in ERPF after administration of AmB was significant (P < 0.05) in males (15.7 +/- 8.1%) but not females (9.5 +/- 14.0%). The GSTpi and GSTalpha indices increased significantly (P < 0.05) by two to fourfold and returned to baseline in males but were unaltered in females. NAG indices were unaffected by AmB. Six patients experienced an IRR that was associated with increased TNF-alpha (P < 0.05) but not IL-1beta (P = 0.09). These results suggest a potential sex-related difference in AmB-induced nephrotoxicity and provide a rationale for use of ERPF, urine GST, and TNF-alpha as subclinical markers of polyene-induced toxicity.

Management of cryptococcosis in non-HIV-related patients

Cryptococcosis is the third most common deep fungal infection in China and has not yet been reported to be associated with HIV infection there. We report the management of non-HIV-related cryptococcosis, including cutaneous cryptococcosis, pulmonary cryptococcosis and cryptococcal infection of central nervous system (CNS). Establishment of the diagnosis of cutaneous cryptococcosis and pulmonary cryptococcosis were mainly based on the histopathologic examination and mycologic culture, with CNS cryptococcal infection based on mycologic examination and latex agglutination test on cerebrospinal fluid. The treatment of cutaneous cryptococcosis included systemic administration of amphotericin B (AMB), 5-flucytosine and triazole agents such as fluconazole and itraconazole combined with topical ketoconazole cream. Treatment of pulmonary cryptococcosis included systemic use of antifungal medication combined with surgical removal of pulmonary lesions. The treatment of CNS cryptococcal infection was challenging. In this study, 53 patients with CNS cryptococcal infection were divided into three groups according to the antifungal regimens applied: eight patients (group I) received intravenous AMB alone or in combination with 5-flucytosine, five patients (group II) received intravenous fluconazole alone or with 5-flucytosine, and 40 patients (group III) received a two-phase therapy, active therapy and consolidation therapy. In active therapy, the patients received intrathecal and intravenous administration of AMB alone or with 5-flucytosine until the mycological culture of cerebrospinal fluid (CSF) became negative. Consolidation therapy followed active therapy by continuous use of oral fluconazole or itraconazole until direct microscopic examination of CSF was negative for three consecutive weeks. In group I, five patients were cured, two improved, one died and one had relapse. In group II, two patients were cured, one improved and two died. In group III, thirty-nine out of forty patients were cured without recurrence. These results indicate that the two-phase protocol was more desirable for the treatment of non-HIV associated cryptococcal infection of CNS.

Can we decrease amphotericin nephrotoxicity?

Amphotericin B (AmB) is considered the drug of choice for the treatment of systemic fungal infections. Nephrotoxicity is a major complication associated with its use, and appears to be related to higher cumulative doses, diuretic use, abnormal serum creatinine at baseline, and the use of concomitant nephrotoxic drugs. The two major hypotheses for the pathogenesis of AmB-related nephrotoxicity are direct effects of the drug on epithelial cell membranes and vasoconstriction. During the last few years, some randomized trials have tested different strategies to reduce AmB-induced renal toxicity. These strategies include sodium supplementation, low-dose dopamine, slower infusion rates, the administration of AmB in lipid emulsions, and in lipid formulations. The results of these trials showed that the lipid formulations of AmB significantly reduce nephrotoxicity. Unfortunately, these agents are costly, restricting their use to patients with a high risk of developing renal failure.

Amphotericin B severely affects expression and activity of the endothelial constitutive nitric oxide synthase involving altered mRNA stability.

The therapeutic use of the antifungal drug amphotericin B (AmB) is limited due to severe side effects like glomerular vasoconstriction and risk of renal failure during AmB administration. As nitric oxide (NO) has substantial functions in renal autoregulation, we have determined the effects of AmB on endothelial constitutive NO synthase (ecNOS) expression and activity in human and rat endothelial cell cultures. AmB used at concentrations of 0.6 to 1.25 microg ml(-1) led to increases in ecNOS mRNA and protein expression as well as NO production. This was the result of an increased ecNOS mRNA half-life. In contrast, incubation of cells with higher albeit subtoxic concentrations of AmB (2.5 - 5.0 microg ml(-1)) resulted in a decrease or respectively in completely abolished ecNOS mRNA and protein expression with a strongly reduced or inhibited ecNOS activity, due to a decrease of ecNOS mRNA half-life. None of the AmB concentrations affected promoter activity as found with a reporter gene construct stably transfected into ECV304 cells. Thus, our experiments show a concentration-dependent biphasic effect of AmB on expression and activity of ecNOS, an effect best explained by AmB influencing ecNOS mRNA stability. In view of the known renal accumulation of this drug the results reported here could help to elucidate its renal toxicity.

Amiloride for the prevention of amphotericin B-induced hypokalemia and hypomagnesemia.

To review the published clinical data assessing the role of amiloride in the prevention of amphotericin B (AmB)induced electrolyte disorders. A MEDLINE search (January 1966-April 1999) of English-language literature pertaining to AmB, amiloride, potassium, and magnesium was performed. Tertiary sources were also used. In vivo and in vitro human and animal data and case reports were included due to the lack of published clinical trials. AmB administration can result in severe hypokalemia and hypomagnesemia requiring chronic supplementation. In one prospective, controlled study of hypokalemia with AmB administration, patients receiving concomitant amiloride had significantly greater potassium concentrations (p < 0.01) and required significantly less potassium supplementation (p < 0.001). Amiloride may also reduce the amount of magnesium supplementation required by sparing elimination through the kidneys. Amiloride may be considered for the prevention of AmB-induced hypokalemia and hypomagnesemia, especially in patients at high risk for complications resulting from these electrolyte disorders. Further studies are needed to assess concomitant use of other potassium-sparing diuretics and AmB.

Pharmacologic modulation of interleukin-1 expression by amphotericin B-stimulated human mononuclear cells.

Fever and chills occur frequently with amphotericin B (AB) administration, but the mechanism that causes these reactions has not been definitively established. A variety of proinflammatory cytokines, including interleukin-1 (IL-1) and tumor necrosis factor, have been shown to be important mediators of fever. In order to clarify the cellular and biochemical responses associated with AB-induced fever, the experiments described sought to (i) establish whether human mononuclear cells exposed to AB in vitro expressed IL-1 beta, (ii) evaluate whether clinically used premedications for fever prophylaxis in AB-treated patients were effective in down-regulating IL-1 beta expression in vitro, (iii) evaluate whether methylxanthine agents with immunomodulatory actions effected in vitro IL-1 beta expression, and (iv) define the dose and time dependency of the modulating effects. Peripheral blood mononuclear cells were isolated by density centrifugation and resuspended to 10(6) cells per ml in culture wells of Linbro plates. When cocultured for 2 h with human mononuclear cells, both Escherichia coli lipopolysaccharide and AB stimulated IL-1 beta expression in a dose-related fashion. AB-induced IL-1 beta expression was suppressed by hydrocortisone (HC), pentoxifylline, and an investigational theobromine, A81-3138, in a linear, dose-related manner. In contrast, indomethacin, meperidine, and diphenhydramine had no effect on IL-1 beta expression. Our in vitro data indicate that serum HC concentrations of greater than 1 to 2 micrograms/ml may be sufficient to modulate IL-1 beta expression. Pentoxifylline and A81-3138 may also be effective in modulating IL-1 beta expression by mononuclear cells at concentrations achievable in serum. These new agents may prove to be effective alternatives to HC or may be added with HC to suppress febrile reactions secondary to AB administration. Clinical studies with pentoxifylline as a premedication for AB seem warranted.

Amphotericin B and sodium deoxycholate induced impairment of renal p-aminohippurate accumulation (PAH) and effect on lipid peroxidation in the rat kidney.

The influence of amphotericin B on PAH transport as well as on lipid peroxidation in rat renal cortical slices was studied in vitro and ex vivo. In vitro, renal cortical slices were incubated with different amphotericin B (AmB) concentrations (2-60 micrograms/mL) or with the corresponding vehicle concentrations of sodium deoxycholate (NaDo) (1.64-49.2 micrograms/mL) and time dependently (15-30-60 min) with 30 micrograms/mL AmB or 24.6 micrograms/mL NaDo. Ex vivo, PAH transport of renal cortical slices was investigated following a 3-day intravenous AmB administration with 3 mg/kg per day or 2.46 mg/kg/day NaDo, respectively. In vitro AmB as well as NaDo decreased PAH transport dose and time dependently. At the highest AmB concentration of 60 micrograms/mL, PAH uptake decreased to 17.6%. The corresponding NaDo concentration (49.2 micrograms/mL) decreased PAH uptake to 33.3%. Time dependently AmB decreased PAH uptake to 25% after 60 min. NaDo caused a decrease to 69%. Administration of AmB for 3 days resulted in a PAH decline to 81%; NaDO decreased PAH uptake to 77%. In vitro as well as in vivo, AmB or its vehicle did not induce lipid peroxidation in renal cortical tissue. In summary, the results show that AmB and its vehicle, NaDo, decrease PAH uptake by renal cortical cells, reflecting a direct effect of AmB on tubular function. The impairment of the PAH transport is not due to enhanced lipid peroxidation.

Enhancement of the Treatment of Experimental Candidiasis with Vascular Decongestants

The mechanism of amphotericin B (AmB) nephrotoxicity may be related to changes in vascular flow within the kidney, resulting in significant decreases in glomerular filtration rate and tubular integrity. The toxic and antifungal effects of AmB with and without the vascular decongestants pentoxifylline (PTX) and a methylxanthine analog, HWA-138, were compared in the murine model of candidiasis. At 48 h after inoculation with Candida albicans, half of the rats received a single intravenous 0.8 mg/kg dose of AmB whereas the others were administered sterile water. After 1 h, rats were randomized to receive three doses of 45 mg/kg PTX intraperitoneally, 5 mg/kg HWA-138 intravenously, or saline every 12 h. Renal function and Candida cell counts were estimated 24 h after AmB administration. Mean inulin clearances were significantly greater in rats coadministered AmB and PTX or HWA-138 than in AmB controls. Candida counts in kidneys of rats administered HWA-138 were similar independent of AmB therapy and markedly reduced compared with other groups. Whereas both vascular decongestants prevented drug-associated renal toxicity, the coadministration of AmB with HWA-138 resulted in a profound antifungal effect.

Validation of the difference in urine and blood carbon dioxide tension during bicarbonate loading as an index of distal nephron acidification in experimental models of distal renal tubular acidosis.

Recent classifications of the several pathophysiologic types of distal renal tubular acidosis (secretory, voltage dependent, and gradient) have been based on the response of acidification parameters to a series of provocative maneuvers in vivo and in vitro. A reduction in the difference in urine and blood CO2 tension during bicarbonate loading (U-B pCO2 gradient), a widely applied parameter, has been employed as an index of reduced distal nephron proton secretion. This study was designed to test the validity of the U-B pCO2 gradient in a variety of experimental models of distal renal tubular acidosis by measuring and comparing disequilibrium pH (a direct technique to detect H+ secretion in situ) with the pCO2 in the papillary collecting duct of the rat in vivo during bicarbonate loading. Chronic amiloride, lithium chloride, and amphotericin-B administration, and the post-obstructed kidney models were employed. Amiloride resulted in an acidification defect which did not respond to sulfate infusion (urine pH = 6.15 +/- 0.08), and was associated with an obliteration of the acid disequilibrium pH (-0.26 +/- 0.05- -0.08 +/- 0.03) and reduction in papillary pCO2 (116.9 +/- 3.2 - 66.9 +/- 2.5 mmHg). The defect induced by lithium administration responded to Na2SO4 (urine pH = 5.21 +/- 0.06) but was similar to amiloride with respect to the observed reduction in disequilibrium pH (-0.04 +/- 0.02) and pCO2 (90.3 +/- 3.0 mmHg). The post-obstructed kidney model was characterized by an abnormally alkaline urine pH unresponsive to sulfate (6.59 +/- 0.06) and a reduction in disequilibrium pH (+0.02 +/- 0.06) and pCO2 (77.6 +/- 3.6 mmHg). Amphotericin-B resulted in a gradient defect as characterized by excretion of an acid urine after infusion of sodium sulfate (5.13 +/- 0.06). Unlike other models, however, amphotericin-B was associated with a significant acid disequilibrium pH (-0.11 +/- 0.05) and an appropriately elevated urine pCO2 (119.8 +/- 6.4 mmHg) which did not differ from the respective values in control rats. Thus, these findings support the use of the U-B pCO2 as a reliable means of demonstrating impaired distal nephron proton secretion in secretory and voltage-dependent forms of distal renal tubular acidosis (RTA) and supports the view that proton secretion is not impaired in gradient forms of distal RTA.

The effect of amphotericin B on the survival of brain-tumor-bearing mice treated with CCNU.

The membrane-active polyene, amphotericin B (AMB) has been shown to enhance or potentiate the effects of various chemotherapeutic agents against tumor cells in tissue culture. Because of the need to increase the efficacy of the nitrosoureas in brain-tumor chemotherapy, we have studied the effect of the nitrosourea, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU), with or without AMB pretreatment. The intraperitoneal administration of 25 mg/kg of AMB 24 hours before 5, 10, 20 or 30 mg/kg of intraperitoneal CCNU did not result in a significant improvement in survival. The failure of intraperitoneal AMB to potentiate the effect of CCNU was likely a failure in drug delivery, since AMB crosses the blood-brain barrier very poorly. To circumvent the drug-delivery problem, AMB was administered intracerebrally directly into the tumor-bearing hemisphere. With 0.5 mg/kg of intracerebral AMB administered 24 hours before 10 mg/kg CCNU was given intraperitoneally, the life-span was significantly increased over the control group. The same dose of CCNU alone did not significantly increase survival. When 0.2, 0.5, or 1.0 mg/kg AMB was administered intracerebrally 24 hours before 20 mg/kg of interaperitoneal CCNU, survival was significantly increased over those groups receiving the same dose of CCNU alone. It is concluded that direct intracerebral administration of AMB enhances or potentiates the therapeutic effect of CCNU in this brain-tumor model.

Interaction of Amphotericin B and Vasopressin in the Rat Kidney and the Toad Urinary Bladder

The interaction of amphotericin B (AmB) and vasopressin (ADH) was studied in the rat and the toad urinary bladder. In the anesthetized rat infused with a sustaining dose of ADH, AmB administration resulted in a decrease in urine osmolality and increases in urine flow and fractional water and Na excretions. However, the urine flow for a given osmolar clearance was higher after AmB than before, indicating that free water reabsorption is inhibited by AmB. Micropuncture experiments suggested an inhibition of proximal Na reabsorption after AmB. In the toad bladder, AmB added to the mucosal side enhanced osmotic water flux and impaired hydroosmotic action of ADH. These results indicate a functional antagonism between AmB and ADH in the renal tisssue.