Highly sensitive UPLC-MS/MS method for the quantification of paromomycin in human plasma.

A highly sensitive method was developed to quantitate the antileishmanial agent paromomycin in human plasma, with a lower limit of quantification of 5 ng/mL. Separation was achieved using an isocratic ion-pair ultra-high performance liquid chromatographic (UPLC) method with a minimal concentration of heptafluorobutyric acid, which was coupled through an electrospray ionization interface to a triple quadrupole - linear ion trap mass spectrometer for detection. The method was validated over a linear calibration range of 5 to 1000 ng/mL (r2≥0.997) with inter-assay accuracies and precisions within the internationally accepted criteria. Volumes of 50 µL of human K2EDTA plasma were processed by using a simple protein precipitation method with 40 µL 20 % trichloroacetic acid. A good performance was shown in terms of recovery (100 %), matrix effect (C.V. ≤ 12.0 %) and carry-over (≤17.5 % of the lower limit of quantitation). Paromomycin spiked to human plasma samples was stable for at least 24 h at room temperature, 6 h at 35 °C, and 104 days at -20 °C. Paromomycin adsorbs to glass containers at low concentrations, and therefore acidic conditions were used throughout the assay, in combination with polypropylene tubes and autosampler vials. The assay was successfully applied in a pharmacokinetic study in visceral leishmaniasis patients from Eastern Africa.

Evaluation of paromomycin sulphate permeation using ex vivo human skin model.

Ex vivo evaluation of drug release and skin permeation from topical formulations of antileishmanial drug paromomycin sulphate was carried out using intact full thickness human skin. Potency-based microbiological assay was used for the analysis of paromomycin concentrations. A total percentage drug recovery of 86 ± 26% was obtained. Incubation periods of 1 and 3 h resulted in percentage drug permeation into deep skin layers ranging from 1.3 ± 0.04% to 5.3 ± 2.0% with paraffin-based ointment and from 1.6 ± 0.8% to 3.9 ± 1% with microemulsion-based emulgel. Although a small percentage, this is still significantly higher than those previously reported using animal skin models.

Pharmacokinetics and tolerability of aminosidine after repeated administrations using an optimal dose regimen in healthy dogs and in dogs with leishmaniosis.

Optimisation of dose schedules of aminoglycosides is required in order to increase efficacy and prevent their toxicity. The objective of this study was to determine the pharmacokinetic profile and the safety of aminosidine in dogs with naturally occurring leishmaniosis and in healthy dogs after once daily administration. Six young-adult, male, healthy, Beagle dogs and 12 dogs with clinical signs of canine leishmaniosis without azotemia and proteinuria were included in the study. Diagnosis of the disease was confirmed by serology, parasitology and molecular techniques. Pharmacokinetics and evaluation of renal function after repeated (once daily for 21 consecutive days) subcutaneous administration of aminosidine, at the dose of 15 mg/kg b.w. in both the healthy and the diseased animals were compared. Concentrations of aminosidine were determined by high-performance liquid chromatography and pharmacokinetic analysis was performed by the non-compartmental method. No significant differences were observed between healthy and diseased dogs considering all pharmacokinetic parameters. In general, mean Cmax ranged between 46.41 and 54.32 µg/mL and between 38.69 and 40.73 µg/mL in healthy dogs and in dogs with canine leishmaniosis, respectively. No accumulation of the drug was observed in either group since total elimination of aminosidine and half-life lambda z were not modified throughout the administration period. Aminosidine was well tolerated in all dogs with no clinical and clinicopathological signs of nephrotoxicity. Once daily administration of high dose of aminoglycosides, resulted in effective serum concentrations and absence of nephrotoxicity.

Development of a liquid chromatographic method for the quantification of paromomycin. Application to in vitro release and ex vivo permeation studies.

We have developed a reversed phase high performance liquid chromatography pulsed amperometric detection (RPHPLC-PAD) method for the determination of paromomycin. It is sensitive, repeatable, and selective without the pretreatment step. Trifluoroacetic acid-water was utilized as the eluent and detected by PAD under NaOH alkaline conditions. The paromomycin detection limit (S/N=3.3) was 2µgmL(-1) and the quantification limit (S/N=10) was 6µgmL(-1). Coefficients of linear regression were higher than 0.99 for concentrations between 6.25 and 200µgmL(-1). The intra and inter-day precision (RSD) was less than 6.5%. The average recoveries were 97.53-102.01%. The proposed HPLC-PAD method presented advantageous performance characteristics and it can be considered suitable for the evaluation of paromomycin loaded nanogel formulation in ex vivo permeation and in vitro release studies.

Pharmacokinetics and absorption of paromomycin and gentamicin from topical creams used to treat cutaneous leishmaniasis.

This study evaluated the pharmacokinetics of topical creams containing 15% paromomycin ("paromomycin alone") and 15% paromomycin plus 0.5% gentamicin (WR 279,396) in patients with cutaneous leishmaniasis. The investigational creams were applied topically to all lesions once daily for 20 days. Plasma samples were analyzed for simultaneous quantitation of paromomycin and gentamicin isomers and total gentamicin. Pharmacokinetic parameters for gentamicin could not be calculated because detectable levels were rarely evident. After one application, the paromomycin area under the concentration-time curve from 0 to 24 h (AUC0-24) was 2,180 ± 2,621 ng · h/ml (mean ± standard deviation [SD]) for the paromomycin-alone group and 975.6 ± 1,078 ng · h/ml for the WR 279,396 group. After 20 days of application, the paromomycin AUC0-24 and maximum concentration of drug (Cmax) were 5 to 6 times greater than those on day 1 for both treatment groups. For the paromomycin-alone group, the AUC0-24 was 8,575 ± 7,268 ng · h/ml and the Cmax was 1,000 ± 750 ng/ml, compared with 6,037 ± 3,956 ng · h/ml and 660 ± 486 ng/ml for the WR 279,396 group, respectively. Possibly due to large intersubject variability, no differences (P ≥ 0.05) in the AUC0-24 or Cmax were noted between treatment or between sites on day 1 or 20. The percentage of dose absorbed on day 20 was 12.0% ± 6.26% and 9.68% ± 6.05% for paromomycin alone and WR 279,396, respectively. Paromomycin concentrations in plasma after 20 days of application were 5 to 9% of those after intramuscular administration of 15 mg/kg of body weight/day to adults for the systemic treatment of visceral leishmaniasis. Effective topical treatment of cutaneous leishmaniasis appears to be possible with limited paromomycin and gentamicin systemic absorption, thus avoiding drug accumulation and toxicity. (The work described here has been registered at ClinicalTrials.gov under registration no. NCT01032382 and NCT01083576.).

Bioanalytical method development, pharmacokinetics, and toxicity studies of paromomycin and paromomycin loaded in albumin microspheres.

Intracellular location of leishmania parasite in macrophages protects them from both hosts defence system as well as from antibiotics like paromomycin (PM) acting against them, thus there is a need of a formulation targeting intracellular parasites. Considering this, PM-loaded albumin microspheres (PM-MS) were prepared to target PM to macrophages where leishmania parasites resides and evaluated for their safety profile. A new bioanalytical method for quantitative determination of PM in rat plasma was developed by pre-column derivatization with 9-fluorenylmethyl chloroformate. The developed bioanalytical method was validated and applied for pharmacokinetic studies of PM administered by intramuscular and intravenous routes as well as for developed PM-MS which were administered by intravenous route. Comparative acute and subacute toxicity studies were also carried out for these formulations. The developed method was found to be very sensitive with a quantification limit of 40 ng/ml. Pharmacokinetic studies demonstrated nearly 80% reduction in C(max) of PM when administered as PM-MS, compared to other formulations at equivalent dose. Toxicity studies indicated increased level of blood urea and blood urea nitrogen in PM intramuscular injection at 90 mg/kg dose, whereas at the same dose level PM-MS showed no symptoms of toxicity. Results obtained suggest that developed PM-MS formulation is a promising alternative to the presently marketed PM intramuscular injection for the treatment of visceral leishmaniasis.

Porcine intestinal epithelial barrier disruption by the Fusarium mycotoxins deoxynivalenol and T-2 toxin promotes transepithelial passage of doxycycline and paromomycin.

BACKGROUND: The gastrointestinal tract is the first target for the potentially harmful effects of mycotoxins after intake of mycotoxin contaminated food or feed. With deoxynivalenol (DON), T-2 toxin (T-2), fumonisin B1 (FB1) and zearalenone (ZEA) being important Fusarium toxins in the northern hemisphere, this study aimed to investigate in vitro the toxic effect of these mycotoxins on intestinal porcine epithelial cells derived from the jejunum (IPEC-J2 cells). Viability of IPEC-J2 cells as well as the proportion of apoptotic and necrotic IPEC-J2 cells was determined by flow cytometry after 72 h of exposure to the toxins. Correlatively, the integrity of the intestinal epithelial cell monolayer was studied using Transwell(®) inserts, in which the trans-epithelial electrical resistance (TEER) and passage of the antibiotics doxycycline and paromomycin were used as endpoints. RESULTS: We demonstrated that the percentage of Annexin-V-FITC and PI negative (viable) cells, Annexin-V-FITC positive and PI negative (apoptotic) cells and Annexin-V-FITC and PI positive (necrotic) IPEC-J2 cells showed a mycotoxin concentration-dependent relationship with T-2 toxin being the most toxic. Moreover, the ratio between Annexin-V-FITC positive and PI negative cells and Annexin-V-FITC and PI positive cells varied depending on the type of toxin. More Annexin-V-FITC and PI positive cells could be found after treatment with T-2 toxin, while more Annexin-V-FITC positive and PI negative cells were found after exposure to DON. Consistent with the cytotoxicity results, both DON and T-2 decreased TEER and increased cellular permeability to doxycycline and paromomycin in a time- and concentration-dependent manner. CONCLUSIONS: It was concluded that Fusarium mycotoxins may severely disturb the intestinal epithelial barrier and promote passage of antibiotics.

Colloidal, in vitro and in vivo anti-leishmanial properties of transfersomes containing paromomycin sulfate in susceptible BALB/c mice.

The aim of this study was to develop transfersomal formulation with respect to dermal delivery of paromomycin sulfate (PM) for possible topical therapy of cutaneous leishmaniasis (CL). PM transfersomal formulations (PMTFs) with different percent of soy phosphatidylcholine, sodium cholate (Na-Ch) and ethanol were prepared and characterized for the size, zeta potential and encapsulation efficiency. The results showed that the most stable formulations with suitable colloidal properties were obtained by 2% Na-Ch which had average size of around 200 nm. The in vitro permeation study using Franz diffusion cells fitted with mouse skin at 37°C for 24h showed that almost 23% of the PMTFs applied penetrated the mouse skin, and the amount retained in the skin was about 67% for both formulations; however, the percent of penetration and retention for PM conventional cream was 49 and 13, respectively. The 50% effective doses of PMTFs against Leishmania major promastigotes and amastigotes in culture were significantly less than cream and/or solution of PM. Selected PMTFs and empty transfersomes showed no cytotoxicity in J774 A.1 mouse macrophage cell line. Selected PMTFs was used topically twice a day for 4 weeks to treat L. major lesions on BALB/c mice, and the results showed a significantly (P<0.05) smaller lesion size in the mice in the treated groups than in the mice in the control groups, which received either empty transfersomes or phosphate-buffered saline (PBS) and also PM cream. The spleen parasite burden was significantly (P<0.01) lower in mice treated with selected PMTFs than in mice treated with PBS or control transfersomes, and PM cream. The results of this study showed that PMTFs prepared with 2% of Na-Ch with and without 5% ethanol might be useful as a candidate for the topical treatment of CL.

Influence of mycotoxins and a mycotoxin adsorbing agent on the oral bioavailability of commonly used antibiotics in pigs.

It is recognized that mycotoxins can cause a variety of adverse health effects in animals, including altered gastrointestinal barrier function. It is the aim of the present study to determine whether mycotoxin-contaminated diets can alter the oral bioavailability of the antibiotics doxycycline and paromomycin in pigs, and whether a mycotoxin adsorbing agent included into diets interacts with those antibiotics. Experiments were conducted with pigs utilizing diets that contained blank feed, mycotoxin-contaminated feed (T-2 toxin or deoxynivalenol), mycotoxin-contaminated feed supplemented with a glucomannan mycotoxin binder, or blank feed supplemented with mycotoxin binder. Diets with T-2 toxin and binder or deoxynivalenol and binder induced increased plasma concentrations of doxycycline administered as single bolus in pigs compared to diets containing blank feed. These results suggest that complex interactions may occur between mycotoxins, mycotoxin binders, and antibiotics which could alter antibiotic bioavailability. This could have consequences for animal toxicity, withdrawal time for oral antibiotics, or public health.

Paromomycin for the treatment of visceral leishmaniasis in Sudan: a randomized, open-label, dose-finding study.

BACKGROUND: A recent study has shown that treatment of visceral leishmaniasis (VL) with the standard dose of 15 mg/kg/day of paromomycin sulphate (PM) for 21 days was not efficacious in patients in Sudan. We therefore decided to test the efficacy of paramomycin for a longer treatment duration (15 mg/kg/day for 28 days) and at the higher dose of 20 mg/kg/day for 21 days. METHODS: This randomized, open-label, dose-finding, phase II study assessed the two above high-dose PM treatment regimens. Patients with clinical features and positive bone-marrow aspirates for VL were enrolled. All patients received their assigned courses of PM intramuscularly and adverse events were monitored. Parasite clearance in bone-marrow aspirates was tested by microscopy at end of treatment (EOT, primary efficacy endpoint), 3 months (in patients who were not clinically well) and 6 months after EOT (secondary efficacy endpoint). Pharmacokinetic data were obtained from a subset of patients weighing over 30 kg. FINDINGS: 42 patients (21 per group) aged between 4 and 60 years were enrolled. At EOT, 85% of patients (95% confidence interval [CI]: 63.7% to 97.0%) in the 20 mg/kg/day group and 90% of patients (95% CI: 69.6% to 98.8%) in the 15 mg/kg/day group had parasite clearance. Six months after treatment, efficacy was 80.0% (95% CI: 56.3% to 94.3%) and 81.0% (95% CI: 58.1% to 94.6%) in the 20 mg/kg/day and 15 mg/kg/day groups, respectively. There were no serious adverse events. Pharmacokinetic profiles suggested a difference between the two doses, although numbers of patients recruited were too few to make it significant (n = 3 and n = 6 in the 20 mg/kg/day and 15 mg/kg/day groups, respectively). CONCLUSION: Data suggest that both high dose regimens were more efficacious than the standard 15 mg/kg/day PM for 21 days and could be further evaluated in phase III studies in East Africa.

Effect of topical liposomes containing paromomycin sulfate in the course of Leishmania major infection in susceptible BALB/c mice.

The aim of this study was to evaluate the antileishmanial effects of topical liposomal paromomycin sulfate (PM) in Leishmania major-infected BALB/c mice. Liposomes containing 10 or 15% PM (Lip-PM-10 and Lip-PM-15, respectively) were prepared by the fusion method and were characterized for their size and encapsulation efficiency. The penetration of PM from the liposomal PM formulations (LPMFs) through and into skin was evaluated in vitro with Franz diffusion cells fitted with mouse skin at 37 degrees C for 8 h. The in vitro permeation data showed that almost 15% of the LPMFs applied penetrated the mouse skin, and the amount retained in the skin was about 60% for both formulations. The 50% effective doses of Lip-PM-10 and Lip-PM-15 against L. major promastigotes in culture were 65.32 and 59.73 microg/ml, respectively, and those against L. major amastigotes in macrophages were 24.64 and 26.44 microg/ml, respectively. Lip-PM-10 or Lip-PM-15 was used topically twice a day for 4 weeks to treat L. major lesions on BALB/c mice, and the results showed a significantly (P < 0.001) smaller lesion size in the mice in the treated groups than in the mice in the control group, which received either empty liposomes or phosphate-buffered saline (PBS). Eight weeks after the beginning of the treatment, every mouse treated with LPMFs was completely cured. The spleen parasite burden was significantly (P < 0.001) lower in mice treated with Lip-PM-10 or Lip-PM-15 than in mice treated with PBS or control liposomes, but no significant difference was seen between the two groups treated with either Lip-PM-10 or Lip-PM-15. The results suggest that topical liposomal PM may be useful for the treatment of cutaneous leishmaniasis.

Paromomycin.

Paromomycin is an aminoglycoside that is active against Gram-negative and many Gram-positive bacteria as well as some protozoa and cestodes. It is out of use as an antibiotic but was licensed in 2007 in India as an effective, well tolerated and affordable treatment for visceral leishmaniasis (VL) at a dose of 11 mg/kg (base) for 21 days. Currently, the non-profit group Drugs for Neglected Diseases Initiative is conducting studies on paromomycin (as monotherapy and in combination) in VL in Africa, and the Institute for OneWorld Health is conducting a Phase IV study in India. Paromomycin in combination with sodium stibogluconate has proven to be effective in African and Indian VL and improves survival in African VL. To prevent the emergence of drug-resistant leishmaniasis in areas of anthroponotic transmission (India and Africa), paromomycin should be used as part of combination therapy for VL. Further trials testing different combinations are much needed. In addition, the distribution of paromomycin (like other drugs for leishmaniasis) should be well regulated and preferably restricted to the public sector. These strategies should ensure the longevity of paromomycin as a useful drug for VL.

Paromomycin in the treatment of leishmaniasis.

BACKGROUND: The treatment options for leishmaniasis are limited. Most of the drugs available need parenteral administration, are toxic, require monitoring and have a prolonged treatment duration. All these factors increase the cost of the treatment. The development of resistance to pentavalent antimonials in patients with visceral leishmaniasis in North Bihar, India, has added another dimension to the problem. OBJECTIVE: To summarise the pharmacological and clinical data on antileishmanial activity of paromomycin and discuss the impact this agent may have on present treatment regimens. METHODS: A literature search on paromomycin and leishmaniasis was done on PubMed and through Google. RESULTS: Paromomycin, with its excellent efficacy, low cost, shorter duration of administration and good safety profile, has the potential to be used as a first-line drug.

In vitro skin permeation and retention of paromomycin from liposomes for topical treatment of the cutaneous leishmaniasis.

Paromomycin (PA), a very hydrophilic antibiotic, has been tested as an alternative topical treatment against cutaneous leishmaniasis (CL). Although this treatment has shown promising results, it has not been successful in accelerating the recovery in most cases. This could be attributed to the low skin penetration of PA. Liposomal formulations usually provide sustained and enhanced drug levels in skin. The aim of this study was to prepare liposomal formulations containing PA and to investigate their potential as topical delivery systems of this antileishmanial. Large multilamellar vesicles (MLVs) were prepared by conventional solvent evaporation method. Large unilamellar vesicles (LUVs) were prepared by reverse-phase evaporation method. The lipids used were soybean phosphatidylcholine (PC) and PC:cholesterol (CH) (molar ratio 1:1). The skin permeation experiments across stripped and normal hairless mice skin were performed in modified Franz diffusion cells. The PA entrapment in LUV liposomes (20.4 +/- 2.2%) was higher than that observed for MLV liposomes (7.5 +/- 0.9%). Drug entrapment was 41.9 +/- 6.2% and 27.2 +/- 2.4% for PC and PC:CH LUV, respectively. The skin permeation was 1.55 +/- 0.31%, 1.29 +/- 0.40%, 0.20 +/- 0.08%, and 0.50 +/- 0.19% for PC LUV, PC:CH LUV, empty LUV +/- PA and aqueous solution, respectively. Controlled topical delivery, across stripped skin, was observed for PA entrapped in LUV liposomes.

Disposition of antimony and aminosidine combination after multiple subcutaneous injections in dogs.

The disposition of a combination of antimony (Sbv) (12.8 mg/kg) and aminosidine (AM) (10 mg/kg) in 10 healthy Beagle dogs after multiple subcutaneous injections is described. Sbvplasma concentrations were determined by atomic absorption spectrometry, and AM by ion-pair liquid chromatography, using a fluorimetric detector. Sbvreached Cmaxat 60 min, and for about 1 h plasma levels were homogeneously stabilized between 10.78 and 11.76 microgram/mL; by 12 h, Sbvplasma concentrations were close to the detection limit (0.3 microgram/mL). AM Cmaxvalues were recorded after 1 h (30.6+/-3.11 microgram/mL, mean +/- SD), and plasma levels reached values close to the detection limit (0.15 microgram/mL) between 7 and 8 h after injection. Sbvkinetic parameters did not appear modified by the presence of AM. Moreover, repeated injections of the combination did not modify the kinetic behaviour of the two drugs and did not alter the renal function of the animals. The superimposition analysis of the Sbvdata suggests that a twice daily injection of the metal at a dose of 12.8 mg/kg would be sufficient to maintain inhibitory Sbvconcentrations similar to those recorded in humans.

Pharmacokinetics of intramuscularly administered aminosidine in healthy subjects.

Aminosidine is an older, broad-spectrum aminoglycoside antibiotic that has been shown to be effective in in vitro and animal models against multiple-drug-resistant tuberculosis and the Mycobacterium avium complex. The objective of this randomized, parallel trial was to characterize the single-dose pharmacokinetics of aminosidine sulfate in healthy subjects (eight males, eight females). Sixteen adults (mean [+/- standard deviation] age, 27.6 +/- 5.6 years) were randomly allocated to receive a single, intramuscular aminosidine sulfate injection at a dose of 12 or 15 mg/kg of body weight. Serial plasma and urine samples were collected over a 24-h period and used to determine aminosidine concentrations by high-performance liquid chromatographic assay. A one-compartment model with first-order input, first-order output, and a lag time (Tlag) and with a weighting factor of 1/y2 best described the data. Compartmental and noncompartmental pharmacokinetic parameters were estimated with the microcomputer program WinNonlin. One subject was not included (15-mg/kg group) because of the lack of sampling time data. On average, subjects attained peak concentrations of 22.4 +/- 3.2 microg/ml at 1.34 +/- 0.45 h. All subjects had plasma aminosidine concentrations below 2 microg/ml at 12 h, and all but two subjects (one in each dosing group) had undetectable plasma aminosidine concentrations at 24 h. The dose-adjusted area under the concentration-time curve from 0 h to infinity of aminosidine was identical for the 12- and 15-mg/kg groups (9.29 +/- 1.5 versus 9.29 +/- 2.2 microg x h/ml per mg/kg; P = 0.998). Similarly, no significant differences (P > 0.05) were observed between dosing groups for peak aminosidine concentration in plasma, time to peak aminosidine concentration in plasma, Tlag, apparent clearance, renal clearance, elimination rate constant, and elimination half-life. A significant difference was observed for the volume of distribution (0.35 versus 0.41 liters/kg; P = 0.037) between the 12 and 15 mg/kg dosing groups. Now that comparable pharmacokinetic profiles between dosing groups have been demonstrated, therapeutic equivalency testing via in vitro pharmacokinetic and pharmacodynamic modelling and randomized clinical trials in humans should be conducted.

Pharmacokinetics and dosing regimen of aminosidine in the dog.

The kinetic behaviour of the aminoglycoside aminosidine, given at 15 mg/kg intravenously, intramuscularly and subcutaneously, was studied in 5 dogs to determine the appropriate dosage schedule. The pharmacokinetic behaviour of aminosidine in dogs was similar to that in other species, except that it was eliminated more slowly (beta = 0.007 +/- 0.0003 min-1). Intramuscular and subcutaneous administration produced peak serum concentrations (Cmax[im] = 32 +/- 6.4 micrograms/ml; Cmax[ac] = 36 +/- 3.4 micrograms/ml) and times to peak concentration (Tmax = 60 min for both) that did not differ significantly; and neither compartmental nor non-compartmental analysis revealed any significant differences between any of the kinetic parameters obtained for these two extravenous routes of administration. Comparison of these results with previously published data suggests that aminosidine given once daily at 15 mg/kg would be as effective all, and safer than, the two or three daily administrations commonly employed in dogs.

Disposition of antimony and aminosidine in dogs after administration separately and together: implications for therapy of leishmaniasis.

The pharmacokinetic behaviour of aminosidine (15 mg kg-1) and antimony (25.65 mg kg-1 as N-methylglucamine antimoniate), administered subcutaneously either separately or together was studied on four dogs. The results demonstrated that antimony (Sb) did not significantly modify the kinetics of aminosidine (AM) but that the kinetic behaviour of the metal was markedly influenced by the antibiotic, as shown by the differences in mean residence time (MRT), elimination rate constant (Kel) and area under the curve (AUC) with and without the antibiotic (MRT[Sb] = 243.8 +/- 29.5 minutes, MRT[Sb+AM] = 1067.9 +/- 199.2 minutes; Kel[Sb] = 0.008 +/- 0.001 min-1, Kel[Sb+AM] = 0.0015 +/- 0.0003 min-1; AUC[Sb] = 21,024.6 +/- 4448.5 micrograms min ml-1, AUC[Sb+AM] = 130,478.5 +/- 30,481.7 micrograms min ml-1). The persistence of high serum concentrations of antimony when it was administered with aminosidine suggests that the therapeutic doses commonly used should be reduced and that the interval between administration should be increased to avoid the metal reaching toxic concentrations.