Identification of Compounds Protecting Pancreatic Islets against Oxidative Stress using a 3D Pseudoislet Screening Platform

Oxidative stress leads to a lower success rate of clinical islet transplantation. Here, FDA-approved compounds are screened for their potential to decrease oxidative stress and to protect or enhance pancreatic islet viability and function. Studies are performed on in vitro "pseudoislet" spheroids, which are pre-incubated with 1280 different compounds and subjected to oxidative stress. Cell viability and oxidative stress levels are determined using a high-throughput fluorescence microscopy pipeline. Initial screening on cell viability results in 59 candidates. The top ten candidates are subsequently screened for their potential to decrease induced oxidative stress, and eight compounds efficient reduction of induced oxidative stress in both alpha and beta cells by 25-50%. After further characterization, the compound sulfisoxazole is found to be the most capable of reducing oxidative stress, also at short pre-incubation times, which is validated in primary human islets, where low oxidative stress levels and islet function are maintained. This study shows an effective screening strategy with 3D cell aggregates based on cell viability and oxidative stress, which leads to the discovery of several compounds with antioxidant capacity. The top candidate, sulfisoxazole is effective after a 30 min pre-incubation, maintains baseline islet function, and may help alleviate oxidative stress in pancreatic islets.

The effect of pH and triethanolamine on sulfisoxazole complexation with hydroxypropyl-beta-cyclodextrin

A novel complexation of sulfisoxazole with hydroxypropyl-beta-cyclodextrin (HP-beta-CD) was studied. Two systems were used: binary complexes prepared with HP-beta-CD and multicomponent system (HP-beta-CD and the basic compound triethanolamine (TEA)). Inclusion complex formation in aqueous solutions and in solid state were investigated by the solubility method, thermal analysis (differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)), Fourier-transform infrared spectroscopy (FT-IR) and dissolution studies. The solid complexes of sulfisoxazole were prepared by freeze-drying the homogeneous concentrated aqueous solutions in molar ratios of sulfisoxazole:HP-beta-CD 1:1 and 1:2, and sulfisoxazole:TEA:HP-beta-CD 1:1:2. FT-IR and thermal analysis showed differences among sulfisoxazole:HP-beta-CD and sulfisoxazole:TEA:HP-beta-CD and their corresponding physical mixtures and individual components. The HP-beta-CD solubilization of sulfisoxazole could be improved by ionization of the drug molecule through pH adjustments. However, larger improvements of the HP-beta-CD solubilization are obtained when multicomponent systems are used, allowing to reduce the amount of CD necessary to prepare the target formulation.

Comparison of the binding characteristics of serum albumins from various animal species

In order to develop an animal model to study the bilirubin displacing effect of various drugs, we compared the bilirubin binding ability of human, pig, dog, rabbit, hamster, rat, guinea pig, and cat albumin. These albumins were used also to study the binding of monoacetyldiaminodiphenyl sulfone (MADDS). Using human, rat, guinea pig, and rabbit albumin, we studied the effect of sulfisoxazole, ceftriaxone, and tin protoporphyrin on bilirubin binding. Our results demonstrate that each animal albumin has different binding characteristics for the various chemicals tested. This variable must be considered before using an animal as a model for studying factors influencing bilirubin deposition in the brain.

Pharmacokinetic analysis of concentration data of drugs with irregular absorption profiles using multi-fraction absorption models

Nonlinear regression analysis of plasma drug concentration data with irregular or stepwise absorption profiles was studied using multi-fraction absorption models in which drugs in the gastrointestinal tract were assumed to be divided into several fractions each with its respective lag time and absorption rate constant. Plasma allopurinol concentration data, with two-phase absorption profiles in dogs after oral administration, were found to be satisfactorily fitted using a two-fraction absorption model. Plasma sulfisoxazole concentration data in humans were also successfully analyzed using a two-fraction absorption model. Plasma and urinary concentrations of pindolol in humans after oral administration of sustained-release preparations were fitted to two- or three-fraction absorption models. The pharmacokinetic absorption behavior of a sustained-release preparation of diltiazem hydrochloride was studied using a multi-fraction absorption model. Pharmacokinetic parameters derived from these models and those from the discontinuous absorption model were compared.

Pharmacokinetics of sulfisoxazole in renal transplant patients

We studied the elimination of sulfisoxazole in eight renal transplant patients. The patients received sulfisoxazole prophylactically for urinary tract infection commencing 7 days postoperatively. The renal elimination of sulfisoxazole (unbound renal clearance) was decreased in this patient population and was highly correlated with creatinine clearance. The unbound metabolic clearance and apparent unbound formation clearance of N4-acetyl sulfisoxazole did not differ from values found in healthy volunteers. The protein binding was marginally lower in this patient population than in healthy subjects after a single dose. The reduced binding was compatible with a reduced albumin concentration. In contrast to the situation for healthy subjects, the binding of sulfisoxazole decreased upon multiple dosing. This is probably due to a relatively higher sulfisoxazole and N4-acetyl sulfisoxazole-to-albumin ratio in this patient population than in healthy subjects. No complications of sulfisoxazole therapy were seen, although in three subjects concentration of the N4-acetyl sulfisoxazole in urine exceeded its theoretical solubility on a few occasions.

Segmental difference and effect of glucose on drug exsorption across the small intestine of rats

An exsorption technique which can assess the transport of a drug from blood to the intestinal lumen was used to study the effects of glucose and to determine the presence of segmental differences in drug transport across the rat small intestinal membrane following intravenous drug administration. The drugs used in the study were un-ionized (sulfanilamide) or ionized (metoclopramide and sulfisoxazole) at the physiological pH (6.5) of rat small intestine. An intestinal segment of 20 cm from the ligament of Treitz to the distal part was used as the jejunum and the same length from the ileocecal junction to the proximal part was regarded as the ileal segment. Isotonic NaCl or glucose was used as the intraluminal perfusate. In the case of sulfanilamide, the exsorption rate remained almost constant during the perfusion of NaCl or glucose and no segmental differences in the exsorption rates were observed. For the weakly basic drug (metoclopramide) the exsorption rate in the jejunum was significantly decreased by glucose. Conversely, for the weakly acidic drug (sulfisoxazole), the exsorption rate in the jejunum was increased during glucose perfusion. In contrast to the effects observed in the jejunum, glucose did not have any significant effect on the exsorption rate of drugs studied in the ileum. These observations might be explained by the intraluminal pH in the respective segments and changes in the pH mediated by glucose perfusion.

Binding and disposition of sulfisoxazole in alcoholic cirrhosis

The disposition of sulfisoxazole was studied in six male patients hospitalized with biopsy-proven Laennec's alcoholic cirrhosis and six normal, healthy volunteers. Four of the patients were restudied at a time their liver disease had improved clinically. On the average, compared to the normal group, the metabolism of sulfisoxazole (clearance values with respect to unbound concentration values) appears to be unaltered for the cirrhotic patients. For patients with alcoholic cirrhosis having normal renal function for age and weight, the renal elimination of sulfisoxazole was normal. For those subjects with decreased renal function, the renal clearance of sulfisoxazole appeared to be disproportionately decreased, as evidenced by a lower-than-normal sulfisoxazole renal clearance-to-creatinine clearance values. The apparent steady-state volume of distribution of unbound sulfisoxazole was not altered in cirrhotic patients when compared to normal subjects, while the apparent volume of distribution of total drug increased by more than what could be expected from protein binding changes alone. The elimination rate constant did not differ from values found in normals. These data suggest that the total binding capacity of sulfisoxazole in cirrhotic patients is not different from that of normal subjects.

Abnormal serum protein binding of acidic drugs in diabetes mellitus

Nonenzymatic glycosylation of proteins is common in diabetes mellitus and glycosylation of serum albumin in this condition has been described. To evaluate whether glycosylation of albumin affects acidic drug binding, sulfisoxazole and diazepam binding was examined in samples of normal serum incubated with glucose and in samples of serum from 42 patients with diabetes mellitus. Incubation of normal serum with 20mM glucose for several days resulted in progressive glycosylation of proteins, with decreased binding of sulfisoxazole (100 micrograms/ml) but not of diazepam (3 micrograms/ml). Free fractions of sulfisoxazole and diazepam were higher in serum from patients with diabetes. The percentage of free sulfisoxazole in serum from 10 normal subjects was 5.1% +/- 0.2%, whereas it was 16.0% +/- 1.3% in serum from 42 patients with diabetes with varying degrees of carbohydrate control. The percentage of free diazepam in plasma was 2.6% +/- 0.1% in the normal group and 3.6% +/- 0.4% in patients with diabetes. Decreased serum albumin levels, increased levels of free fatty acids, and glycosylation of plasma proteins seem to play a role in the defective acidic drug binding in diabetes. Elevated free fatty acid levels explain the abnormal binding of diazepam and the increased free fraction of sulfisoxazole is directly related to glycosylation of plasma proteins.

Influence of protein binding and metabolic interconversion on the disposition of sulfisoxazole and its N4-acetyl metabolite by the isolated perfused rat kidney

The renal clearances of sulfisoxazole (SX) and N4-acetylsulfisoxazole (NSX) were studied in the isolated perfused rat kidney (IPK). Studies were conducted with conventional bovine serum albumin perfusates as well as with dextran perfusates to assess the influence of perfusate protein binding on the disposition of these compounds by the IPK. The results presented herein indicate that the disposition of sulfisoxazole by the IPK involves both metabolism and excretion. The metabolism of SX to NSX is reversible and is influenced by protein binding since metabolism increased with increased free fraction (Ff). The excretion of SX and NSX reflects a complex interaction of filtration, secretion, and reabsorption. A comparison of clearance values between kidneys perfused with bovine serum albumin perfusate (Ff 0.1) and dextran perfusate (Ff 1.0) suggests that tubular secretion of SX is a function of total (unbound plus bound) rather than free (unbound) drug in the perfusate.

Pharmacokinetics of sulfisoxazole in young and elderly subjects

The pharmacokinetics of sulfisoxazole was studied in 6 elderly (age 63-75 years) and 7 young (age 22-37 years) healthy nonsmoking volunteers following the oral administration of 2 g of Gantrisin. The plasma levels of sulfisoxazole obtained in the postabsorption phase were higher in the elderly subjects. There was no significant variation between the two groups of volunteers in the absorption rate constant, Cmax, bioavailability, the fraction of the dose of sulfisoxazole excreted unchanged, the area under the plasma curve of the N4-acetyl conjugate formed, and in the apparent volume of distribution of the drug. The tmax value and plasma half-life of sulfisoxazole were significantly longer, and the total body and renal clearances of the drug decreased in the elderly subjects. Diminished renal function as estimated by the creatinine clearance and urinary flow may explain the slower elimination of sulfisoxazole in the elderly subjects. Therefore, advancing age should be considered as a factor in the adjustment of sulfisoxazole dosage.

Use of PKM-MULTI program for fitting discontinuous absorption profiles using a microcomputer

The programs for the pharmacokinetic models with discontinuous absorption, written in BASIC, were connected to MULTI, which had been proposed for nonlinear least squares for a microcomputer by Yamaoka et al. Using this program (designated as PKM-MULTI), the same data sets previously calculated by HFCM, FITSI2 and NONLIN were fitted and the finally obtained estimates were in close agreement with those obtained previously. The plasma data of nalidixic acid were also fitted to the pharmacokinetic model with discontinuous absorption, which were suggested to be more valid compared with one compartment model with continuous absorption.

Use of metzler's NONLIN program for fitting discontinuous absorption profiles

An alternative to the use of integral hybrid flow/compartmental model (HFCM) equations in fitting cases I and II discontinuous absorption profiles is presented. It is proposed that HFCM-integral equations be replaced by a system of differential equations in which sequential sets of equations describe the absorption profile from time zero to infinity. The required sets of differential equations for these two cases are presented as they apply to a two-compartment drug, potentially undergoing multiple absorption steps. It was shown that the use of the NONLIN program in the differential equation mode provides good fits for some unusually shaped absorption profiles of buformin, sulfisoxazole, and griseofulvin. The values of the parameter estimates and the sum of squared deviations, sigma SD, obtained with NONLIN were almost identical to those obtained with the FITS12 program utilizing HFCM equations. While HFCM-integral equations required less computer time, they introduced the potential for negative absorption times. This problem is avoided by use of the differential equations method.

Isoniazid, quinidine, and sulphafurazole absorption in patients with jejunum transposition 15 years earlier

Gastric surgery has formerly been shown to affect drug absorption. The absorption of oral isoniazid (INH), quinidine, and sulphafurazole (sulfisoxazole) was therefore studied in 19 ulcer patients operated on some 15 years earlier with resection of the ventricle combined with jejunum transposition. Twelve medical inpatients served as controls. The operated patients had all experienced relief of their ulcer symptoms, and there was no evidence of clinical malabsorption. In operated patients the peak serum levels of all three drugs were reached earlier than in controls. At 1 and 6 h the INH serum levels were increased in operated patients, but the sulphafurazole serum levels were at no time different in operated and control patients. As measured by the 24-h urinary excretion, jejunum transposition did not modify the total amounts of INH or sulphafurazole absorbed. In contrast, the quinidine absorption was decreased by about 50% in operated patients, which seems to be the result of increased gastric pH in the operated patients, leading to a poor dissolution and/or precipitation of quinidine in the gastric contents. Obviously, the jejunum transposition per se may not affect the total amounts of drugs absorbed, provided the physiochemical effects resulting from, for example, pH changes due to antrectomy and/or vagotomy are taken into account.

Penetration of amoxicillin, cefaclor, erythromycin-sulfisoxazole, and trimethoprim-sulfamethoxazole into the middle ear fluid of patients with chronic serous otitis media

Penetration into the middle ear of four antibiotics commonly used in treatment of otitis media was studied by administering a single oral dose of amoxicillin, cefaclor, erythromycin-sulfisoxazole, or trimethoprim-sulfamethoxazole to 83 children with chronic serous otitis media. The antibiotic was given 15-240 min before the removal of middle ear fluid (MEF) by ventilation tubes inserted through the tympanic membrane. At the time MEF was obtained, a sample of blood was drawn from the patient, and concentrations of antibiotic in both specimens were assayed either microbiologically by a disk diffusion method or by high-pressure liquid chromatography. Amoxicillin had the highest ratio of mean peak concentration in MEF to minimal inhibitory concentration (MIC) for the three most common pathogens of otitis media (Streptococcus pneumoniae, ampicillin-sensitive Haemophilus influenzae, and Streptococcus pyogenes), whereas trimethoprim-sulfamethoxazole had the highest ratio of mean peak concentration in MEF to MIC for ampicillin-resistant Haemophilus influenzae.

Effects of phenobarbital on the distribution pharmacokinetics and biological half-lives of model nonmicrosomal enzyme metabolizable sulfonamides in rats

The pharmacokinetics of sulfisoxazole and sulfanilamide were studied in control rats and in rats treated for 5 days with a daily 100 mg/kg ip dose of phenobarbital. These drugs represent the organic anionic and nonionized drugs, respectively, whose nonmicrosomal enzymatic metabolisms were unstimulated by phenobarbital. Sulfisoxazole showed the characteristics of a two-compartment open model. However, its biological half-life and the apparent distribution volume of the central compartment were significantly lower and the intercompartmental transport rate constants and the urinary excretion rate constant were significantly greater, in phenobarbital treated rats than in control rats. The apparent steady-state distribution volume of sulfisoxazole was smaller in the phenobarbital treated rats at the 90% confidence level. Sulfanilamide showed characteristics of a one-compartment model in both the control and phenobarbital treated rats, but none of the pharmacokinetic parameters of the compound in the phenobarbital treated rats were significantly different from those in the control rats.

Effects of carbamylation of plasma proteins and competitive displacers on drug binding in uremia

The effects of in vitro carbamylation of plasma with potassium cyanate on the binding of sulfisoxazole and diazepam have been investigated. Incubation of plasma with potassium cyanate produced varying degrees of carbamylation of plasma proteins which were associated with a decrease in the binding of sulfisoxazole (100 mg/l), a drug bound to site I on the human albumin. Scatchard plots showed that this decreased binding resulted from a decrease in affinity without changes in the number of binding sites. Similar changes were detected in uremia. Carbamylation of plasma proteins did not affect the binding of diazepam (3 mg/l), a drug bound to site II. The plasma protein binding of sulfisoxazole and diazepam was decreased in samples from uremic patients. Charcoal treatment did not modify the binding of sulfisoxazole to normal or carbamylated plasma while it reduced, but did not normalize, the binding defect in uremic plasma. On the other hand, charcoal treatment brought the binding of diazepam in uremic plasma to normal values. It seems that only drug binding site I is carbamylated in uremia, while competitive displacers bind to sites I and II.

Surgically affected sulfisoxazole pharmacokinetics in the morbidly obese

Intestinal bypass surgery in 4 morbidly obese female (110-150 kg) had no permanent effect on the rate or amount of sulfisoxazole absorption. The loss of weight up to 44 per cent within an individual over a year's time had no significant effect on the apparent volumes of distribution or other pharmacokinetic parameters of sulfisoxazole and its N4-acetylsulfisoxazole metabolite. Dosing of this drug on a mg kg-1 basis is contraindicated. Renal clearances of sulfisoxazole were reasonably constant within a study but those of the N4-acetylsulfisoxazole decreased with time. Integrated pharmacokinetic models were applied to plasma and urine data to estimate the metabolic clearance of sulfisoxazole and the apparent volume of distribution of the N4-acetylsulfisoxazole. Sulfisoxazole solution is absorbed readily by primarily a zero order process after a short lag period, indicative of rate-determining gastric emptying. The classical Bratton-Marshall assays were compared with an HPLC assay of both drug and metabolite. There was greater confidence in plasma levels of the metabolite from the HPLC method.

Kinetics of sulphafurazole in undernutrition

1 An oral dose of 75 mg/kg body weight was used to study the kinetics of sulphafurazole in wellnourished and undernourished adult subjects. 2 There were no differences in the half-life, volume of distribution and total body clearance of the drug in the two groups of subjects. 3 The plasma protein binding of sulphafurazole was significantly reduced in the undernouished subjects. 4 It is concluded that alternations in the dosage schedule may not be necessary in the treatment of undernourished adults with sulphafurazole.

Serum protein binding of drugs during and after pregnancy in humans

The serum protein binding of three weakly acidic drugs (salicylic acid, sulfisoxazole, and phenytoin), one week base (diazepam), and one steroid (dexamethasone) was determined in pregnant women at seven time periods during pregnancy and at two periods post partum, as well as in a group of nonpregnant women of childbearing age. The serum free fraction values (ratio of concentrations, free to total drug) of all drugs rose during pregnancy, primarily after 15 wk of gestation, and remained elevated for at least 1 to 5 days post partum. Pregnancy had the greatest effect on protein binding of sulfisoxazole, diazepam, and salicylic acid. The magnitude of this effect is such that quantitatively significant changes in the pharmacokinetic and pharmacodynamic characteristics of certain drugs may be expected to occur during pregnancy (in addition to possible changes caused by other pregnancy-related effects such as altered activity of drug-metabolizing enzyme systems). All drugs but dexamethasone exhibited significant negative correlations between free fraction values and serum albumin concentrations during pregnancy. The serum protein binding of salicylic acid, but not the other drugs tested, was more extensive in nonpregnant women who were not taking oral contraceptives than in those who were.

Discontinuous absorption processes in pharmacokinetic models

The limited contact time of absorbable drug with absorbing surfaces is, in some cases, a significant factor determining the fraction of the dose absorbed. A simple modification of customary linear compartmental models is presented to account for this situation, and a general input function in the Laplace domain for truncated first-order absorption is derived. An extension to series of truncated absorption processes is discussed.

The effects of some sweetening agents and osmotic pressure on the intestinal absorption of sulfafurazole in the rat

The effects of some sugars and osmotic pressure have been examined on the absorption of sulfafurazole in the rat. Statistically significant correlations were found among the hypertonic solutions between the reciprocal of osmotic pressure and AUC0--infinity or Cmax. In addition, negative correlation existed between plasma concentrations at 15 min and osmotic pressure. No significant correlations were noted among the hypotonic solutions. More attention should be paid to the osmotic pressure of formulations. The osmotic pressure of hypertonic solutions, especially, might affect absorption of drug from its dosage form.

Ascitic fluid modifying the distribution of sulphafurazole in rats with intestinal occlusion

In order to confirm our previous findings of increased sulphafurazole (sulfisoxazole, SF) inactivation by intestinal occlusion, SF was given intravenously 20 mg/kg to rats with a low small intestinal occlusion and to sham-operated controls 40-45 hours after the operation. Occlusion did not cause major changes in the distribution of SF to various tissues, but there were some indications of increased SF acetylation after occlusion. The occlusion rats produced ascitic fluid into the abdominal cavity and the total SF levels in the ascitic fluid were almost identical to those in blood, also after oral administration of SF, 50 mg/kg. After intraperitoneal administration of 2 ml of SF (60 microgram/ml) more SF accumulated into the small intestinal wall in occlusion rats than in controls, and the acetyl SF levels were increased in the small and large intestine. So, our previous suggestion of an increased excretory function of the large intestine in occlusion states may not be the only explanation for increased drug levels in the large intestine found after oral administration of SF. Part of the SF in the intestinal wall can also result from ascitic fluid SF, and ascites must be taken into account when considering drug pharmacokinetics.

Effect of serum protein binding on sulfisoxazole distribution, metabolism, and excretion in rats

This investigation determined the effect of serum protein binding on the kinetics of sulfisoxazole distribution, metabolism, and excretion. Adult rats, whose serum free fraction of sulfisoxazole (at a total concentration of 81 +/- 6 micrograms/ml) was 0.05-0.24, received a rapid intravenous injection of 20 mg/kg. Sulfisoxazole concentrations in plasma declined biexponentially with time. There were pronounced and reproducible interindividual differences in the total, metabolic, and renal sulfisoxazole clearances, each positively correlated with the serum free fraction of sulfisoxazole. The renal sulfisoxazole clearance had a component unaffected by serum protein binding. The apparent central compartment volume increased with an increasing serum free sulfisoxazole fraction, but the latter had not apparent effect on the first exponential term of the biexponential equation describing sulfisoxazole elimination kinetics in rats. Serum protein binding was a major determinant of intersubject differences in sulfisoxazole excretion and biotransformation kinetics.

Critical evaluation of the potential error in pharmacokinetic studies of using the linear trapezoidal rule method for the calculation of the area under the plasma level--time curve

The linear trapezoidal rule method is commonly used for the estimation of the area under the plasma level-time curve. Error analyses are performed when the method is used in first-order absorption and first-order elimination kinetics in the one-compartment system. It is found that significant underestimations and overestimations in area during the absorption phase and postabsorption phase, respectively, can occur when the method is improperly used. During the exponential postabsorption phase the relative error is only a function of the ratio (n) of the time interval over the half-life of the two plasma data points in the interval. The error from the linear trapezoidal rule method at n = 0.5 is about 1%. The error increases to 15.5% and 57.1% when n is increased to 2 and 4, respectively. It is recommended that for most absorption studies the linear trapezoidal method be used for prepeak and plateau plasma data and the logarithmic trapezoidal method for postpeak plasma data.

Effect of colchicine on drug absorption from the rat small intestine in situ and in vitro

The effect of colchicine (1 mg/kg intraperitoneally on two successive days) on the absorption of isoniazid, quinidine and sulphafurazole (sulfisoxazole) from the rat small intestine was studied in situ and in vitro. Colchicine produced two different types of histological damage in the small intestine, one with degenerative and the other with regenerative changes predominating. The small intestinal surface area was variably reduced. The colchicine-treated rats were lethargic and hypothermic as compared to controls. Colchicine retarded the disappearance of fluid and all three drugs from the small intestinal lumen in situ 2 days after the first colchicine injection. In vitro the total amounts of fluid and drugs passed through the intestinal wall were not significantly changed by colchicine, although there was a slight tendency towards an increased absorption of quinidine. Hence, colchicine as an antimitotic drug decreases drug absorption from the rat small intestine in situ, apparently due to the decreased surface area of the small intestine, the decreased water flux through the intestinal wall, the retarded intestinal motility and hypothermia of the rats. In vitro the changes are small, which makes the in vitro tests less suitable for studying the effect of colchicine on absorption.

Displacement of bilirubin from human albumin by three diuretics

The interaction of three diuretics with bilirubin-albumin complexes was studied using the peroxidase assay, erythrocyte uptake, and sephadex gel filtration. On a molar basis, each diuretic was as potent or more potent than sulfisoxazole in displacing bilirubin from albumin. Furosemide and ethacrynic acid, when used at the recommended dosage (1 mg/kg), would probably not produce a significant increase in free bilirubin in most infants. Chlorothiazide could introduce a significant risk to jaundiced infants because of the higher dosage required.

The displacement of bilirubin from albumin by furosemide

Since furosemide, a sulfonamide diuretic, has been recommended for use in the newborn infant, a study was made of its effect on the bilirubin-binding capacity of albumin. Furosemide was compared to sulfisoxazole, a known displacer of bilirubin, by means of three methods. First, aliquots of whole blood from 20 icteric infants were diluted in phosphate buffer along with expected clinical concentrations of furosemide and sulfisoxazole. The red cells and globulins were then isolated and bilirubin concentrations were measured in these two fractions. The addition of Furosemide resulted in the displacement of bilirubin from albumin to red cells and globulins. Mole for mole, furosemide displaced bilirubin about as well as sulfisoxazole. Second, the hydroxybenzeneazobenzoic acid dye binding test of Porter and twaters was performed using the sera of eight jaundiced newborn infants. The mean dye binding capacity of the sera was significantly reduced with the addition of furosemide to a final concentration of 2 mug/ml. Third, the administration of furosemide (5 mg/kg) or sulfisoxazole (50 mg/kg) to adult Gunn rats resulted in a significant fall in mean serum bilirubin concentration compared to saline controls. Furosemide, like sulfisoxazole, is a potent displacer of bilirubin and should be used with caution in jaundiced infants.

GI drug absorption in rats exposed to cobalt-60 gamma-radiation II: in vivo rate of absorption

The rate of absorption of sulfanilamide, bretylium tosylate, sulfisoxazole acetyl, and riboflavin was studied in rats exposed to 850 rad of cobalt-60 gamma-radiation either 1 or 5 days before oral drug administration. Polyethylene glycol 4000 was administered with sulfanilamide; its distribution along the GI tract indicated that the gastric emptying rate was reduced threefold at 1 day postirradiation but returned to normal at 5 days postirradiation; the small intestinal transit rate was not detectably altered by irradiation. At 1 day postirradiation, there was a marked decrease in the absorption rate of sulfanilamide, a smaller, although significant, decrease in the absorption rate of sulfisoxazole acetyl and bretylium, and an increase in the absorption rate of riboflavin. At 5 days postirradiation, the drug absorption rate was normal. The changes in the absorption rate of the drugs were due to a radiation-induced reduction in the gastric emptying rate; the permeability of the GI epithelium did not appear to be affected by radiation. The results indicate that, immediately following irradiation, a marked reduction in the gastric emptying rate causes a pronounced reduction in the absorption rate of rapidly absorbed drugs, a less pronounced reduction in the absorption rate of drugs that are absorbed slowly because of slow dissolution or slow diffusion across the GI epithelium, and an increase in the absorption rate of drugs that are absorbed by a saturable mechanism provided the mechanism is not impaired by irradiation.

Lung pH and pulmonary absorption of nonvolatile drugs in the rat

The effect of pH on pulmonary absorption of nonvolatile drugs was investigated in the rat. Krebs-Ringer phosphate solutions (pH 6.2 and 7.4), Krebs-Ringer pyrophosphate solution (pH 8.4), or an unbuffered salt solution containing a drug were administered through tight-fitting tracheal cannulas to anesthetized animals. After 3 min, the lungs were removed and assayed for the amount of drug that remained. Weak acids and a weak base were absorbed most rapidly at pH values at which the drugs were least ionized. For example, with the base procainamide, 36% of the dose was absorbed at pH 6.2 and 76% at pH 8.4. With the acid sulfisoxazole, 71% was absorbed at pH 6.2 and 55% at pH 8.4. Similarly, with p-aminosalicylic acid, 77% was absorbed at pH 6.2 and 40% at pH 8.4. In contrast to these results, compounds such as urea and amitrole, which remain completely nonionized over the pH range studied, showed no change in absorption rate when the pH was varied. The two weak acids and the weak base were absorbed from an unbuffered solution as though the pH at the site of drug absorption was between 6.2 and 7.4. The absorption rate for each weak electrolyte from unbuffered solution, when compared graphically with the respective absorption rates from buffered solutions, indicated that the pH at the site of drug absorption is about 6.6.

Bioavailability of 11 sulfisoxazole products in humans

Single lots of 11 commercially available 500-mg sulfisoxazole tablets were evaluated in vitro and in vivo. All products tested met USP XVIII specifications for weight variation and product assay. However, three products failed to meet the USP XVIII dissolution requirement. The only statistically significant difference observed between the 11 products was a lower peak plasma level exhibited by one product. No useful correlation was observed between the in vivo and in vitro studies for the dosage forms tested.