Nalidixic acid kinetics in renal insufficiency.

1 A pharmacokinetic study of nalidixic acid (NA) and metabolites was carried out in 23 patients with differing renal function so as to determine the influence of renal insufficiency on the excretion and biotransformation rate of this antibacterial agent. Plasma and urine concentration of NA and of its 7-hydroxy (HNA) and 7-carboxy (CNA) derivatives were measured after a single oral administration. 2 Renal insufficiency did not markedly affect the renal clearance of NA while it significantly decreased the elimination rate of HNA, a compound which largely excreted into the urine. 3 Interestingly, CNA which could never be detected in the plasma of patients with normal renal function appeared in that of patients with renal insufficiency. Plasma concentrations of CNA and creatinine were positively related, and the amount of urinary CNA increased with the renal impairment. 4 These results suggest that HNA can still be biotransformed into CNA by the impaired kidney. Since CNA cannot be easily excreted in the urine of patients with renal insufficiency it is hypothesized that this compound back diffuses into the plasma. 5 Finally, the study of the urinary concentrations of NA and metabolites shows that a standard NA dosage can be used, at least in patients with mild renal insufficiency.     

The human biotransformation of nalidixic acid.

Authors have developed new chemical methods for studying the human metabolism of nalidixic acid. The methods are suited for the quantitative determination of nalidixic acid, hydroxynalidixic acid, nalidixic acid glucuronide, hydroxynalidixic acid-glucuronide, and of free and total glucuronic acid excretion. The total urinary excretion of NA and its metabolites was found to be 50 to 100% of the ingested dose. The percentual distribution of the individual metabolites was as follows: NA 0,5-5, HNA2,5-6, NAG24-80, and HNAG11-26%. It was unanimously proved by enzymatic decomposition and specific chemical reactions that the excreted conjugates were monoglucuronides. The significance of individual differences, bilirubin metabolism, urinary pH and the pharmacokinetical behaviour of the individual metabolites is discussed from the therapeutic view.     

Dissolution behaviour of nalidixic acid solid dispersions using water soluble dispersion carriers

The oral bioavailability of nalidixic acid (NA) is low due to its poor solubility and slow dissolution. Solid dispersions of NA containing varying concentrations of polyvinylpyrrolidone (PVP), beta-cyclodextrin (BCD) and sodium starch glycolate (SSG) were prepared by solvent evaporation technique in an attempt to improve dissolution rate of NA. Physical characterization of NA, physical mixtures (PM) and solid dispersions were investigated by a variety of analytical methods including scanning electron microscopy (SEM), infrared (IR) spectroscopy and powder X-ray diffraction (XRD). SEM was useful in the verification of possible nalidixic acid inclusion in the dispersion system by studying its surface and shape characteristics of different samples. IR analysis demonstrated no strong interaction between the drug and the carrier exists in the solid dispersions. The degree of crystallinity of nalidixic acid decreased and also differed with the dispersion systems of different carriers. Disolution studies indicated that the dissolution rate and percent dissolution efficiency (DE) were significantly increased in the solid dispersions compared with drug alone. The relative potency of the carriers to enhance the dissolution rate of nalidixic acid was in the order: BCD > PVP > SSG. The dissolution rate of the drug in the solid dispersions was faster when the ration of the drug to carrier was smaller. F-test suggests that first order model may be used for explaining the kinetics of drug release from all the solid dispersion systems.     

Antibacterial and Synergy of Clavine Alkaloid Lysergol and its Derivatives Against Nalidixic Acid‐Resistant Escherichia coli

Antibacterial activity of lysergol ( 1 ) and its semi‐synthetic derivatives ( 2–14 ) and their synergy with the conventional antibiotic nalidixic acid (NA) against nalidixic acid‐sensitive (NASEC) and nalidixic acid‐resistant (NAREC) strains of Escherichia coli were evaluated. Lysergol ( 1 ) and derivatives ( 2 – 14 ) did not possess antibacterial activity of their own, but in combination, they significantly reduced the minimum inhibitory concentration (MIC) of NA. All the derivatives showed two‐ to eightfold reduction in the MIC of NA against NAREC and NASEC. Further, lysergol ( 1 ) and its derivatives 10 and 11 brought down eightfold reductions in the MIC of tetracycline (TET) against multidrug‐resistant clinical isolate of E. coli (MDREC). Treatment of these strains with the combinations of antibiotics and lysergol and its derivatives 10 and 11 (at reduced concentrations) significantly decreased the viability of cells. In an another observation, lysergol and its derivatives 10 and 11 inhibited ATP‐dependent efflux pumps, which was evident by ATPase inhibition and down‐regulation of multidrug ABC transporter ATP‐binding protein (yojI) gene. These results may be of great help in antibacterial drug development from a very common, inexpensive, and non‐toxic natural product.     

Effect of some selected salts and non-ionic surfactants on the antimicrobial activity of nalidixic acid

The effect of different concentrations of some selected salts, namely, sodium chloride, potassium chloride, ammonium chloride, monosodium dihydrogen phosphate, calcium chloride, dibasic sodium phosphate, sodium sulphate, aluminium chloride and sodium citrate on the antimicrobial activity of nalidixic acid was investigated. It was found that all the salts tested, except aluminium chloride and sodium citrate, exert no antimicrobial activity. The effect of 10% non-ionic surface active agents, namely, Myrj 51, 52, 59, Brij 35, 58, 98, Tween 20, 40, 60, and 80 on the antimicrobial activity of nalidixic acid was studied. The results indicated that the activity of nalidixic acid was decreased in the presence of these surfactants. Furthermore, the effect of different concentrations of sodium chloride on the antimicrobial activity of nalidixic acid-surfactants systems was reported.     

The effect of infinitesimal drug dilutions on the pharmacokinetics of nalidixic acid and atenolol.

1. Ten healthy subjects received two treatments: a single 1 g oral dose of nalidixic acid (NA) followed 1 h later by either an infinitesimal dilution of the drug (NA 7CH) or by succussed water which served as placebo. The study was repeated 18 months later in 10 different subjects. 2. A further 10 healthy subjects received three treatments: a single 100 mg oral dose of atenolol (AT) followed 3 h later by either placebo or a dilution of AT (AT 7CH) or of bisoprolol (BI 7CH). The homoeopathic preparations were administered by the sublingual route. 3. In the first NA experiment NA 7CH significantly shortened the elimination half-life of NA from 8.6 +/- 2.2 (placebo) to 6.4 +/- 1.6 h (NA 7CH). In the second NA experiment none of the pharmacokinetic parameters was modified significantly by the administration of NA 7CH. Neither AT 7CH nor BI 7CH modified the pharmacokinetics of AT.     

Norfloxacin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Norfloxacin is one of the new 4-quinolone antibacterial agents. A fluorinated piperazinyl-substituted congener of nalidixic acid, it demonstrates a much wider in vitro antibacterial spectrum and greater potency than the parent compound. Its antibacterial activity against most Gram-negative pathogens is enhanced in comparison to nalidixic acid, but is similar to that of some of the other new 4-quinolones like enoxacin, and slightly less than that of ciprofloxacin. Unlike nalidixic acid, norfloxacin is also active against Pseudomonas aeruginosa and some Gram-positive organisms. In acute or uncomplicated urinary tract infections, norfloxacin has repeatedly been shown to be as effective as co-trimoxazole. Single studies have demonstrated a significantly better bacteriological cure rate with norfloxacin than with pipemidic acid, and similar cure rates with norfloxacin and both a nalidixic acid/sodium citrate mixture and amoxycillin. Similar results were found in a few studies comparing norfloxacin to pipemidic acid or amoxycillin in patients with chronic and/or complicated urinary tract infections. Norfloxacin is as effective as spectinomycin in gonorrhoea due to penicillin-resistant N. gonorrhoeae, and cures bacterial gastroenteritis caused by several gastrointestinal pathogens. Norfloxacin appears to be well tolerated and may have a low propensity to select for bacterial resistance during clinical use, although the latter needs further confirmation.     

The determination in human plasma of 1-hydroxy-2-naphthoic acid following administration of salmeterol xinafoate

The clinical development of salmeterol xinafoate, the 1-hydroxy-2-naphthoic acid salt of salmeterol, a potent long acting β₂ agonist bronchodilator, has required the development of a method for the determination of 1-hydroxy-2-naphthoic acid (HNA), in human plasma. A sensitive, accurate and precise method was, therefore, required to enable the pharmacokinetic profile to be established. HNA was determined in human plasma using a semi-automated procedure with solid-phase extraction using an automated analytical sample processor (AASP) and high-performance liquid chromatography (HPLC) with fluorescence detection. The method was sensitive to 10 ng ml⁻¹. The method is specific for HNA with respect to endogenous plasma components and has been shown to be robust, accurate and precise. Over four independent assay runs, the relative standard deviations (RSD) of the quality control samples (QC) were 1.6, 2.4 and 5.5% at 180, 100 and 40 ng ml⁻¹, respectively. A pharmacokinetic profile of HNA in man has been established from a single dose kinetic study in healthy volunteers following an oral dose of 500 μg salmeterol xinafoate, equivalent to 225 μg HNA. Maximum plasma concentrations attained at 1 h after dosing ranged between 35.3 and 66.8 ng ml⁻¹ and were within the calibration range of the assay.     

Pharmacokinetic properties and clinical efficacy of once-daily sustained-release naproxen

Summary The pharmacokinetics and clinical efficacy of a once-daily sustained-release formulation of naproxen (sodium salt) have been compared with those of conventional-release agents.In a single dose pharmacokinetic study, the rate of absorption of the sustained-release preparation was less than that of a conventional-release preparation but the extent of absorption was the same. As is the case with conventional-release naproxen, food decreased the rate but not the extent of absorption of the sustained-release formulation.On multiple dose administration for 7 days, the AUC and average concentrations of the sustained release preparation (1 g daily) were the same as those for conventional release preparations of naproxen sodium (250 mg four times daily) and naproxen free acid (500 mg daily). The conventional-release sodium salt was absorbed more quickly with no differences in bioavailability. A double-blind clinical comparison in patients with osteoarthritis showed the sustained-release preparation (1 g daily) to be equivalent in efficacy to conventional naproxen capsules (500 mg twice daily) but to have a significantly lower incidence of gastrointestinal side-effects.The results suggest that sustained-release naproxen sodium has potential for use as a once-daily treatment for inflammatory disease.     

Comparative bioavailability of diclofenac hydroxyethylpyrrolidine vs diclofenac sodium in man

Summary A pharmacokinetic study in man has been made of a new dosage form of diclofenac hydroxyethylpyrrolidine (DIEP); soluble salt packed in sachets was compared with diclofenac sodium as enteric coated tablets.Oral DIEP 2×50 mg showed a significant difference in absorption kinetics (ka, lag time and t_max) as compared to oral diclofenac sodium 2×50 mg. A relevant plasma concentration of diclofenac was detected just 15 min after DIEP, while diclofenac sodium produced a measurable plasma concentration only 0.5–1 h after the treatment. C_max and t_1/2 after DIEP and diclofenac sodium were comparable. Comparison of the two AUC values showed that DIEP was bioequivalent to diclofenac sodium (Q=100%).     

Predictive value of nalidixic acid resistance for detecting salmonellae with decreased ciprofloxacin susceptibility

Seventy-three Salmonella isolates classified as ciprofloxacin susceptible when using the criteria of the National Committee for Clinical Laboratory Standards were studied for nalidixic acid (NA) resistance. The aim of the study was to determine the predictive value of nalidixic acid resistance in screening for decreased ciprofloxacin susceptibility. We observed that isolates with decreased ciprofloxacin susceptibility were all resistant to nalidixic acid. Identification of nalidixic acid resistance by the disk diffusion method provided 100% sensitivity and a specificity of 98.4% in strains with minimum inhibitory concentrations (MICs) >0.008 mg/l.     

Laboratory and clinical studies on norfloxacin in the pediatric field

In bacteriological, pharmacokinetic and clinical studies on norfloxacin (NFLX, AM-715), the following results were obtained: 1. Antibacterial activity of NFLX, nalidixic acid (NA), amoxicillin (AMPC), cefaclor (CCL), erythromycin (EM) and fosfomycin (FOM) against clinically isolated bacteria was examined, and it was found that MIC80 of NFLX against Staphylococcus aureus was 3.13 micrograms/ml, thus NFLX exhibited stronger antimicrobial activity than NA, AMPC, CCL, EM and FOM. NFLX also showed good activities to those strains of S. aureus which were resistance to NA, AMPC, CCL, EM and FOM. 2. MIC80 of NFLX against Escherichia coli was 0.05 micrograms/ml or lower, thus NFLX showed better activity than NA, AMPC, CCL, EM and FOM. 3. In single oral administration at fasting of NFLX at dose levels of 1.5-2.4 and 2.5-3.4 mg/kg in tablet form mean peak values of serum concentration were 0.32 micrograms/ml reached in 1 hour and 0.38 micrograms/ml in 2 hours, T1/2's obtained were 1.7-4.0 and 2.2-2.9 hours and AUC's were 1.54 +/- 0.52 and 2.02 +/- 0.93 micrograms.hr/ml, respectively. Urinary recovery rates of 11.6-46.9%, 13.8-35.4% in 6-8 hours were demonstrated with the 2 ranges of dose levels, respectively. 4. NFLX was administrated to 34 patients consisting of 8 cases of acute pneumonia, 3 cases of acute tonsillitis, 3 cases of bacterial colitis, 19 cases of urinary tract infections and 1 case of purulent parotitis. The clinical efficacy rate was 97.1% including 34 cases with excellent results in 28, good in 5 and fair in 1. 5. The bacterial eradication rate was 96.8% (30/31) with one exception of a Campylobacter jejuni strain. 6. NFLX was given to patients according to a dosing regimen with 4.5-21.4 mg/kg/day dose levels for 3 doses daily except 1 case of UTI where 2 daily doses were given daily. 7. No adverse reactions were observed. Abnormal laboratory test value was obtained in 1 case where eosinophilia was found. The above results have suggested that NFLX is a useful and safe antimicrobial agent against bacterial infections in children.     

Cefuroxime axetil

Cefuroxime is the first commercially-available second-generation cephalosporine to be widely used in therapy; it is a semi-synthetic cephalosporin obtained from the 7-cephalosporanic acid nucleus of cephalosporin C. Cefuroxime axetil is the acetoxyethyl ester of cefuroxime. The majority of micro-organisms associated with respiratory infections are highly sensitive to cefuroxime. These include Haemophilus influenzae, Streptococcus pneumoniae, Streptococcus pyogenes and the other streptococci (excluding group D streptococci), and Moraxella catarrhalis. Bacteria sensitive to cefuroxime include the enterobacteria (Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Salmonella and Shigella and Straphylococcus aureus (methicillin-sensitive strains). The pharmacokinetic studies show that the maximum plasma concentration of cefuroxime after oral administration of 250 mg and 500 mg of cefuroxime axetil after a meal are respectively 4.6 and 7.9 mg/l. The absolute bioavailability of tablets is 68% (extremes 63-73%) after oral administration of 500 mg cefuroxime axetil. The protein binding is 33+/-5.7%. Tissue diffusion was studied in the interstitial fluid, the bronchial mucosa, the tonsils, and the bronchial secretions. Cefuroxime axetil is available as capsule-shaped tablets containing 125, 250 or 500 mg. An oral suspension dosage form for paediatric purposes is also available as granules in multidose bottles and sachets. Constitution gives a suspension containing 125 mg or 250 mg cefuroxime (as cefuroxime axetil). Cefuroxime axetil is indicated for the treatment of infections caused by susceptible bacteria. Indications include: lower respiratory tract infections (e.g., acute and chronic bronchitis and pneumonia); upper respiratory tract infections (e.g., ear, nose and throat infections such as otitis media, sinusitis tonsillitis and pharyngitis); genito-urinary tract infections (e.g., pyelonephritis, cystitis and urethritis, gonorrhoea, acute uncomplicated gonococcal urethritis and cervicitis); and skin and soft tissue infections (e.g., furunculosis, pyoderma and impetigo). For most infections, a dose of 250 mg twice daily is appropriate. In some urinary tract infections, 125 mg twice daily has been shown to be effective. If pneumonia is suspected or in more severe lower respiratory tract infection, doses of 500 mg bd should be used. Uncomplicated gonorrhoea has been shown to respond to a single 1-g dose of cefuroxime axetil. Adverse reactions to cefuroxime have generally been mild and transient in nature (gastrointestinal disturbances, including diarrhoea, nausea and vomiting).     

Plasma Levels of Nicotinic Acid Compounds in Niceritrol *-Treated Rabbits

Abstract: Some pharmacokinetic properties of nicotinic acid (NA) and niceritrol (pentaerythritoltetranicotinate) were investigated in rabbits. Niceritrol released NA at a faster rate on incubation in vitro with plasma or liver homogenate than in a pure buffer solution, indicating that niceritrol was actively hydrolyzed. After administration of niceritrol to rabbits no niceritrol was present in the plasma but metabolites, probably lower esters of niceritrol, free NA and nicotinamide were found. On oral administration of NA in a dose of 16 mg/kg higher maximal plasma levels of free NA (~6 μg/ml) were noted than after adminstration of niceritrol (1.4 μg/ml) in the same dose. A diet producing hyperlipaemia and containing 0.5% niceritrol elevated the levels of free NA in the plasma by about 2 μg/ml. It also reduced the increase in plasma cholesterol. The investigation suggests that the pharmacological and pharmacokinetic properties of niceritrol in the rabbit are similar to those in man.     

Toxicity and carcinogenicity studies of nalidixic acid in rodents

Toxicity and carcinogenicity studies of nalidixic acid, an antimicrobial agent used to treat bacterial infections of the urinary tract, were conducted in F344/N rats and B6C3F1 mice of each sex for 13 weeks or 2 years. In the 13-week studies, nalidixic acid was administered at dietary concentrations ranging from 1,000 to 16,000 ppm. Body weights of both rats and mice were reduced in the groups receiving diet containing 8,000 and 16,000 ppm, and feed consumption of rats in the highest treatment groups was approximately two-thirds that of controls. Degeneration of the germinal epithelium in the seminiferous tubules of the testis was observed in male rats that received 16,000 ppm; no other compound-related histopathologic effects were observed in either species. Two-year studies were conducted by feeding diets containing 0, 2,000, or 4,000 ppm nalidixic acid to groups of 50 rats and mice/sex/group. The average daily feed consumption was slightly reduced compared to control groups and resulted in approximate daily doses of 82 or 175 mg nalidixic acid/kg for low dose and high dose rats, and 220 or 475 mg/kg for low dose and high dose mice. Mean body weights of dosed rats and mice were lower than those of controls, except for groups of low dose female rats and male mice. The incidences of preputial gland neoplasms in dosed male rats and of clitoral gland neoplasms in dosed female rats were significantly increased compared to those in controls; responses in low dose groups were similar to those in high dose groups. There were decreased incidences of leukemia and mammary gland neoplasms in dosed female rats and of pituitary gland neoplasms in dosed male rats. Subcutaneous tissue fibrosarcomas were marginally increased in dosed male mice. There were no increased incidences of neoplasms in dosed female mice. Under the conditions of these studies, the dietary administration of nalidixic acid was carcinogenic for rats, causing preputial gland or clitoral gland neoplasms in males and females, respectively. The association of subcutaneous neoplasms with administration of nalidixic acid to male mice was equivocal.     

Citric acid-enhanced Helicobacter pylori urease activity in vivo is unrelated to gastric emptying

BACKGROUND: In a previous study, the use of a citric acid test meal produced a rapid dose-dependent increase in urease activity that was significantly greater than that resulting from a pudding meal, ascorbic acid or sodium citrate. The mechanism was hypothesized to be related to the ability of citric acid to delay gastric emptying and possibly to enhance intragastric distribution of the urea. OBJECTIVE: To compare the effects of sodium citrate, two doses of citric acid and a pudding meal on gastric motor function. METHOD: Eleven normal healthy volunteers were investigated using non-invasive techniques to measure gastric emptying and gastric motility. We evaluated gastric emptying using the Meretek 13Ceebiscuit solid phase gastric emptying breath test, which employs a 340-calorie biscuit containing 200 mg of the edible 13C-blue-green alga Spirulina platensis, after the administration of test meals of pudding, 2 g and 4 g of citric acid and 2 g of sodium citrate. Electrogastrograms (Digitrapper EGG) were also recorded for 30 min before and 180 min after the test meal. RESULTS: Gastric emptying, as assessed by the half-time (T1/2), was delayed similarly with the pudding (136.8 +/- 9 min) and with 4 g of citric acid (144.5 +/- 7 min) (P > 0.7). Sodium citrate (108.7 +/- 6 min) and 2 g of citric acid (110.1 +/- 6 min) had similar effects on gastric emptying (P=0.986), and were significantly less effective in delaying gastric emptying (P < 0.01) compared to pudding or 4 g of citric acid. The electrogastrograms remained normal and there were no differences among meals and no relation with the gastric emptying results. CONCLUSIONS: The increased intragastric urea hydrolysis associated with citric acid test meals cannot be attributed to delayed gastric emptying. Changes in the intragastric distribution of urea or a direct effect of citric acid on the bacteria (e.g. via the cytoplasmic protein, UreI) are more likely to be responsible.     

Bioenhancing and antimycobacterial agents from Ammannia multiflora

The methanolic extract of Ammannia multiflora (Lythraceae) showed significant bioenhancing activity with the antibiotic nalidixic acid. Bioassay-guided fractionation of MeOH extract resulted in the isolation of a novel compound, 2,5-bis-(3,3'-hydroxyaryl)tetrahydrofuran, named as ammaniol (5), along with 9 other known compounds (1-4, 6-10). Furthermore, compound 4-hydroxy- α-tetralone (1) was converted into five semisynthetic acyl derivatives, 1A-1E, which were evaluated along with compounds 1, 5, 6, 9, and 10 for their bioenhancing activity in combination with nalidixic acid against the two strains, CA8000 and DH5 α, of Escherichia coli. The results showed that the methanolic extract of A. multiflora and compounds 1 and 9 possessed significant bioenhancing activity and reduced the dose of nalidixic acid fourfold while compounds 5, 6, 10 and semisynthetic derivatives 1A- 1E reduced the dose of nalidixic acid twofold. Compound 5 was also tested for antimycobacterial activity against Mycobacterium H37Rv and was found to show moderate activity (MIC 25?μg/mL) against this pathogen.     

Lack of pharmacokinetic interaction of colestipol and fenofibrate in volunteers

Summary The possibility of a pharmacokinetic interaction between two hypolipidemic drugs, colestipol, an ion exchange resin, and fenofibrate, a phenoxyacid derivative, was studied in 6 male volunteers. The investigation followed a four-step protocol during 18 days, and relied on determination of plasma and urinary levels of fenofibric acid, the active metabolite of fenofibrate. The kinetics of a single dose of fenofibrate 300 mg was established over 3 days. Thereafter, from Days 4 to 9 fenofibrate was given daily as 200 mg in the morning and 100 mg in the evening; the plasma fenofibric acid level reached about 10 µg/ml. From Days 9 to 15 the same dose of fenofibrate was administered together with colestipol 10 g in the morning and 5 g in the evening. Plasma fenofibric acid concentrations remained unchanged and the 24 h urinary excretion of fenofibric acid did not fall. On Day 15, a last single dose of fenofibrate 300 mg was given with colestipol 15 g. The pharmacokinetic pattern of fenofibric acid on Days 15 to 18 did not differ significantly from that found previously (Days 1 to 3). From these results, it is likely that there is no pharmacokinetic interaction between the two hypolipidemic drugs.     

Toxicity and Carcinogenicity Studies of Nalidixic Acid in Rodents

ABSTRACT

Toxicity and carcinogenicity studies of nalidixic acid, an antimicrobial agent used to treat bacterial infections of the urinary tract, were conducted in F344/N rats and B6C3F mice of each sex for 13 weeks or 2 years. In the 13–week studies, nalidixlc acid was administered at dietary concentrations ranging from 1,000 to 16,000 pp. Body weights of both rats and mice were reduced in the groups receiving diet containing 8,000 and 16,000 ppm, and feed consumption of rats in the highest treatment groups was approximately tw-thirds that of controls. Degeneration of the germinal epithelium in the seminiferous tubules of the testis was observed in male rats that received 16,000 ppm; no other compound-related histopathologic effects were observed in either species. TWo-year studies were conducted by feeding diets containing 0, 2,000, or 4,000 ppm nalidixic acid to groups of 50 rats and mice/sex/group. The average daily feed consumption was slightly reduced compared to control groups and resulted in approximate daily doses of 82 or 175 mg nalidixic acidfig for low dose and high dose rats, and 220 or 475 mg/kg for low dose and high dose mice. Mean body weights of dosed rats and mice were lower than those of controls, except for groups of low dose female rats and male mice. The incidences of preputial gland neoplasms in dosed male rats and of clitoral gland neoplasms in dosed female rats were significantly increased compared to those in controls; responses in low dose groups were similar to those in high dose groups. There were decreased incidences of leukemia and mammary gland neoplasms in dosed female rats and of pituitary gland neoplasms in dosed male rats. Subcutaneous tissue fibrosarcomas were marginally increased in dosed male mice. There were no increased incidences of neoplasms in dosed female mice. under the conditions of these studies, the dietary administration of nalidixic acid was carcinogenic for rats, causing preputial gland or clitoral gland neoplasms in males and females, respectively. The association of subcutaneous neoplasms with administration of nalidixic acid to male mice was equivocal.     

Drug Resistance Reversal Potential of Ursolic Acid Derivatives against Nalidixic Acid‐ and Multidrug‐resistant Escherichia coli

As a part of our drug discovery program, ursolic acid was chemically transformed into six semi‐synthetic derivatives, which were evaluated for their antibacterial and drug resistance reversal potential in combination with conventional antibiotic nalidixic acid against the nalidixic acid‐sensitive and nalidixic acid‐resistant strains of Escherichia coli. Although ursolic acid and its all semi‐synthetic derivatives did not show antibacterial activity of their own, but in combination, they significantly reduced the minimum inhibitory concentration of nalidixic acid up to eightfold. The 3‐O‐acetyl‐urs‐12‐en‐28‐isopropyl ester (UA‐4) and 3‐O‐acetyl‐urs‐12‐en‐28‐n‐butyl ester (UA‐5) derivatives of ursolic acid reduced the minimum inhibitory concentration of nalidixic acid by eightfold against nalidixic acid‐resistant and four and eightfold against nalidixic acid‐sensitive, respectively. The UA‐4 and UA‐5 were further evaluated for their synergy potential with another antibiotic tetracycline against the multidrug‐resistant clinical isolate of Escherichia coli‐KG4. The results showed that both these derivatives in combination with tetracycline reduced the cell viability in concentration‐dependent manner by significantly inhibiting efflux pump. This was further supported by the in silico binding affinity of UA‐4 and UA‐5 with efflux pump proteins. These ursolic acid derivatives may find their potential use as synergistic agents in the treatment of multidrug‐resistant Gram‐negative infections.