The antibacterial activities of aditoprim and its efficacy in the treatment of swine streptococcosis.

Aditoprim (ADP) has potential use as an antimicrobial agent in animals. However, its pharmacodynamic properties have not been systematically studied yet. In this study, the in vitro antibacterial activities of ADP and its main metabolites were assayed, and the in vivo antibacterial efficacy of ADP for the treatment of swine streptococcosis was evaluated. It was shown that Salmonella and Streptococcus from swine, Escherichia coli and Salmonella from chickens, E. coli, Streptococcus, Mannheimia, Pasteurella from calves, Streptococcus and Mannheimia from sheep, and E. coli, Flavobacterium columnare, Acinetobacter baumannii and Yersinia ruckeri from fishes were highly susceptible to ADP. Haemophilus parasuis from swine, Staphylococcus aureus, Aeromonas punctate, Mycobacterium tuberculosis, Streptococcus agalactiae from fishes, and Klebsiella from calves and sheep showed moderate susceptibility to ADP, whereas E. coli, Actinobacillus pleuropneumonia, Pasteurella, S. aureus, Clostridium perfringens from swine, S. aureus, C. perfringens from chickens, and S. aureus from calves were resistant to ADP. The main metabolites of ADP showed equal activity to that of their parent compound, and the prevention and therapeutic dosages of ADP recommended for swine streptococcosis were 10 and 20~40 mg/kg b.w., respectively. This study firstly showed that ADP had strong antibacterial activity and had potential to be used as a single drug in the treatment of bacterial infectious diseases.

Molecular modelling of trimethoprim complexes of human wild-type and mutant dihydrofolate reductases: identification of two subsets of binding residues in the antifolate binding site.

Computer-assisted molecular modelling was used to generate structures for the trimethoprim (TMP):NADPH:dihydrofolate reductase (DHFR) ternary complexes for human wild-type DHFR and for five DHFR mutants (L22R, L22F, F31S, F31W and Q35P). The mutants correspond to DHFR proteins that have been isolated from tissues exposed to chronic or high dose methotrexate (MTX) and show decreased sensitivity to antifolate inhibition. Analysis of the TMP:DHFR interactions suggest the presence of two subsets of TMP binding residues in the DHFR antifolate binding site. One subset of these residues (GLU30, PHE34, ILE60 and VAL115) are common to each DHFR complex studied and are referred to as core residues. The other TMP binding residues vary among the DHFR complexes studied and are referred to as noncore residues. The core residues exhibit a greater number of TMP contacts/residue and form more stable TMP interactions than noncore residues. Additionally, the core and noncore residues make contact with different regions of the TMP structure. Information presented here provides additional insight into the design of new agents for the improved inhibition of wild-type DHFR and the simultaneous inhibition of both wild-type and mutant DHFR molecules.

The disposition of five therapeutically important antimicrobial agents in llamas.

The disposition of five therapeutic antimicrobial agents was studied in llamas (Lama glama) following intravenous bolus administration. Six llamas were each given ampicillin, tobramycin, trimethoprim, sulfamethoxazole, enrofloxacin and ceftiofur at a dose of 12 mg/kg, 1 mg/kg, 3 mg/kg, 15 mg/kg, 5 mg/kg, and 2.2 mg/kg of body weight, respectively, with a wash out period of at least 3 days between treatments. Plasma concentrations of these antimicrobial agents over 12 h following i.v. bolus dosing were determined by reverse phase HPLC. Disposition of the five antimicrobial agents was described by a two compartment open model with elimination from the central compartment, and also by non-compartmental methods. From compartmental analysis, the elimination rate constant, half-life, and apparent volume of distribution in the central compartment were determined. Statistical moment theory was used to determine noncompartmental pharmacokinetic parameters of mean residence time, clearance, and volume of distribution at steady state. Based on the disposition parameters determined, and stated assumptions of likely effective minimum inhibitory concentrations (MIC) a dose and dosing interval for each of five antimicrobial agents were suggested as 6 mg/kg every 12 h for ampicillin; 4 mg/kg once a day or 0.75 mg/kg every 8 h for tobramycin; 3.0 mg/kg/15 mg/kg every 12 h for trimethoprim/sulfamethoxazole; 5 mg/kg every 12 h for enrofloxacin; and 2.2 mg/kg every 12 h for ceftiofur sodium for llamas. Steady-state peak and trough plasma concentrations were also predicted for the drugs in this study for llamas.

Effect of pectin and kaolin on bioavailability of co-trimoxazole suspension.

Bioavailability of co-trimoxazole suspension was determined with and without concurrent administration of pectin and kaolin in 8 volunteers. Twenty ml suspension of co-trimoxazole containing 160 mg trimethoprim (TMP) and 800 mg sulphamethoxazole (SMX) and co-trimoxazole suspension along with 20 ml of pectin-kaolin suspension were administered in a random order with 7 days interval. Plasma estimation of trimethoprim and sulphonamide was carried out at serial intervals. Area under curve (AUC) and Cmax of TMP were significantly higher when co-trimoxazole suspension alone was used. No statistically significant changes were observed in case of sulphamethoxazole. Clinical study is necessary to verify whether concurrent administration of co-trimoxazole and pectin-kaolin leads to loss of antibacterial efficacy.

Benefit from high intrarenal levels of gentamicin in the treatment of E. coli pyelonephritis.

The importance of high intrarenal levels of gentamicin on the outcome of experimental pyelonephritis was studied in rats receiving either a short course (three days) of gentamicin (G) alone or combined with a longer course (14 days) of ampicillin (A), cephalothin (C), or trimethoprim (T), or two weeks of therapy with ampicillin, cephalothin, trimethoprim and gentamicin given alone. While ampicillin, cephalothin and trimethoprim were undetectable in the medulla within six hours of cessation of therapy, gentamicin was still detectable in levels six folds above the MIC up to six months after treatment had ceased. Six months after the end of treatment, the percentage of sterile left kidneys in animals treated with ampicillin (50%), cephalothin (15%), trimethoprim (20%) was lower than the percentage of animals receiving 14 days of gentamicin (100%), or the combinations AG:89%, CG:67% and TG:60%, P less than 0.01. Following three days of gentamicin, 50% of the left kidneys were sterilized. When compared to ampicillin, cephalothin or trimethoprim alone, combined therapies significantly reduced the number of CFU in the kidneys P less than 0.01. These combinations were almost as effective as two weeks of therapy with gentamicin. Short-term therapy (three days) with an aminoglycoside which concentrates in the renal parenchyma, combined with an antibiotic which will accumulate in other parts of the nephron, may result in "pharmacological synergy". This new approach to therapy of pyelonephritis may be promising.

Conformational energy calculations and electrostatic potentials of dihydrofolate reductase ligands: relevance to mode of binding and species specificity.

Classical potential energy calculations are reported for a series of 11 structurally diverse substrates, products, and inhibitors of dihydrofolate reductase. In almost every case, the calculations reveal a range of potential biologically active conformations accessible to the molecule, and geometry optimization with molecular mechanics and molecular orbital calculations further expands the range of accessible conformations. The energy calculations are supplemented with electrostatic potential energy surfaces for the heterocyclic components of each molecule. These data are used in conjunction with the energy calculations and the crystallographically determined enzyme structures to compare two alternative proposed binding modes of folates known to bind with their pteridine rings inverted relative to that of methotrexate. It is shown that the conformational flexibility of the connecting chain between the benzoyl glutamate and pteridine moieties in the folates actually allows the pteridine ring to shift between these alternative binding modes, a combination of which may offer the best explanation for the observed activity. The electrostatic potentials and conformational energy data are also used in an attempt to account for the species specificity of inhibitors of mammalian, bacterial, and protozoal dihydrofolate reductases. The results show that while these techniques can be used to explain many of the observed results, others require recourse to the observed crystal structures to provide a satisfactory explanation.

Significance of the sulfonamide component for the clinical efficacy of trimethoprim-sulfonamide combinations.

The reasons for combining trimethoprim (TMP) with sulfonamides (SUL) are still mainly theoretical but are supported by results from experimental infections and treatment of specific pathogens in humans, such as Branhamella catarrhalis, Neisseria gonorrhoeae, Brucella, Nocardia asteroides and perhaps Bordetella pertussis and Chlamydia trachomatis. Addition of SUL to TMP confers a therapeutic advantage also in patients with complicated urinary tract infection but probably not in young women with acute cystitis. Conditions that may enable TMP-SUL synergy in vivo can be expected to occur only in occasional cases of infection due to staphylococci, streptococci, Haemophilus or enteric bacteria. This fact together with ethical problems and availability of alternative therapies make further evaluations of the clinical significance of the SUL component of TMP-SUL very difficult. Although the use of TMP alone has shown promise in exacerbations of chronic bronchitis the role of the SUL component in TMP-SUL treatment of infections outside the urinary tract remains to be defined in comparative clinical trials.

A comparative study of cefadroxil and co-trimoxazole in patients with lower respiratory tract infections.

The most common causative pathogens in lower respiratory disease are S. pneumoniae, H. influenzae and S. pyogenes. Cefadroxil and co-trimoxazole, both orally administered broad spectrum antibiotics, are effective against these organisms when given in a twice-daily regimen. In this open randomised study, 42 patients with lower respiratory tract infections received cefadroxil 1 g or co-trimoxazole 1 double-strength tablet every 12 hours for a mean duration of 11 and 13 days, respectively. Pathogens were isolated in the pre-treatment sputum of 51% of patients given cefadroxil and in 25% of those who received co-trimoxazole. Similar overall cure rates were observed after treatment with cefadroxil (67%) and co-trimoxazole (60%); sputum purulence was similarly diminished by both drugs (91% and 85%, respectively). Neither antibiotic caused serious side effects. Thus, in a convenient twice-daily regimen, cefadroxil and co-trimoxazole are comparably effective in treating lower respiratory tract infections.

Trimethoprim-sulfamethoxazole for bacterial meningitis.

Trimethoprim-sulfamethoxazole has excellent microbiologic activity against most pathogens that produce meningitis; both components of this drug have high penetration into tissues, including the cerebrospinal fluid. Clinical experience shows that trimethoprim-sulfamethoxazole may be beneficial in the treatment of gram-negative bacillary meningitis caused by organisms only moderately susceptible to third-generation cephalosporins (Enterobacter cloacae, Serratia marcescens) or resistant to these antibiotic agents (Pseudomonas cepacia, Acinetobacter). The success of trimethoprim-sulfamethoxazole in the treatment of four patients with Staphylococcus aureus and two patients with Listeria monocytogenes meningitis shows that this drug may also be useful in treating infrequent types of gram-positive meningitis.

Effect of magnesium trisilicate and kaolin-pectin on the bioavailability of trimethoprim.

Variability in the bioavailability of orally administered trimethoprim due to Magnesium trisilicate and Kaolin-pectin has been investigated. The concentration of trimethoprim in blood was determined spectrofluorometrically at 0, 15 and 30 minutes and 1, 2, 4 and 6 hours. The area under the blood concentration curve of trimothoprim was significantly decreased, when the drug was given concurrently with magnesium trisilicate or kaolin-pectin. The mean decrease in maximum blood concentration of trimethoprim in magnesium trisilicate and kaolin-pectin treated groups was 49.94% and 29.42% respectively. The data suggest that a clinically significant interaction may occur due to concurrent administration of trimethoprim with these drugs.

Clinical effect and pharmacokinetics of trimethoprim-sulphadiazine in children with urinary tract infections.

The clinical effect and pharmacokinetics of the combination trimethoprim (TMP)-sulphadiazine (SD) were studied in 18 children with acute urinary tract infections (UTI), aged 2-56 months. A suspension of TMP-SD (9 + 41 mg/ml) was taken orally twice daily for 10 days. Various doses of TMP (2.9-3.7 mg/kg/day) and SD (12.9-16.7 mg/kg/day) were also given to children of different ages. After 2-4 days of treatment, bacterial cultures of urine were negative and C-reactive protein in serum, WBC count and ESR in all patients had become normal. Steady state serum levels for both components were reached after 4 or more days of treatment. At steady state, mean peak serum concentrations of TMP and SD of 1.4 micrograms/ml and 27 micrograms/ml, respectively, were found within 2-4 h after a fasting morning dose. The biological half-lives of TMP and SD were of the same order of magnitude, but the total clearance of TMP was 5 times greater than that of SD. The concentrations of TMP-SD in urine were invariably more than 10 times the minimum inhibitory concentrations (MIC) for the causative organisms (tested at the ratios 1:20 and 1:4 of TMP and SD). Non-metabolized SD constituted 77% of total SD in urine of infants, and 55% of total SD in children of 1 year or more. The TMP-SD combination showed a satisfactory clinical effect and favourable pharmacokinetic properties in children with UTI.

Urinary tract infections: the efficacy of trimethoprim/sulfamethoxazole.

The diagnosis of bacterial urinary infections is reasonably exact and routine in medical practice. In contrast, therapeutic regimens have been arbitrary with little rationale and no relationship to infection site or therapeutic objective. During the past decades a series of careful prospective studies have carefully characterized episodes of infection to the site within the urinary tract, and adequate follow-up has been obtained to determine the pattern of response. This has led to the emergence of definite guidelines on dose and duration for antimicrobial therapy. The antimicrobial combination of trimethoprim and sulfamethoxazole has been employed in many of these studies and has been found to be a particularly effective agent for both the treatment and prevention of urinary infections. These studies and their implications for optimal treatment of urinary infections are reviewed.

Pharmacokinetics and clinical experiences of the combination sulfadiazine-trimethoprim in the short-term treatment of acute urinary tract infections.

The pharmacokinetics of sulfadiazine (SD) combined in a small dose (250 mg) with trimethoprim (TMP, 160 mg) and given twice daily were studied in eight healthy subjects. Both drugs were rapidly absorbed from the gastrointestinal tract and their concentrations in serum as well as in urine could be considered high enough for the treatment of acute urinary tract infections (UTI). In none of the subjects did the concentration of SD in urine exceed the experimental limit established for crystallization of the drug. Serum half-lives of SD and TMP were 10.8 and 11.8 hrs, respectively. In microbiological assay synergistic interaction was found in human urine with both the combination of SD + TMP and SM (sulfamethoxazole) + TMP on all the tested strains of E. coli, Str. faecalis, Str. agalactiae, Klebsiella pneumoniae and Proteus mirabilis. A double-blind clinical trial was carried out with patients having acute UTI, using either the combination SD + TMP (250 mg + 160 mg) or the combination SM + TMP (800 mg + 160 mg) twice daily for one week. The results of the treatment were equally successful in both groups. Treatment failed in only 4 out of 85 cases, although in 12 cases the causative micro-organism was resistant in vitro to the combination of SM + TMP.

Secretion of various antimicrobial substances in dogs with experimental bacterial prostatitis.

Bacterial prostatitis in dogs was induced by injection of an E. coli 06 suspension into a branch of the prostatic artery. Three to six days later, secretion from the inflamed glands was obtained by pilocarpine stimulation and the concentrations of trimethoprim, sulphamethoxazole, erythromycin, doxycycline and ampicillin were measured during constant infusion of these drugs. In the prostatic secretion, only the concentrations of the lipid soluble substances trimethoprim and erythromycin exceeded the corresponding plasma levels. These two substances may therefore be of value in the treatment of bacterial prostatitis.