Mode of action and quantitative structure-activity correlations of tuberculostatic drugs of the isonicotinic acid hydrazide type.

Quantitative structure-activity studies have been performed for a series of 2-substituted isonicotinic acid hydrazides by correlating electronic, steric, and lipophilic properties of the substituents with the biological activity date (MIC) from serial dilution tests with Mycobacterium tuberculosis (strain H 37 Rv). The reaction rates for the quaternization of 2-substituted pyridines with methyl iodide were also determined. The rate constants show a similar dependence on the steric and electronic effects of the substituents as the antibacterial activities of the corresponding pyridine-4-carboxylic acid hydrazides. The obtained correlations give evidence that the reactivity of the pyridine nitrogen atom is essential for the biological activity of 2-substituted isonicotinic acid hydrazides and seem to support the hypothesis that isonicotinic acid derivatives are incorporated into an NAD analogue.

A simple, fast and inexpensive kinetic method to differentiate between total and viable bacteria using Coulter counter technique.

A new kinetic approach is described using Coulter Counter technique to differentiate between viable and total counts in bacterial cultures (E. coli) inhibited by chemotherapeutics (trimethoprim, tetracycline, and a nitrofurane derivative, 2,4-diamino-6-(5-nitrofuryl-2)-5-ethylpyrimidine (HN 32). The results are compared with data obtained by plate count technique.

[Studies on synergistic behaviour and pharmacokinetics of the combination sulfonamide/trimethoprim. IV. A comparative study on potentiating the trimethoprim effect by various sulfonamides and critical observations on its dosing (author's transl)]. / Untersuchungen zum synergistischen Verhalten und zur Pharmakokinetik von Sulfonamid-Trimethoprim-Kombinationen. IV. Eine vergleichende Untersuchung zur Potenzierung der Trimethoprim-Wirkung durch verschiedene Sulfonamide und eine kritische Betrachtung ihrer Dosierung.

The maximum possible inhibitory effect of sulfonamide-(SA)-trimethoprim (TMP) combinations on E. coli is obtained with rather small concentrations of SA according to the results obtained with bacterial growth kinetic studies. In these studies the TMP concentration (significantly below the minimum plasma level) was kept constant and the SA concentration varied. An "antagonistic" effect of high SA concentrations on the synergistic effect of the combination and a reduction of the inhibitory effect of TMP has been observed. According to the results of the bacterial growth kinetics obtained with E. coli and pharmacokinetic studies presented, the suggested dose for the combination 2-sulfa-4,5-dimethyl-oxazole/TMP seems to be sufficient, the dosage regimen is correct, whereas the amount of 3-sulfa-5-methyl-isoxazole (SMZ) in the dose proposed for the combination SMZ/TMP seems to be unreasonably high and the dosage scheme is incorrect.

Kinetics and mechanisms of action of 'folate synthesis inhibitors', alone or in combination, on Escherichia coli. III. Pyrimethamine, trimethoprim and sulfamethoxazole.

The inhibitory activity of pyrimethamine (PMA) is 1/290 of the activity of trimethoprim (TMP) against E. coli as evaluated from a plot of C.ko/ko-kapp VS. C. Even at high concentrations the effect of PMA in contrast to TMP seems to be cateriostatic. Combinations of TMP and PMA reveal an additive effect. In PMA-treated cultures, the slope of the logarithmic growth curve decreases after an initial inhibited growth, and a second steady state is established. This second steady state has a different reason than the one observed in TMP-treated cultures; whereas the second phase in TMP-inhibited cultures depends on the number of germs, in the case of PMA it depends on the number of generations. Using prewashed cell cultures, it was shown that there is no influence on the two steady states in PMA-inhibited cultures; for TMP, however, it was shown that the presence of the first phase is due to an antagonist excreted into the culture medium. These observations hint at differences in the mode of action of TMP and PMA in addition to differences in the affinity to the target enzyme dihydrofolate reductase. Combination of PMA with sulfamethoxazole (SMZ) at concentrations where both drugs are acting only bacteriostatically leads to effects considerably greater than would be expected from simple additivity. The kill rate observed is the same as observed for TMP/SMZ combinations despite of the considerable lower activity of PMA and SMZ. The results support the assumption that it might be possible to select drug combinations considering the best pharmacokinetical fit and not necessarily the most effective drugs in the series studied.

Bacterial growth kinetics of "M. lufu" in the presence and absence of various drugs alone and in combination. A model for the development of combined chemotherapy against M. leprae?

Bacterial growth kinetic studies were performed in a series of potential inhibitors of M. leprae using "M. lufu" as a model strain. Reasons why "M. lufu" is considered to be a better model than M. tuberculosis are presented. The inhibitory power of the single drugs has been quantified, the activity constants are calculated, and the synergistic, additive, or antagonistic behavior of the combinations is evaluated. It is demonstrated that a combination consisting of dapsone (DDS), prothionamide (PTH), isoniazid (INH), and rifampin (RAMP) is a very powerful inhibitor of "M. lufu" and prevents or delays the development of resistance under the experimental conditions described. This finding is in agreement with the therapeutic effect of this combination (Isoprodian + rifampin) achieved in a leprosy eradication program on the Island of Malta. Whereas there is no direct proof that "M. lufu" is the best suitable model for drug evaluation against M. leprae, there is, however, nothing in the presented results which is against this model, especially as the actions of DDS and PTH or RAMP is concerned. A new combination of DDS with trimethoprim (TMP) or TMP derivatives has also been studied and seems to be a promising candidate. In addition, a technique is described to differentiate between bacteriostatic and bactericidal action of the tested inhibitors against "M. lufu."

Bacterial growth kinetics of E. coli in the presence of various trimethoprim derivatives alone and in combination with sulfonamides.

Bacterial growth kinetic experiments have been performed to study the potentiating effect of trimethoprim (TMP) AND TMP derivatives on the antibacterial action of sulfonamides (SA). The TMP derivatives showed different inhibitory effects when used alone. Derivatives with decreased inhibitory activity excerted 'bactericidal' effects only at high concentrations. A rather fast development of bacteria with lower sensitivity against these derivatives has also been observed. In the combined action with SA, however, the same maximal 'kill' rate was observed for TMP derivatives as tetroxoprim or derivative IV (TABLE I) at low concentrations of these inhibitors. Under the experimental conditons there is no significant difference between the studied TMP derivatives and various SA in the combined action.

Mechanism of action of the folate blocker diaminodiphenylsulfone (dapsone, DDS) studied in E. coli cell-free enzyme extracts in comparison to sulfonamides (SA).

The antibacterial activity of DDS has been studied in whole cell (E. coli), cell-free folate synthesizing enzyme extracts and compared to effects obtained for sulfonamides (SA). It is shown that DDS acts as a synthetase inhibitor in the folate synthesizing enzyme system. DDS reacts with the substrate 7,8-dihydro-6-hydroxymethylpterinopyrophosphate to form a 7,8-dihydropteroic acid analog. Bacterial growth kinetic studies were performed to test for possible synergistic activity of the analog in combination with DDS. Possible reasons for the extremely large inhibitory power of DDS against M. leprae are discussed.

Bacterial growth kinetics of Escherichia coli and mycobacteria in the presence of brodimoprim and metioprim alone and in combination with sulfamerazine and dapsone (VI).

Bacterial growth kinetics and checkerboard titration experiments have been performed to determine the inhibitory power of metioprim (I) and brodimoprim (II) alone and in combination with diaminodiphenylsulfone (DDS) using Escherichia coli and mycobacteria as test organisms. The evaluated potency of the new TMP derivatives alone and in combination is compared to TMP and other derivatives. A strongly synergistic activity of I and II in combination with DDS against E. coli and various mycobacteria is observed which is also operative in case of highly DDS-resistant mycobacterial strains. The implication of these findings for the development of a combined chemotherapy with these drugs against atypical mycobacterial infections - especially leprosy - is discussed.

[Pharmacokinetic studies with the combination sulfamoxole/trimethoprim in animals and men (author's transl)]. / Pharmakokinetik der Kombination Sulfamoxol/Trimethoprim (CN 3123) bei Tier und Mensch

The pharmacokinetics of the 5:1 combination of N1-(4,5-dimethyl-2-oxazolyl)-sulfanilamide (sulfamoxole) and 2,4-diamino-5-(3,4,5-trimethoxy-benzyl)-pyrimidine (thrimethoprim) (CN 3123, Nevin, Supristol) corresponds to the well known data of the single substances. Investigations on blood level, concentration in plasma water and excretion via urine and bile were done on experimental animals and with therapeutic dosage (single and repeated administration) on men. There were no alterations of the kinetics of the single substances due to drug interaction during simultaneous administration, neither qualitatively nor quantitatively. The dosage schedule elaborated is as follows: dosage interval=12 h, ratio initial dose: maintenance dose=2:1. For adults this regimen with a maintenance dose of 400 mg sulfamoxole and 80 mg trimethoprim results in a steady state of the minimal concentrations immediately before the following dose. These minimal concentrations in plasma water exceed the minimal inhibitory concentrations determined in vitro for most pathogens by several times.

In vitro and in vivo experiments with the new inhibitor of mycobacterium leprae brodimoprim alone and in combination with dapsone.

The antibacterial effect of brodimoprim alone and in combination with dapsone has been studied in vitro in cell-free systems and in whole mycobacterial cells as well as in vivo in mice and humans. The obtained inhibitory effects in vitro and in vivo against model mycobacterial strains and M. leprae, the pharmacokinetic properties in human and its synergistic effect with the most used drug in the chemotherapy of leprosy, dapsone, make brodimoprim a promising candidate in the therapy of leprosy.

In vitro activity of the new quinoline derivative ciprofloxacin alone and in combination against various Mycobacterium-, Salmonella- and Escherichia coli strains.

The antibacterial effect of 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-piperazine-1-ylquinoline++ + 3-carboxylic acid (ciprofloxacin, Bay o 9867) has been tested using different test systems and various strains, especially of Escherichia coli, Mycobacterium and Salmonella. Ciprofloxacin shows low MIC's against most of the tested strains. The high in vitro and in vivo activity against Salmonella is most promising for cure of salmonellosis.

Mechanism of action of the folate blocker diaminodiphenylsulfone(dapsone, dds)studied in e. coli cell -free enzyme extracts in comparison to sulfonamides(sa)

The antibacterial activity of DDS has been studied in whole cell (E. coli), cell-free folate synthesizing enzyme extracts and compared to effects obtained for sulfonamides (SA). It is shown that DDS acts as a synthetase inhibitor in the folate synthesizing enzyme system. DDS reacts with the substrate 7,8-dihydro-6-hydroxymethylpterinopyrophosphate to form a 7,8-dihydropteroic acid analog. Bacterial growth kinetic studies were performed to test for possible synergistic activity of the analog in combination with DDS. Possible reasons for the extremely large inhibitory power of DDS against M. leprae are discussed