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Serum disappearance and urinary excretion of sulfamethoxypyridazine in goats.

Pharmacokinetics and urinary excretion of sulfamethoxypyridazine were determined in goats following single intravenous administration (100 mg/kg body weight). The disposition kinetics of sulfamethoxypyridazine could be best described by a 2-compartment open model. The distribution and elimination half life of the drug were 0.10 +/- 0.03 and 6.28 +/- 0.44 h, respectively. The values of apparent volume of distribution at steady state and total body clearance were found to be 0.39 +/- 0.02 l/kg and 0.73 +/- 0.06 ml/kg/min, respectively. The degree of acetylation was low as it ranged between 4.49 +/- 1.96 to 25.07 +/- 6.31% of the total drug in serum with an overall mean of 11.99 +/- 1.66%. Cumulative urinary excretion of sulfamethoxypyridazine was very low as only 2.97 +/- 0.50% of the total administered dose was excreted in urine during 24 h. The dosage regimen in goats would be 37.00 and 27.15 mg/kg body weight as the priming and maintenance doses respectively, to be repeated at 12 h intervals by intravenous route to achieve the bacteriostatic level of > or = 25 micrograms/ml.

Animals↗

Different inhibitory effects of 2,4-dinitrophenol, iodoacetate, and probenecid on renal excretion of p-aminohippurate, cyclopenthiazide, and sulfamethoxypyridazine in rats.

The present study was undertaken to determine whether the renal excretion of drugs can be modified by inhibition of the carrier system for organic acids in vivo. The renal excretion of p-aminohippurate is not influenced by 2,4-dinitrophenol but is reduced by iodoacetate and probenecid. The renal excretion of cyclopenthiazide is decreased by all inhibitors. Rats excrete only a very small portion of the administered dose of sulfamethoxypyridazine. Renal sulfamethoxypyridazine excretion is 3 times higher when the tubular reabsorption is blocked by simultaneous administration of NaHCO3. However, even then only a small portion of the injected dose is excreted. Renal sulfamethoxypyridazine excretion is only reduced by probenecid. This finding can be explained by the reduction of the urine volume. It can be concluded that p-aminohippurate and cyclopenthiazide are renally excreted by tubular secretion, whereas sulfamethoxy-pyridazine is excreted by glomerular filtration.

Aminohippuric Acids↗

Predicting the solubility of sulfamethoxypyridazine in individual solvents. I: Calculating partial solubility parameters.

Sulfamethoxypyridazine, a representative model of a drug molecule, is used to test the extended Hansen method for estimating partial solubility parameters of solid compounds. Solubilities are determined in polar and nonpolar solvents. The method provides reasonable partial parameters for the sulfonamide, and it may be useful in obtaining partial parameters for other drug molecules. A four-parameter extended Hansen approach involving proton donor and acceptor parameters is used in fitting the data to a theoretical model. A term, Wh, is introduced as an empirical measure of solute-solvent interactions due to hydrogen bonding. The use of the empirical term Wh allows the researcher to fit experimental solubilities and thus design regression models and equations which provide a reasonable prediction of solubilities of a polar drug in a number of very different solvents. A Flory-Huggins size correction term improves the prediction of sulfamethoxypyridazine solubilities in these irregular solutions.

Chemical Phenomena↗

[Pharmacokinetics and plasma protein binding of sulfamethoxypyridazine in camels (Camelus dromedarius)].

The pharmacokinetics of sulfamethoxypyridazine (SMPD) were investigated in the camel after intravenous and oral administration. After intravenous injection, the plasma concentration of the drug followed the kinetics of a two-compartment model. The steady-state volume of distribution (Vss) of 0.47 l/kg suggested that sulfamethoxypyridazine was mostly distributed within the vascular compartment and the strongly vascularized tissues. The elimination from the body was rather slow, with a biological half-life [t1/2(beta)] and a total plasma clearance of about 9.5 h and 0.037 l/kg.h, respectively. Oral treatment showed that the maximum plasma concentration was reached 17 hours post drug administration and that the bioavailability ranged around 57%. Study of the plasma protein binding showed that the percentage of SMPD binding to plasma proteins varied from 47 to 72% and seemed to be concentration-dependent. The total binding capacity and the dissociation constant at equilibrium were 196 micrograms/ml and 335 micrograms/ml, respectively.

Animals↗

Structure and solid-state chemistry of anhydrous and hydrated crystal forms of the trimethoprim-sulfamethoxypyridazine 1:1 molecular complex.

The crystal structure of the equimolar trimethoprim (TMP) and sulfamethoxypyridazine (SMPD) complex in the anhydrous form (TMP. SMPD) and that of the species with 1.5 molecules of water of crystallization (TMP.SMPD.W) are reported in this article. X-ray powder diffraction patterns (both computer generated and experimental) and thermal analytical data from differential scanning calorimetry (DSC) and thermogravimetry useful for the characterization of TMP.SMPD and TMP.SMPD.W are provided. The stability of TMP.SMPD.W, which retains its crystallographic order under 0% relative humidity (RH) conditions at room temperature (22 degrees C) and 20 mmHg, is accounted for in terms of crystal structure and hydrogen bonding. Transformation of TMP.SMPD to the hydrate complex by exposure to approximately 100% RH, suspension in water, and wet granulation, and dehydration of TMP.SMPD.W by thermal treatment and by desiccation with methanol were investigated and tentatively interpreted in terms of crystal properties. Interactions in the physical mixture of TMP and SMPD by grinding, compression, heating, and contact with water were also studied. Water-mediated formation of TMP.SMPD.W by wetting and metastable eutectic melting-mediated formation of TMP.SMPD by heating was demonstrated. Mechanical activation by milling makes the physical mixture prone to solid-state transformation into dimorphic anhydrous cocrystals by supply of thermal energy during a DSC scan.

Crystallization↗

Predicting the solubility of sulfamethoxypyridazine in individual solvents. II: Relationship between solute-solvent interaction terms and partial solubility parameters.

In the first paper in the series, an expanded system of parameters was devised to account for orientation and induction effects, and the term Wh was introduced to replace delta 1h delta 2h of the extended Hansen solubility approach. In the present report, a new term, Kh = Wh/delta 1h delta 2h is observed to take on values larger or smaller than unity depending on whether the hydrogen bonded solute-solvent interaction is larger or smaller than predicted by the term delta 1h delta 2h. The acidic delta a and basic delta b solubility parameters are used to represent two parameters, sigma and tau, suggested by Small in his study of proton donor-acceptor properties. The Small equation, including a heat of mixing term for hydrogen bonded species, is shown to be capable of semiquantitative evaluation. A partial molar heat delta H2h of hydrogen bonding is calculated using delta h and Wh terms; delta H2h is found to be correlated with the logarithm of the residual activity coefficient, In alpha R, a term representing strong solute-solvent interaction. The terms Wh, delta H2h, and In alpha 2R may be used to test the deviation from the geometric mean assumed in regular solution theory, and to replace the hydrogen bonding terms of the extended Hansen three-parameter model. The solubility of sulfamethoxypyridazine in 30 solvents is used to test the semiempirical solubility equations. The results are interpreted in terms of partial solubility parameters and the proton donor-acceptor properties of the solvents.

Chemical Phenomena↗

Sulfamethoxypyridazine-responsive pemphigoid nodularis: a report of two cases.

Pemphigoid nodularis is a chronic and uncommon variant of bullous pemphigoid. The condition is characterized by the presence of prurigo nodularis-like lesions, possible history of blistering, and immunohistochemical findings of bullous pemphigoid. These patients are often unresponsive to conventional therapy with potent topical and systemic steroids and different immunosuppressive agents used alone or in combination. We describe two cases of pemphigoid nodularis treated successfully with sulfamethoxypyridazine without any adverse effects.

Anti-Bacterial Agents↗

Efficacy of sulfamethoxypyridazine in a murine model of Pneumocystis carinii pneumonia.

Sulfamethoxazole is the component of co-trimoxazole responsible for its efficacy against Pneumocystis carinii pneumonia, but this drug is associated with frequent adverse effects. Sulfamethoxypyridazine is significantly more effective than sulfamethoxazole against a murine model of P. carinii and might be a candidate for testing in infected patients.

Animals↗

Biological availability of sulfamethoxypyridazine and sulfisomidine polymers.

Dissolution rates and apparent solubilities of forms I, II and III of Sulfamethoxypyridazine (1) and forms I and II of sulfisomidine (2) were determined in water at 37 degrees C. The ratios of apparent solubilities of I:II:III for 1 forms and I:II for 2 forms were 1:1.18:1.25 and 1:1.32 respectively. Upon long contact of 2 with water the ratio of II:I decreased. This has been attributed to gradual transformation of 2 from form II to I. Gastrointestinal absorption of form III of 1, in human volunteers, was studied in comparison with the more stable form I. The same study was carried out on forms I and II of 2. Data were correlated and expressed in availability rate constants (K1), applying the one compartment open: model. This and other parameters show that form III of 1 is 1.4 times as much absorbed as form I, and that the availability of the metastable form II of 2 is 1.2 times as much absorbed as the stable form I.

Biological Availability↗

The effect of protein concentration on the binding of sulfamethoxypyridazine by human and bovine serum albumin.

Several methods of analyzing data obtained for ligand-macromolecule interactions at various concentrations of protein have been examined. Of the methods examined, only the constants ni, the number of binding sites of class i, and ki, the association constant for the i'th class of binding sites, were found useful in the detection of protein concentration dependent binding. The values of niki and sigma niki were calculated from previously obtained data for the interaction of sulfamethoxypyridazine with human and bovine serum albumin at seven protein concentrations. In disagreement with a previous report, the results obtained suggest that this protein-ligand interaction is either independent of protein concentration or that the protein concentration dependence of the binding constants is small relative to the experimental error involved in their determination.

Animals↗

[Sensitivity to dapsone, sulfamethoxypyridazine and ethionamide of mycobacterium leprae taken from patients treated by the drugs].

Suspensions of M. leprae from skin biopsies of patients treated with dapsone (DDS) (four cases), sulfamethoxypyridazine (SMP) (six cases), and ethionamide (ETH) (seven cases), were inoculated into mouse foot pads and their sensitivity for the different drugs determined. Two strains were DDS resistant. Resistance appeared after 13 and 14 years respectively after the start of treatment. Five strains were isolated from patients treated with SMP. Relapses during sulfonamide treatment are considered to be due to the low effective serum concentrations reached by SMP, a situation which is aggravated by irregularities in drug intake. Fortunately all strains were sensitive to SMP and DDS as well. Four strains were ETH resistant. ETH resistance at the present moment reaches 4% and appeared in two cases six years after the start of treatment. It is concluded that SMP is not indicated for the treatment of multibacillary leprosy and that ETH can be used only in association with other drugs during the introductory phase of treatment of multibacillary forms of leprosy.

Animals↗

Bioavailability of sulfamethoxypyridazine following intramuscular or subcutaneous administration in goats.

The pharmacokinetics of sulfamethoxypyridazine (SMP) was investigated in goats after a single intramuscular (im) or subcutaneous (sc) administration (100 mg/kg body weight). The biological half lives of SMP following im and sc administration were found to be 11.0 and 13.7 h, respectively. The systemic availabilities of the drug were calculated to be 68.6 and 58.7% following im and sc injections, respectively. The rapidity of absorption, almost similar availability, comparatively longer biological half-life and ease of administration suggest that the sc route of administration might be preferred over the im route. To achieve and maintain serum concentrations 25 micrograms/mL, a rational dosage regimen of SMP for goats would be 55 and 38 mg/kg body weight as the loading and maintenance doses, respectively, with a dosage interval of 24 h by the sc route.

Absorption↗