The pharmacokinetics and pharmacodynamics of a new sustained-release leuprolide acetate depot compared to market references.

OBJECTIVE: The aim of this study was to compare the efficacy of Lutrate 3.75 and 7.5 mg depot to marketed references Lucrin 3.75 mg and Procrin 7.5 mg depot. METHODS: 20 healthy male volunteers were randomly assigned to receive 1 of 4 active single dose treatments in this double-blind, parallel-group pilot study. Leuprolide acetate and testosterone levels were quantified by radioimmunoassays. RESULTS: The pharmacokinetic profile of leuprolide could be well-described by a 4-step release curve. Leuprolide levels were detectable 14 days longer after injection of the test formulations as compared to the reference products. The total AUC observed with 3.75 and 7.5 mg of the test product were approximately 1.5- and 2.2-fold higher, compared to the reference products, respectively. After the expected testosterone "flare-up" effect, castration was achieved in 4 of 4 subjects with the test formulations, 4 of 5 subjects with Procrin and 2 of 5 subjects with Lucrin. On average, castration lasted more than 1 month with both test formulations compared to 2 weeks with the reference products. CONCLUSION: Sustained release of leuprolide from this new depot formulation suppressed testosterone levels at least as effectively and for a longer period of time than the reference products.

Gastrointestinal transit and release of 5-aminosalicylic acid from 153Sm-labelled mesalazine pellets vs. tablets in male healthy volunteers.

BACKGROUND: Mesalazine (5-aminosalicylic acid)-containing formulations, designed to optimize drug delivery to the ileo-caecal region, represent a cornerstone in the treatment of inflammatory bowel diseases. AIM: : To test, by means of pharmaco-scintigraphy, whether novel mesalazine-containing pellets release 5-aminosalicylic acid in the same target region as mesalazine tablets (Salofalk). METHODS: Fourteen healthy male volunteers received a single dose of either pellets or tablets containing 500 mg of mesalazine and 2 mg of 152Sm2O3 with a 1-week washout period. The gastrointestinal transit of 153Sm, incorporated into the formulations, was followed by gamma-scintigraphy. Mesalazine release was verified by assessing 5-aminosalicylic acid plasma pharmacokinetics. RESULTS: The formulations reached the ileo-caecal target region almost at the same time (3.3 +/- 1 and 3.8 +/- 1 h for pellets and tablets, respectively). Plasma 5-aminosalicylic acid tmax values were comparable and corresponded to the time during which the formulations were located in the target region. Plasma AUC values were significantly lower for pellets, which might be explained by a more prolonged release of 5-aminosalicylic acid. CONCLUSIONS: Novel mesalazine pellets and Salofalk tablets release active 5-aminosalicylic acid in the same target region and pass through the gastrointestinal tract under fasting conditions in healthy volunteers in a comparable time. From a comparison of in vitro dissolution and plasma concentration data, a slower and more prolonged release of 5-aminosalicylic acid from pellets is suggested.

Gastrointestinal transit and 5-ASA release from a new mesalazine extended-release formulation.

BACKGROUND: Mesalazine (5-aminosalicylic acid, 5-ASA)-containing formulations represent a cornerstone in the treatment of inflammatory bowel diseases. Recently, a new formulation has been developed to provide selective and more homogeneous release of 5-ASA compared to traditional systems. METHODS: In a first study, gastrointestinal transit was followed by gamma-scintigraphy after single-dose application of tablets containing 1200 mg mesalazine to 12 healthy male volunteers. 5-ASA release was verified by the assessment of plasma pharmacokinetics. In a second, 7-day, multiple-dose study, the steady state plasma pharmacokinetics, urinary excretion and safety profile were characterized after twice-daily tablet administration to 12 healthy volunteers. RESULTS: Tablet erosion started after 6.9 +/- 1.1 h in the ascending or transverse colon. Radioactivity spread homogeneously throughout the colon, indicating the sustained release of active 5-ASA. Plasma kinetics indicated an earlier initial absorption of 5-ASA, i.e. during transit of the small intestine and ileum. Mean Cmax values (350.6 +/- 322.6 ng/mL) were observed during location in the ileo-caecal region. The mean relative absorption of 5-ASA was 19.9 +/- 18.2% in the small intestine and ileum and 80.1 +/- 18.2% in the colon. CONCLUSIONS: The administration of the new mesalazine formulation was well tolerated, and 5-ASA was continuously released along the whole colon, a favourable prerequisite for the therapy of distally located inflammatory bowel disease.

Analysis of the oxidation-reduction potentials of recombinant ferredoxin-NADP+ reductase from spinach chloroplasts.

Midpoint oxidation-reduction potentials for the two-electron reduction of the bound FAD in spinach ferredoxin-NADP+ reductase were measured by potentiometry (Em = -342 +/- 1 mV at pH 7 and 10 degrees C). They were used with the semiquinone formation constant, obtained by spectroscopic measurement of the semiquinone concentration, to calculate values for the redox potentials of the two one-electron steps in the reduction. The redox potential for the oxidized enzyme/enzyme semiquinone couple (EOX/SQ) at pH 7 is -350 +/- 2 mV (10 degrees C) while the value for the enzyme semiquinone/enzyme hydroquinone couple (ESQ/HQ) under the same conditions is -335 +/- 1 mV. These values correspond to a semiquinone formation constant of 0.55. Measurement of the effects of pH on the potentials showed that EOX/SQ varies linearly with pH (slope -46 +/- 4 mV), while ESQ/HQ is independent of pH at high pH values, but below about pH 7.5 the potential becomes less negative with decreasing pH. indicating that there is a redox-linked protonation of the fully reduced enzyme (pKa = 7.2, 10 degrees C). The absorption spectrum of the fully reduced enzyme was found to depend on pH with the changes giving a calculated pKa of 7.5 (at 15 degrees C). The spectrum at high pH is similar to that of the anionic form of free flavin hydroquinone. The observations suggest that at physiological pH, the enzyme FAD cycles between the three redox states: oxidized, neutral semiquinone and hydroquinone anion.

Involvement of lysine-88 of spinach ferredoxin-NADP+ reductase in the interaction with ferredoxin.

A mutant of spinach ferredoxin-NADP+ reductase, in which Lys-88 has been changed to glutamine, has been obtained by site-directed mutagenesis. The mutant enzyme was fully active as a diaphorase, but partially impaired in ferredoxin-dependent cytochrome c reductase activity. By steady-state kinetics, the Km for ferredoxin of the K88Q enzyme was found to have increased 10-fold, whereas the kcat was unaffected by the amino acid replacement. The interaction between oxidized ferredoxin and the enzyme forms was also studied by spectrofluorimetric titration: Kd values of 110 and 10 nM were determined for the mutant and wild-type proteins, respectively. These data point out the importance of a positive charge at position 88 of the reductase for the interaction with ferredoxin, confirming previous cross-linking studies.