Amoxicillin/clavulanic acid (875/125): bioequivalence of a novel Solutab tablet and rationale for a twice-daily dosing regimen

A new amoxicillin/clavulanic acid tablet formulation (Solutab tablet, Forcid Solutab) containing amoxicillin/clavulanic acid (875/125) has been developed. The aim of the present study was to demonstrate bioequivalence between the new tablet formulation (test), taken as an intact tablet and after prior dispersal, versus the originator product viz. Augmentan film-coated tablet (875/125) used as reference. The study was performed in 48 healthy volunteers according to an open, single-dose, crossover design. Bioequivalence was demonstrated using Cmax and AUC(0-infinity) as primary parameters of evaluation for both amoxicillin and clavulanic acid with 90% confidence intervals of the ratios Solutab tablet/Augmentan within the range of 0.8-1.25. The duration of the plasma concentration exceeding the amoxicillin minimal inhibitory concentration (MICs) was calculated using individual plasma concentration-time curves and compartmental analysis. The data showed that the bioavailability characteristics of the test tablet, taken intact or in dispersed form, and the reference tablets were very similar. The analysis, moreover, also confirmed the appropriateness of using a b.i.d. dosage regimen for both formulations, taking into account the pharmacodynamic breakpoint values for some major pathogens.

Bioequivalence study of a novel Solutab tablet formulation of amoxicillin/clavulanic acid versus the originator film-coated tablet

With amoxicillin/clavulanic acid Solutab tablet, a new tablet formulation of amoxicillin/clavulanic acid (500/125), was developed. The aim of the present study was to demonstrate bioequivalence between the new tablet formulation, taken as an intact tablet and after prior dispersal, versus the originator product viz. Augmentan film-coated tablet. The study was performed in 48 healthy volunteers, according to an open, single-dose three-period, crossover design. Blood samples were taken prior to each administration and at 10 time points after dosing. Plasma concentrations of amoxicillin and clavulanic acid were determined by validated high performance liquid chromatography with UV detection. With regard to amoxicillin, the results were within the preset bioequivalence range of 0.8 to 1.25 for the ratios of the primary parameters AUC(0-t) and Cmax. In terms of clavulanic acid the 90% confidence intervals of the ratios for AUC(0-t) and Cmax versus the reference lay outside the predefined bioequivalence range of 0.75 to 1.33. This result, however, was mainly due to the large variability of the reference formulation compared to the amoxicillin/clavulanic acid Solutab tablet. Based on statistical indications that 3/48 subjects with extremely low levels on the reference formulation could be regarded as "outliers" and after excluding these subjects' data from the statistical analysis, results for clavulanic acid were within the predefined bioequivalence range of 0.75 to 1.33. Overall, the amoxicillin/clavulanic acid Solutab tablet provided, in comparison to the reference tablet, less variable levels of clavulanic acid, thus giving more appropriate protection to the available amoxicillin. Thirteen adverse events were reported post dosing by 7 subjects. There were no differences in incidence of adverse events between amoxicillin/clavulanic acid Solutab tablet taken intact or dispersed and Augmentan.

Phototransduction: different mechanisms in vertebrates and invertebrates

The photoreceptor cells of invertebrate animals differ from those of vertebrates in morphology and physiology. Our present knowledge of the different structures and transduction mechanisms of the two animal groups is described. In invertebrates, rhodopsin is converted by light into a meta-rhodopsin which is thermally stable and is usually re-isomerized by light. In contrast, photoisomerization in vertebrates leads to dissociation of the chromophore from opsin, and a metabolic process is necessary to regenerate rhodopsin. The electrical signals of visual excitation have opposite character in vertebrates and invertebrates: the vertebrate photoreceptor cell is hyperpolarized because of a decrease in conductance and invertebrate photoreceptors are depolarized owing to an increase in conductance. Single-photon-evoked excitatory events, which are believed to be a result of concerted action (the opening in invertebrates and the closing in vertebrates) of many light-modulated cation channels, are very different in terms of size and time course of photoreceptors for invertebrates and vertebrates. In invertebrates, the single-photon events (bumps) produced under identical conditions vary greatly in delay (latency), time course and size. The multiphoton response to brighter stimuli is several times as long as a response evoked by a single photon. The single-photon response of vertebrates has a standard size, a standard latency and a standard time course, all three parameters showing relatively small variations. Responses to flashes containing several photons have a shape and time scale that are similar to the single-photon-evoked events, varying only by an amplitude scaling factor, but not in latency and time course. In both vertebrate and invertebrate photoreceptors the single-photon-evoked events become smaller (in size) and faster owing to light adaptation. Calcium is mainly involved in these adaptation phenomena. All light adaptation in vertebrates is primarily, or perhaps exclusively, attributable to calcium feedback. In invertebrates, cyclic AMP (cAMP) is apparently another controller of sensitivity in dark adaptation. The interaction of photoexcited rhodopsin with a G-protein is similar in both vertebrate and invertebrate photoreceptors. However, these G-proteins activate different photoreceptor enzymes (phosphodiesterases): phospholipase C in invertebrates and cGMP phosphodiesterase in vertebrates. In the photoreceptors of vertebrates light leads to a rapid hydrolysis of cGMP which results in closing of cation channels. At present, the identity of the internal terminal messenger in invertebrate photoreceptors is still unsolved.(ABSTRACT TRUNCATED AT 400 WORDS)

The development of the static vestibulo-ocular reflex in the southern clawed toad, Xenopus laevis. I. Intact animals

In the clawed toad, Xenopus laevis, the static vestibulo-ocular reflex appears in 3 days old tadpoles (developmental stage 42) (Fig. 2). The amplitude and gain of this reflex increase up to stage 52, and then decrease to an almost constant value at stage 60 and older tadpoles (Fig. 3). The most effective roll angle gradually increases during development (Fig. 4). The size of the sensory epithelia reaches the final value at the end of the premetamorphic period (stage 56) (Fig. 5). The small-cellular medial ventral vestibular nucleus (VVN) reaches its maximal number of neurons before the large-cellular lateral VVN. Cell death is more pronounced in the medial than in the lateral part of the VVN. In the dorsal vestibular nucleus (DVN), the numerical development of the small and large neurons is similar to that in the small-cellular medial and large-cellular lateral portion of the VVN (Fig. 7). The results demonstrate that labyrinth and oculomotor centres are anatomically connected before the labyrinth and the vestibular nuclei are fully developed. We discuss the possibility that the ciliary polarity pattern of the sensory epithelium is radial during the first period of life, and changes to the vertebrate fan-type pattern during the second week of life. According to the increase of gain during the first three weeks of life, an increase of the spontaneous activity of vestibular neurons may occur during this period.

The development of the static vestibulo-ocular reflex in the southern clawed toad, Xenopus laevis. III. Chronic hemilabyrinthectomized tadpoles

The static vestibulo-ocular reflex was investigated in tadpoles at different times following unilateral destruction of the labyrinth during the period of early organogenesis and premetamorphosis. Balance compensation is completed after a few weeks, while gain compensation only occurs partially (Figs. 2-4). Tadpoles hemilabyrinthectomized in the age of 2.5 days (stage 38) develop no vestibular nuclei on their lesioned side, while tadpoles operated later in their life, possess these nuclei (Figs. 5, 6) even if they were not detectable at the operation day (Fig. 7). For their dorsal vestibular nucleus (DVN), the number of neurons is usually larger on the intact than on the lesioned side; while for the ventral vestibular nucleus (VVN), there is either numerical symmetry or a transient decrease of cell number on the intact side (Fig. 5). The results demonstrate that vestibular compensation occurs even if vestibular nuclei have developed only on one side, i.e. the vestibular commissure is not a prerequisite for a successful compensation process. It is discussed whether the use of extra-vestibular error signals for balance but not for gain compensation may cause the differences in time courses of both compensation processes.

A hormonal component in central vestibular compensation

In developing clawed toads Xenopus laevis, the compensation mechanism of behavioural defects caused by unilateral labyrinthectomy consists of two components, a vestibular one and a hormonal one. Thyroxine accelerates this compensation.