Bioequivalence evaluation of two roxithromycin formulations in healthy human volunteers by high performance liquid cromatography coupled to tandem mass spectrometry

The bioequivalence of two different formulations containing roxithromycin (SPE-712-1). Oral suspension 300mg/ 15mL as test formulation and Rotram©, tablets 300mg as reference formulation, both by Schering Plough S.A., Brazil) was evaluated in 24 healthy volunteers of both sexes (12 male and 12 female). The study was conducted open with randomized two-period crossover design and a 14-day washout period. Each subject received 300 mg of each roxithromycin formulation. Plasma samples were obtained over a 72-hour interval and roxithromycin concentrations were analyzed by combined LC-MS/MS with positive ion electrospray ionization using selected ion monitoring method. From the plasma roxithromycin concentration vs time curves the following pharmacokinetic parameters were obtained: AUC(0-72h), AUC(0-oo), Cmax,t1/2 ratios and tmax individual differences. The 90 percent for confidence interval (CI) of geometric mean SPE-712-L/ Rotram© individual percent ratio were 105.0-128,3 percent for AUC(0-72h), and 78.4-96.9 for Cmax. Although this 90 percent Cl were marginally outside the interval proposed by the Food and Drug Administration, the probability assessed by the two-one sided West for ratios was included in the 0.8-1.25 interval, as we concluded that SPE-712-L oral suspension formulation was bioequivalent to Rotram tablet formulation for the extent and rate of absorption.

Electrophysiological and ultrastructural analysis of the neuromuscular blockade and miotoxicity induced by the Micrurus nigrocinctus snake venom

Micrurus nigrocinctus is the most abundant coral snake in Central America. The venom of this specie induced a concentration-dependent (10-20 mug/ml) depolarization in the isolated mouse phrenic nerve-diaphragm preparations incubated ate 37 degree. D-Tubocurrarine (10 mug/ml) and alpha betaungarotoxin (3-5 mug/ml) were able to partially protect against the depolarization induced by the venom (10 mug/ml), suggesting the involvement of subsynaptic cholinergic receptors. This venom (10 mug/ml) also increased the frequency and amplitude of miniature end-plate potentials (mepps) during the first 10-20 min of incubation. Subsequently, the mepps progressively decreased and disappeared after 60 min. These responses were accompanied by ultrastructural changes involving the nerve terminals, the subsynaptic junctional folds and the muscle mitochondria. The synaptic gutter was shallow and, very often, "shrunken" terminal with omega-shaped axolemmal identations and a decreased number of synaptic vecicles were present. A common finding was the presence of numerous finger-like, membrane-bounded bodies interposed between the terminal and the Schwann cells or postsynaptic sarcolemma. The preincubation of the venom with specific antivenom or the incubation of the preparations at room temperature (24-26 degree) reduced the number and intensity of the ultrastructural alterations. The last finding suggests the involvement of a enzymatic process, probably a phospholipase A2, present in the venom. There was a good correlation between the electrophysiological and ultrastructural effects induced by the venom which allow us to conclude that M. nigrocinctus venom has a presynaptic action in the initial stages of intoxication followed by sub- and postsynaptic effects, the last being the most important cause of neuromuscular blockade. A direct action of the venom on muscle fibers may also contributes to the irreversible blockade.

Antinociceptive effects of calcium channel blockers in the rat

1. The effects of cinnarizine and nifedipine on the nociceptive threshold and opiate antinociception were e evaluated by the rat rail-flick test. 2. male Wistar rats (390-410 g) treated with intraperitoneal (ip) or intrathecal (it) cinnarizine, but not with it nifedipine, displayed a dose-dependent antinociception. The estimated AD50 values of cinnarizine were 3.55 microng/Kg (coeficience limits, 1.99 to 6.32) and 125.9 microng/Kg (46.1 to 343.7) for the it and ip routs of administration, respectively. The effect of it cinnarizine was reduced by subsequent it administration of calcium chloride (0.1 micron mol). 3. The it morphine-induced antinociception was potentiated by the previous it adminsitration of cinnarizine (1.0 micring/rat). The stimated AD50 if morphine was reduced from 10.4 (6.8 to 16.1) to 4.9 microng (3.6 to 6.5) by this dose of cinnarizine. The calculated potency ratio for these values was 2.14 (1.28 to 3.57). A similar potentiation was obtained with it nifedipine, but only when drug was injected in combination with morphine. 4. It is concluded that the antinociception evoked by a systemically injected calcium channel blocker is dependent on passage of the drug across the blood brain barrier to act, at least in part, at a spinal site of action. 5. The mechanism of the antinociception induced by it injected calcium channel blockers appears to depend on the interaction of the drugs with Ca2+ binding sites in the spinal cord and, probably, on the type of voltage-sensitive calcium channel involved

Train-of-four as an index of neuromuscular block in cats: changes induced by atropine

1. The present study reevaluates the effect of atropine on the rate of recovery from tetanic fade caused by intraarterial administration of neostigmine or antinicotinic agents in cat anterior tibial muscle preparations submitted to a train-of-four (TOF) pattern of nerve stimulation. The study also compares the sensitivity of the TOF and tetanic responses as indices of residual nondepolarizing block. 2. Neostigmoine, hexamethonium and d-tubocurarine all produced short-lived TOF fade. Both single and TOF twitches were increased by neostigmine and depressed by the antinicotinic agents. 3. Prior administration of atropine reduced the TOF fade induced by the antinicotinic drugs but potentiated that by anticholinesterase drugs. 4. These results indicate that TOF fade is not the most sensitive index for studyint neuromuscular blockade when drugs other than neuromuscular vlockers ara also present

Aminoglycoside antibiotics as a tool for the study of the biological role of calcium ions. Historical overview

Beginning with the pioneering work of Vital-Brazil and Corrado (1957), which suggested a possible interaction between aminoglycoside antibiotics (AGA) and calcium ions at the neuromuscular junction, the authors review the studies that demonstrated the existence of a competitive antagonism between AGA and calcium ions. In view of the low liposolubility of AGA and their inability to cross biological membranes, this antagonism seems to occur exclusively at calcium-binding sites at the level of the outer opening of calcium channels of the N-subtype, which are also the sites of interaction of omega-conotoxin. Being highly water soluble, AGA are easily removed from their binding sites with a consequent rapid reversal of their effects, a factor of primary importance to explain their wide use as tools in the pharmacological analysis of the study of the biological role of calcium ion on the membrane’s outer surface. This use has advantages over the use of inorganic di- and trivalent cations such as Mg2+, Mn2+, Cd2+, Ni2+, La3+, etc., since the latter, though they are considered to be the most specific competitive antagonists of calcium ions, may induce biphasic effects due to their ability to cross the membranes and replace calcium and/or increase intracellular calcium concentration. The performance of AGA is also superior when compared with the so-called [quot ]specific[quot ] organic calcium antagonists--verapamil and nifedipine derivatives--since the latter, in addition to inducing possible biphasic effects, antagonize calcium in a non-competitive manner. Finally, the authors remark that AGA-Ca2+ antagonism relevance is not limited only to basic aspects and that it may have therapeutic implications since it provides alternatives for reducing the toxic adverse effects of this important group of antibiotics.