Pharmacokinetics and penetration of linezolid into inflamed soft tissue in diabetic foot infections

Objective  Physiological changes and local and systemic inflammation may affect plasma and tissue pharmacokinetics of antimicrobial agents in diabetics. The aim of the study was to investigate the penetration of linezolid into inflamed areas of infected diabetic foot wounds and the pharmacokinetics in the risk population of diabetics. Methods  Pharmacokinetics and tissue penetration of linezolid into inflamed diabetic foot infection (DFI) tissue were determined at steady state in 15 patients with diabetes type 2 and DFI following administration of multiple oral doses of 600 mg given every 12 h. Second debridement was performed on days 4–6, 3 h after linezolid administration. Linezolid concentrations were determined in perinecrotic wound tissue of inflamed diabetic foot by high-performance liquid chromatography (HPLC). Results  A mean maximum plasma concentration (C_max) in plasma of 14.3 mg/L was attained at a median of 2.0 h [time to reach C_max (T_max) range 0.5–6.0 h). Area under the concentration time curve from zero to 12 h (AUC_0–12 h) with a mean of 114.1 mg∙h/L and C_min of 5.4 mg/L were achieved in patients with diabetes mellitus type 2. Penetration of linezolid into inflamed areas of DFI with tissue/plasma ratios of mean 101.7% [95% confidence interval (CI) 56; 148%] produced a mean concentration of 9.6 μg/g (95% CI 7.4; 11.8 μg/g) greater than those predicted to be effective against methicillin-resistant staphylococci [minimum concentration that inhibits 90% of organisms (MIC₉₀) of 4 mg/L]. Tissue/plasma ratios correlated positive with systemic inflammation. Conclusion  Plasma pharmacokinetics of linezolid in diabetics and adequate levels in inflamed areas of diabetic foot wound suggest that an oral dose of 600 mg bd of linezolid provides effective concentrations for treating methicillin-resistant Staphylococcus aureus (MRSA) in DFI. Presented in part at the 41th Annual Meeting of the European Association for Study of Diabetes, September 2005 in Athens, Greece, and at the 7th Annual Congress of the German Clinical Pharmacology, November 2005 in Dresden, Germany     

Selective inhibition of NS-398 on prostanoid production in inflamed tissue in rat carrageenan-air-pouch inflammation

Abstract— NS-398 (N-(2-cyclohexyloxy-4-nitrophenyl) methane sulphonamide), a newly synthesized potent non-steroidal antiinflammatory drug (NSAID) has a much lesser degree of toxicity, as compared with presently available NSAIDs. We have investigated the inhibition of prostanoid production in inflammatory exudate, gastric mucosa and renal papillary tissue, following oral administration to carrageenan-air-pouch rats. The ID50 values of NS-398 in the inflammatory exudate, gastric mucosa and renal papillary tissue were 0·18, 62·2 and 261·7 mg kg^?1, respectively. In contrast, indomethacin decreased the PGE₂ concentration in the inflammatory exudate, gastric mucosa and renal papillary tissue, with the same dose range, the ID50 values being 0·23, 0·14 and 0·15 mg kg^?1, respectively. The same tendency was seen for 6-keto-prostaglandin F₁ and thromboxane B₂. Moreover, NS-398 inhibited excess PGE₂ production in inflamed tissue but did not affect physiological production of PGE₂ in non-inflamed tissue. Indomethacin, in both inflamed and non-inflamed tissues, inhibited PGE₂ production to the same degree. These results indicated that NS-398 has some specificity for inflamed tissue, by inhibiting prostanoid synthesis, and this effect may explain the decreased side-effects of this drug.     

Contribution to the course of enzymatic processes in inflamed tissue of rat paw (author's transl)

With the method of gel filtration we found fraction in rat paw homogenates which was smaller in inflamed tissue than in normal tissue. Our data suggest a substrate degradation by inflammation. The enzymatic processes were also seen invivo and inhibited by sodium salicylate.     

Physico-chemical modification of lidocaine uptake in rat lung tissue.

The uptake of lidocaine, methyllidocaine, bupivacaine, etidocaine was studied in rat lung slices at different pH-values. The accumulation of the quaternary analogue, methyllidocaine, was not changed in the pH interval 7.0--8.0. The uptake of the three other substances was about 3--4 times lower at pH 7.0 than at pH 8.0. The rank order of distribution at a fixed cation/base ratio was bupivacaine greater than etidocaine greater than lidocaine. Interactions between lidocaine and other substances were studied in lung slices and in isolated perfused lungs. Bupivacaine and nortriptyline counteracted the accumulation of 14C-lidocaine in lung slices in a dose-dependent manner. Nortriptyline was more effective than bupivacaine. In isolated perfused lung, bolus injections of nortriptyline and lidocaine rapidly displaced 14C-lidocaine from the tissue. In this study we suggest that the base form of local anaesthetics accumulate in the lung tissue, while the cationic form binds to accessible binding sites in the cell membranes.     

Carbamazepine uptake into rat brain following intra-olfactory transport

Targeting the brain via nasal administration of drugs has been studied frequently over the last few years. In this study, a suitable gel formulation was designed to provide the absorption of a highly lipophilic drug through nasal mucosa. For this purpose, carbamazepine was chosen as the model drug. Hypromellose and Carbopol were used as mucoadhesive polymers in the formulation to increase the residence time of the gel on the mucosa. The objective of this study was to confirm the existence of a transport pathway for a drug (carbamazepine) to the brain directly from the nasal cavity, by comparing the concentration of drug in the brain after intranasal (i.n.), intravenous (i.v.), and oral (p.o.) administration. A statistically significant high level of the drug was found in the brain following intranasal administration compared with the intravenous and oral routes. These findings suggested the existence of a direct transport pathway for carbamazepine from the nasal cavity to the brain. This pathway may represent a new delivery route to the brain and central nervous system of such drugs which are needed in high and rapid concentration in the brain, especially in emergencies.     

Stereoselectivity of noradrenaline uptake into synaptic vesicles of the rat brain

Summary To investigate the stereoselectivity of the ATP-Mg²⁺-dependent uptake of noradrenaline, synaptic vesicles were isolated from the rat brain by differential centrifugation and incubated with ³H-(±)-, ³H-(–)- or ¹⁴C-(+)-noradrenaline in the absence and in the presence of ATP-Mg²⁺. The K _m values of the ATP-Mg²⁺-dependent uptake were found to be different for the two isomers (mol/l): ³H(±)-noradrenaline 14.9 ± 2.2 × 10^–1, ³H-(–)-noradrenaline 7.7 ± 0.5 × 10^–1, ¹⁴C-(+)-noradrenaline 17.3 ± 3.7 × 10^–1, whereas the V _maX of the racemate was identical with those of the two isomers (pmol/mg protein/min): ³H-(±)-noradrenaline 5.5 ± 0.4, ³H-(–)-noradrenaline 4.9 + 0.1, ¹⁴C-(+)-noradrenaline 5.1 ± 0.4. Moreover, (+)-noradrenaline inhibited competitively the ATP-Mg²⁺-dependent uptake of ³H-(±)-noradrenaline (K_i 19.2 + 1.0 × 10^–1 mol/l) and ³H-(–)-noradrenaline (Ki 17.7 ± 1.8 × 10^–1 mol/l), the K_i values being nearly identical with the K _m of the ATP-Mg²⁺-dependent uptake of ¹⁴C-(+)-noradrenaline. It is concluded that the ATP-Mg²⁺-dependent uptake of noradrenaline into synaptic vesicles of the rat brain is stereoselective and that both isomers share the same transport system.The experiments were carried out at the Institut für Pharmakologie and Toxikologie der Universitat Würzburg, FRG. This work was supported by the Deutsche Forschungsgemeinschaft Send offprint requests to A. Philippu at the above address     

Norepinephrine uptake by hypothalamic tissue from the rat related to feeding.

Norepinephrine (NE) uptake by rat hypothalamus in vitro was studied in relation to food intake. Significant daily variations in NE uptake were observed in caudal hypothalamus from freely feeding rats. A maximal elevation occurred at the beginning of the night when food intake is also increasing to a maximum. NE uptake by caudal hypothalamus from relatively hungry rats previously adjusted to restricted feeding during the daytime was enhanced in afternoon and evening when compared with uptake by tissue from ad lib feeding animals. Determination of NE uptake by caudal hypothalamus from freely feeding individual rats and registration of individual meals taken by these rats revealed a relation between hypothalamic neuronal activity and the feeding pattern of the rat. A positive correlation was observed between NE uptake in vitro and feeding rate during a 2- to 4-hr interval. It also appeared that NE uptake by caudal hypothalamus is dependent on the time elapsed after the last meal. The data were evaluated in view of physiological studies concerning the onset of feeding and the hypothesis of hypothalamic adrenergic control of food intake.     

Effect of ethanol on adrenaline-stimulated glucose uptake in rat white adipose tissue

The effect of ethanol on adrenaline-stimulated glucose uptake by rat white adipose tissue has been examined in vitro. Ethanol (3%) inhibited the stimulatory effect of adrenaline on glucose uptake whereas it failed to inhibit the effect of adrenaline on free fatty acid production. Addition of calcium (12·5mM) to the incubation medium restored adrenaline's effect on glucose uptake. Addition of propranolol also restored the effect of adrenaline inhibited by ethanol. Ethanol did not inhibit insulin-stimulated glucose uptake. These results suggest that ethanol modifies the coupling of the adrenoceptor to the glucose transport system in adipose tissue that is stimulated by adrenaline.     

Pain-relieving action of voltaren and methindole determined in inflamed tissue

As measured on an inflamed rat paw, voltaren raised the pain sensitivity threshold 4-5-fold, whereas on a non-inflamed paw, 2-2.5-fold. The effect seen was dose-dependent. Methindole yielded to voltaren as regards analgetic action determined on inflamed tissues. The method of mechanical irritation of inflamed tissues modified by the authors provides more complete information on analgetic action of non-steroidal anti-inflammatory agents as compared to other methods.     

Evidence for the presence of histamine uptake into the synaptosomes of rat brain

Histamine has many physiological roles in the brain and periphery. Neuronal histamine is metabolized almost exclusively by histamine N-methyltransferase. Although several neurotransmitter systems such as dopamine and 5-hydroxytryptamine have their specific reuptake system in their neurons and glial cells, a specific histamine reuptake system into the corresponding nerve terminals or glial cells has not yet been clearly elucidated. We characterized the uptake of histamine into the P2 fractions of rat brain homogenized in 0.32 mol/l sucrose using in vitro uptake techniques. [3H]histamine uptake increased with the increment of added protein amount and elapsed time. [3H]histamine uptake was also temperature-dependent. The uptake of [3H]histamine into the P2 fractions occurs by two saturable processes, a high-affinity and a low-affinity, characterized by K(m) values of 0.16 and 1.2 micromol/l, respectively. Na(+), Cl(-) and HCO(3)(-) ions were essential for the uptake of histamine in P2 fractions. [3H]histamine uptake was inhibited in the presence of several tricyclic antidepressants. In accordance with this, the endogenous release of histamine from brain slices evoked by 100 mmol/l K(+) was augmented in the presence of 20 micromol/l imipramine. These results further support the existence of a specific histamine uptake system in the brain, although the precise molecular entities have not been identified until now.     

Stimulation of the hypothalamo-pituitary-adrenal axis by compounds formed in inflamed tissue.

1 Rat paws were injected with carrageenin, and their subcutaneous tissue perfused 135 min later. These perfusates were injected intravenously into receptor rats in which they caused an attenuation of inflammatory responses. 2 The effect was not observed in adrenalectomized receptor rats nor in receptors with electrolytic lesions in the median eminence of the hypothalamus but persisted in adrenal-demedullated animals. 3 The active perfusates also induced eosinopenia in normal or adrenal-demedullated animals, but not in adrenalectomized rats, and produced an increase in blood corticosterone with a concomitant decrease in the amounts of adrenal ascorbic acid. 4 The active perfusates did not affect the responses of isolated preparations to histamine, bradykinin, prostaglandins and 5-hydroxytryptamine neither did they elicit changes of the arterial blood pressure in receptor animals. 5 The anti-inflammatory activity present in perfusates from inflamed paws seems to be formed slowly at the site of the developing inflammatory reaction, since perfusates collected 30-65 min after the injection of carrageenin were ineffective, as was plasma taken from donor rats at various time intervals after carrageenin injections. 6 It is suggested that the anti-inflammatory factor present in the active perfusates exerts its action by stimulation of the hypothalamo-pituitary-adrenal axis.     

Cholestatic steroid hormones inhibit taurocholate uptake into isolated rat hepatocytes

The effect of three cholestatic steroids (norethandrolone, 17-β-estradiol and progesterone) on hepatocellular uptake and secretion of taurocholate was studied in isolated rat liver cells. The steroids decreased the rate of taurocholate uptake. Norethandrolone inhibited uptake noncompetitively with a K_i of 18 μM, but had no effect on the activation energy of uptake. 17-β-estradiol and progesterone reduced taurocholate uptake by 50 per cent at concentrations between 40 μM and 50 μM. The secretion of taurocholate from taurocholate-loaded cells was slightly increased by all three steroids at concentrations below 100 μM. A 60 per cent inhibition of secretion was observed in the presence of 500μM norethandrolone. Interference of cholestatic steroids with hepatocellular bile acid uptake may be an important step in the pathogenesis of intrahepatic cholestasis.     

Brain uptake, pharmacokinetics, and tissue distribution in the rat of neurotoxic N-butylbenzenesulfonamide.

The pharmacokinetics, cerebrovascular permeability, and tissue distribution of the neurotoxic plasticizer N-butylbenzenesulfonamide (NBBS) were determined in rats. A stable isotope-labeled form ([(13)C(6)]NBBS) was used to circumvent ubiquitous contamination that was evident whenever the native form was measured. Plasticizer decline in plasma, following an iv dose of 1 mg/kg, was described by a triexponential decay function. NBBS was cleared from plasma at a rate of 25 ml/min/kg, and 24 h after administration, plasma concentrations represented 0.04% of the administered dose. These data suggest rapid elimination and uptake into tissue; however, NBBS was not accumulated by any of the tissues studied (i.e., liver, kidney, muscle, adipose tissue, and brain). Given the critical interest in NBBS neurotoxicity, the brain uptake of [(13)C(6)]NBBS was further explored in experiments using the in situ brain perfusion technique. During perfusion with protein-free saline for 15-30 s, the single-pass brain extraction for free [(13)C(6)]NBBS was very high (73-100%) with a unidirectional blood-brain barrier transfer constant (K(in)) of > 0.08 ml/s/g. No significant differences were found in [(13)C(6)]NBBS content among the measured brain regions. Plasma protein binding (70%) only slightly lowered the single-pass brain extraction to 48%. In summary, the results demonstrate that NBBS distributes rapidly to tissues, including brain. Though highly lipophilic with a Log octanol/water partition coefficient of 2.17 +/- 0.09, brain:blood ratios (2:1) for NBBS were consistent throughout the experimental duration, with little indication of accumulation.     

Amitriptyline enhances extracellular tissue levels of adenosine in the rat hindpaw and inhibits adenosine uptake

Local administration of amitriptyline into the rat hindpaw produces peripheral antinociception; this is reduced by adenosine receptor antagonists and appears to involve endogenous adenosine. The present study used peripheral microdialysis: (a) to determine whether amitriptyline could enhance extracellular tissue levels of endogenous adenosine in the rat hindpaw and (b) to examine mechanisms by which such an increase could occur. Local injection of amitriptyline into the plantar hindpaw, at doses that produce peripheral antinociception (100-300 nmol), produced an increase in local extracellular levels of adenosine. When injected in combination with formalin, which also enhances such levels of adenosine, an additive increase was observed. This adenosine originated partly as nucleotide, as inhibition of ecto-5'-nucleotidase reduced the amount of adenosine detected in the probe following administration of amitriptyline. When administered in combination with exogenous adenosine, amitriptyline augmented recovery of adenosine in the probe. Pretreatment of rats with capsaicin augmented the ability of amitriptyline to increase adenosine levels detected in the dialysis probe; it also enhanced tissue recovery of exogenously administered adenosine. In uptake studies using cultured rat C6 glioma cells, amitriptyline inhibited adenosine uptake by an adenosine transporter (IC50 0.37 +/- 0.12 mM). In enzyme assays, amitriptyline had no effect on adenosine kinase or adenosine deaminase activity. These results demonstrate that amitriptyline: (a) enhances extracellular tissue levels of adenosine in the rat hindpaw following local administration in vivo and (b) inhibits adenosine uptake but has no effect on metabolism in vitro. Therefore, increased extracellular adenosine levels in vivo appear to result partially from extracellular conversion of nucleotide and partially from inhibition of uptake.     

Effect of ethanol on adrenaline-stimulated glucose uptake in rat white adipose tissue.

The effect of ethanol on adrenaline-stimulated glucose uptake by rat white adipose tissue has been examined in vitro. Ethanol (3%) inhibited the stimulatory effect of adrenaline on glucose uptake whereas it failed to inhibit the effect of adrenaline on free fatty acid production. Addition of calcium (12.5 mM) to the incubation medium restored adrenaline's effect on glucose uptake. Addition of propranolol also restored the effect of adrenaline inhibited by ethanol. Ethanol did not inhibit insulin-stimulated glucose uptake. These results suggest that ethanol modifies the coupling of the adrenoceptor to the glucose transport system in adipose tissue that is stimulated by adrenaline.