Development and validation of an LC-MS/MS method for the determination of tigecycline in human plasma and cerebrospinal fluid and its application to a pharmacokinetic study.

Tigecycline (TGC) is an important antibiotic in treating various drug-resistant bacteria. The dosage regimen for cerebral intraventricular TGC is still unknown. The aim of the study was to develop and validate liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods for the determination of TGC in human plasma and cerebrospinal fluid (CSF) to obtain an applicable regimen. The ion transitions under ESI positive model were performed at m/z 586.3 > 513.2 and m/z 595.3 > 514.3 for TGC and d9-TGC internal standard (IS). For plasma and CSF samples, the calibration curve of TGC was linear within the ranges 25-2000 and 250-100,000 ng/mL; the IS normalized matrix effect was within the ranges 96.46-101.06% and 101.13-103.58%, respectively, for all. TGC was stable under all tested conditions. The patient received 1 mg intraventricular and 49 mg intravenous administration of TGC. The AUC0-12 in plasma and CSF calculated according to our noncompartment model were 4713 and 23,0238 h ng/mL, respectively. Given our findings cerebral intraventricular TGC may be a choice for clinicians to treat drug-resistant Gram-negative bacterial-induced meningitis and the safety and efficacy of this administration route warrants further study.

Chronic oral administration of minocycline to sheep with ovine CLN6 neuronal ceroid lipofuscinosis maintains pharmacological concentrations in the brain but does not suppress neuroinflammation or disease progression.

BACKGROUND: The neuronal ceroid lipofuscinoses (NCLs; or Batten disease) are fatal inherited human neurodegenerative diseases affecting an estimated 1:12,500 live births worldwide. They are caused by mutations in at least 11 different genes. Currently, there are no effective treatments. Progress into understanding pathogenesis and possible therapies depends on studying animal models. The most studied animals are the CLN6 South Hampshire sheep, in which the course of neuropathology closely follows that in affected children. Neurodegeneration, a hallmark of the disease, has been linked to neuroinflammation and is consequent to it. Activation of astrocytes and microglia begins prenatally, starting from specific foci associated with the later development of progressive cortical atrophy and the development of clinical symptoms, including the occipital cortex and blindness. Both neurodegeneration and neuroinflammation generalize and become more severe with increasing age and increasing clinical severity. The purpose of this study was to determine if chronic administration of an anti-inflammatory drug, minocycline, from an early age would halt or reverse the development of disease. METHOD: Minocycline, a tetracycline family antibiotic with activity against neuroinflammation, was tested by chronic oral administration of 25 mg minocycline/kg/day to presymptomatic lambs affected with CLN6 NCL at 3 months of age to 14 months of age, when clinical symptoms are obvious, to determine if this would suppress neuroinflammation or disease progression. RESULTS: Minocycline was absorbed without significant rumen biotransformation to maintain pharmacological concentrations of 1 µM in plasma and 400 nM in cerebrospinal fluid, but these did not result in inhibition of microglial activation or astrocytosis and did not change the neuronal loss or clinical course of the disease. CONCLUSION: Oral administration is an effective route for drug delivery to the central nervous system in large animals, and model studies in these animals should precede highly speculative procedures in humans. Minocycline does not inhibit a critical step in the neuroinflammatory cascade in this form of Batten disease. Identification of the critical steps in the neuroinflammatory cascade in neurodegenerative diseases, and targeting of specific drugs to them, will greatly increase the likelihood of success.

Results of a phase II placebo-controlled randomized trial of minocycline in acute spinal cord injury.

Preclinical studies have attributed neuroprotective properties to the antibiotic minocycline. Animal studies and early clinical trials support its use in several neurological diseases. In animal spinal cord injury models, minocycline improved neurological and histological outcomes, reduced neuronal and oligodendroglial apoptosis, decreased microglial activation and reduced inflammation. A single-centre, human, double-blind, randomized, placebo-controlled study of minocycline administration after spinal cord injury was undertaken for the purposes of dose optimization, safety assessment and to estimate outcome changes and variance. Neurological, functional, pharmacological and adverse event outcomes were compared between subjects administered 7 days of intravenous minocycline (n = 27) or placebo (n = 25) after acute traumatic spinal cord injury. The secondary outcome used to assess neurological differences between groups that may warrant further investigation was motor recovery over 1 year using the American Spinal Cord Injury Association examination. Recruitment and analyses were stratified by injury severity and injury location a priori given the expected influence of these on the sensitivity of the motor exam. Minocycline administered at higher than previously reported human doses produced steady-state concentrations of 12.7 µg/ml (95% confidence interval 11.6-13.8) in serum and 2.3 µg/ml (95% confidence interval 2.1-2.5) in cerebrospinal fluid, mimicking efficacious serum levels measured in animal studies. Transient elevation of serum liver enzymes in one patient was the only adverse event likely related to the study drug. Overall, patients treated with minocycline experienced six points greater motor recovery than those receiving placebo (95% confidence interval -3 to 14; P = 0.20, n = 44). No difference in recovery was observed for thoracic spinal cord injury (n = 16). A difference of 14 motor points that approached significance was observed in patients with cervical injury (95% confidence interval 0-28; P = 0.05, n = 25). Patients with cervical motor-incomplete injury may have experienced a larger difference (results not statistically significant, n = 9). Functional outcomes exhibited differences that lacked statistical significance but that may be suggestive of improvement in patients receiving the study drug. The minocycline regimen established in this study proved feasible, safe and was associated with a tendency towards improvement across several outcome measures. Although this study does not establish the efficacy of minocycline in spinal cord injury the findings are encouraging and warrant further investigation in a multi-centre phase III trial. ClinicalTrials.gov number NCT00559494.

Cerebral spinal fluid penetration of tigecycline in a patient with Acinetobacter baumannii cerebritis.

OBJECTIVE: To describe cerebral spinal fluid (CSF) penetration of tigecycline. CASE SUMMARY: A 38-year-old woman experienced a right internal carotid artery dissection and right anterior and middle cerebral artery strokes due to unknown causes and subsequently developed vasogenic edema requiring right hemi-craniectomy. Her postoperative course was complicated by multiple infections, and she developed multidrug, carbapenem-resistant Acinetobacter baumannii cerebritis. She was treated with a prolonged course of multiple antibiotics, including 18 days of therapy with tigecycline. Time-paired serum and CSF samples were obtained, and tigecycline concentrations were analyzed by high-performance liquid chromatography. We report serial, steady-state, serum, and CSF concentrations of tigecycline when administered in the Food and Drug Administration-approved dose of 50 mg every 12 hours. CSF concentrations remained relatively stable, suggesting that tigecycline did not accumulate in the CSF, at least in our patient. Tigecycline concentrations in the CSF were between 0.035 and 0.048 mg/L, while corresponding serum concentrations were 0.097-0.566 mg/L. The calculated tigecycline penetration ratio in this patient ranged from 0% to 52%, depending on the calculation methodology utilized. DISCUSSION: Concentrations, regardless of sample timing relative to dose, remained relatively stable in the CSF of our patient. The pharmacodynamic profile of tigecycline is not completely elucidated; however, it is presumed that the drug must be at the site of infection for efficacy. Our patient never obtained tigecycline concentrations in excess of the minimum inhibitory concentration for A. baumannii in either the serum or the CSF. CONCLUSIONS: Our patient experienced low CSF tigecycline concentrations and failed to achieve a clinical response while on therapy. CSF drug disposition of tigecycline requires further systematic study to fully elucidate the pharmacokinetic profile. Reduced CSF concentrations urge caution in the treatment of cerebritis with standard dosing of tigecycline.

Multiple neuroprotective mechanisms of minocycline in autoimmune CNS inflammation.

Axonal destruction and neuronal loss occur early during multiple sclerosis, an autoimmune inflammatory CNS disease that frequently manifests with acute optic neuritis. Available therapies mainly target the inflammatory component of the disease but fail to prevent neurodegeneration. To investigate the effect of minocycline on the survival of retinal ganglion cells (RGCs), the neurons that form the axons of the optic nerve, we used a rat model of myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis. Optic neuritis in this model was diagnosed by recording visual evoked potentials and RGC function was monitored by measuring electroretinograms. Functional and histopathological data of RGCs and optic nerves revealed neuronal and axonal protection when minocycline treatment was started on the day of immunization. Furthermore, we demonstrate that minocycline-induced neuroprotection is related to a direct antagonism of multiple mechanisms leading to neuronal cell death such as the induction of anti-apoptotic intracellular signalling pathways and a decrease in glutamate excitotoxicity. From these observations, we conclude that minocycline exerts neuroprotective effects independent of its anti-inflammatory properties. This hypothesis was confirmed in a non-inflammatory disease model leading to degeneration of RGCs, the surgical transection of the optic nerve.

Serum, tissue and body fluid concentrations of tigecycline after a single 100 mg dose.

OBJECTIVES: The purpose of this study was to determine the tissue and corresponding serum concentration of tigecycline at selected time points in gall bladder, bile, colon, bone, synovial fluid (SF), lung and CSF in subjects undergoing surgical or medical procedures. METHODS: One hundred and four adult subjects (aged 24-83 years; 64 women, 40 men) received a single intravenous (i.v.) dose of tigecycline (100 mg infused over 30 min). Subjects were randomly assigned to one of four collection times at 4, 8, 12 and 24 h after the start of the infusion. For CSF, samples were collected at approximately 1.5 and 24 h after the start of the infusion. All subjects had serum samples collected before the administration of tigecycline, at the end of the infusion and at the time corresponding to tissue or body fluid collection. Drug concentrations in serum, tissues and body fluids were determined by LC/MS/MS. The area under the mean concentration-time curve from 0 to 24 h (AUC(0-24)) was determined for the comparison of systemic exposure between tissue or body fluid to serum. RESULTS: The mean serum concentrations of tigecycline were similar to those previously published. Tissue penetration, expressed as the ratio of AUC(0-24) in tissue or body fluid to serum, was 537 for bile, 23 for gall bladder, 2.6 for colon, 2.0 for lung, 0.41 for bone, 0.31 for SF and 0.11 for CSF. CONCLUSIONS: A single 100 mg dose of intravenous tigecycline produced considerably higher tissue/fluid concentrations in bile, gall bladder, colon and lung compared with simultaneous serum concentrations. On average, the systemic exposure of tigecycline in bone, SF and CSF ranged from 11% to 41% of serum concentrations. The results in bone are inconsistent with previous radiolabelled studies in animals and it is unclear if tight binding to bone (versus low bone uptake) or poor extraction of tigecycline for LC/MS/MS detection or both may have contributed to the differences we observed in humans.

Optimal delivery of minocycline to the brain: implication for human studies of acute neuroprotection.

Minocycline is currently under development as a neuroprotective agent in many different brain diseases. In more than a dozen experimental investigations in various models of brain injury, high doses of minocycline have been administered intraperitoneally. This report details new concerns with this route of administration and makes a case for intravenous dosing in experimental animals, particularly for acute neuroprotection, to optimize delivery to the brain and facilitate translation to human studies.