Monitoring tissue drug levels by microdialysis

Monitoring tissue drug levels by microdialysis
Presentation lecture from: Universitätsklinik für Klinische Pharmakologie
Conventional Assumption
“Blood / Target equilibrium can be taken for granted”
Drug distribution can solely be explained by laws of diffusion

Active Transporters

Distribution is not always driven by instantaneous diffusion
Equilibrium at steady state (but delayed)
* capillary density and blood flow (Krogh cylinder)
* capillary permeability

Inequilibrium at steady state
* active transporters (e.g. P-GP)
* pH - partition
* Gibbs-Donnan inequilibrium
* filtration gradient (may decrease/reverse)
* Starling laws (oncotic pressure)
* elimination by lymph vessels

Conventional Assumption

“Tissue is a homogenous matrix”
The misleading partition coefficient / Binding issues
Interstitium
Capillary
Cell
Regulatory View
“Distribution studies should be done”
Critical Path
2003 CDER Report to the Nation

We continue ... to extend our long-standing interest in the application of dose-response principles by viewing drugs and their actions directly at the level of the drug target, rather than indirectly via plasma concentrations

Insertion of a microdialysis probe

Probe
Guide cannula
Interstitium
Capillary
Cell
Perfusate
Dialysate
Interstitial concentration in vivo (PK)
Concentration in culture in vitro (PD)
PK in Drug Resistant Tumors
Future Concepts
* Biomarkers in tissues
* Topical BE
* Dose finding (PK / PD)
* “Critical Path”
* Preclinical screening (CNS)

Where are my keys?
PET scanner
GE Advance
Siemens µPET Focus 220


Conclusions

* µD is a safe, reproducible, ethically acceptable and realtively inexpensive technique for studying tissue distribution in humans
* µD is a well established technology with standard clinical applications
* Most organs can be studied today in appropriate clinical situation
* Regulatory documents indicate a rationale for µD
* µD affects decision making in clinical R&D and routine practice

Monitoring tissue drug levels by microdialysis.ppt

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Microdialysis

Microdialysis
Presentation by:Steve Milway

Microdialysis A technique used to study the biochemical activity in the extracellular space.

Micro : refers to the extremely small scale.
Dialysis: the movement of chemicals across a permeable membrane.
Microdialysis allows us to monitor chemical changes in a behaving animal Most commonly, a concentric microdialysis probe is used. Usually the fluid flows in the opposite direction to the arrows in the diagram, but it doesn’t really matter as long as the fluid flows by the membrane.

A microdialysis probe is similar in size to a bipolar stimulating electrode.
It can therefore be implanted stereotaxically for both Acute and Chronic experiments.
The fluid circulating through the dialysis probe is artificial cerebrospinal fluid (ACSF). ACSF is very similar to the CSF in the extracellular space so a negligible amount of ACSF or CSF will cross the membrane. There is thus very little tissue damage or trauma.
Soluble molecules will cross the membrane down their concentration gradient.
Molecules can cross in either direction. A dialysis probe can be used to deliver chemicals to the brain. If a higher concentration of the chemical of interest is in the probe, it will tend to cross the membrane and enter the extracellular space.
This application is often called Retrodialysis.


Calibration

The recovery capabilities of probes vary. Before a microdialysis probe can be used, it must be calibrated. This is done in vitro by testing the probe with a known concentration of the molecule of interest in ACSF.
The recovery in brain will not be as efficient as the recovery in vitro.
Once the probe has been calibrated it can be used.
Before samples are collected, ACSF is run through the probe for approx. 20 minutes to allow the probe to equilibrate.

Factors influencing the dialysis rate
* Surface area of dialysis membrane.
* Magnitude of concentration gradient.
* Rate of flow through the probe.
* Type of dialysis membrane. Different membranes have different pore sizes
* The size of the molecule.

Applications

* Temporal characteristics of a drug crossing the BBB.
* Release of neurotransmitters during behaviour.
* Activation of brain areas by various agonists (Retrodialysis)
* Activation of one brain area with one probe. Recording neurotransmitter release from another area with a second probe.
* Mixed use? Using a probe to both deliver and sample.

Pitfalls

* Although microdialysis provides the sample, you still need a suitable method to analyze the sample.
* Some methods require only microlitres of solution while others might require millilitres. Temporal resolution will be limited. If it takes 10 minutes to collect a sample, that is the temporal resolution.
* Some areas of interest are too small for the probe.

Microdialysis.ppt
Microdialysis lecture

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Evaluation of Laboratory Data in Nutrition Assessment

Evaluation of Laboratory Data in Nutrition Assessment
Presentation lecture by:Cinda S. Chima, MS, RD

Laboratory Data and the NCP

* Used in nutrition assessment (a clinical sign supporting nutrition diagnosis)
* Used in Monitoring and Evaluation of the patient response to nutritional intervention

Specimen Types

* Serum: the fluid from blood after blood cells and clot removed
* Plasma: fluid from blood centrifuged with anticoagulants
* Erythrocytes: red blood cells
* Leukocytes: white blood cells
* Other tissues: scrapings and biopsy samples
* Urine: random samples or timed collections
* Feces: random samples or timed collections
* Less common: saliva, nails, hair, sweat

Interpretation of Routine Medical Laboratory Tests

* Clinical Chemistry Panels
o Basic metabolic panel
o Comprehensive metabolic panel
* Complete blood count
* Urinalysis
* Hydration status

Clinical Chemistry Panels: Basic Metabolic Panel (BMP)

o Electrolytes: Na+, K+, Cl-, HCO3 or total CO2
o Glucose
o Creatinine
o BUN

Basic Metabolic Panel Charting Shorthand
Clinical Chemistry Panels: Comprehensive Metabolic Panel Includes
* BMP except CO2
* Albumin
* Serum enzymes (alkaline phosphatase, AST [SGOT], ALT [SGPT]
* Total bilirubin
* Total calcium
Phosphorus, total cholesterol and triglycerides often ordered with the CMP
Complete Blood Count (CBC)
* Red blood cells
* Hemoglobin concentration
* Hematocrit
* Mean cell volume (MCV)
* Mean cell hemoglobin (MCH)
* Mean cell hemoglobin concentration (MCHC)
* White blood cell count (WBC)
* Differential: indicates percentages of different kinds of WBC

Clinical Chemistry Panels: Urinalysis
Types of Assays

* Static assays: measures the actual level of the nutrient in the specimen (serum iron, white blood cell ascorbic acid)
* Functional Assays: measure a biochemical or physiological activity that depends on the nutrient of interest (serum ferritin, TIBC)
o (Functional assays are not always specific to the nutrient)
Assessment of Nutrient Pool
Assessment of Hydration Status

* Dehydration: a state of negative fluid balance caused by decreased intake, increased losses, or fluid shifts
* Overhydration or edema: increase in extracellular fluid volume; fluid shifts from extracellular compartment to interstitial tissues
o Caused by increase in capillary hydrostatic pressure or permeability
o Decrease in colloid osmotic pressure
o Physical inactivity
* Use laboratory and clinical data to evaluate pt
Hypovolemia
Symptoms of Hypovolemia
* Orthostatic Hypotension (caused by change in position)
* Central venous and pulmonary pressures 
* Increased heart rate
* Rapid weight loss
* Decreased urinary output
* Patient cool, clammy
* Decreased cardiac output
* Ask the medical team!!
Treatment of Hypovolemia

* Replace lost fluids with fluids of similar concentration
* Restores blood volume and blood pressure
* Usually isotonic fluid like normal saline or lactated Ringer’s solution given IV
* Excess of isotonic fluid (water and sodium) in the extracellular compartment
* Osmolality is usually not affected since fluid and solutes are gained in equal proportion

Causes of Hypervolemia

* Results from retention or excessive intake of fluid or sodium or shift in fluid from interstitial space into the intravascular space
* Fluid retention: renal failure, CHF, cirrhosis of the liver, corticosteroid therapy, hyperaldosteronism
* Excessive intake: IV replacement tx using normal saline or Lactated Ringer’s, blood or plasma replacement, excessive salt intake
* Fluid shifts into vasculature caused by remobilization of fluids after burn tx, administration of hypertonic fluids, use of colloid oncotic fluids such as albumin

Symptoms of Hypervolemia

* No single diagnostic test, so signs and symptoms are key
* Cardiac output increases
* Pulse rapid and bounding
* BP, CVP, PAP and pulmonary artery wedge pressure rise
* As the heart fails, BP and cardiac output drop
* Distended veins in hands and neck
* Anasarca: severe, generalized edema
* Pitting edema: leaves depression in skin when touched
* Pulmonary edema: crackles on auscultation
* Patient SOB and tachypneic
* Labs: low hematocrit, normal serum sodium, lower K+ and BUN (or if high, may mean renal failure)
* ABG: low O2 level, PaCO2 may be low, causing drop in pH and respiratory alkalosis

Treatment of Hypervolemia

* Restriction of sodium and fluid intake
* Diuretics to promote fluid loss; morphine and nitroglycerine to relieve air hunger and dilate blood vessels; digoxin to strengthen heart
* Hemodialysis or CAVH

Dehydration

* Excessive loss of free water
* Loss of fluids causes an increase in the concentration of solutes in the blood (increased osmolality)
* Water shifts out of the cells into the blood
* Causes: prolonged fever, watery diarrhea, failure to respond to thirst, highly concentrated feedings, including TF

Symptoms of Dehydration

* Thirst
* Fever
* Dry skin and mucus membranes, poor skin turgor, sunken eyeballs
* Decreased urine output
* Increased heart rate with falling blood pressure
* Elevated serum osmolality; elevated serum sodium; high urine specific gravity

Treatment of Dehydration

* Use hypotonic IV solutions such as D5W
* Offer oral fluids
* Rehydrate gradually

Laboratory Values and Hydration: BUN
Laboratory Values and Hydration Status: BUN:Creatinine Ratio
Laboratory Values and Hydration: HCT
Laboratory Values and Hydration: Alb, Na+
Other factors influencing result
Hyper-volemia
Laboratory Values and Hydration Status
Serum albumin
Other factors influencing result
Hypokalemia (K+< 3.5 mEq/L)
Serum Calcium
Hypocalcemia (serum calcium <9.0 mg/dL; ionized Ca+ <4.5 mg/dL)
Serum Phosphorus (normal 3.0-4.5 mg/dL)
Hypophosphatemia (<3.0 mg/dL)
Hyperphosphatemia (>4.5 mg/dL)
Hypomagnesemia <1.3 mEq/L (normal 1.3-2.1 mEq/L)
Hypermagnesemia (>2.1 mEq/L)
Assessment for Protein-Calorie Malnutrition
Hormonal and Cell-Mediated Response to Inflammatory Stress
Nitrogen Balance Studies
Nitrogen Balance Calculations
Nitrogen Balance Challenges
Visceral Proteins: Serum Albumin
Plasma Transferrin
Transthyretin (Prealbumin)
Retinol-Binding Protein
C-Reactive Protein
Inflammation
Urinary Creatinine
Markers of Malabsorption
Lipid Indices of Cardiovascular Risk
Nutrition Diagnoses and Laboratory Indices
Examples of Nutrition Diagnostic Statements Related to Lab Values

Evaluation of Laboratory Data in Nutrition Assessment.ppt

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