PK/PD

In vitro toxicology is the study of the effects of chemicals and drugs on cultured bacteria or mammalian cells. Drug effect can be both time and concentration dependent and these parameters can be species specific. In the case of antibiotic development, there have not been effective tools for examining the effects of both time and concentration in an in vitro model, mimicking human kinetics. The emergence of drug resistant strains of pathogenic bacteria mandates that new tools be available for the study of antibiotics. The use of hollow fiber bioreactor cartridges for these assays represents an important advancement in the fields of pharmacokinetics, pharmacodynamics and in vitro toxicology.

(Figure 1)  Cross section of a hollow fiber cartridge. The test organism is retained in the small volume outside the fiber while nutrient broth and drug circulate through the insides of the fiber. Small molecules such as drugs can freely cross the fiber along with nutrients and waste products, while bacteria and cells cannot cross the fiber.

Figure 1: Cross section of a hollow fiber cartridge. The test organism is retained in the small volume outside the fiber while nutrient broth and drug circulate through the insides of the fiber. Small molecules such as drugs can freely cross the fiber along with nutrients and waste products, while bacteria and cells cannot cross the fiber.

IMAG2030-pkpdCurrent assays for the determination of antibiotic efficacy are also not able to examine the potential for the development of resistance since antibiotic resistance develops over time.  A dynamic model controlling drug concentration over time precisely mimicking human pk/pd would bridge the gap between static assays, animal models and clinical trials.  A time related assay capable of examining the effects of antibiotic pharmacokinetics on a population of organisms large enough to reveal the emergence of resistance is also required.

IMAG2029-pkpdThe design of the two compartment model is quite similar to the one compartment model except that the organism to be tested is confined within the ECS, physically separated from the central reservoir by the semi-permeable membrane.  The concentration of the drug in the central reservoir equilibrates rapidly with the medium in the ECS containing the organisms.  The volume of the central reservoir can be adjusted to permit rapid changes in drug concentration. Hollow fiber cartridges offer the advantages of having an extremely high surface area to volume ratio, in excess of 150 cm2 per milliliter of volume, providing rapid and uniform distribution of the drug within the ECS. Several different types of hollow fiber polymers are commercially available to allow for compatibility with drugs of different chemistries.

 

IMAG1384

The animation BELOW shows the hollow fiber two compartment model. Test organisms are retained in the hollow fiber cartridge. The central reservoir is continuously re-circulating the nutrient broth. Drug is added to the central reservoir and the elimination kinetics are controlled by the addition of diluent to the central reservoir. The volume in the central reservoir is kept constant.

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ordway set up 1The advantages of the two-compartment hollow fiber system are numerous.  The target bacteria are contained within a very small volume, 10-20 mls, so they are at a similar concentration to in vivo infections and the drug can equilibrate rapidly within the compartment.  Representative samples can be taken easily without significantly affecting the bacteria population.  Drug resistant, highly pathogenic and highly biohazardous organisms are safely contained in a sealed environment. Large numbers of organisms can be tested in one experiment so the emergence of drug resistance is easily quantified.  Both absorption and elimination kinetics of the drug being testing can be precisely and independently controlled. The kinetics of multiple drugs can also be controlled so drug/drug interactions and combination therapies can readily be examined. The system is compact enough that multiple cartridges can be conveniently manipulated in a relatively small space.

Advantages of Hollow Fiber vs. Static Methods

  • Dosage profiles can be controlled over time
  • Mechanisms of resistance can be revealed
  • Data is more clinically relevant.

Advantages of Hollow Fiber vs. the One Compartment Model

  • Bacterial load remains constant
  • Biohazardous organisms safely contained
  • Both absorption and elimination curves can be modeled.
  • Rapid half lifes can be modeled.

Advantages of Hollow Fiber vs. Animal Models

  • High bacterial and viral loads can be tested, dosage profiles that result in resistance will more likely be revealed.
  • Absorption, excretion and metabolic profiles can be more closely modeled on the human half-life.
  • Not all animals can be infected with the organism of interest.
  • Extreme doses can be modeled
  • Combination therapies can be easily controlled and tested
  • No animal testing protocols, restrictions.
  • Less expensive
  • Closed, bio-safe system for pathogens
  • Easier to test multiple pathogens with the same drug
  • Larger N per experiment (cartridges in series)
  • Bacteria, viruses, cancer and parasites can be tested.
  • Dosage and metabolic profiles can be more precisely controlled.
(Figure 6, ABOVE) Typical laboratory set up of the hollow fiber two compartment model. The large volumes of diluent and the waste reservoirs are kept outside the incubator. Micro-processor controlled peristaltic pumps add and remove the diluent from the central reservoir inside the incubator. Sampling is performed via the side ports on the hollow fiber cartridge.

Figure 5: Typical laboratory set up of the hollow fiber two compartment model. The large volumes of diluent and the waste reservoirs are kept outside the incubator. Micro-processor controlled peristaltic pumps add and remove the diluent from the central reservoir inside the incubator. Sampling is performed via the side ports on the hollow fiber cartridge.

Hollow fiber technology offers higher levels of reproducible control of both concentration and time of drug exposure in complex growth, infection, treatment, and sampling regimens.  This system permits more realistic simulation of in vivo drug effects in a dynamically controlled system providing data that more accurately reflects biological responses. They are fully disposable and provide a biosafe environment for the potential testing of drug resistant, weaponized, or genetically modified organisms. The two-compartment model can be a cost effective supplement to the evaluation of clinical efficacy both for existing antibiotics and in the development process for new antibiotics as part of the submission process for FDA approval.

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Figure 6: Two-drug model with different half-lives.

Suggested Ordering for PK/PD

Bioreactor

P3202 The FiberCell® Systems Duet more info

Cartridges

Catalog No. Size Surface Area Fiber Type Packing Density ECS Vol MWCO 50% Max. Cell#
C2011 Medium 3000 cm2 high flux PS 50% 15 ml 20 kd 109 more info
C3008 Medium 2000 cm2 Cellulosic 38% 12 ml 5 kd 109 more info

Reservoir Caps

A1006 38 mm Reservoir Cap more info

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