respiratory safety pharmacology ptsm2.pptx

describe about screening models for respiratory safety pharmacology.

1. Respiratory Safety Pharmacology Praveen Kumar. S M.Pharm 2nd semester. Department of pharmacology. PSG College of pharmacy . 1

2. Safety pharmacology Safety pharmacology studies that investigate the potential undesirable pharmacodynamic effects of a substance on physiological function in relation to exposure in therapeutic range and above. Primary organ system (s o Called core battery system),Tier-1 Central nervous system. Cardiovascular system. Respiratory system. Secondary organ system (Tier-2) Gastro intestinal tract Renal 2

3. Respiratory system The respiratory system contributes to homeostasis by providing for the exchange of gases—oxygen and carbon dioxide—between the atmospheric air, blood, and tissue cells. It also helps adjust the pH of body fluids. Image source:pin interest.com 3

4. Respiratory function assay General approach The objectives of a safety pharmacology study of the respiratory system are to determine whether a drug has the potential to produce a change in respiratory function and to establish whether this change is a liability. Such changes can result from either the primary or secondary pharmacological properties of a drug or from organ dysfunction resulting from the toxicological properties of a drug. The respiratory system consists of two functional units, The pumping apparatus The gas exchangeunit. 4

5. Pumping apparatus The function of the pumping apparatus is to ensure the appropriate movement of gases between the environment and the central airways, which is evaluated bymeasuring ventilatory patterns. Ventilatory parameters include , Measures of respiratory rate Tidal volume, and Minute volume, since normal ventilation requires that the pumping apparatus provide both adequate total pulmonary ventilation (minute volume) and the appropriate depth (tidal volume) and frequency (rate) of breathing. If a change in these parameters occurs, inspiratory flow (mean or peak), expiratory flow (mean or peak), fractional inspiratory time(inspiratory time/total breath time), and time between breaths (expiratory pause or apnea). 5

6. 6

7. Gas exchange unit The function of the gas exchange unit is to ensure that gas which enters the airways from the environment reaches the alveoli during inspiration and is removed from the alveoli during expiration. The function of the gas exchange unit is evaluated by measuring the mechanical properties of the lung. This is most effectively accomplished in conscious animals by obtaining dynamic measurements of Airway resistance or conductance (to assess airway patency) and Lung compliance (to assess elastic recoil). Airway resistance (measured as total pulmonary resistance) defines the change in pleural, airway, or transpulmonary pressure (DP) required to produce a defined change in lung airflow (DF) and is calculated as DP/DF 7

8. 8

9. Another method for assessing airway resistance involves measuring the excursions of the thorax and abdomen during breathing. During normal breathing, the thorax and abdomen move in synchrony during both inspiration and expiration. A shift from this synchronous movement to asynchronous movement can be quantified as a phase angle shift. Such phase angle shifts have been used as indexes of airway resistance. Dynamic compliance is calculated by measuring the differences in airway or transpulmonary pressure (DP) and volume (DV) that occur at the beginning and end of each inspiration (i.e at zero flow points) 9

10. Procedures for ventilatory function Ventilatory patterns: Respiratory rate and Tidal volume. Plethysmograph chambers Head out or head enclosed volume displacement champers 2.Champer pressure changes = Lung airflow = Tidal volume and breathing rate Facemask with pneumotachmeter Differential pressure change=Mouth airflow= Tidal volume and breathing rate Inductance strap or impedence electrodes. Thoracic and abdominal movement= lung airflow=Tidal volume and breathing rate. 10

11. Procedures for Lung Function Airway Resistance & Lung Compliance • Dynamic Measurements • Spontaneously breathingVentilated Dynamic Restrained Models • Head-out or head-enclosed plethysmograph chambers, • facemask with pneumotachometer • Lung airflow & volumepressure sensitive catheter. • Pleural pressure( esophageal, pleural or subpleural spaceDynamic non-restrained Models • Inductance straps or impedance sensors + pleural pressureStatic Anesthetized/Paralyzed Model 11

12. Respiratory function in conscious Rats🐁 Purpose The rat is considered an appropriate species for general use in safety pharmacology studies of the respiratory system. The physiology of the respiratory system has been well characterized in this species and much of the information on drug-induced effects on ventilatory control and mechanisms of airway disease have been obtained in the rat. Selecting a species that is used in toxicology studies provides additional supportive information including (1) pharmacokinetic data that can be used to define the test measurement intervals, (2) acute toxicity data that can toxicology to select the appropriate high dose, and (3) toxicology/ pathology findings that can be used to help define the mechanism of the functional changes measured in safety pharmacology studies 12

13. Procedure To provide a direct measure of ventilatory parameters, a head-out plethysmograph chamber is used, while measurement of pleural pressure is used to provide a direct measure of airway resistance Pleural pressure measurement Catheter placement. Surgical procedure. 13

14. Catheter placement Pleural pressure is measured chronically in conscious rats by surgically implanting a fluid-filled polyurethane catheter (length ¼ 10 cm; O.D. ¼ 0.7cm) attached to a pressure-sensitive radiotelemetry transmitter. Beneath the serosal layer of the esophagus and within the thoracic cavity 14

15. Surgical procedure Surgery is initiated by anesthetizing the rat with isoflurane (2–3%) delivered by inhalation in 100% oxygen. The surgical area is prepared by shaving the abdomen with surgical clippers and scrubbing with a Betadine and 70% ethanol wash. Once the area has been prepared, an abdominal incision (approximately 4–5 cm in length) is made along the linea alba. Lobes gently packed against the abdominal wall using moist 2 × 2 in. Versalon (or equivalent) squares. The esophagus is isolated approximately 2 cm below the Hiatus oesphagicus (junction with the diaphragm), a 22-gauge needle (1 in. in length with an approximate 90 bend) is inserted into the esophagus between the serosa and muscularis layers, This will generally Lead to encapsulation of the catheter tip and resultA loss or dampening of the pressure signal. 15

16. Cont.. Once the needle is advanced to a point approximately 1 cm beyond the diaphragm junction, the needle is removed and the catheter from the telemetry transmitter During this step, care must be taken not to apply pressure to the catheter for risk of damaging the fluid-filled catheter and telemetry unit. A pair of vessel cannulation forceps can be used to successfully advance the catheter without damaging the unit. Pleural pressure should be monitored during these procedures to ensure an optimal signal is obtained. Pleural pressures during isoflurane induced anesthesia should be between approximately 8 and 20 cm H2O. The signal may be altered by slowly moving the catheter up and down the channel in the esophagus. 16

17. Surgical recovery and training If wound clips are used, they are removed approximately 8–10 days post surgery. Rats are placed in clean polycarbonate boxes with soft bedding for approximately 7–10 days, observed daily for any signs of distress, and weighed at least twice weekly. A rat may initially lose 10% of its body weight after surgery, but should begin gaining weight by day 5 post surgery. Prior to the initiation of a study, all rats must be trained To the plethysmograph chamber by placement in the chamber on three to five occasions. The first training session should be conducted prior to surgery to eliminate any rat that does not accept the chamber. The duration of time in the chamber should be at least equal to the time selected in the study. Rats can tolerate these types of chambers for up to a maximum of approximately 6 hr. 17

18. Lung pressure Changes in lung airflow are measured in conscious, Restrained rats using a head-out, volume displacement plethysmograph chamber (approximately 1–3 L capacity) In this type of chamber, the head is exposed to ambient conditions, while the trunk is enclosed in the chamber. A seal is made around the neck using neoprene collar (1/8 in. thickness). Pressure changes within the chamber are measured using a differential pressure transducer with a sensitivity of approximately 2 cm H2O . The pressure changes converted to flow rates using a pneumotach port (1 in. diameter opening with six layers of 325 mesh stainless steel wire cloth). The analog flow signal is conditioned using a preamplifier and then converted to a telemetry (frequency) signal using a voltage analog to frequency converter 18

19. A telemetry receiver is placed beneath the plethysmograph chamber to transmit the pleural pressure telemetry signal in parallel with chamber flow signal to a software application. Eg: DSI Dataquest ART Analog system. 19

20. Respiratory function in Dogs and monkeys:restrained methadologies PURPOSE AND RATIONALE Species other than the rat may be required to specific study requirements. For example, the development of humanized monoclonal antibodies or other biotechnology-derived proteins requires species that have homologous target proteins and do not produce an antigenic response to the drug. Since both dogs and monkeys are used in toxicology studies of new drugs, either of these species may also be required to investigate pathological changes that are suspected of having an effect on the function of the respiratory pumping apparatus or gas exchange unit. 20

21. Pleural and arterial pressure measurement Catheter Placements Pleural pressure is measured chronically in conscious monkeys by surgically implanting a fluid-filled polyurethane catheter (length ¼ 35 cm; O.D. ¼ 1.2 mm) Attached to a pressure-sensitive radiotelemetry transmitter beneath the serosal layer of the esophagus and within the thoracic cavity. Arterial pressures may also be measured by implanting a second fluid-filled polyurethane catheter (length ¼ 35 cm; O.D. ¼ 1.2 mm) attached to the same radiotelemetry transmitter into the abdominal aorta. 21

22. 22

23. Surgical procedure: 23 A pressure-sensitive catheter (attached to a radiotelemetry transmitter) was surgically implanted beneath the serosal layer of the esophagus within the thoracic cavity This was accomplished by performing a midline laparotomy, making a small incision in the serosal layer of the esophagus caudal to the diaphragm, and advancing the catheter cranially along the esophagus and beneath the serosal layer into the thoracic cavity. The catheter was secured to the esophageal wall and the telemetry transmitter was sutured to the inner abdominal wall. Respiratory airflow measurements were obtained using a restraint chair equipped with a clear plastic helmet (plethysmograph chamber) that seals around the neck and encloses the head.

24. Cont.. The pleural pressure is visually verified and a negative deflection is confirmed with each respiratory effort. The catheter is either retracted or advanced until a maximal change in pressure(>4 mmHg) was obtained. To monitor arterial blood pressure, a 4 cm incision is made over the right femoral region and the femoral artery is isolated. A trocar is used to pass the blood pressure catheter from the abdomen to the femoral incision. An arterotomy is made in the femoral artery and the catheter introduced 10cm into the artery. 24

25. Respiratory function in non restrained animals like monkeys and dogs 25

26. Procedure Non-restrained dogs are acclimated to wearing a custom-fit jacket, which contains the inductive coil straps and an accelerometer, by placing the jacket on each animal for increasing periods of time up to a target time of approximately 26 h. Acclimation to the jacket on at least one occasion for a period of 4–6 h and a second occasion for 20–24 h is considered an acclimation schedule As indicated by the acceptance of the animal of the jacket and no overt evidence of animal stress. 26

27. Ventilatory measurement The phase angle is calculated using the following equation : sin1(M/S), where is the phase angle, M is the distance between the intercepts of the thoracic abdominal loop on a line drawn parallel to the x-axis. To calibrate volume measurements of the RIP system, a qualitative diagnostic calibration (QDC) and a fixed volume calibration are performed each time the jacket is placed on an animal. The calibrated tidal volume (Dvcal) is then calculated using the equation Dvcal ¼ M[(KDVT) + DVAB] 27

28. Continuous measurement of expiredCO2 PURPOSE AND RATIONALE Changes in ventilatory parameters help define the mechanism and potential cause of a respiratory disorder, whereas changes in the partial pressure of arterial CO2 (PaCO2) define the physiological consequences, or liability, of a ventilatory change. A ventilatory disorder resulting in a Decrease in PaCO2 is defined as hyperventilation, Increase in PaCO2 is defined as hypoventilation. 28

29. Procedure : Ventilatory parameters are measured using a head-out, volume displacement plethysmograph chamber (approximately 1–3 L capacity). While the trunk is enclosed in the chamber A seal is made around the neck using neoprene collar (1/8 in. thickness). The pressure changes converted to flow rates using a pneumotach port (1in. diameter opening with six layers of 325 mesh stainless steel wirecloth). The analog flow signal is conditioned using a preamplifier and then sent to a data acquisition and analysis software application. . (OH) for calculation of ventilatory parameters. . The values for tidal volume, respiratory rate, and minute volume are determined for each breath and average values calculated for every 0.1 min. 29

30. 30

31. 31 Capnograph for small rodents

32. End tidal volume measurement End-tidal CO2 (peak expired CO2) was measured for each breath with a microcapnometer. The microcapnometer is calibrated using an analyzed gas mixture containing 5% CO2 and 95% O2. To convert the percentage CO2 values measured by the microcapnometer (in dry air and at room temperature) to partial pressure values of CO2 present in the alveoli (PACO2), the following formula is used: PACO2 mmHg = %CO2 × BP mmHg - PAH2O mmHg 32

33. Thank you 33