Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Patent
1994-07-07
1995-04-25
Yasko, John D.
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
604154, 604 67, 128DIG13, A61M 3100, A61M 3700
Patent
active
054094569
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method and device for the precise dosing of intravenously administered drugs and in particular anaesthetic agents.
BACKGROUND OF THE INVENTION
Precision in dosing infused anaesthetic agents has the advantage of providing adequate operating conditions in each patient, avoiding unwanted unconsciousness in sedated patients, avoiding respiratory arrest and severe hypotension in anaesthetized patients and particularly, avoiding awareness where unconsciousness is desired. The conventional approach to determining the bolus and variable infusion rate required to achieve a nominated target blood level is to derive a compartmental pharmacokinetic model following the administration of a single dose.
In U.S. Pat. No. 4,741,732 to Crankshaw et al and Austrailian Patent No. AU-B-42019/85 to The University of Melbourne the entire contents of both documents being hereby incorporated by cross-reference, there is described a plasma drug efflux method to determine infusion rates of a given drug to achieve a constant concentration necessary to achieve an effect in the patient. The present applicant has shown for a number of drugs that the infusion rate required to achieve a therapeutic effect differs to a considerable extent from the prediction made from giving a single dose of each of these drugs. there is also described in subsequent U.S. Pat. No. 5,034,004 Crankshaw et al improvements in a device to administer drugs intravenously, particularly during anaesthesia.
In summary, the disclosures of U.S. Pat. No. 4,441,732 and Australian Patent 42019/85 show that: volume of blood from which drug is removed each minute (liters/minute), and varies with time as it depends on the rate of elimination from the body plus the accumulation of drug in the body. influences both the elimination and the accumulation of the drug. rate of removal of the drug we term Plasma Drug Efflux (Ep). chosen as the mid-point within the range of concentrations normally used during anaesthesia. expected rate of loss of drug from the circulation is calculated by multiplying Ep (litres/min) by Ct (mg/liter), administered to maintain to constant concentration, and as Ep varies with time, Q varies with time in direct proportion. single infusion rate profile for each drug to permit the generation of Q for each value of Ct.
Since this original disclosure, the applicant has noted that, for anaesthetic agents, a number of concentrations can be defined which produce different therapeutic effects, for example:
(a) sedation where the subject is drowsy but not fully unconscious
(b) lightly anaesthetized where another drug such a nitrous oxide is required to achieve complete anaesthesia
(c) moderately anaesthetized when the drug alone produces anaesthesia
(d) deeply anaesthetized when the high concentration of the drug is used to achieve effects as well as anaesthesia, such as lowering of the arterial blood pressure or protection of the brain from lack of oxygen.
When evaluating the ability to implement plasma drug efflux rate profiles obtained according to the method of U.S. Pat. No. 4,471,732 at a number of different desired or target concentrations (C.sub.T), the applicant has found, particularly with the anaesthetic agent propofol, that the infusion rates required to maintain a constant concentration at each of these different clinically useful concentrations are not in direct proportion to each other. Thus as a result of observation of the method of the U.S. patent it has been determined that Ep during sedation for light anaesthesia, average anaesthesia and deep anaesthesia, does not remain constant in the case of Propofol, and both the size and the shape of the Ep curve varies for different levels of anaesthesia. This new observation that Ep is concentration dependant and that the simple proportion described in the U.S. patent does not apply means that in the case of propofol the amount of blood from which drug is removed actually falls as the concentration of the drug increases. The magnitude of this fall is
REFERENCES:
patent: 3809871 (1974-05-01), Howard et al.
patent: 4502488 (1985-03-01), Degironimo et al.
patent: 4741732 (1988-05-01), Crankshaw et al.
patent: 4880014 (1989-11-01), Zarowitz et al.
patent: 5034004 (1991-07-01), Crankshaw
patent: 5254087 (1993-10-01), McEwen
International Search Report dated Nov. 10, 1992 for PCT/AU92/00485.
The University of Melbourne
Wilkens III Frank
Yasko John D.
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