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Dosage control for drug delivery systemRelated Patent Categories: Surgery, Controlled Release Therapeutic Device Or SystemDosage control for drug delivery system description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070191817, Dosage control for drug delivery system. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED PATENT APPLICATION [0001] This is a continuation of U.S. patent application Ser. No. 10/886,255, filed on Jul. 7, 2004. FIELD OF THE INVENTION [0002] The present invention relates generally to drug delivery systems, and more particularly to a method of calculating a drug infusion profile for a drug delivery system. While the invention can be used in administering a variety of intravenous drugs it is particularly useful as an anesthetic delivery system. BACKGROUND OF THE INVENTION [0003] Three conditions or objectives control the administration of an anesthetic, namely, to rapidly produce the desired pharmacologic effect (hypnosis, analgesia, etc.); to maintain the desired effect throughout the medical procedure; and to enable the patient to recover quickly from the effect following completion of the procedure. [0004] In order to achieve the objective of rapidly inducing the desired anesthetic effect, the anesthesiologist typically delivers a so called "Loading Dose." A Loading Dose is a bolus (mg/kg, mg, etc.) of drug that rapidly brings the patient to a desired level of effect. In order to maintain the level of effect the anesthesiologist often uses an infusion pump to deliver a so called "Maintenance Rate." A Maintenance Rate is a constant infusion rate (.mu.g/kg/min, mg/min, etc.) required to maintain the patient at a certain target, in this embodiment anesthetic, effect. The anesthesiologist may have to titrate this Maintenance Rate during the procedure as the patient's anesthetic needs change. A method that allows for rapidly adjusting the patient's level of effect is desired. Finally, in order to enable the patient to recover quickly from the anesthetic following completion of the procedure, the anesthesiologist attempts to deliver as little drug as needed. This can include tapering down the Maintenance Rate prior to the end of the procedure. [0005] The term "anesthesia" is used herein to refer to the continuum of hypnosis and analgesia, achieved via anesthetic drugs, from anxiolysis through general anesthesia. In producing a level of anesthesia known as conscious sedation, as practiced by endoscopists, the anesthetic(s) is typically delivered through frequent boluses. This technique results in varying depths of anesthesia throughout the procedure. At times the patient may be so heavily anesthetized as to be classified in general anesthesia. At other times the patient may be under-anesthetized and exhibit pain and agitation. A patient responding to pain is uncooperative, making the procedure more difficult. As a result, the clinician tends to err on the over-anesthetized side. In addition to placing the patient at greater risk for adverse events, over-anesthetizing causes the patient's recovery from anesthesia to be much longer. Accordingly, a method is desired that enables the clinician to control the level of anesthesia without over- or under-anesthetizing the patient. [0006] The term "sedation drug" is used herein to refer to the classes of drugs employed by anesthesiologists in inducing sedation including hypnotics and analgesics. Propofol and remifentanil are preferred drugs for sedation, principally due to their rapid onset and offset. However, this rapid action presents additional concerns for someone using an intermittent bolus technique, as typically done by non-anesthesiologists. With a rapid onset/offset more frequent boluses will be required. Consequently, anesthesiologists often use infusion pumps to continuously deliver these rapid action sedation drugs. However, non-anesthesiologists are not familiar with pharmacokinetic (PK) principals, and will have difficulty determining a Loading Dose/Maintenance Rate combination that will both rapidly achieve and maintain the desired level of anesthesia. The Anesthetic Delivery System (ADS) is intended to enable a non-anesthesiologist to safely and effectively use these rapid action anesthetic agents typically reserved for use by anesthesiologists. [0007] What is desired is an algorithm that will allow the clinician to program an ADS with a desired maintenance rate, selected by the clinician to maintain a desired level of anesthesia, and then the ADS automatically calculates the appropriate sized loading dose based on the pharmacokinetics of the chosen sedation drug. The loading dose is then delivered by the ADS to rapidly achieve the level of sedation, immediately followed by a constant infusion of the sedation drug at the maintenance rate, to maintain the level of anesthesia. Moreover, a method is desired where the patient's level of anesthesia is rapidly adjusted, each time the clinician changes the maintenance rate, in response to the patient's changing anesthetic needs. Specifically, what is needed is an ADS that integrates the initiation and maintenance of anesthesia in an equation so that the appropriate sized loading dose may be calculated and administered to rapidly bring the patient's depth of anesthesia to a level maintained by the programmed maintenance rate. Further, when a change in the maintenance rate is requested, the dosage controller (DC) can calculate an incremental loading dose to rapidly achieve the new level of anesthesia. SUMMARY OF THE INVENTION [0008] In one embodiment, the invention provides a method of drug infusion for maintaining or rapidly adjusting a patient's level of anesthesia comprising programming an automated drug delivery system with a maintenance rate (MR); causing the drug delivery system to calculate the loading dose (LD) using a formula that relates loading dose and maintenance rate; the drug delivery system infusing the loading dose into patient to achieve a desired level of anesthesia and administering the drug at the maintenance rate to maintain the level of anesthesia. [0009] In another embodiment, the invention provides a method of drug infusion for maintaining or rapidly adjusting a patient's level of anesthesia comprising the clinician programming an automated drug delivery system with a loading dose (LD); causing the drug delivery system to calculate the maintenance rate (MR) using a formula that relates loading dose and maintenance rate; the drug delivery system infusing the loading dose into the patient to achieve a level of anesthesia and administering the drug at the maintenance rate to maintain the level of anesthesia. [0010] In a further embodiment, the level of anesthesia is rapidly adjusted when the clinician programs a new maintenance rate, by a method that further comprises: calculating the cumulative loading dose based on the drug already administered to the patient; calculating a new loading dose based on the cumulative loading dose and a new maintenance rate based on a formula relating loading dose and maintenance rate; the ADS infusing the new loading dose into patient to achieve the new level of anesthesia and the administering the drug at the desired new maintenance rate to maintain the new level of anesthesia. [0011] Still a further embodiment is a drug delivery system that includes an infusion pump and a controller and is programmed to control infusion as described herein. In one embodiment, the system includes sensors for monitoring patient physiology and can be programmed to discontinue administering the drug if adverse physiology or trends are detected. BRIEF DESCRIPTION OF THE DRAWINGS [0012] FIG. 1 is a drawing of the Automated Response System (ARM) utilized in an embodiment of the invention. [0013] FIG. 2 is a collection of flow charts (FIGS. 2A-2F) for a DC program useful in accordance with an embodiment of the invention. [0014] FIGS. 3 and 4 are graphs illustrating the determination of a ramped infusion rate for a loading dose that culminates in the maintenance rate. DETAILED DESCRIPTION OF THE INVENTION [0015] For the purposes of illustration, the invention is explained using the delivery of propofol to achieve and maintain a level of anesthesia referred to as conscious sedation. However, the invention can be applied to any intravenous drug where it is appropriate to deliver a loading dose followed by a maintenance infusion. The equations will be adjusted for different pharmacokinetics (loading dose/maintenance rate relationships) for these other drugs. Examples of classes of drugs in addition to sedation drugs that can be administered in accordance with the invention are antibiotics, pain management drugs, cardiovascular drugs, anticancer drugs, and others. [0016] A. Initiation of Sedation [0017] An anesthetic drug such as propofol provides labeling recommendations for initiating sedation (loading dose)--0.0 to 0.5 mg/kg, and infusion rates for maintaining the patient's level of sedation (maintenance rate)--0.0 to 75 .mu.g/kg/min. DC is designed to correlate these two ranges, such that a clinician simply enters a maintenance rate (MR) and DC will calculate the appropriate loading dose (LD) with the following equation in the case of propofol: LD=0.5*W*(MR/75) where, [0018] LD=loading lose (mg), [0019] MR=maintenance rate (.mu.g/kg/min), [0020] W=weight (kg) of the patient [0021] 0.5=0.5 mg/kg [0022] 75=75 .mu.g/kg/min. [0023] For other drugs, and application, similar correlations can be developed. While these correlations will often be defined in terms of the weight of the patient, this does not have to be true for all cases. Some drugs may have dosages that are less dependent or essentially independent of patient weight for typical patients. The equation that has been developed for propofol above is based on the maximum loading dose (0.5 mg/kg) recommended for the drug and the therapy (e.g., conscious sedation) in which the drug is used and the maximum maintenance rate (75 .mu.g/kg/min). In this case the formula is a linear proportion or linear interpolation. The clinician may select a maintenance rate corresponding to the level of anesthesia he desires to achieve, e.g., ASA guidelines are drafted in terms of mild, moderate and deep anesthesia and based on the ratio of that maintenance rate to the maximum maintenance rate recommended for that application of the drug, a loading dose is determined. Thus, in accordance with certain embodiments of the invention, the equation relating loading dose to maintenance rate will represent a linear proportion or interpolation based on the loading dose and maintenance rate ranges suggested by the supplier and still more specifically based on the maximum loading dose and maintenance rate suggested by the supplier. These ranges may be therapy specific, for example, a different proportion or interpolation based on the drug label's recommended loading dose and maintenance rate for that therapy would be used if general anesthesia as opposed to conscious sedation was the objective. The loading dose calculation flow chart is provided in FIG. 2F where the calculation based on the maximum label dose is shown as program step 260. Continue reading about Dosage control for drug delivery system... 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