Self-regulating Therapeutic Inhaler

Abstract

An inhaler for self-administration of a volatile drug for analgesic purposes and comprising a tubular body with a mouthpiece at one end for insertion into a patient's mouth, an absorbent material within the tubular body for holding the liquid agent and a cap on the end of the tubular body opposite the mouthpiece, the cap having openings therein arranged to provide evenly distributed charging of liquid drug.

Description

The present invention provides an inhaler for self-administration of analgesia by a patient which may be simply manipulated, is of light weight and of low cost so that it can be disposed of after a single use. Present types of inhalers for self-administration of analgesia by the patient are generally somewhat heavy, bulky, expensive pieces of equipment. In contrast, the inhaler of the present invention is small and of light weight, thereby greatly simplifying logistic problems of storage and availability. It can easily be stocked and used in delivery rooms, emergency rooms, wards, ambulances, rescue vehicles, and it may be carried by the physician and used in the office for painful procedures or minor surgery. Repeated inhalations through the inhaler relieve pain on demand without inducing unconsciousness. With the remission of pain, the patient loses the ability to concentrate on mouth breathing and to hold the inhaler to his mouth, thus avoiding excessive drowsiness.

Briefly described, the inhaler of the present invention basically comprises a tubular body section with a mouthpiece at one end. The tubular body contains an absorbent material, such as a rolled wick, to absorb the liquid agent. In the tubular body, between the wick and the mouthpiece, are located one or more openings for dilution of inhaled drug concentration. In the end of the tubular body opposite the mouthpiece is a cap which retains the absorbent material within the body. As described hereinafter, the cap is formed in the shape of a shallow liquid drug into the inhaler, the openings being arranged, together with several small ribs, to produce uniform charging of the unit and minimize the possibility of droplets of liquid drug from escaping through the mouthpiece or dilution openings during the charging.

DRAWINGS

The invention will be better understood upon consideration of the following description with reference to the drawings, in which:

FIG. 1 is a top perspective view of one embodiment of the invention.

FIG. 2 is a side elevation view, in cross section.

FIG. 3 is a cross-sectional view, taken along the line3-3 of FIG. 2 and showing the ribs and lips of the mouthpiece.

FIG. 4 is a cross-sectional view, taken along the line 4-4 of FIG. 2 and showing a rolled wick within the inhaler.

FIG. 5 is a rear elevation view taken along the line 5-5 of FIG. 2 and showing the cap.

FIG. 6 is a side elevation view, in section, of the cap of FIG. 5 and taken along the line 6-6 of FIG. 5.

FIG. 7 is a rear elevation view of the cap of FIG. 5, taken along the line 7-7 of FIG. 6.

FIG. 8 is a graph showing the vapor concentration of drug as a function of time as produced with a mechanical ventilator connected to the mouthpiece of the inhaler.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2 of the illustrative drawings, there is shown an inhaler 10 made in accordance with one embodiment of the present invention and comprising a tubular body 11 with a mouthpiece 12 projecting from one end thereof. As illustrated, the mouthpiece comprises an elongated oblong portion 13 for insertion into a patient's mouth and having an inhalation orifice 14 and an enlarged portion 15 of substantially equal diameter or cross section as the tubular body 11. In the embodiment illustrated, the enlarged portion 15 of the mouthpiece is a slightly small diameter than the body 11 in order to provide a shoulder 16. By making the shoulder 16 of approximately 7/8 -inch diameter, the mouthpiece 12 of the inhaler 10 may be inserted into a standard anesthesia mask or other standard 7/8 -inch inside diameter anesthesia fitting. The mouthpiece 12 may be a unitary part of the tubular body 11 or may be formed separately and then affixed to one end of the body 11. Projecting internally from the elongated oblong portion 13 of the mouthpiece into the chamber 16 defined by the enlarged portion 15 and shoulder 16 of the mouthpiece 12 is a short continuous peripheral lip 18. The lip 18 in effect serves as a baffle and prevents droplets of liquid anesthetic or drug from entering the mouthpiece 12. Positioned between the inhalation orifice 14 and the end of the wick 19 is a first opening 20 which may be left open to permit air to enter the mouthpiece 12 to thereby dilute the concentration of inhaled vapor, or may be covered by the patient's finger to thereby increase the concentration. By positioning the diluter opening 20 proximate the mouthpiece 12 and beyond the end of the wick 19, self-administration of drug vapor becomes self-limiting. It is apparent that inhalation through the mouthpiece 12 with the diluter opening 20 uncovered will result in the inhalation of air containing a very low concentration of drug vapor. Because the opening 20 is positioned beyond the end of the wick 19 and close to the mouthpiece 12, when it is uncovered, air will be drawn through the opening 20 and directly into the mouthpiece 12 without first passing over the surface of the absorbent material 19 and therefore will contain very little drug vapor. Thus the opening 20 must be covered in order to provide an effective concentration of drug vapor. Inhalation through the inhaler 10 therefore becomes self-limiting since when somnolence occurs, the patient's hand will fall away uncovering the opening 20. Even if breathing through the inhaler 10 is continued thereafter, air will be passing directly into the mouthpiece 12 through the opening 20 and will contain very little drug vapor so that surgical anesthesia will be avoided. This aspect becomes particularly important when the inhaler 10 is used with a face mask (not shown). With some prior devices, which are set to deliver a specified and relatively constant drug vapor concentration and which concentration cannot easily be reduced by the patient, unconsciousness may occur if the patient continues to inhale through the device once drowsiness occurs. With the inhaler of the present invention, once drowsiness occurs, the patient will lose his ability to hold the inhaler and even if it is retained in his mouth, drug vapor concentration will decline to a relatively ineffective concentration with the opening 20 uncovered. Contained within the tubular body 11 is absorbent liquid retaining material, which in the illustrated embodiment is a rolled wick 19 of polypropylene felt, which is charged with liquid drug immediately prior to use of the inhaler 10. To prevent the absorbent material from entering the mouthpiece 12 or impeding the flow of air through the diluter opening 20, one or more retaining means such as ribs 21 may be formed in the tubular body 11 extending inwardly away from the mouthpiece 12 to a point just beyond the opening 20. A second opening is positioned in the tubular body 11 to permit air to pass over substantially all of the absorbent liquid retaining means 19. When the first opening 20 is covered, inhaled air will pass only through the second opening and over the surface of the wick 19 thereby providing an effective concentration of drug vapor. With the first opening 20 uncovered, most of the air will pass through the opening 20 and directly into the mouthpiece 12 so that the patient will breath a relatively ineffective drug vapor concentration as described above. In the illustrated embodiment there is shown a cap 22 sealing the end of the tubular body 11 opposite from the mouthpiece 12 and having openings therein. In addition to serving as a source of entry for air, the cap 22 serves as a retainer for the absorbent material or wick 19 and may be used as a convenient means for charging the inhaler 10 with liquid drug. The cap 22 illustrated in FIGS. 5, 6, and 7 comprises a ring portion 23 having a peripheral ridge 24 extending therefrom. The outside diameter of the ring 23 of the cap 22 corresponds to the inside diameter of the tubular body 11 so that the cap 22 may be inserted within the body 11, the ridge 24 acting as a stop to prevent the cap 22 from being inserted too far into the tubular body 11. Affixed by means of bridges 25 to the end of the ring 23 opposite the ridge 25 is a flat circular plate 26 of slightly lesser diameter than the ring 23 so that arcuate openings 27 result through which the liquid drug may be charged. It can be seen that the ring 23 and plate 26 define a cap 22 which has the general configuration of a shallow cup having a small cavity 28. Extending from the bridge 25 and the plate 26 are several small ribs 29 which, when the cap is inserted into the tubular body 11, project inwardly toward the mouthpiece 12. A cap 22 having the illustrated configuration serves a number of purposes. It serves as a retainer for the absorbent wick 19 and it facilitates convenient, evenly distributed charging of the liquid drug. Thus, in charging the inhaler 10, it is held vertically with the mouthpiece 12 down. The liquid drug is poured into the cavity 28 of the cap 22 where it flows through the arcuate openings 27 and around the small ribs 29. Too rapid charging of the liquid drug, which might cause it to flow past the absorbent wick 19 and into the mouthpiece 12 is thus minimized. If desired, instead of using a cap 22, the end of the tubular body 11 away from the mouthpiece 12 may be formed as a solid piece with an opening therein or the end may be solid and an opening can be formed in the tubular body 11 positioned so as to permit air to pass over most of the wick 19. An eyelet 30 may be formed in the body 11 of the inhaler 10 through which may be threaded a wrist tie 31 which is fastened to a patient's wrist to prevent dropping of the inhaler should the patient become drowsy or forgetful.

The tubular body 11, mouthpiece 12 and cap 22 may be injection molded in one piece or separately, from high-density polyethylene. Other suitable materials are nylon, polypropylene or acetal. The absorbent material 19 may be polypropylene felt, woven cotton, nylon felt or even absorbent paper.

Use of the inhaler 10 will be described with reference to methoxyflurane as the volatile drug. With a charge of 15 milliliters (ml.) of methoxyflurane, the inhaler 10 will deliver 0.5 to 0.8 percent methoxyflurane vapor for up to 2 hours of intermittent use. To activate the inhaler 10 for use, it is held vertically with the mouthpiece 12 down and 15 ml. of methoxyflurane is poured into the cup-shaped cap 21. The inhaler 10 is then attached to a patient's wrist by means of the tie 31 and the patient is instructed to inhale through the inhaler 10 by mouth and exhale through the nose. A number of inhalations can be taken by the patient with the diluter orifice 20 open in order to become accustomed to the taste of vapor. Thereafter, the patient can close the orifice 20 with a finger in order to increase the concentration of drug and obtain analgesia.

Using a mechanical ventilator to simulate human breathing, variation in drug vapor concentration delivered by different inhalers 10 was found to be minimal. For the first 10 minutes of use, concentrations were found to fall slightly which may be caused by equalization of saturation of the absorbent material 19. Thereafter, the output is steady until the concentration begins an exponential decline as the liquid drug is exhausted. This is illustrated by the curves of FIG. 8 which were produced with a ventilator connected to the mouthpiece of an inhaler 10 and adjusted to "breathe" with different rates and tidal volumes. The ventilator did not "exhale" through the inhaler, but vented to the room.

Vapor concentrations of methoxyflurane adequate for analgesia were produced for an hour of continuous use. In clinical practice, with the patient laying the inhaler 10 aside from time to time, much longer periods of effective concentrations can be expected.

The curves were drawn from gas chromatographic analysis data plotted against time, when inhalers of the present invention were "breathed through" by a mechanical ventilator at different respiratory rates (F) tidal Volumes (V.sub.T), and minute volumes (V). Ventilator "breathing" was continuous over the whole time scale, not intermittent as in clinical practice. With intermittent use, one 15-ml. methoxyflurane charge may be expected to last for 2 or more hours.

The middle curve is best taken as the "usual" or "mean" performance of the inhaler, at a "normal" respiratory rate of 20 breaths/minute and with a 500-ml. volume at each breath. It will be seen that effective concentration of delivered vapor rises, and duration of effect is extended, when slower respiratory rates (upper curve) are in operation. Conversely, during "hyperventilation" with a respiratory rate of 27 and a larger tidal volume (lower curve) concentrations fall slightly and duration of the charge is decreased.

All three of the curves were derived from the results of tests performed with the diluter hold 20 closed. When similar testing was performed on inhalers 10 with the diluter opening 20 of each left open, the height of the curves was decreased by about 50 percent in every case; i.e., vapor concentration with the orifice 20 open was about half that with the opening 20 covered, and duration of vaporization was prolonged.

Claims

We claim:

1. A self-limiting inhaler for analgesic purposes and adapted for self-administration of a volatile drug by a patient, the inhaler comprising a substantially tubular body, a mouthpiece projecting from one end of the body, said mouthpiece having an elongated oblong portion with an inhalation orifice adapted for insertion into a patient's mouth, absorbent liquid-retaining means for storing the volatile drug positioned within the tubular body along the walls thereof to thereby define a longitudinal passageway through the absorbent material, a first opening which may be covered by the patient's finger to provide effective vapor concentration and positioned in the inhaler between the inhalation orifice of the mouthpiece and the end of the absorbent liquid retaining means proximate to the mouthpiece to permit the inhalation of relatively ineffective drug concentrations when said first opening is uncovered, retaining means positioned internally in the inhaler on the side of the first opening away from the mouthpiece to prevent the absorbent liquid-retaining means from obstructing the first opening or entering the mouthpiece, and a second opening positioned in the inhaler communicating with said longitudinal passageway to permit air inhaled through said second opening to pass through said longitudinal passageway and over substantially the entire surface of the absorbent liquid-retaining means when the first opening is covered.

2. The inhaler of claim 1 including a cap in the tubular body opposite the mouthpiece, said cap having the general configuration of a cup and providing the second opening, said cap comprising: a ring portion, the outside diameter of the ring corresponding to the inside diameter of the tubular body so that the cap may be inserted within the tubular body, a plate of lesser diameter than the ring affixed to the ring by a plurality of bridges, the ring, plate and bridges defining a plurality of arcuate openings through which liquid drug can be charged into the inhaler and through which air can be inhaled to pass over substantially the entire surface of the absorbent liquid-retaining means prior to reaching the mouthpiece.

3. The inhaler of claim 2 which includes a continuous lip projecting internally from the oblong portion of the mouthpiece into the tubular body to prevent passage of liquid drug into the oblong portion.

4. The inhaler of claim 3 wherein the absorbent liquid-retaining means comprises a rolled wick.