the present invention refers to hypodermic needles 101 , 201 or 301 for the administration of solutions and suspensions of drugs , medicines and vaccines , that contain at their sharp - end a water - soluble obstruction 102 , 202 or 302 , as is represented in fig1 a - d , 2 a - b and 3 a - b . penetration of the hypodermic needles 101 , 201 or 301 in living tissue of a human or animal subject results in the almost instantaneous dissolution of the obstruction 102 , 202 or 203 , and permits the injection of the liquid containing the drug or vaccine . the incorporation of the obstruction 102 , 202 or 302 avoids the user from expelling part of the liquid contained within the injection device prior to the needle penetrating the tissues of the receiving animal or human subject . the hypodermic needles 101 , 201 or 301 have preferred internal diameters ranking from 0 . 1 mm y 1 mm , and the capacity of administering drugs and vaccines by injection to depths up and over 5 cm . however it is acknowledged that larger internal diameter needles may be applicable in other fields of animal and plant health . the obstruction 102 , 202 or 302 is preferably composed by materials which are rapidly soluble in aqueous media and that dissolve once the needle penetrates living tissues . examples of these include , with out limitation , carbohydrates , sugar alcohols , amino acids , proteins , polymers , salts and / or mixtures thereof . applicable carbohydrates and sugar alcohols include , with out limitation , maltodextrin , trehalose , raffinose , cellobiose , melezitose , glucose , fructose , maltulose , iso - maltulose , lactulose , maltose , gentobiose , lactose , galactose , isomaltose , manose , maltitol , lactitol , eritrol , palatinitol , inositol , xilitol , mannitol , sorbitol , dulcitol and / or ribitol and mixtures thereof . preferably the carbohydrates are chosen from those that are acceptable for injection , with great solubility , and solid at a temperature of at least 45 ° c ., like for example mannitol , trehalose , raffinose , sucrose and / or glucose . preferably the amino acids are chosen among those that are acceptable for injection , highly soluble and solid at a temperature up to 45 ° c . like for example proline , cysteine , arginine , glutamine and / or glycine , and mixtures thereof . applicable proteins include , with out limitation , collagen , hyaluronic acid , fibronectin , gelatine , and / or agaroses , and mixtures thereof . the applicable polymers , include with out limitation , polyvinyl alcohols , polyvinylpyrrolidone and / or polyethylene glycols , and mixtures thereof . compatible solutes such as , with out limitation , glycine - betaine , ectoin , hydroxyectoin , can also be incorporated . moreover , the obstruction 102 , 202 or 302 can incorporate materials that result in an effervescent reaction when in contact with an aqueous media . examples of this , with out limitation , include sodium carbonates . other acceptable salts which are rapidly soluble and have the additional benefit of being efflorescent include , sodium sulphate , acetate trihydrate , tetraborate decahydrate ( borax ), bromoiridite dodecahydrate , carbonate heptahydrate metaperiodate trihydrate , metaphosphate hexahydrate , hydrogen orthophosphate dodecahydrate , sulphite heptahydrate , thiosulphate pentahydrate , calcium lactate , magnesium salicylate tetrahydrate , magnesium sulphate heptahydrate , and ammonium sulphate . the incorporation of the obstruction 102 , 202 or 302 in the hypodermic needle can be done by means of the incorporation of solutions of the soluble material and subsequent solidification by evaporation . the obstruction can also be incorporated by heating of the solid obstruction materials at temperatures in which they become malleable or liquid . the incorporation of a predetermined volume and subsequent cooling results in the fabrication of the desired soluble obstruction . other methods that permit the incorporation of a soluble obstruction include the incorporation of soluble membranes or puncture with the needle of a solid matrix that becomes incorporated at the needle end . the present invention is applicable , among others , to preloaded devices such as those represented in fig2 a - b . the incorporation of the obstruction 202 ensures that administration of the drug or vaccine 2004 contained in the reservoir 203 is only possible once the hypodermic needle has been injected and the obstruction 202 has dissolved in the receiving living tissues . one preferred realisation of the present invention incorporates devices preloaded with solutions or suspensions of the drug or vaccine in non aqueous liquids , such as , and with out limitation , oils or fluorocarbons . preferably the material that composes the obstruction 202 is not soluble in these non - aqueous liquids and therefore does not dissolve until the needle has penetrated the receiving living tissue . in another realisation represented in fig3 a - b , the hypodermic needle 301 that incorporates at its sharp - end the obstruction 302 , also incorporates a cartridge 305 that contains the drug or vaccine 306 stabilised in a solid format . administration of the drug or vaccine involves the assembly with an injector device 303 containing saline or water for injection 304 . injection of the hypodermic needle into living tissues results in the dissolution of the obstruction 302 permitting the flow of the water for injection 304 through the cartridge , and carry over of the dissolved drug or vaccine 306 . the hypodermic needles describes in the present invention incorporate at their sharp - end a soluble obstruction 102 , 202 or 302 which makes them functional only once they encounter an aqueous media such as a living tissue , as is illustrated , with out limitation , in the following three examples . injection of tetanus vaccine formulated as suspension in oil by means of a preloaded device incorporating a hypodermic needle with a soluble obstruction at its sharp - end the device represented in fig2 a - b was made to incorporate a soluble obstruction 202 of trehalose at the sharp - end of a 0 . 6 mm internal diameter stainless steel bevelled hypodermic needle 201 . for this , the sharp - end of the needle was dipped in a trehalose melt at about 100 ° c . cooling of the tip resulted in the formation of an obstruction 202 of solid amorphous trehalose glass . the needle incorporating the obstruction was assembled to a flexible pvc ampoule as injector device 203 . as a model drug or vaccine 204 , the ampoule contained 1 ml of a suspension in sesame seed oil of 1 - 10 μm trehalose particles containing stabilised tetanus vaccine . pressure of the final user on the pre - filled ampoule did not result in the ejection of any amount of the contained suspension . intramuscular injection of the needle in a guinea pig resulted in the immediate dissolution of the obstruction 202 and permitted the administration of the complete dose of the vaccine suspension by gentle pressure by the user over the ampoule . injection of a hepatitis b vaccine stabilised in a solid format in a cartridge located at the syringe end of a hypodermic needle incorporating a soluble obstruction at its sharp - end the device represented in fig3 a - b was manufactured to incorporate a soluble obstruction 303 of mannitol at the sharp end of a 0 . 3 mm internal diameter stainless steel bevelled hypodermic needle 201 . for this the sharp - end tip of the hypodermic needle was introduced in a 60 % mannitol solution in water at about 70 ° c . removal of the needle and cooling of the tip resulted in the formation of a solid obstruction with a mannitol crystal at the sharp - end of the needle . the needle carried at the syringe end a cartridge 305 containing as a model drug or vaccine 306 a hepatitis b vaccine stabilised in an amorphous water - soluble trehalose glass . prior to injection a conventional syringe 303 containing 1 ml of water for injection , was assembled to the hypodermic needle 301 . once assembled , pressure over the syringe 303 did not result in the ejection of any amount of liquid trough the syringe . subcutaneous injection of the needle into a guinea pig and gentle pressure over the syringe resulted in the immediate dissolution of the obstruction 302 permitting the flow of water for injection 304 through the cartridge 305 and administration of a full dose of the drug 306 . a hypodermic bevelled stainless steel needle , as for example in 101 , with an internal diameter of 0 . 8 mm was used to evaluate suitability of different materials to create the sharp - end obstruction 102 . the needles containing approximately 1 - 3 mm 3 volume of the different obstruction materials were assembled on to a syringe containing 1 ml sesame seed oil and injected into a set 3 % gelatine block at 25 ° c . as a model of a living tissue 103 . dissolution time was estimated from the time of injection . rapidly dissolving materials generally categorised as suitable needle - end obstruction materials (++++) while slower dissolving materials generally resulted in delayed injection and were categorised as less suitable obstructing materials (+).
the application refers to hypodermic needles for the parenteral administration of liquids . the needles incorporate at their sharp - end an obstruction of rapidly water - soluble material that dissolves within living tissues once the needle is injected . these needles ensure that the end user can only operate the syringe , or injection device , once the needle has been injected . the use of these hypodermic needles avoids the possibility of the user expelling any amount of liquid prior injection , ensuring the administration of the complete dose . these hypodermic needles are of special interest in preloaded injection devices and in the administration of small volumes of liquid were ejection of part of the dose by the user may result in the administration of only a fraction of the intended dose .