while the invention is described in connection with certain preferred embodiments , it is not intended that the present invention be so limited . on the contrary , it is intended to cover all alternatives , modifications , and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims . the invention is a novel dosing method for botulinum toxin based on the quantity and distribution of neuromuscular junctions in a target tissue . previous recommendations for dosing were based on , for example , body mass and / or age . in the present invention , therapeutic dosing is based on 1 ) the quantity and distribution of neuromuscular junctions and 2 ) the volume of liquid or other carrier material in which that dose is delivered to the target tissue . this results in decreased incidences of under or over - dosing , minimized direct costs of administrating the substance due to the more efficient use of the toxin itself , and minimized indirect costs resulting from the medical costs avoided by eliminating the likelihood of anaphylaxis and immuno - challenge resulting from too high a dose . ideal dose in units is therefore based upon the number of nsf attachment receptor ( snare ) containing organelles ( i . e ., neuromuscular junctions to be blocked ); the volume or concentration calculated from the muscle mass ; and the number of injection sites is dictated by the length and width of the target tissue . as shown in the dose response recovery graph of fig2 , because its efficacy is dependant on the quantity of neuromuscular junctions in the target tissue , dosing of botulinum toxin exhibits clear maximum dosing behavior beyond which an increased dose shows no appreciable change in effect . the neuromuscular junctions of the target tissue are saturated such that additional availability of toxin produces no additional effect . the graph of fig3 , however , shows clearly that proper titration of the dose is important . while suboptimal amounts of toxin obviously produce lower degrees of relaxation , supraoptimal doses produce similarly reduced results . it is believed that the reduced results occur because toxin molecules diffuse away from the target site resulting in the dilution of the effect of the toxin at the desired target and inappropriately expose other regions to the toxin . hence determination of the most efficacious dosage for a target muscle is critical . botulinum toxin a is produced by allergan pharmaceuticals as botox ® and by ipsen limited phannaceuticals as dysport ®. each vial of botox ® contains 100 units of c . botulinum type a neurotoxin complex , 0 . 5 mg of human albumin , and 0 . 9 mg of sodium chloride as a vacuum - dried frozen powder that requires reconstitution . one unit of botox ® is equal to the median intraperitoneal lethal dose ( ld50 ) in swiss - webster mice weighing 18 to 20 g . the ld50 for botox ® has been calculated in primates at 39 to 56 units / kg body wt . however , the exact lethal dose in humans is unknown . the calculated human ld50 of 59 units is based on an extrapolation of data . dysport ® clostridium botulinum type a toxin - hemogglutinin complex is available in 500 - unit vials . dysport ® units of activity equal 1 mouse ld50 based on their specific assay technique and is sometimes referred to in nanograms , with 1 nanogram equal to 40 units . in the united kingdom and many other countries , it is approved and labeled for multiple indications , including spasticity of the arm in patients following stroke , dynamic equinus foot deformity due to spasticity in ambulant pediatric cerebral palsy patients , two years of age or older , spasmodic torticollis , blephorospasm , and hemifacial spasm . with regard to cerebral palsy , dysport ® dosing is recommended as “ 30 units / kg body weight divided between both calf muscles .”. existing clinical data supports that botox ® and dysport ® potencies are different ; one botox ® unit is equal to 2 to 4 dysport ® units . units are not interchangeable between companies or toxin types using package guidelines and suggested dilution tables . both botox ® and dysport ® are reconstituted in injectable physiologic saline prior to intramuscular injection . both the volume of fluid and number of units of drug must be considered when preparing the toxin for injection . dosage is defined in absolute terms , based on the number of units per target muscle diluted to volume based on the size of the structure to be injected and quantity and distribution of neuromuscular junctions . the number of units to be injected is calculated by the quantity of neuromuscular junctions to be neutralized , and the volume is determined by the mass of the target muscle , and the number of injection sites by the anatomic distribution of the neuromuscular junctions . once the appropriate number of active toxin molecules ( units ) for a given muscle is determined , the dose in units remains constant and the volume and number of injection sites is adjusted based upon growth and anatomy . for example , there are an estimated pikamole of active toxin molecules in 100 units of botox ® and an estimated 250 , 000 neuromuscular junctions in the human biceps brachii . hence , there are sufficient active toxin molecules to block effectively all neuromuscular junctions of the “ target ” muscle . the toxin is thereafter injected within the muscle or skin as close to the neuromuscular junctions ( or other snare - containing organelle ) as possible using ultrasonography to localize their position . visualization of extremity and trunk muscles is performed reliably using linear probe ultrasonography with a frequency of 5 - 12 mhz . for injection localization , linear beam applications better define and delineate the anatomic relationships between muscles , tendons or bones . higher frequencies are recommended for the localization of the superficial muscles or layers , while lower frequencies may be used for deep structures . the muscles are covered by the epimysium which is the connective tissue that surrounds the entire muscle . the epimysium extends into the muscle to become the perimysium , which divides the fascicle into muscle fibers . the perimysium and the muscular fascicles can be identified because the muscular bundles are hypoechoic ( less bright ) while the epimysium and perimysium appear as hyperechoic structures . on longitudinal scanning , the fascia is depicted as a fibrillar hyperechoic sheath surrounding the muscle . there are approximately 250 , 000 neuromuscular junction in the human biceps brachii muscle . other human extremity muscles ( e . g ., the lateral and medial head of the gastrocnemius ) have a similar neuromuscular junction density . the total dosage of botulinum toxin ( i . e ., the absolute number of toxin molecules administered ) is given based on the mass of the muscle rather than on the body weight of the individual and injected within 3 . 0 cm of the area of the muscle containing the neuromuscular junctions ( based on ultrasound localization ). thus , for muscles like the soleus where junctions are distributed along the length of muscle fibers , toxin is delivered in multiple locations following the full length of the muscle . in contrast , for muscles like the biceps brachii or medial and lateral head of the gastrocnemius the injection pattern is an inverted u shape following the distribution of the neuromuscular junctions . for example , where 75u is sufficient to produce blockade of the neuromuscular junctions in the lateral gastrocnemius , the biceps brachii has a mass 22 % larger than the lateral gastrocnemius , therefore requiring 91u for efficacy . these absolute amounts are then diluted relative to increasing mass and injected adjacent the neuromuscular junctions in the target muscle . table 1 shows muscles relative to the lateral gastrocnemius and recommended dosages . table 1 provides a multiplication factor by which the appropriate dosage for other muscles may be determined . for example , the soleus muscle has a mass approximately 2 . 63 times greater than the lateral gastrocnemius . where 75u of toxin is efficacious for relaxation of the lateral gastrocnemius , and approximately 0 . 8 ml of a 100 u / ml concentration of toxin is administered in a patient with a body weight of up to 5 kg , approximately 2 . 0 ml ( i . e ., 2 . 63 times 0 . 8 ml ) is efficacious for relaxation of the soleus . note that as body weight doubles to 10 kg , 20 kg , and 40 kg , toxin is diluted accordingly but injected in sufficient volume such that the absolute amount of botulinum toxin administered remains the same regardless of muscle size . increasing muscle mass does not require additional toxin because the number of neuromuscular junctions does not change . fig4 shows a unipennate muscle 10 with a single transverse band of neuromuscular junctions 50 . intramuscular injection of toxin is most efficacious when delivered within 3 . 0 cm of this band . similarly fig5 shows unipennate gracilis muscle 11 with two transverse bands of neuromuscular junctions 50 . fig6 shows a bipennate converging biceps brachii muscle 12 having neuromuscular junctions 50 located in an inverted “ u ” shape . fig7 shows a rectus femoris muscle 13 with two bands of neuromuscular junctions 50 running along its length , and fig8 shows a deltoid muscle 14 with an irregular pattern of neuromuscular junctions 50 . the principles , preferred embodiments and modes of operation of the present invention have been described in the foregoing specification . however , the invention should not be construed as limited to the particular embodiments which have been described above . instead , the embodiments described here should be regarded as illustrative rather than restrictive . variations and changes may be made by others without departing from the scope of the present invention as defined by the following claims :