A 2% iodine in oil counterirritant injectable had before the FDA stepped in during the  mid-1980's been a very useful formulation for treating sore horses suffering from strained muscles, ligaments and tendons.  Some of  the commercial brands back  then were Hypoderim (also contained ether) and McKay's Maxliin.  Now in the 21st century, only a few old timers will even know of this treatment or ever have actually witnessed it.   Plus since the FDA suppression back in the 1980's,  it has become very hard to obtain  a 2% iodine in almond oil formulation.  Before the mid-1980s, it could have been purchased over-the-counter at many tack shops.  I would go into my trackside tack shop and purchase McKay's  by the case without a prescription.  Now, the only way is to have your vet write a prescription to a compounding pharmacy that specializes in equine remedies and then hope they know what they are doing which may be a bit too hopeful in this world  of less and less equine knowledge.

     I would like on this page to outline an efficient procedure on how one can make a very useable form of this formulation with a little expenditure of time and money for used lab equipment--perhaps even better than the old formula!  For the average horseman this may be too much of a bother and expense for treating just a few patients.  So this page will be geared more to the veterinary practitioner that will treat many horses over time though I plan in my book to try to simplify a formulation that even a horseman can make in his kitchen.  For now, this is the best way  and will be the method I discuss.

     Most vets may already possess the below equipment in their clinic and if that is the case all well and good.  If not, used equipment can often be very cheaply had on eBay.

1)   Scales sensitive to .1 gram
2)    Depending on volumes being formulated, appropriate lab beakers,
3)   A combination hotplate-magnetic stirrer along with a stir-bar,
4)   An ultrasonic bath,
5)   A large lab centrifuge,
6)   Appropriate 0.45 micron (pore size) syringe filters,  large 60cc syringe and caulking gun type of pump,
7)   Sterile serum vials and caps.

     The good  news is that the innate property of a 2% iodine in almond oil formula is by nature,  antiseptic.  It kills pathogens on contact.  So, having a sterile clean room is not high on the priority list when one is  making this formula though I highly recommend  using as aseptic of technique as is possible.   On the other hand, one will have to be a stickler in trying to produce a formula with minimum of particulate which can be remedied by centrifugation and filtering  with a .45 micron filter or smaller.   The bad news is that almond oil is viscous and very hard to filter.  It can be done,  but it wont be easy like  an aqueous solution.

     First things, first, lets discuss iodine crystals and the oil carrier.  One needs to purchase as pure of materials as possible.  Normally, we would prefer the USP grade though ACS is just as pure.  The highest purity level of chemicals is the ACS grade.  It is even higher than the much coveted USP grade in some instances though the two can often be used interchangeably!  Iodine crystals ACS is fairly easily purchased and eBay may be an economical place to do this.  As far as the carrier oil,  Sweet Almond Oil USP has been the one of choice though other vegetable oils may be interchanged.  I do recall having purchased McKay's Maxlin injection that used peanut oil though they mostly seemed to prefer sweet almond oil.  I see no reason why other carrier oils such as hemp seed oil, avocado oil, cottonseed oil, grapeseed oil, etc. could not be used.  Try to find a USP grade.  Below, I will use Sweet  Almond Oil USP  as my carrier oil.  This can be often purchased online at various supply houses and tends be a  more economical oil to purchase than the others.

To make a 2% iodine solution, one would add 2 grams of Iodine crystals to each 100 ml of Sweet Almond Oil.  Below, I will make a 200  ml volume and, accordingly, will  measure 4 grams of Iodine crystals into the glass beaker placed on the scales,  then add enough sweet almond oil to reach the 200 ml mark.  This will give me a 200 ml solution of 2% iodine or approximately two, 100cc vials  when finished.

Note:  Though it is not pictured below, I place a glass lid or plastic wrap on the beaker during stirring, heating, and sonication steps to prevent contamination from air.

Injecting the stifle ligaments with a 2% iodine formula  is a very effective treatment for sore stifles in the racehorse.
Weigh out approximately 4 grams of Iodine crystals on digital scales into a 400 ml Pyrex beaker.
Pour enough Sweet Almond Oil into the beaker containing the weighed crystals to reach the 200 ml mark.  Beaker is placed on a combination hotplate and magnetic stirrer.  The magnetic stir-bar to the left is dropped in the beaker and stirring is started for 2 hours  on medium heat,  below boiling. 
Approximately 2 hours of stirring on medium heat results in iodine crystals dissolved in sweet  almond oil.  Note the dark rich color.  Next,  I like to place the beaker into an ultrasonic bath and sonicate for another hour  for added dispersion of the iodine as seen to the right.
The 2% iodine filled centrifuge tubes are placed in the rotor shields and spun  down at 3000 rpm for 30 minutes. This will help remove large particulate from the solution before filtering.  I am using a Sorvall GLC-2B table top lab centrifuge that can handle over 100 ml tubes.  If you only have the typical smaller physician's clinical centrifuge that uses 15 ml tubes--that may work, but is more tedious to  employ in spinning down larger volumes.   After the run, the large particulate should be plastered to the bottom of the bottle allowing easy supernatant pour off.
Remove the magnetic stir-bar and place beaker with 2% solution into an ultrasonic bath and sonicate for approximately 1  hour.  This will aid in further dispersion and breakdown of particulate.  Placing beaker in warm water with a dab of dish soap,  suspended on a  rack as pictured above aids in efficient sonication.
After sonication, reheat beaker. Next, two centrifuge bottles containing 100 ml each are filled and placed in centrifuge to right.
After centrifugation, pour the 2% into a clean beaker, reheat to a warm temperature.  Next pour warm contents into the above syringe (monoject 60cc with luer lock) with a syringe filter attached.  The plunger will be removed and replaced  when filled.  There are many types of syringe filters, but I prefer the stainless steel 25 mm one as pictured.  In it I will place a .45 micron (pore size),  25 mm diameter nylon membrane filter.
This is my syringe filter pump gun with a monoject 60cc luer  lock syringe in place with a millipore stainless steel 25mm (diameter) filter holder attached.   This is the least tedious method to filter viscous almond oil through a .45 micron nylon filter.  Pump slowly not to blow-out the syringe.  Pump freely until stiff resistance is encountered and then I generally like to build up enough pressure to get 1-2 drops every second into the vial, 60-120 drops  per minute.
Filtration Notes:

     There are many  "Roads to Rome" and filtering a challenging viscous carrier oil like Sweet Almond Oil is no exception.  You may want to try or prefer another method than my above.  By all means go for it!  Here are some facts I have discovered that might help you decide your method.  Before I go into the instrumentation, note that if one warms up the almond oil before filtering, it becomes thinner and is more easily pressure-filtered.

     It is my opinion that the 2% iodine formula which I make on this page is superior to anything we  could buy back  in the 1980s or  earlier!  Back then, filter membranes and filtration were not as advanced as today.   This formula will filter out most all large particulate allowing better dissemination of the formula into the tissue  without undue reaction sometimes seen in the older remedies.

     Basically, there are two pore sizes commonly available though one can find many variations for specialized laboratory jobs.  The common pore sizes are 0. 22 micron and 0. 45 micron membrane filters.  I think a pore size of 0.45 micron is sufficient for our use of making 2% and we don't need to go to a smaller pore size for several reasons.  One,  a 0.45 micron membrane is much easier and faster to filter an oil through than the smaller, 0.22 micron pore size.  It is considered vital to use a 0. 22 micron pore filter or smaller to filter  bacteria, fungi and perhaps the larger viruses that our  solution may contain.  Since 2% iodine in almond oil is anti-microbial by nature,  we really don't have to worry about filtering pathogenic organisms.   Bacteria, fungi and filterable viruses will be killed,  if this formula accidentally is contaminated.  The 0.45  micron filter is used to reduce particulate size in an injectable and that is what we are after.  You most certainly can use the 0..22 micron size,  but it will be much more tedious to filter an oil through and if you try using hand power on a syringe, you will quickly change your mind!  Your hand and fingers will  soon ache!  This is why it is much less labor consuming to modify a caulking gun for this procedure as I did above.  One can go to a store and purchase a common cheap caulking gun and get by.  I have found that caulking guns, particularly the cheaply made ones are not the best.  I chose to buy a high-end adhesive caulking type gun, modifying it with a new tube that will contain a large syringe much more efficiently.  Below is a photo of my finished product.  I have found that most store bought caulking guns are too small with one only able to get a partially filled syringe on the rack.  My modification allowed a monoject 60cc syringe to be placed in the tube with plunger fully extended.  It also more securely cradled a 60cc syringe and it allowed a more efficient clamping of the gun into a common laboratory stand and clamps.

     There are a number of materials,  membrane filters are made of and marketed.  Many are only designed to be used for an aqueous (water based) solution.  If one is trying to filter Sweet Almond Oil as we are, some filter membrane materials will not work!  Nylon is probably the best material to buy in a 0.45 micron membrane filter for oil filtration.  There are other materials that may work as well i.e.  PVDF  polyvinylidene fluoride) and  PTFE (polytetrafluoroethylene) are others. 

     Generally, one can only expect to get less than 100 ml from each syringe filter or membrane.  You will need to use a new one as soon as resistance gets so high as flow is very limited.  The filter membrane will fill full of particulate requiring a fresh membrane.  Play it by feel.

     Next, you can either go with a syringe filter or a more sophisticated vacuum flask system of micro-filtration as pictured below.  I tend to favor the syringe filter for small volumes, using a caulking type gun to pump the syringe during this long process.  Some may prefer the more expensive micro-filtration vacuum flask particularly for larger volumes.  Syringe filters come in several versions.   The easiest is to simply purchase an individually packaged,  disposable unit.  For a more economical version, one can purchase a filter holder, either plastic or metal construction and insert cheaper pre-cut membrane filters in the holder for each use.  Filter holders come in several diameter sizes,  but I tend to prefer either the 25 mm or 47 mm  disk sizes.  Pictured below are some examples:
Example of a plastic filter holder designed for a 47 mm size (diameter) membrane filter. A luer lock system should be on this  device.
A Millipore stainless steel, 25 mm (diameter)  filter holder.  A luer lock inlet  should be a feature of this holder. Tighten with wrenches before use!
A popular style of disposable individually packaged syringe filter.  Easy to use.    Buy one with a luer lock syringe capability.
This is a glass micro-filtration flask system that uses a vacuum pump. Most of these employ a 47 mm (diameter) size filter membrane which one buys by  a 100 count lot.  Some swear by this system, but I prefer the syringe filter system. 
This is a high-end caulking gun,  I purchased for a few bucks at a garage sale and modified to use as a syringe filter pump.  It has cast alloy metal handles and heavy steel parts.  One may be better off  buying a more expensive gun like this one rather than fooling with the more common pressed & bent metal cheapie found in most hardware stores.   My modification worked admirably!  As I wrote above, many of the commercially made caulking guns tend to only allow a large syringe to be inserted partly filled.  I lengthened out the barrel on this to allow a full 60 cc plunger pull-out.  I simply cut off the front part of this caulking gun and welded a thin-walled 1.75" diameter steel tube onto its plunger base.  A  concave steel washer was added in front with a slot cut in it for easy insertion of syringe.  I cut out a slot in the tube to allow a large 60  cc  monoject disposable syringe to be easily inserted.  A  steel hook was also added to help clip to a lab ring. This design is very practical to use with typical lab stand & clamps for the desired vertical position pointing down into a sterile  receiving vial as pictured above.
The final bottled product, two 100cc vials.  Use amber glass to preserve all iodine solutions.
Above is a diagram of how a 25mm millipore  stainless steel  syringe filter is constructed. This is the filter system,  I prefer.

1)  Stainless steel base with outlet
2)  flat Teflon gasket
3)  stainless steel screen (supports the filter membrane)
4)   25mm filter membrane of your choice
5)  optional pre-filter that can be used, I don't
6)  O-ring  Teflon gasket
7)  Stainless steel cover with a luer lock for syringe inlet

NOTE:   When cleaning after use, rinse with distilled  water and let air dry.  The use  of lint free  kimpwipes  may be the exception. Avoid paper towels, etc.
     Below  is a YouTube video of a thought-to-be promising race prospect Thoroughbred in Argentina that was purchased very sore in late  2014.  He  could hardly walk out of his stall being so lame in his shoulder, nor could he be mounted. The vet thought the old fashion technique of  injecting his shoulder with a 2% iodine in almond oil was the answer, but this formulation is very hard to come by in these post-1980's times.  Only a few compounding pharmacies specialize in formulating this  injectable. Owner  came to me and I  sent two vials of the above 2% to Argentina  for his treatment.  Vet injected horse twice  in January with a successful outcome.   He raced on April 19, 2015  in a 1000 meter  Handicap as seen below which was his first start back since racing two years ago.  The treated horse went a very spectacular come-from-behind performance goiing way wide on the last turn.  He is the # 3  horse coming in second.
When working with injectables, it is always a good policy to formulate in as sterile conditions as possible. Accordingly, I use a lab glovebox similar to the above which I made and will keep your materials isolated from contamination form the outside air. It can be made cheaply and I have a webpage detailing construction.