Human chorionic gonadotrophin comes on the market as a highly soluble powder which is the pure substance extracted from the urine of pregnant women. Such preparations are carefully standardized, and any brand made by a reliable pharmaceutical company is probably as good as any other. The substance should be extracted from the urine and not from the placenta, and it must of course be of human and not of animal origin. The powder is sealed in ampoules or in rubber-capped bottles in varying amounts which are stated in International Units. In this form HCG is stable; however, only such preparations should be used that have the date of manufacture and the date of expiry clearly stated on the label or package. A suitable solvent is always supplied in a separate ampoule in the same package.
Once HCG is in solution it is far less stable. It may be kept at room-temperature for two to three days, but if the solution must be kept longer it should always be refrigerated. When treating only one or two cases simultaneously, vials containing a small number of units say 1000 I.U. should be used. The 10 cc. of solvent which is supplied by the manufacturer is injected into the rubber- capped bottle containing the HCG, and the powder must dissolve instantly. Of this solution 1.25 cc. are withdrawn for each injection. One such bottle of 1000 I.U. therefore furnishes 8 injections. When more than one patient is being treated, they should not each have their own bottle but rather all be injected from the same vial and a fresh solution made when this is empty.
As we are usually treating a fair number of patients at the same time, we prefer to use vials containing 5000 units. With these the manufactures also supply 10 cc. of solvent. Of such a solution 0.25 cc. contain the 125 I.U., which is the standard dose for all cases and which should never be exceeded. This small amount is awkward to handle accurately (it requires an insulin syringe) and is wasteful, because there is a loss of solution in the nozzle of the syringe and in the needle. We therefore prefer a higher dilution, which we prepare in the following way: The solvent supplied is injected into the rubbercapped bottle containing the 5000 I.U . As these bottles are too small to hold more solvent, we withdraw 5 cc., inject it into an empty rubber-capped bottle and add 5 cc. of normal saline to each bottle. This gives us 10 cc. of solution in each bottle, and of this solution 0.5 cc. contains 125 I.U. This amount is convenient to inject with an ordinary syringe.