This section is from the book "Botanic Drugs Their Materia Medica, Pharmacology and Therapeutics", by Thomas S. Blair. Also available from Amazon: Botanic Drugs, Their Materia Medica, Pharmacology and Therapeutics.
Canadian Hemp, Apocynum Cannabinum. Official in the U. S. P., Eighth Revision, and now listed in the National Formulary.
Long used in domestic practice, and conceded to possess properties akin to digitalis, there has been disagreement over its practical employment; but the work of Taub and Fickewirth (Arch. f. d. ges. Physiol., cliii, 239) in isolating its active (neutral, nonglucosidal) principle has established the drug on a scientific basis. This substance is known in trade as Cymarin, and it is about equal in activity to the official amorphous strophanthin and quite similar in effect, being far more active after intravenous or intramuscular injection than when ingested. Toxic doses cause central vomiting.
As indicated by the action of cymarin, apocynum lowers the pulse-rate and increases blood-pressure. As a heart remedy it is very slowly absorbed from the gastro-intestinal tract, even more slowly than digitalis. So, in general, it must be classed as of less range in cardiac affections than that possessed by digitalis. On the other hand, owing to the confusion over digitalis proximates, the ampules of Cymarin (see N. N. R.) (1-60 grain) intravenously, or the tablets (1 to 3 of the 1-200 grain tablets) injected intramuscularly, are of certain action akin to that of strophanthin.
Marked emetic and cathartic properties are possessed by apocynum in full dosage; and it is diuretic, especially in infusion or decoction, which is unfortunately, very disagreeable. It requires doses of about 15 grains of the drug to secure this effect, sometimes gradually increasing, or reducing if nausea is induced.
The pharmacology of this drug exactly indicates its therapy. It is highly valuable in various types of dropsy, especially cardiac forms. To nearly the same degree is it effective in that of renal type, many nephritic cases doing well under its administration. Wherever atonic blood vessels favor exudation, apocynum may be used with reasonable hope of benefit.
Only in most urgent cases is it necessary to inject cymarin. As with digitalis, there is more or less difficulty with the administration and deciding in which form to administer in a given case. In my experience, a good alcoholic extract is usually effective. As the Eclectics have stressed this remedy and used it for years in its proper indications, I have given preference to their preparations of the drug. Unless the case is urgent, it is well to begin with small doses; but I never found very small dosage effective, seldom giving less than 5 minims fl. four times a day. But there are cases, especially nephritic ones, in which a decoction seems to be more effective than any other form in which the drug may be exhibited.