So far as Europe is concerned, the definition of API "Any substance or mixture of substances intended to be used in the manufacture of a drug (medicinal) product and that, when used in the production of a drug, becomes an active ingredient of the drug product. Such substances are intended to furnish pharmacological activity
or other direct effect in the diagnosis, cure, mitigation, treatment
, or prevention of disease or to affect the structure and function of the body." (Eudralex Vol 4 Part 2, with my emphasis) makes it clear that electrolytes in electrolyte infusions ARE considered to be APIs.
HOWEVER, you need also to look at the registration details for the products, which would give an unequivocal definition for your particular products - eg glucose or salts may be present in some infusions for osmotic purposes, not therapeutic ones.
Regarding sampling though, Annex 19 of the EU Guidelines makes no distinction between active substances and excipients: for parenterals it is expected that all containers be sampled for identification. The rest of the testing should be based on your documented
assessment of risk, which for parenterals normally results in a decision of "full testing per the marketing Authorisation/Pharmacopoeia"
Other jurisdictions may have other interpretations: I'm not enough of an expert to advise!
Hope this helps,
CMBarnett Pharma Services Ltdwww.cmbarnettpharma.com