Two types of morphine ampoules appear to be on the market. One species contains metabisulfite as anti-oxydance. The other contains methyl and propyl-parahydroxybenzoate. Can the 2 types be mixed

I would certainly never mix the two compositions as you make the case cluttered. After all, both sulfite and nipa esters work allergizing! So make use of one or the other wording. They seem equivalent to me unless the Pati ë NT would exhibit any allergic reaction to the said substances. Better ware a formulation without those excipients!