Stable analgesic homopyrimidazole compsn. for oral administration - contains an acid stabiliser to prevent tautomeric colouration

Pyrido (1,2-alpha) pyrimidine compsns. suitable for oral administration contain cpds. of formula (I): (where X = carboxy (deriv), their (quaternary) salts or their mixts; pharmaceutical supports and adjuvants; opt. other active substances and a stabilising acid which dissolves in the moisture adsorbed at the surface of the solids and is formulated at the same time as the compsn. by known methods to give a prepn. suitable for oral administration pref. as tablets, coated tablets, multilayer tablets or capsules. Used as an analgesic. Small quantities of moisture produce a reversible, tautomeric transformation converting the white crystalline (I) to a yellow tautomer which although it does not influence the activity worries patients and is preferably avoided. The present composition is more stable to this change.