Doxycycline soluble salt

Doxycycline is available as a hydrate salt, a hydrochloride salt solvated as the hcmicthanolatc hemihydratc. and a monohydrate. The hydrate form is sparingly soluble in water and is used in a capsule the monohydrate is water insoluble and is used for aqueous suspensions, which are stable for up to 2 weeks when kept in a cool place. 

Occasionally salts may demonstrate lower aqueous solubilities and dissolution rates than expected due to the common ion effect. For example, the dissolution rate of doxycycline hydrochloride dihydrate salt was determined as four times greater in water than in O.IM HCl solution. Changing the dissolution medium from O.IM HCl to O.IM methanesul-fonic acid resulted in an increase in rate, clearly demonstrating specificity for chloride ions. This effect is due to the presence of chloride ions in the dissolution medium, which disturb the position of equilibrium for the drug solubilization process ... 

Drugs of the tetraeycline group are amphoteric, forming salts with both acids and bases. They are used as parent compounds (e.g., oxytetracycline dihydrate) or as salts (e.g., oxytetracycline hydrochloride). Their lipid solubilities range from moderate (oxytetracycline and chlortetracycline) to high (doxycycline and minocycline), so that they are able to traverse cell membranes moderately or readily. The former two drugs are natural tetracyclines, while the latter two are semi-synthetic. 

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