Improvements are described for a previously patented procedure for prepn. of alkali metal salts of .alpha.-6-deoxy-5-hydroxytetracycline (doxycycline) [564-25-0] metaphosphate complexes, which have a water soly. at 20.degree. >4.5 mg/mL. According to the previous procedure, 1 mol of metaphosphoric acid (H6P6O18) was first reacted with 1-5 mol Na or K hydroxide, and then with 1-5 mol doxycycline. In the present procedure, metaphosphoric acid is first reacted, in an org. medium, with 1-5 mol doxycycline, the residual metaphosphate is neutralized by addn. of MeOH or EtOH solns. of K or Na hydroxide, and the doxycycline complex is subsequently pptd. by addn. of EtOH, iso-PrOH, Et2O, or isopropyl ether. Blood levels of doxycycline in human subjects following administration of a gelatin capsule contg. doxycycline monosodium polyphosphate [64716-93-4] (100 mg doxycycline) were 50% higher than after administration of a capsule contg. doxycycline hyclate (100 mg doxycycline). The newly described preparative method is compared to other patented procedures.