The administration of leucovorin as well as other active, reduced folates is useful as an antidote to drugs which act as folic acid antagonists and in combination chemotherapy with 5-FU. The most often used calcium salts of the folates have a low solubility in water and form almost insoluble degradation products. Therefore, aqueous solutions are unstable and precipitates result. Precipitates in injectable products present an unacceptable safety risk to patients. Stable high strength pharmaceutical aqueous compositions are formed containing calcium salts, magnesium or zinc salts of the reduced folates leucovorin, (6R,S)-tetrahydrofolic acid, (6S)-tetrahydrofolic acid, 5,10-methylene-(6R,S)-tetrahydrofolate, 5,10-methylene-(6R)-tetrahydrofolate, 5-methyl-(6R,S)-tetrahydrofolate or 5-methyl-(6S)-tetrahydrofolate and one or more of the compounds sodium gluconate, potassium gluconate, glycerophosphate disodium salt or glycerophosphate dipotassium salt.
