1. A liposome composition comprising:
a hydrophilic polymer-modified diacylphosphatidylethanolamine;
a dihydrosphingomyelin; and
cholesterols as components of a liposome membrane,
wherein the liposome composition encapsulates a drug, an inner water phase thereof contains ammonium sulfate, and a molar ratio of sulfate ions in the inner water phase to the drug in an entire water phase is 0.36 or more.
2. The liposome composition according to claim 1,
wherein the drug is topotecan or a salt thereof, doxorubicin or a salt thereof, irinotecan or a salt thereof, or sunitinib or a salt thereof.
3. The liposome composition according to claim 1 or 2,
wherein the molar ratio of sulfate ions in the inner water phase to the drug in the entire water phase is 0.6 or more and 1.8 or less.
4. The liposome composition according to any one of claims 1 to 3,
wherein the hydrophilic polymer-modified diacylphosphatidylethanolamine is a
polyethylene glycol- or methoxy polyethylene glycol-modified
diacylphosphatidylethanolamine.
5. The liposome composition according to any one of claims 1 to 4,
wherein the percentage of the hydrophilic polymer-modified diacylphosphatidylethanolamine in the components of the liposome membrane is 2 to 10 mol%.
6. The liposome composition according to any one of claims 1 to 5,
wherein the percentage of cholesterols in the components of the liposome membrane is 35 to 43 mol%.
7. The liposome composition according to any one of claims 1 to 6 which has a particle size

of 150 nm or less.
8. The liposome composition according to any one of claims 1 to 7,
wherein the outer water phase has a pH of 5.5 to 8.5.
9. The liposome composition according to any one of claims 1 to 8,
wherein the dihydrosphingomyelin is a dihydrosphingomyelin containing a long-chain alkyl group having 16 carbon atoms and a long-chain alkyl group having 18 carbon atoms, and the encapsulated medicine is topotecan or a salt thereof.
10. The liposome composition according to any one of claims 1 to 9,
wherein the percentage of the sulfate ions contained in the inner water phase of the liposome to the sulfate ions in the entire liposome composition is at least 80%, and the percentage of the drug contained in the inner water phase of the liposome to the drug in the entire liposome composition is at least 80%.
11. The liposome composition according to claim 9,
wherein a drug release rate from the liposome in plasma having an ammonium concentration of 1 mmol/L or less is 20%/24 hours or less at 37°C, and the drug release rate from the liposome in plasma having an ammonium concentration of 4 to 6 mmol/L is 60%/24 hours or more at 37°C.
12. The liposome composition according to any one of claims 1 to 11,
wherein the number of particles of more than 10 pm contained in 1 jimol of lipid of the liposome composition after storage for 1 month at 5°C is 150 or less, and the number of particles of more than 25 jam contained in 1 umol of lipid of the liposome composition is 15 or
less.
13. A pharmaceutical composition comprising:
the liposome composition according to any one of claims 1 to 12.
14. The pharmaceutical composition according to claim 13, which is an anticancer agent.

15. A liposome composition comprising:
a hydrophilic polymer-modified diacylphosphatidylethanolamine;
a dihydro sphingomyelin; and
cholesterols as components of a liposome membrane,
wherein the liposome composition encapsulates a drug, an inner water phase thereof contains ammonium sulfate, and the dihydrosphingomyelin is a dihydro sphingomyelin containing a long-chain alkyl group having 16 carbon atoms and a long-chain alkyl group having 18 carbon atoms.