Lipid containing formulations

1. An association complex comprising:

a. one or more compounds, each individually having a structure defined by formula (I) or a pharmaceutically acceptable salt thereof

wherein:

each X a and X b , for each occurrence, is independently C 1-6 alkylene;

n is 0, 1, 2, 3, 4, or 5;

each R is independently H or

wherein:

at least n+2 of the R moieties in at least about 80% of the molecules of the compound of formula (I) in the preparation are not H;

m is 1, 2, 3 or 4; Y is O, NR 2 , or S;

R 1 is alkyl or alkenyl; each of which is optionally substituted with one or more substituents; and

R 2 is H, alkyl or alkenyl; each of which is optionally substituted each of which is optionally substituted with one or more substituents;

provided that, if n=0, then at least n+3 of the R moieties are not H;

b. PEG-lipid having the structure shown in formula (XV)

wherein:

each L 1 and L 2 are independently a bond or C(O);

each R 1 and R 2 are independently alkyl alkenyl or alkynyl; each of which is optionally substituted with one or more substituents;

X is —C(O)NH—, C(S)NH, —C(O)C 1-3 alkylC(O)NH—; or —C(O)C 1-3 alkyl-C(O)O—;

m is an integer from 0-11 and

n is an integer from 1-500;

c. a steroid; and

d. a nucleic acid.

2. The association complex of claim 1 , wherein said cationic lipid is one of the following or a mixture thereof:

3. The association complex of claim 2 , wherein said cationic lipid is:

4. The association complex of claim 2 , wherein said cationic lipid is:

5. The association complex of claim 1 , wherein said PEG-lipid has the structure

wherein:

each L 1 and L 2 are independently a bond or C(O);

each R 1 and R 2 are independently alkyl, alkenyl or alkynyl; each of which is optionally substituted with one or more substituents;

m is an integer from 0-11 and

n is an integer from 1-500.

6. The association complex of claim 5 , wherein said PEG-lipid has the structure

wherein:

n is an integer from 1-500.

7. The association complex of claim 6 , wherein said PEG-lipid has an enantiomeric excess of the R isomer.

8. The association complex of claim 1 , wherein said steroid is cholesterol.

9. The association complex of claim 1 , wherein molar ratio of said cationic lipid, said steroid and said PEG-lipid is 36-48:42-54:6-14.

10. The association complex of claim 9 , wherein molar ratio of said cationic lipid, said steroid and said PEG-lipid is 38-48:44-52:8-12.

11. The association complex of claim 10 , wherein molar ratio of said cationic lipid, said steroid and said PEG-lipid is 42:48:10.

12. The association complex of claim 1 , wherein weight ratio of total lipids to nucleic acid is less than about 15:1.

13. The association complex of claim 12 , wherein weight ratio of total lipids to nucleic acid is about 10:1.

14. The association complex of claim 12 , wherein weight ratio of total lipids to nucleic acid is about 7.5:1.

15. The association complex of claim 12 , wherein weight ratio of total lipids to nucleic acid is about 5:1.

16. The association complex of claim 1 , wherein said nucleic acid is a siRNA.

17. The association complex of claim 1 , wherein said nucleic acid is a single stranded nucleic acid or derivative thereof.

18. The association complex of claim 17 , wherein said nucleic acid is an antisense nucleic acid.

19. The association complex of claim 17 , wherein said nucleic acid is a microRNA.

20. The association complex of claim 17 , wherein said nucleic acid is an antimicroRNA.

21. The association complex of claim 1 , wherein:

said cationic lipid is

said steroid is cholesterol;

said PEG lipid is

wherein: n is an integer from 1-500;

in a molar ratio of 36-48:42-54:6-14.

22. The association complex of claim 21 , wherein molar ratio of said cationic lipid, said steroid and PEG-lipid is 42:48:10.

23. A method of forming an association complex of claim 1 , wherein the method comprises:

mixing a plurality of lipid moieties in ethanol and aqueous NaOAc buffer to provide a particle; and

adding the therapeutic agent to the particle, thereby forming the association complex.

24. The method of claim 23 , further comprising extruding the lipid containing particles.