We claim:
1. A once daily pharmaceutical composition of isotretinoin comprising:
(i) isotretinoin or a pharmaceutically acceptable salt thereof,
(ii) at least one solubility improving polymer; and
(iii) at least one rate controlling agent,
wherein said composition exhibits at least one of the following dissolution profiles when measured in USP type I apparatus at 100 rpm in 900 ml of borate buffer with a pH of 8.0 at 37 °C:
(a) about 1% to about 10% of isotretinoin in 1 hour,
(b) about 10% to about 25% of isotretinoin in 2 hours,

(d) about 25% to about 45% of isotretinoin in 4 hours,
(e) about 45% to about 60% of isotretinoin in 6 hours, and (d) about 60% to about 80% of isotretinoin in 12 hours.

2. The composition of claim 1, wherein said solubility improving polymer is selected from ionizable polymer, non-ionizable polymer, and mixtures thereof.
3. The composition of claim 2, wherein said solubility improving polymer comprises from about 10% w/w to about 40% w/w of the composition.
4. The composition of claim 1, wherein said composition comprises solubility improving polymer and isotretinoin present in a weight ratio of not more than about 3.0: 1.0.
5. The composition of claim 1, wherein said rate controlling agent is selected from pH independent polymer, pH dependent polymer, and mixtures thereof.
6. The composition of claim 6, wherein said rate controlling agent comprises from about 5% w/w to about 20% w/w of the composition.
7. The composition of claim 1, wherein at least about 60% of said isotretinoin is in an amorphous form.

8. The composition of claim 1, wherein said composition comprises (i) an extended release (ER) portion and (ii) a delayed release (DR) portion and/or an immediate release (IR) portion, containing isotretinoin with one or more pharmaceutically acceptable excipients.
9. A method of treating acne in a patient in need thereof comprising orally administering to the patient a once daily pharmaceutical composition of isotretinoin comprising:
(i) a daily dose of isotretinoin or a pharmaceutically acceptable salt thereof,
(ii) at least one solubility improving polymer; and
(iii) at least one rate controlling agent,
wherein said composition upon administration to the patient exhibits at least one of the following plasma level differences for AUC0-24 compared to commercially available twice daily isotretinoin composition that provides the same daily dose:
(a) about 5 to about 10 % lower between 0 to 5 hours,
(b) about 15 to about 20 % higher between 5 to 14 hours; and
(c) about 4 to about 8 % lower between 14 to 24 hours.
10. The method of claim 15, wherein said composition upon administration to
the patient under fasting condition, exhibits at least one of the following
pharmacokinetic parameters: (a) a Cmax of about 350.00 ng/ml to about 600.00
ng/ml, (b) an AUC(0-t) of about 5500.00 ng.hr/ml to about 7700.00 ng.hr/ml, and
(c) an AUC(0-∞) ranging from about 5600.00 ng.hr/ml to about 7900.00 ng.hr/ml.