The study will be conducted in a total of 24 subjects before their 6th birthday, requiring replacement therapy for adrenal insufficiency due to either CAH, primary adrenal failure or hypopituitarism.

The study will consist of three consecutive cohorts. Cohort 1 will include 12 subjects aged between 2 and < 6 years. If no safety concerns emerge, then 6 subjects aged 28 days to <2 years will be enrolled (Cohort 2). A review of accumulated data will be undertaken and only if again no safety concerns emerge, then 6 neonates aged from birth to <28 days will be enrolled (Cohort 3).

The decision to continue after each cohort will be based on the recommendation of an Independent Data Monitoring Committee (IDMC).

This is a Phase 3, open label, single centre study of Infacort® in neonates, infants and children less than 6 years of age with adrenal insufficiency. The study will be conducted in a total of 24 subjects, before their 6th birthday, requiring replacement therapy for adrenal insufficiency due to either CAH, primary adrenal failure or hypopituitarism. Due to the rare occurrence of adrenal insufficiency it is expected that for the third cohort of this study (neonates) only subjects with CAH will be recruited.

The study will consist of three consecutive parts. Cohort 1 will include 12 subjects aged between 2 and < 6 years. If no safety concerns emerge, then 6 subjects aged 28 days to <2 years will be enrolled (Cohort 2). A review of accumulated data will be undertaken and only if again no safety concerns emerge, then 6 neonates aged from birth to <28 days will be enrolled (Cohort 3).

The decision to continue after each cohort will be based on the recommendation of an Independent Data Monitoring Committee (IDMC).

The study will consist of a screening visit (Visit 1 performed as a minimum the day before the intake of study drug), one treatment visit (Visit 2, Day 1), a follow-up visit (Visit 3) one to three days after intake of study drug (Day 2, Day 3 or Day 4) and a follow-up telephone call (Visit 4) 7 - 10 days after intake of study drug. Study completion evaluation will be performed at Visit 3. Parents/ carers will have at least 1 night to consider participation of their child before completing written informed consent. Children aged 3 - 6 years will be informed about their involvement in the study in the presence of their parents/carers.

All subjects will receive their standard treatment including fludrocortisone other than the dose of hydrocortisone that is to be substituted by Infacort®.

Subjects who meet the eligibility criteria at screening (Visit 1) will attend for Visit 2 at a suitable time before the next planned dose of hydrocortisone is due. Subjects may have insertion of an intravenous cannula (with suitable local anaesthesia) allowing blood samples to be taken as well as their routine clinical samples (where required) prior to their next dose of hydrocortisone given as Infacort®. If a cannula is not used, direct venous sampling may be carried out instead. After all planned study procedures have been completed the subjects will go home and will return one to three days later for the follow-up assessments (Visit 3). A follow-up telephone call (Visit 4) 7 - 10 days after intake of study drug will be undertaken.

Inclusion Criteria:

1. Male and female children less than 6 years of age.
2. A diagnosis of adrenal insufficiency as confirmed by an inappropriately low cortisol usually with other supporting tests.
3. Receiving appropriate adrenocortical replacement therapy (hydrocortisone with/without fludrocortisone).
4. Adequately hydrated and nourished.
5. Ability of parents/carers to understand and give written Informed Consent

Exclusion Criteria:

1. Clinically evident acute adrenal insufficiency (adrenal crisis).
2. Inability of the child to take oral therapy.
3. Concomitant therapy (other than that required to treat adrenal insufficiency, Vitamin D, Fluoride, Thyroxine and growth hormone).
4. Subjects with clinical signs of acute infection or fever on Day 1.
5. Any surgical or medical condition which in the opinion of the investigator may place the subject at higher risk from his/her participation in the study.
6. Parents/carers of subjects unwilling to consent to saving and propagation of pseudonymised medical data for study reasons.
7. Subjects who are dependent on the investigator or the sponsor.

Adverse Events will be recorded from the time of first intake of Infacort® until Visit 4. Serious Adverse Events (SAEs) will be recorded from the time of first intake of Infacort® until 7 days following administration of Infacort®. Any SAEs experienced after this 7-day period will be reported to the sponsor if the investigator suspects a causal relationship to the study drug.