Here is the design of a clinical trial:

Official Title: Nutritional Support for Lactating Women and Azithromycin to Infants to Improve Growth Outcomes in Peri-urban Slums of Karachi, Pakistan - Randomized Controlled Trial

Included conditions:
- Undernutrition

Study Armgroups:
- {'label': 'Arm A', 'type': 'NO_INTERVENTION', 'description': 'Control arm: Lactating women (LW) randomized in this arm will only receive standard of care which comprises of standard nutritional counseling, key messages of exclusive breastfeeding, essential newborn and infant care and immunization.'}
- {'label': 'Arm B', 'type': 'EXPERIMENTAL', 'description': "Intervention arm B: Lactating women (LW) randomized in this arm will receive ready-to-use nutritional supplement, 'Balanced energy-protein (BEP)' for next 6 months to be consumed in a dose of 2 sachets of 75 grams per day. Further, LW will also receive standard of care which comprises of standard nutritional counseling, key messages of exclusive breastfeeding, essential newborn and infant care and immunization.", 'interventionNames': ['Dietary Supplement: Balanced energy-protein (BEP)']}
- {'label': 'Arm C', 'type': 'EXPERIMENTAL', 'description': "Intervention arm B: Lactating women (LW) randomized in this arm will receive ready-to-use nutritional supplement, 'Balanced energy-protein (BEP)' for next 6 months to be consumed in a dose of 2 sachets of 75 grams per day. Further, the same infant of LW will receive a single dose of Azithromycin (20mg/kilogram) at day 42 of age. Further, LW will also receive standard of care which comprises of standard nutritional counseling, key messages of exclusive breastfeeding, essential newborn and infant care and immunization.", 'interventionNames': ['Dietary Supplement: Balanced energy-protein (BEP)', 'Drug: Azithromycin']}

Interventions:
- {'type': 'DIETARY_SUPPLEMENT', 'name': 'Balanced energy-protein (BEP)', 'description': 'Lactating women in the intervention arms will receive approximately 800 Kcal/day and around 16-21 gram of protein in a day in the form of ready-to-use supplement.', 'armGroupLabels': ['Arm B', 'Arm C'], 'otherNames': ['RUSF']}
- {'type': 'DRUG', 'name': 'Azithromycin', 'description': 'A single prophylaxis dose of 20 mg/kg in suspension form, reconstituted by trial staff before dose administration by the same.', 'armGroupLabels': ['Arm C'], 'otherNames': ['Suspension']}

Primary Outcomes:
- {'measure': "Length velocity at 6 months of infant's age", 'description': 'Mean difference in length velocity of \\>0.12 cm /month to look at comparisons between multiple arms', 'timeFrame': '6 months of infant age, after birth and enrollment through monthly assessment'}

Please estimate the sample size based on the assumption: 
The study uses a 1-sided test with a power of 80% and an alpha of 0.025 to account for multiple comparisons. A drop-out rate of 14% is assumed, including 10% loss to follow-up and 4% infant mortality rate.
Sample size
        There are limited data available on the impact of BEP on length velocity over the first 6âmonths of life in infants. However, in one of the studies, the mothers received only perinatal supplement, and the overall increase in length (cm/month) was bâ=â3.289 among the LNS group and bâ=â3.346 among the MMN group [15]. However, the women in this trial received supplements with smaller doses/energy than the women in our study will receive, and the intervention time was also different, i.e., the perinatal period rather than the infancy period. Another study showed that the difference in length velocity (cm/month) was 0.02 between the MMN and IFA groups over a period of 0â18âmonths [17]. Therefore, in the absence of clear evidence on the impact of these interventions, we hypothesized the effect size to be 0.12âcm/month. This is also based on learning through field experience; when severely malnourished lactating women (MUAC <â19.0âcm) were provided with chickpea-based ready-to-eat supplements (100âg/day for 3âmonths), the difference was 0.06âcm/month at 3âmonths of age between these women and women who did not receive any supplements (unpublished data that was used purely for implementation and was not included in a study).
        The null hypothesis for this trial is that the mean difference in length velocity between an infant of a lactating woman receiving standard breastfeeding counseling with BEP alone (intervention arm 1) for 6âmonths or in combination with a single prophylactic dose of azithromycin at 42âdays of age (intervention arm 2) and an infant of a lactating woman receiving standard breastfeeding counseling alone (control arm) is equal or less than 0.12âcm/month (primary outcome). Due to the absence of evidence of such interventions on length velocity, we based this hypothesis on our local experience and field data from our field sites. The alternate hypothesis for this trial is that an infant of a lactating woman receiving BEP alone for 6âmonths or in combination with a single prophylactic dose of azithromycin at 42âdays of age has a mean length velocity is greater than 0.12âcm/month that of an infant of a lactating woman not receiving an intervention at 6 months. The sample size takes multiple comparisons into account and is based on the primary outcome of length velocity with an effect size difference of at 0.12âcm per month between the arms, a 1-sided test, power of 80% and an alpha of 0.025 to account for multiple comparisons (the lower alpha). A drop-out rate of 14% (i.e., 10% loss to follow-up and infant mortality rate of 4%) is assumed in the study, so the minimum total sample size required is 957 (319 lactating women in each arm).