How much ranitidine should my 19week 13lb 5 baby be taking ?

Depends: The dosing is different based on what is being treated. It is most commonly used in that age group to treat gastroesophageal reflux disease (gerd.) the dosing is 5-10 mg/kg/day divided into two doses. Your baby weights about 6 kg, so his or her dose would be 15 - 30 mg (or 1-2 ml) twice a day.

Typical dosing: You should review your medications and their dosing with your pediatrician. No infant should be on this medication without the doctor's knowledge. Typical infant dosing for ranitidine is 5-10 mg/kg/day --> 1-2 mL (15-30 mg) twice daily would typically be appropriate for a 6 kg (13 lb 5 oz) infant.