Children ≥ 40 kg may receive adult doses. Below that weight, the oral dosage is ranitidine 2 mg/kg q 12 h and cimetidine 10 mg/kg q 12 h. For GERD, H 2 blockers are now mostly used for pain management. Gastritis heals with famotidine or ranitidine given bid for 8 to 12 wk.uration of action is proportional to dose and ranges from 6 to 20 h. Doses should often be reduced in elderly patients. For duodenal ulcers, once daily oral administration of cimetidine 800 mg, ranitidine 300 mg, famotidine 40 mg, or nizatidine 300 mg given at bedtime or after dinner for 6 to 8 wk is effective.