Drug Concentrations Theophylline quickly equilibrates plasma and milk. Peak milk levels occur 1 to 3 hours after immediate-release product oral intake and virtually immediately after intravenous delivery. Because of this rapid absorption, milk does not affect the dose that reaches the blood; therefore, milk is not expected to change the effect of the drug. The duration of theophylline in breast milk is variable but appears to be short lived (i.e., less than 24 hours). Because the risk of toxicity outweighs any possible benefit, the administration of theophylline to nursing mothers is not recommended. Your doctor may recommend that you stop breastfeeding if you are taking theophylline because of the potential for its effects to be passed on to your baby through the milk. Once you begin taking the medication, don't stop without first talking to your doctor about how to wean your child off it.