Re tobramycin dosing schedule - I would check w your own pulmonologist and/or pharmacist. I agree it is difficult to stay on the every 12 hour dosing schedule but at the same time maintaining the level of the dose is important so the drug continues to zap the pseudomonas aeruginosa. A dip might give the darned thing an advantage. An 16-18 hour gap before the next dose seems excessive when on a twice a day dosage.