This is difficult it is not really possible to monitor trough levels if giving a daily dose of gentamicin IP and there is little evidence to guide practice, many units therefore do different things. We use small daily IP dose and only start montitoring after 2 weeks if prolonged treatment necessary.We occasionally use gentamicin IV in which case it is easier as the trough levels are well documented for IV dosing.You should discuss this with your local microbiologist, pharmacist and MDT. The patients should be given clear instructions of the signs of toxicity.