Why is it important to use the correct dilutions of medicines? (More questions too)?

ifs its not diluted correctly you risk toxicity/ OD  or run the risk of it not working...

safety will have been calculated based on correct dilution

babies and old people are more sensitive to potency and metabolise drugs at a different speed to adults

if dose if too low it won't work, if too high you risk toxic side effects... damage to liver or kidneys from having to over work to remove toxins

Why is it important to use the correct dilutions of medicines? - I'm taking dilution to mean concentration rather than dose (obviously using the correct dose is important, so that's a given). Some medications can be harmful/painful if not diluted first. As an example, take potassium chloride. Given IV, potassium chloride is well-recognized as causing a painful, burning feeling if not diluted correctly or if administered too rapidly.

Why (and how) does dosage vary with age? - There are many potential reasons with this question, but probably the most well-recognized in my practice would be decreasing renal function. Many medications are eliminated by the kidneys, and kidney function declines with age in a predictable fashion.  As such, many medications require dose reductions for elderly patients.  Some meds also have a more pronounced effect (or a paradoxical effect) in the elderly, though this is often more difficult to predict.

What problems might arise if a dose is too low, or too high? - The answer here depends entirely on the medication. In general, though, doses that are too low will be unable to produce the effect we are looking for in treatment, and doses that are too high usually carry an added risk of side effects.