Is the dose of Gentamicin 2x 40mg (2ml) 2x a day sufficient for an adult who weighs 68kg?

You did not specify exactly what drug is currently used in therapy. I assume it is Gentamycin Krka: https://www.gdziepolek.pl/produkty/32393/gentamicin-krka-iniekcja/apteki?pvid=31021#stacjonarne If you have another medicine in mind, please clarify your question. I presume that you use ampoules of 2 ml, i.e. the dose of gentamicin in one ampoule is 80mg. The daily dose is 160 mg. The manufacturer in the Summary of Product Characteristics gives only the recommended doses: 3-6mg / kg body weight. Treatment begins with doses of 1.5-2mg / kg b.w., which ensures adequate max. serum concentration. I assume that you have just started treatment and hence your doubts. The recommended dose is typical for starting treatment with Gentamycin. The doctor's task is to adjust the dose individually depending on the severity of the infection, the sensitivity of the microorganism causing the infection, the patient's condition, age and weight. Only a doctor can therefore make decisions on this topic, because he knows the state of health of his patient. If you are concerned about the choice of dose, it is best to talk to your doctor about it, who is familiar with your health in detail. If you are unable to get to your primary care doctor, the gdziepolek.pl Service also allows you to obtain a teleconsultation with a doctor: https://www.gdziepolek.pl/telekonsultacja