Читать книгу Clinical Pharmacology and Therapeutics - Группа авторов - Страница 47

Gentamicin is cleared by excretion through the kidneys and its clearance can be approximated by creatinine clearance. The volume of distribution of gentamicin is around 0.25 L/kg. A dosage interval of about three half‐lives will allow the concentration to fall from 8 to 1 mg/L (8 → 4 → 2 → 1). The elimination half‐life can be calculated from Eqn 1.3, i.e.

It will therefore take 3 × 6.6 = 20 hours for the concentration to fall from 8 to 1 mg/L. Because the ‘peak’ is measured 1 hour after the dose, the dosage interval should be 21 hours. A ‘practical’ dosage interval is therefore 24 hours. The dose administered should increase the concentration by 7 mg/L (i.e. from 1 to 8 mg/L). It can be calculated from the volume of distribution, i.e.

Mr J.L. was started on a daily dose of 140 mg and after 2 days of therapy his peak concentration (1 hour post‐dose) was 6 mg/L and his trough (24 hours post‐dose) was 0.5 mg/L.