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The peak is slightly lower than the target and the trough is satisfactory. As these represent steady‐state concentrations and gentamicin has linear pharmacokinetics, the dose can be adjusted by proportion. Increasing the dose to 200 mg/day should achieve a peak of (200/140) × 6 = 8.6 mg/L and a trough of (200/140) × 0.5 = 0.7 mg/L.

Comment. Elimination half‐life is a useful guide to dosage interval and is particularly important when the target concentration–time profile includes both peak and trough concentrations. In this case, because the peaks and troughs were both low, the dose can be adjusted by direct proportion. If the trough had been high, an increase in the dosage interval would also have been necessary.