We describe the case of an intravenous drug user affected by life-threatening Staphylococcus aureus-complicated skin and soft tissue infection with associated bacteraemia who, while on replacement therapy with methadone, required 11 mg/kg/day daptomycin to achieve trough (Cmin) and peak (Cmax) plasma levels similar to those observed with the standard dosage of 6 mg/kg in healthy volunteers (mean ± standard deviation: Cmin 12.35 ± 0.80 mg/L, Cmax 63.90 ± 8.71 mg/L). Clinical pharmacological advice based on real time therapeutic drug monitoring may be helpful for optimizing daptomycin exposure in these patients. Physicians should take into account that dosages much higher than the standard ones may be needed, probably as a consequence of augmented drug clearance.