A conventional nomogram, based on serum creatinine (sCr) and age, was developed in order to determine the correct initial dosage regimen for meropenem (MEPM) infusions in elderly patients with severe community-acquired pneumonia (CAP), using a target minimum inhibitory concentration (MIC) of 2 mg/L. A correlation between age and actual bodyweight (BW) in a development cohort of 44 males and 45 females was performed by linear regression using the least-squares method (male: y=−0.4676x+80.281, R²=0.4888; female: y=−0.4373x+77.502, R²=0.3194). There were no significant differences between actual BW and the BW (e-BW) estimated using this equation in this cohort (male: e-BW 41.6±3.1 kg, BW 41.7±3.5 kg, p=0.93; female: e-BW 39.5±2.1 kg, BW 39.5±3.7 kg, p=0.20). By integrating these equations using the Monte Carlo simulation method, a dosage regime was calculated which would have an 80% probability of maintaining plasma drug levels above the MIC for more than 40% of the time (>40%TAM), using only the age and sCr of individual patients. This relationship was summarized as a nomogram. The nomogram was validated using an independent validation cohort (n=28) of patients. An optimized dosage regimen could be predicted in 84 patients (94.4%) in the development cohort and 25 patients (89.3%) in the validation cohort. This nomogram may be a useful tool for clinicians and pharmacists in determining an initial MEPM regimen in elderly patients with severe CAP, based only on age and sCr.