Electrical resistivity, magnetization, and specific heat measurements were performed on polycrystalline samples of the filled-skutterudite systems La1−xMxPt4Ge12 (M = Ce, Th). Superconductivity in LaPt4Ge12 was quickly suppressed with Ce substitution and no evidence for superconductivity was found down to 1.1 K for x > 0.2. Temperature-dependent specific heat data at low temperatures for La1−xCexPt4Ge12 show a change from power-law to exponential behavior, which may be an indication for multi-band superconductivity in LaPt4Ge12. A similar crossover was observed in the Pr1−xCexPt4Ge12 system. However, the suppression rates of the superconducting transition temperatures, Tc(x), in the two systems are quite disparate, indicating a difference in the nature of superconductivity, which is conventional in LaPt4Ge12 and unconventional in PrPt4Ge12. In comparison, a nearly linear and smooth evolution of Tc with increasing Th was observed in the La1−xThxPt4Ge12 system, with no change of the superconducting energy gap in the temperature dependence of the specific heat, suggesting similar types of superconductivity in both the LaPt4Ge12 and ThPt4Ge12 compounds.