This work reports a low-power low-noise amplifier (LNA) designed for highly sensitive, low-power, duty-cycled wireless receivers operating at the band of from 401MHz to 406MHz for Medical Implant Communication Systems (MICS). The LNA core with an output buffer is implemented in a lowcost 180-nm CMOS technology. Measurement results show that at 405 MHz, the LNA features a small signal voltage gain of 53.5 dB with a 3-dB bandwidth of 8.6 MHz and a noise Figure of 3. 19dB. The LNA is also able to be switched on and off quickly. The 110% settling time is 100ns. Excluding the output buffer, the LNA with its bias circuitry draws 470$\mu$A from a 1.8-V supply. When operating in the duty-cycled mode with an active time of 200ns and a data rate of 1kbps, which corresponds to a duty cycle of 0.01%, the LNA consumes only 85nW.