There is only 20 seats and they enroll it according to the merit list of their entrance examination usually held in July/Aug, you can get the idea from the folloing links:
You can also get further information from:
PATAN HOSPITAL MEDICAL LIBRARY, GPO
BOX 252, KATHMANDU,NEPAL
Tel. No.: 521034, 522266
Fax No.: 977-1-22559
Email address: pathosp@healthnet.org.np or patan@hospital.wlink.com.np
best of luck