Multiple create operation request

Is there a standard design pattern to solve multiple concurrent create requests on the server? For eg) multiple clients (from browsers/mobile) can call the webservice to create an appointment for a doctor for a given time. Though, webservice can initially check if the doctor is free and then create, still there is a race condition and might end up creating multiple requests on server. How do we stop the server from creating multiple appointments ? Given the webservice runs on mulitple servers and the appointments dont have any fixed timing.