How much promethazine is "safe" to take if you don't want to overdose?

This the infomation: Parenteral: 25 mg IV or im once, followed by close observation for response. This dose may be repeated within 2 hours if needed. Oral therapy should be started as soon as feasible if continued medication is required. Oral: 25 mg orally once. This dose may be repeated every 4 hours as needed. Rectal: 25 mg administered rectally once. This dose may be repeated every 4 hours as needed.