537
Until additional data are available, if intravenous acyclovir is administered concurrently with lithium, we recommend closely monitoring patients for signs of lithium toxicity and measuring serum lithium levels every second or third day.
 adverse event: signs 
Please tell me event type and its trigger word from given type options. Output format is "type: trigger".  Option: adverse event, potential therapeutic event 
Text: {0} 
Answer:
 adverse event: signs 