You've been here long enough to know how to do this. 
Here is a formatted version, for all those who struggle to optimise embedded SQL:

DECLARE @PatientVisit_ID BIGINT = 379964759;

SELECT TherapyAdmin_ID,
  RowVersionNumber,
  Order_ID,
  PatientVisit_ID = @PatientVisit_ID,
  AdminNumber,
  AdminComments,
  AdminStartDateTime,
  AdminEndDateTime,
  ScheduledAdminNumber,
  SchedAdminStartDateTime,
  SchedAdminEndDateTime,
  AdministeringStaff_ID,
  CompletionStatus,
  NotAdministeredCode,
  OnHold,
  AdminRouteCode,
  AdminSiteCode,
  AdminDeviceCode,
  AdminMethodCode,
  AdministeredAmount,
  AdministeredUnits,
  AdminRecordMethod,
  Retrieved,
  PrevAdminStartDateTime,
  PrevAdminEndDateTime,
  PreparationTime,
  FollowUpTime,
  LastPatientScanSeconds,
  RetrieveTime,
  AdminReportingSource,
  AdministeredLocation_id,
  UserDefinedFields,
  ConsentGiver,
  ConsentGivenDateTime,
  WitnessStaff_ID,
  WitnessTime
FROM TherapyAdmin WITH (INDEX(PatientOrder_TherapyAdmin_FK1_idx))
WHERE Order_ID IN
  (
    SELECT Order_ID
    FROM PatientOrder
    WHERE PatientOrder.PatientVisit_ID = @PatientVisit_ID
  )
ORDER BY Order_ID,
  ScheduledAdminNumber;