OnPropertyChange does not exist in the current context?

You should implement INotifyPropertyChanged interface, which has single PropertyChanged event declared. You should raise this event if some of object's properties changed. Correct implementation:

public class MedicationList : INotifyPropertyChanged
{
    private string _description; // storage for property value

    public event PropertyChangedEventHandler PropertyChanged;

    public string Description
    {
        get { return _description; }
        set
        {
            if (_description == value) // check if value changed
                return; // do nothing if value same

            _description = value; // change value
            OnPropertyChanged("Description"); // pass changed property name
        }
    }

    // this method raises PropertyChanged event
    protected void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null) // if there is any subscribers 
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

I bet you want to do something like this:

public class MedicationList : INotifyPropertyChanged {
  public int MedicationID { get; set; }
  private string m_Description;

  public string Description {
    get { return m_Description; }
    set {
      m_Description = value;
      OnPropertyChanged("Description");
    }
  }

  private void OnPropertyChanged(string propertyName) {
    if (string.IsNullOrEmpty(propertyName))
      throw new ArgumentNullException("propertyName");

    var changed = PropertyChanged;
    if (changed != null) {
      changed(this, new PropertyChangedEventArgs(propertyName));
    }
  }

  public event PropertyChangedEventHandler PropertyChanged;
}