tokens: Following a 3 - week observation period , volunteers were treated with zidovudine 600 mg / day for 18 weeks , 900 mg / day for 9 weeks and 1200 mg / day for 9 weeks , followed by a washout period of 6 weeks after which they were re - started on 1200 mg / day or the highest tolerated dose at 8 - hourly intervals .