PEP with Combivir - dosing intervals


Hi Dr,

After an unfortunate condom breakage through insertive vaginal sex with a high risk individual I was offered PEP which I accepted. I started Combivir within 18hours, and have been on it for 4 days. My concern is the following. I started the Combivir at about 6pm the day after the incident ( about 18 hours) and then didnt take the next dose until about 8:30 the next day. I realise that the gap could have been about 15 hours, and have come across information on the site that one must stick to exact 12 hours intervals. This has me very worried as I am thinking that I blew my chances of PEP working as the second dose was not taken exactly 12 hours after the first. I only found this out recently, and have generally been taking one tab at about 6pm each day, and the next at about 9 the next day ( 15 hours). I was told by the doctor that I must take the tablet twice daily, and not miss a dose which I have done, but was not told at any time to stick to every 12 hours. Even the insert in the package says twice daily - why dont they warn about every 12 hours. According to evidence and studies does the drug have far less impact after about 12 hours or so. I would really appreciate your reply



Thanks for your question.

In your circumstance, the timing of medications need not be precisely 12 hours apart-- some medications are truly dosed every 12 hours, while others are dosed "twice daily". For the twice daily variety (as many HIV medications are), I generally don't worry much about a deviation of 2 or 3 hours on a twice-daily treatment regimen, though striving to be close to 12 hours apart remains ideal.

good luck, BY