Potential drug interactions & missed pill rules for women on CHC

Box 3: CHC and potential drug interactions (adapted from https://bnf.nice.org.uk/treatment-summary/contraceptives-interactions.html)

Medications that reduce CHC potency (Enzyme Inducing drugs)
  • Carbamazepine
  • Eslicarbazepine acetate
  • Griseofulvin
  • Nevirapine
  • Oxcarbazepine
  • Phenytoin
  • Phenobarbital
  • Primeidone
  • Rifabutin
  • Rifampicin
  • Ritonavir
  • St John's Wart
  • Topiramate
 Medications affected by CHC use
  •  Lamotrigine (potentially lowers seizure threshold)

 

Box 4: Missed pill rules for women on CHC (adapted from FSRH guidelines on Incorrect use of combined hormonal contraception December 2018)

1 missed pill
  • Take the missed pill as soon as remembered
  • Take next pill at usual time
  • No need EC or extra precautions
2/more missed pills
In first week after pill free interval      
  • Take latest missed pill ASAP
  • Take next pill at usual time
  • Extra precautions for 7 days
  • If SI occurred since start of pill free interval consider EC & pregnancy test in 3/52             
In week 2 or 3 after pill free interval
  • Take latest missed pill ASAP
  • Take next pill at usual time
  • Omit the pill free interval if week 3
  • Take extra precautions for 7 days
  • No need EC*
Late restarting CHC after pill free interval
  • Take the missed pill as soon as remembered
  • Take next pill at usual time
  • Extra precautions for 7 days
  • Consider EC if SI occurred since start of pill free interval and pregnancy test in 3/52

*theoretically this applies up to 7 missed pills if the CHC has been taken reliably prior to missed pills.  

Review

Women on CHC should be reviewed every year. This follow-up should include: medical eligibility, up to date drug history, method adherence and satisfaction, recording of BP and BMI. It is also important to reiterate when to seek urgent medical review as well as exploring other contraceptive options if they wish to change.  Some practices may wish to undertake these reviews without a face-to-face consultation. FSRH and GDG suggest that CHC is appropriate for remote prescribing so long as the above has been checked (e.g. using self-completed checklist).


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