Drug interactions between rifamycin antibiotics and hormonal contraception: a systematic review

Rifamycin antibiotics are commonly used for treatment of tuberculosis, but may reduce the effectiveness of hormonal contraception (HC).

To determine whether interactions between rifamycins and HC result in decreased effectiveness or increased toxicity of either therapy.

We searched MEDLINE, Embase, Cochrane and clinicaltrials.gov through May 2017.

We included trials, cohort, and case-control studies addressing pregnancy rates, pharmacodynamics or pharmacokinetic (PK) outcomes when HC and rifamycins were administered together versus apart. Of 7291 original records identified, 11 met inclusion criteria after independent review by two authors.

Two authors independently abstracted study details and assessed study quality using the United States Preventive Services Task Force grading system. Findings are reported descriptively.

Studies only addressed combined oral contraceptives (COCs) and none reported pregnancy rates. Quality ranged from good to poor. Rifampin increased the frequency of ovulation in two of four studies, and reduced estrogen and/or progestin exposure in five studies. Rifabutin led to smaller PK changes than rifampin in two studies. In one study each, rifaximin and rifalazil did not alter hormone PK.

No studies evaluated pregnancy risk or non-oral HCs. PK and ovulation outcomes support a clinically concerning drug interaction between COCs and rifampin, and to a lesser extent rifabutin. Data are limited for other rifamycins.

Rifampin and rifabutin reduce systemic exposure of oral contraceptives, but no studies have evaluated pregnancy risk.