A 17-year-old girl comes to the office due to worsening acne. The patient's acne had been well controlled with oral doxycycline therapy. However, over the past month, the acne has worsened on her face and back. The patient was recently diagnosed with iron deficiency anemia due to abnormal uterine bleeding and began taking a combined oral contraceptive and an iron supplement. Physical examination shows comedones and pustules on her face and upper back. The remainder of the examination shows no abnormalities. Which of the following is the most likely cause of this patient's worsening symptoms?

Question

A 17-year-old girl comes to the office due to worsening acne.  The patient's acne had been well controlled with oral doxycycline therapy.  However, over the past month, the acne has worsened on her face and back.  The patient was recently diagnosed with iron deficiency anemia due to abnormal uterine bleeding and began taking a combined oral contraceptive and an iron supplement.  Physical examination shows comedones and pustules on her face and upper back.  The remainder of the examination shows no abnormalities.  Which of the following is the most likely cause of this patient's worsening symptoms?

Quizplus · Accepted Answer

11ec160b_3c2c_4c4b_9249_dfabfbfd017f_MD0001_00 This young patient with acne had a good initial response to tetracycline (eg, doxycycline) therapy. However, after the initiation of new medications, she experienced a significant loss of effectiveness, suggesting a possible drug-drug interaction. In this case, it is likely that the new iron supplement is interacting with tetracycline to cause decreased absorption of the antibiotic. Tetracyclines interact with polyvalent cations to form nonabsorbable chelate complexes in the gastrointestinal tract. This effect is prominently seen with iron and is also common with other polyvalent metals (eg, aluminum, calcium, magnesium) found in widely used over-the-counter preparations (eg, antacids). Other drugs susceptible to chelation include fluoroquinolones and thyroxine. The extent of chelation is influenced by gastric pH; the introduction of medications that raise gastric pH (eg, H2-blockers [eg, famotidine], proton pump inhibitors [eg, omeprazole]) can sometimes lead to increased chelation and loss of drug effect. Chelation can often be avoided by taking the medications at different times of the day. (Choice A) Combination oral contraceptives suppress androgenic activity and reduce production of sebum. This typically leads to improvement, rather than worsening, of acne. (Choice B) Clinically significant resistance to tetracyclines is uncommon in acne and unlikely to occur abruptly. In addition, besides antimicrobial effects, tetracyclines have anti-inflammatory effects in acne that would likely provide residual benefit. (Choice D) Tetracyclines such as doxycycline and tigecycline are eliminated by hepatic excretion. Neither iron nor oral contraceptives would increase drug elimination. (Choice E) Estrogens increase the synthesis of sex hormone-binding globulin, which can affect plasma levels of certain steroid hormones and related agents (eg, danazol, levonorgestrel). Tetracyclines are not significantly affected. Educational objective: Tetracyclines interact with polyvalent cations (eg, iron, calcium, aluminum, magnesium) to form nonabsorbable chelate complexes in the gastrointestinal tract. This can lead to significantly decreased drug absorption and therapeutic effect. Fluoroquinolones and thyroxine are also susceptible to chelation.

A 17-Year-Old Girl Comes to the Office Due to Worsening