Postmenopausal women treated with conjugated estrogens and medroxyprogesterone acetate experienced reductions in zinc excretion of 35% after 3 months and 26% after one year (Herzberg et al. 1996). The reduction was more pronounced in women with osteoporosis who had elevated zinc excretion at the beginning of the study. The clinical significance of this interaction is unknown.

There is a case report of a 58-year-old woman who developed a lupus erythematosus-like syndrome within 1 week following the addition of zinc sulphate therapy (200 mg po tid) to her drug regimen (30 to 200 mg/day hydralazine; 120 to 640 mg/day propranolol; polythiazide; potassium chloride; propylthiouracil; and thyroxine) for the treatment of leg ulcers (Fjellner 1979). Her symptoms included fever, abdominal distress, facial butterfly rash, enlargement of the leg ulcers, oral ulcers, and maculopapular eruptions on legs, trunk, and arms. Withdrawal of zinc prompted clinical improvement, including healing of the oral ulcers and remission of the fever and abdominal distress. However, the patient's condition did not resolve completely until all the medications except thyroxine also were discontinued.

Zinc interacts with anti-inflammatory medications by forming complexes with these drugs (Dendrinou-Samara et al. 1998).

Quinolone antibiotics form chelates with metal cations, such as aluminum, magnesium, calcium, iron, zinc, copper, and manganese (Kara et al. 1991; Li et al. 1999), which significantly reduces the absorption of these medications (Balfour and Wiseman 1999; Brouwers 1992; Campbell and Hasinoff 1991). Dietary supplements and antacids containing aluminum and magnesium should be taken two to four hours before or after administration of these antibiotics (Hines Burnham et al. 2000; Li et al. 1999).

Tetracyclines form chelates with divalent and trivalent cations, including iron, aluminum, magnesium, and calcium (Neuvonen 1976). These chelates are poorly soluble and can significantly reduce the absorption and efficacy of tetracyclines (Hines Burnham et al. 2000; Neuvonen 1976). However, in an in vitro study, zinc-drug interactions in gastrointestinal fluid influenced the bioavailability of both zinc and tetracycline or tetracycline analogs (Brion et al. 1985).

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