From the gastrointestinal tract:
anorexia, nausea, vomiting, dysphagia, diarrhea, anal itching, esophagitis, ulcer of the esophagus, dark staining of the tongue. With prolonged therapy, a deficiency of B vitamins can be observed in connection with the suppression of vitamin B-producing bacteria growth in the normal intestinal microflora.
Allergic reactions:
exacerbation of systemic lupus erythematosus, a syndrome similar to serum sickness, erythema multiforme, lowering of arterial pressure, tachycardia,Stevens-Johnson syndrome, toxic epidermal necrolysis, drug rash with eosinophilia and systemic symptoms (DRESS syndrome).
From the skin:
urticaria, photosensitization, angioedema, anaphylactic reactions, maculopapular and erythematous rash, exfoliative dermatitis, Schonlein purpura - Genocha, photoionicholysis.
From the cardiovascular system:
pericarditis.
From the side of the liver:
liver damage, sometimes associated with pancreatitis (with long-term drug intake or in patients with renal or hepatic insufficiency), cholestasis.
From the side of the kidneys:
an increase in residual urea nitrogen due to the anti-anabolic effect of the drug, aggravation of azotemia in patients with renal insufficiency. The use of products containing citric acid on the background of doxycycline may cause symptoms similar to Fanconi's syndrome: albuminuria, glucosuria, hypophosphatemia, hypokalemia and renal
tubular acidosis.
On the part of the hematopoiesis system:
hemolytic anemia, thrombocytopenia, neutropenia, eosinophilia, decreased prothrombin activity.
From the nervous system:
benign increase in intracranial pressure (anorexia, vomiting, headache, tinnitus, tremor, edema of the optic nerve), vestibular disorders (dizziness or instability), hallucinations, blurred vision, scotoma, double vision.
From the side of the thyroid gland:
in patients who received antibiotics for a long time from the group of tetracyclines, a reversible dark brown staining of the thyroid tissue is possible, in most cases not accompanied by a violation of its function.
From the teeth and bones:
doxycycline slows down osteogenesis, disrupts the normal development of teeth in children (the color of teeth changes irreversibly, and enamel hypoplasia develops).
From the musculoskeletal system:
arthralgia, myalgia.
Other:
Superinfection: candidiasis, glossitis, staphylococcal enterocolitis, pseudomembranous colitis, anogenital candidiasis, stomatitis, and vaginitis.