Evaluate allergy history, pregnancy status, and esophageal health before doxycycline.
Absolute: tetracycline hypersensitivity. Relative: prolonged use in children <8 years, pregnancy, lactation, esophageal motility disorders, and concomitant hepatotoxic drugs.
Documented immediate hypersensitivity to doxycycline or other tetracycline-class antibiotics — prior anaphylaxis, angioedema, or severe cutaneous reactions require permanent avoidance and selection of an alternate class.
Pregnancy, particularly after the first trimester, because fetal tooth discoloration and impaired bone growth are dose-related; reserve use for life-threatening infections when no safer agent is available and counsel on contraception and folate support.
Breastfeeding premature or jaundiced infants, since small amounts enter milk and can disturb gut flora; short courses may be acceptable with pediatric monitoring for diarrhea, thrush, or rash.
Children under 8 years needing prolonged or repeated courses, as enamel hypoplasia risk increases with cumulative exposure; short 5–7 day regimens are acceptable when benefits outweigh risks but require dental follow-up.
Severe esophageal dysmotility or history of pill-induced esophagitis; capsules should be taken upright with water or switched to a liquid formulation to prevent ulceration.
Concurrent isotretinoin or other vitamin A derivatives owing to additive risk for intracranial hypertension; coordinate therapy or choose alternative antimicrobials.