What are the potential side effects of taking 100 mg of doxycycline (antibiotic)?

Side Effects of 100 mg Doxycycline

Doxycycline 100 mg is generally well-tolerated, but gastrointestinal symptoms (particularly nausea, vomiting, and diarrhea) and photosensitivity are the most common side effects, while serious complications like esophagitis, severe skin reactions, and hematologic abnormalities are rare but important to recognize. 1

Common Side Effects

Gastrointestinal Effects

• Nausea, vomiting, and diarrhea are the most frequently reported side effects, occurring in approximately 25% of patients on prolonged therapy 2
• Anorexia, glossitis, dysphagia, and enterocolitis can occur 1, 3
• Esophagitis and esophageal ulcerations are notable risks, particularly when tablets/capsules are taken immediately before lying down 1, 3
• The incidence of GI adverse effects increases significantly with the 200 mg daily dose compared to 100 mg daily 4

Dermatologic Effects

• Photosensitivity is a characteristic side effect of doxycycline, occurring in approximately 3% of patients at 100 mg daily and 22% with prolonged use 5, 2
• Photosensitivity reactions typically occur within days of starting treatment and require sun or UV exposure 6
• Maculopapular and erythematous rashes can develop 1, 3
• Doxycycline is more photosensitizing than minocycline 1

Other Common Effects

• Vaginal candidiasis can occur with any antibiotic therapy 1
• Tooth discoloration may occur, reported in approximately 5.5% of patients on prolonged therapy 2

Serious but Rare Side Effects

Severe Dermatologic Reactions

• Stevens-Johnson syndrome, toxic epidermal necrolysis, and erythema multiforme are rare but potentially life-threatening 1, 3
• Exfoliative dermatitis has been reported but is uncommon 1, 3
• Photo-onycholysis (nail separation due to light exposure) can occur 1

Hematologic Effects

• Hemolytic anemia, thrombocytopenia, neutropenia, and eosinophilia have been reported 1, 3

Hepatotoxicity

• Hepatitis, jaundice, hepatic failure, and pancreatitis are rare complications 1, 3

Hypersensitivity Reactions

• Urticaria, angioneurotic edema, anaphylaxis, anaphylactoid purpura, serum sickness, and pericarditis can occur 1, 3
• Exacerbation of systemic lupus erythematosus has been reported 1, 3

Neurologic Effects

• Benign intracranial hypertension (pseudotumor cerebri) is a rare phenomenon associated with tetracyclines 1
• Bulging fontanels in infants and intracranial hypertension in adults 3

Renal Effects

• Rise in blood urea nitrogen (dose-related) has been reported 1
• Renal dysfunction is less common with doxycycline than with other tetracyclines 1

Gastrointestinal Complications

• Pseudomembranous colitis (C. difficile infection) can occur 1
• Inflammatory lesions with monilial overgrowth in the anogenital region 1, 3

Risk Factors for Increased Side Effects

• Age ≥50 years significantly increases the incidence of GI adverse effects 4
• Higher doses (200 mg daily) are associated with more frequent GI side effects compared to 100 mg daily 4
• Prolonged therapy duration increases risk of photosensitivity and tooth discoloration 2
• Previous tetracycline exposure may lead to faster onset of reactions due to sensitization 6

Critical Prevention Strategies

To Prevent Esophagitis

• Take doxycycline with a full glass of water (8 ounces) and remain upright for at least 1 hour after administration 1, 6
• Take with food to reduce gastrointestinal intolerance 1
• Never take immediately before lying down 1, 3

To Prevent Photosensitivity

• Advise patients to avoid direct sun exposure or UV radiation during treatment 1, 6
• This is particularly important since infections requiring doxycycline often occur during summer months 1

Drug Interactions to Avoid

• Separate doxycycline doses by at least 2 hours from dairy products, antacids, and supplements containing calcium, iron, magnesium, or sodium bicarbonate 1, 6
• Be aware of interactions with oral anticoagulants, anticonvulsants, hormonal contraceptives, and penicillins 1

Monitoring Recommendations

• Patients should be monitored for skin reactions throughout the entire treatment course, with particular vigilance during the first 2 weeks 6
• For long-term therapy (>1 month), routine toxicity monitoring with complete blood count, renal function, and liver function tests should be performed intermittently 1
• Patients should report any skin changes immediately, regardless of timing during treatment 6

Special Populations

Contraindications

• Pregnancy (Category D) - doxycycline is contraindicated except for life-threatening illness 1
• Breastfeeding - distributed into milk; discontinue nursing or the drug 1
• Children <8 years of age - risk of permanent tooth discoloration and enamel hypoplasia 1
• Hypersensitivity to any tetracycline 1

Cautions

• Hepatic impairment and concurrent use of hepatotoxic drugs 1
• Myasthenia gravis (potential for neuromuscular blockade) 1
• Systemic lupus erythematosus (risk of exacerbation) 1

Management of Side Effects

• Most adverse effects resolve with discontinuation of the medication 1
• Provide symptomatic treatment for pruritus and discomfort from skin reactions 6
• For severe reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis, anaphylaxis), immediate discontinuation and emergency management are required 1