Doxycycline Hyclate 100 mg Injection (Single-Dose Vial)

Doxycycline Hyclate 100 mg Injection is an antibiotic that belongs to the tetracycline class of medications. It is the injectable form of doxycycline, often used when oral administration is not possible or appropriate.

Doxycycline is a broad-spectrum tetracycline antibiotic with bacteriostatic action (it inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit). The injection form is a powdered preparation (100 mg doxycycline per vial) that is reconstituted and given intravenously (IV) – for infusion use only, not for IM or oral use. Each vial (100 mg) is typically reconstituted with 10 mL sterile water (making 10 mg/mL) and then diluted further for IV infusion.

Uses

Doxycycline injection is indicated for many bacterial infections where IV therapy is needed. Common uses include:

• Tick-borne/rickettsial infections: The drug of choice for Rocky Mountain spotted fever, typhus, Q fever, rickettsial pox, and other rickettsial fevers.
• Atypical pneumonia: Mycoplasma pneumoniae, Legionella, Chlamydia (psittacosis/ornithosis), Mycoplasma and others.
• Sexually transmitted infections: Chlamydia trachomatis (especially lymphogranuloma venereum, granuloma inguinale) and syphilis/treponemal diseases (when penicillin cannot be used). Trachoma (Chlamydia in eyes) is also treated with tetracyclines.
• Spore-forming pathogens: Anthrax prophylaxis (post-exposure use of doxycycline) and plague/tularemia (Yersinia pestis/Francisella tularensis). Inhalational anthrax post-exposure, 100 mg IV twice daily (then oral) for 60 days, is FDA-approved.
• Gram-negative/Gram-positive bacteria: Susceptibility-based treatment for infections caused by susceptible Haemophilus, E. coli, Enterobacter, Klebsiella, Shigella, non-antrax Bacillus, Legionella, S. pneumoniae, Nocardia, and some anaerobes (Bacteroides, Clostridia). Neisseria gonorrhoeae/meningitidis or Treponema pallidum (syphilis) if penicillin is contraindicated. Listeria and Actinomyces can also be treated if penicillins are not used.
• Miscellaneous uses: Rocky Mountain spotted fever prophylaxis (e.g. after tick bite), infections by Protozoa (as adjunct for malaria prophylaxis or amebiasis), Borrelia recurrentis (relapsing fever).

Note: This IV form should only be used when oral doxycycline is unsuitable (e.g. patient cannot swallow, hospitalized, or needs immediate high blood levels) because overuse of IV antibiotics promotes resistance. As soon as clinically possible, switch to oral doxycycline to complete therapy.

How is it Given?

• Dosage: 100 mg (sometimes 200 mg initially, then 100 mg every 12 hours)
• Administration: Intravenous (IV) infusion over a period of 1–4 hours (Injection into a vein, not into the muscle or under the skin)
• The dose and length of treatment depend on the infection being treated and patient factors.
• The injectable form is typically reserved for hospitalized or severely ill patients who cannot take oral antibiotics.

Brand Names:

• Vibramycin® (for oral forms)
• Injectable forms are typically referred to by the generic name, “doxycycline hyclate for injection.”

Dosage and Administration

• Adults: The typical IV regimen is 200 mg on Day 1 (in 1 or 2 divided infusions), then 100–200 mg per day thereafter. For most infections, 100 mg IV every 12–24 hours is used (often 200 mg on day 1 to rapidly achieve blood levels, then 100 mg q12h). In severe infections or anthrax: 100 mg IV twice daily (200 mg/day) is common. Infants <8 years old are generally not given tetracyclines (teeth discoloration risk) unless life-threatening (e.g. anthrax).
• Pediatric: Not for children <8 (see Warnings). For kids >8, dose ~2 mg/kg on first day, then 1–2 mg/kg/day, up to adult doses. For pediatric post-exposure anthrax: 2.2 mg/kg IV q12h (total ~2 mg/lb) for 60 days.
• Infusions: Each 100 mg dose is infused over ≥60 minutes. More dilute infusion (0.5–1 mg/mL) over 60–90+ minutes is standard to minimize vein irritation and thrombophlebitis. Rapid IV bolus should be avoided (causes pain, hypotension). The label notes infusion times of 1–4 hours depending on dose, with 1 hour for 100 mg at 0.5 mg/mL. If long-term IV is needed, monitor for phlebitis or use a central line.
• Reconstitution: The 100 mg vial is reconstituted with 10 mL sterile water (giving 10 mg/mL), then diluted further into compatible IV fluids (D5W, NS, Ringer’s, etc.) to 0.1–1 mg/mL. (Particles may form if diluted outside those ranges.) Use within 48 hours if stored at room temperature (protected from light). The solution is acidic (pH ~2), so flush carefully if changing IV lines to avoid tissue injury.
• Avoid IM injection: The label warns DO NOT inject IM; accidental injection into soft tissue causes severe pain and necrosis.
• Storage: The lyophilized powder and reconstituted solution should be used promptly. The vial is “single-dose” – unused portion after opening should be discarded (it contains benzyl alcohol as preservative, posing neonatal risk). Detailed stability data: reconstituted to 0.1–1 mg/mL, stable 48h at 25°C (protected from light).
• Renal/Hepatic: No dose adjustment is typically needed for renal impairment. Doxycycline is primarily excreted unchanged in feces; in renal failure renal excretion falls but half-life is unchanged. However, in severe renal impairment (CrCl <10 mL/min), be cautious and ensure adequate hydration (to avoid crystalluria). Hepatic impairment: moderately safe (no dosage change in mild-to-moderate); monitor liver enzymes in severe hepatic disease as with any tetracycline.
• Duration: Generally treat at least 24–48 hours after symptoms resolve. Duration matches usual oral doxycycline (e.g. 7–10 days for pneumonia, at least 10–14 days for STDs). For anthrax, a full 60-day course is mandated regardless of route.

Side Effects and Safety

• Pain or irritation at the injection site
• Nausea, vomiting, diarrhea
• Loss of appetite
• Photosensitivity (increased risk of sunburn)
• Possible liver or kidney effects (especially in high doses or prolonged use)
• Hypersensitivity reactions (rash, itching, swelling)
• Yeast infections (due to disruption of normal flora)
• Rare: Blood disorders or severe allergic reactions

Common reactions: Similar to oral doxycycline. These include gastrointestinal effects – nausea, vomiting, diarrhea, esophagitis (if refluxed, though IV bypasses GI), abdominal pain, anorexia. Injection site reactions (phlebitis, pain, extravasation) can occur if infusion is too rapid or veins are fragile. Some patients may get photosensitivity rash (sunburn-like reactions) on sun exposure, advise sun protection. Hypersensitivity (rash, drug fever) can occur, as with all tetracyclines. Other effects: headache, dizziness, confusion (rare). Rarely, doxycycline can increase intracranial pressure (benign intracranial hypertension) – watch for headache or visual changes.

Serious risks:

• Bone/teeth: Because tetracyclines bind calcium, do not use in pregnancy or in children <8 years old (permanent tooth discoloration, bone growth retardation). (The label explicitly says avoid in dental/enamel formation period.)
• Clostridium difficile colitis: All antibiotics (esp. broad-spectrum) can trigger C. diff diarrhea or pseudomembranous colitis. If severe diarrhea or colitis develops (bloody, watery, abdominal pain), stop doxycycline and seek care.
• Allergy/anaphylaxis: Though rare, true allergy to tetracyclines can occur. Anaphylactic reactions have been reported. Discontinue if signs of anaphylaxis (hives, swelling, difficulty breathing) appear.
• Liver toxicity: Rarely, tetracyclines may cause fatal hepatotoxicity, especially if overdose or in pregnancy. Monitor LFTs if on high doses or with liver disease.
• Renal effects: Doxycycline itself is not typically nephrotoxic, but accumulation of doxycycline crystals can occur if patient is dehydrated or gets very high doses. Ensure adequate hydration. Monitor renal function on prolonged IV therapy.
• Blood & electrolytes: Doxycycline can predose potentiate warfarin (increase INR) as tetracyclines kill gut flora that synthesize vitamin K. Monitor INR if on warfarin. Also caution if patient is on other anticoagulants (may need dose adjustment). Doxycycline can slightly depress WBC or platelets rarely; be vigilant if used long-term.

Drug interactions: There are relatively few serious drug interactions. Commonly noted ones:

• Antacids, calcium, iron, magnesium bind tetracyclines and reduce absorption – less relevant for IV, but do not mix doxycycline injection with solutions containing calcium or iron. Infuse separately.
• Anti-coagulants: As above, can potentiate warfarin. Monitor coagulation parameters closely when starting or stopping doxycycline.
• Retinoids (isotretinoin): Risk of pseudotumor cerebri (intracranial hypertension). Avoid combination.
• Other antibiotics: Doxycycline is bacteriostatic, so may antagonize bactericidal agents like penicillin or aminoglycosides. Avoid mixing in the same IV line with calcium-containing solutions (risk of precipitate).

Precautions:

• Avoid in patients with known tetracycline allergy.
• Use sunscreen and protective clothing due to photosensitivity risk.
• Use caution in liver/kidney disease (see above).
• Check pregnancy status; not for pregnant women (Category D).
• Advise patients to complete therapy even if feeling better and to report severe diarrhea.
• Store injection per label; protect from light after reconstitution for up to 48 h.

Summary

Doxycycline hyclate 100 mg injection is an IV formulation of the antibiotic used when oral therapy is not feasible. It covers a wide range of infections including rickettsial diseases, pneumonia, certain STDs, anthrax, and others. The typical regimen is 200 mg IV on day 1 (divided into one or two infusions), then 100–200 mg IV daily (often 100 mg q12h) depending on infection severity. Each dose is infused over at least 1 hour (250–500 mL IV fluids) to minimize vein problems. The total dose should not exceed ~200 mg/day to avoid excessive toxicity. After reconstitution, the injected solution can be mixed into various IV fluids but must be clearly labeled “For IV use only”.