A/T/S
Clinical safety rating: caution
Antithrombin (AT) is a serine protease inhibitor used as an anticoagulant for prophylaxis and treatment of thromboembolic events, particularly in patients with hereditary antithrombin deficiency. It inactivates thrombin and factor Xa, providing endogenous anticoagulant activity.
A/T/S (erythromycin) is a macrolide antibiotic that acts by binding to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis and bacterial growth.
| Metabolism | Antithrombin is a glycoprotein; its metabolism involves cellular uptake and catabolism, but specific CYP450 enzymes are not involved. Degradation occurs via proteolysis and reticuloendothelial system clearance. |
| Excretion | Renal: 10-20% (active drug and metabolites); Fecal: minimal; Biliary: not significant. |
| Half-life | Terminal elimination half-life: 1–2 hours (prolonged in hepatic impairment). |
| Protein binding | 70-90% bound to serum albumin. |
| Volume of Distribution | 0.5–0.8 L/kg (low Vd, minimal tissue penetration). |
| Bioavailability | Topical: 1–5% (minimal systemic absorption). |
| Onset of Action | Topical: within 1–2 days of continuous application; Oral: not applicable. |
| Duration of Action | Topical: 8–12 hours after single application; repeated use maintains therapeutic effect. |
| Molecular Weight | 733.93 |
Dosing is individualized based on antithrombin activity level. For acute thrombotic events: initial bolus of 30-50 IU/kg followed by maintenance dosing to achieve target activity levels (80-120% of normal). Prophylaxis: 40-60 IU/kg every 24 hours.
| Dosage form | SOLUTION |
| Renal impairment | No specific adjustment required; drug is not renally eliminated. |
| Liver impairment | No specific adjustment; antithrombin is produced in the liver, but exogenous replacement does not require dose adjustment in hepatic impairment. |
| Pediatric use | Dosing based on weight and antithrombin levels; typical initial dose 30-50 IU/kg, followed by maintenance to achieve target levels. Clinical trial data limited in neonates. |
| Geriatric use | No specific adjustment; use standard dosing with monitoring of antithrombin activity and bleeding risk. |
| 1st trimester | Topical erythromycin is considered safe; systemic absorption minimal. No teratogenicity in animal studies. |
| 2nd trimester | Safe; no known fetal risk. |
| 3rd trimester | Safe; avoid prolonged high-dose use near term due to theoretical risk of infantile hypertrophic pyloric stenosis. |
Clinical note
Antithrombin is a plasma-derived anticoagulant used for hereditary antithrombin deficiency. There are no adequate studies in pregnant women; use only if clearly needed and potential benefit justifies risk to fetus.
| Placental transfer | Unknown but likely negligible due to low systemic absorption with topical use. |
| Breastfeeding | Minimal systemic absorption; considered compatible with breastfeeding. Use on limited skin areas. |
| Lactation Rating |
■ FDA Black Box Warning
None.
| Common Effects | Bleeding (minor: bruising, epistaxis), Hypersensitivity (rash, urticaria), Fever, Dizziness, Nausea, Injection site reactions, Headache |
| Serious Effects | Bleeding (intracranial, retroperitoneal, gastrointestinal); anaphylaxis; thromboembolism if discontinued abruptly; antibody formation against antithrombin. |
Hypersensitivity to erythromycin or any component
| Precautions | Hypersensitivity reactions including anaphylaxis have occurred., Prolonged use may result in overgrowth of nonsusceptible organisms including fungi., Use with caution in patients with hepatic impairment., Potential for QT prolongation and ventricular arrhythmias, especially with intravenous administration or concomitant drugs that prolong QT interval. |
| Food/Dietary |
Loading safety data…
| L2 (Probably Compatible) |
| Teratogenic Risk | FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; no adequate human studies in first trimester. Topical erythromycin has minimal systemic absorption; risk to fetus is low across all trimesters. |
| Fetal Monitoring | No specific monitoring required for topical use. For prolonged use, monitor for signs of maternal hypersensitivity or secondary infection. |
| Fertility Effects | No known impact on fertility. Topical erythromycin does not affect reproductive function or fertility outcomes. |
| No specific food interactions. Avoid excessive alcohol consumption as it may increase skin dryness. |
| Clinical Pearls | A/T/S (erythromycin 2% topical solution) is indicated for acne vulgaris. Avoid contact with eyes, mouth, and mucous membranes. May cause skin dryness or irritation; use moisturizer. Effectiveness may decrease with prolonged use due to bacterial resistance. Not recommended for use with other topical erythromycin products or clindamycin to avoid antagonism. |
| Patient Advice | Apply a thin layer to affected areas twice daily after washing. · Avoid contact with eyes, lips, and mouth; if contact occurs, rinse thoroughly with water. · May cause stinging, burning, or peeling; if irritation persists, consult your doctor. · Use sunscreen daily as this medication may increase sensitivity to sunlight. · Do not use more than prescribed; overuse may increase side effects without improving results. · Inform your doctor if you are pregnant, planning to become pregnant, or breastfeeding. · Keep away from open flames or heat sources; product is flammable. |