CETAMIDE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for CETAMIDE (CETAMIDE).
CETAMIDE is an antimicrobial combination of sulfadiazine (a sulfonamide) and trimethoprim. Sulfonamides inhibit dihydropteroate synthase, blocking folate synthesis; trimethoprim inhibits dihydrofolate reductase, producing sequential blockade of folic acid metabolism.
| Metabolism | Sulfadiazine is metabolized via acetylation (N-acetyltransferase) and glucuronidation; trimethoprim is metabolized by oxidative pathways (N-oxidation, N-demethylation) and conjugated with glucuronic acid. |
| Excretion | Primarily renal (85-90%) as unchanged drug; biliary/fecal (5-10%). |
| Half-life | 6-8 hours; prolonged (up to 30 hours) in severe renal impairment (CrCl <30 mL/min). |
| Protein binding | 20-25% bound to albumin. |
| Volume of Distribution | 0.5-0.8 L/kg; indicates distribution into total body water. |
| Bioavailability | Oral: 90-100% (well absorbed). |
| Onset of Action | Oral: 2-4 hours; IV: immediate; IM: 1-2 hours. |
| Duration of Action | 12-24 hours; clinical response correlates with trough levels of 15-40 mg/L. |
500 mg orally every 6 hours; maximum 4 g per day.
| Dosage form | OINTMENT |
| Renal impairment | CrCl 10-50 mL/min: 250 mg every 6 hours. CrCl <10 mL/min: 250 mg every 12 hours. |
| Liver impairment | Child-Pugh Class C: avoid use; Class A or B: no adjustment needed. |
| Pediatric use | 10-15 mg/kg orally every 6 hours; maximum 100 mg/kg/day. |
| Geriatric use | Consider dose reduction based on renal function; initial dose not to exceed 2 g per day. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for CETAMIDE (CETAMIDE).
| Breastfeeding | Excreted in breast milk in low quantities. M/P ratio not established. Potential risk of adverse effects in nursing infants (e.g., renal dysfunction, bleeding). Use with caution if alternative therapies are not available. |
| Teratogenic Risk | Pregnancy category C. First trimester: Potential risk of neural tube defects based on animal studies. Second and third trimesters: Increased risk of premature closure of ductus arteriosus and oligohydramnios due to prostaglandin synthesis inhibition. Limited human data; avoid unless benefit outweighs risk. |
■ FDA Black Box Warning
Sulfonamides have been associated with fatal reactions such as Stevens-Johnson syndrome, toxic epidermal necrolysis, agranulocytosis, aplastic anemia, and other blood dyscrasias.
| Serious Effects |
Hypersensitivity to sulfonamides or trimethoprim; severe hepatic or renal impairment; megaloblastic anemia due to folate deficiency; pregnancy (especially first trimester and near term); lactation; pediatric patients <2 months of age.
| Precautions | Increased risk of hypersensitivity reactions (SJS, TEN); hematologic toxicity (agranulocytosis, thrombocytopenia); hepatotoxicity; renal toxicity due to crystalluria; hemolytic anemia in G6PD-deficient patients; photosensitivity. |
| Food/Dietary | No significant food interactions known. No dietary restrictions required. |
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| Fetal Monitoring |
| Monitor amniotic fluid volume (oligohydramnios risk) and ductus arteriosus patency via fetal echocardiography after 20 weeks. Maternal renal function and platelet count should be assessed regularly. |
| Fertility Effects | Reversible inhibition of ovulation and luteolysis due to prostaglandin synthesis inhibition. May impair implantation and delay conception. Effects resolve upon discontinuation. |
| Clinical Pearls | Cetamide (sulfacetamide sodium) is a topical ophthalmic sulfonamide used for bacterial conjunctivitis. Monitor for hypersensitivity, as cross-allergy with other sulfonamides may occur. Use with caution in patients with dry eye syndrome or corneal abrasions. Avoid prolonged use to prevent superinfection. Administer with clean hands and do not touch dropper tip to any surface. |
| Patient Advice | Wash hands before and after applying the eye drops. · Do not touch the dropper tip to your eye or any other surface. · Wait 5 minutes between different eye drops if using more than one type. · Complete the full course of treatment even if symptoms improve. · Do not wear contact lenses during treatment unless directed by your doctor. · Stop use and contact your doctor if you experience rash, itching, or swelling. · Keep the bottle tightly closed when not in use and store at room temperature. |