Pharmacology · patient case question
What is the most important age-related consideration when prescribing an antibiotic for Patient B?
Patient case: Five medication lists in one session
Patient: Four separate patients
Chief Complaint: A: denture soreness. B: needs an antibiotic before an extraction. C: routine review. D: brought in obtunded by her daughter.
Background: A, 68-year-old male: benign prostatic hyperplasia on terazosin, hyperlipidaemia on simvastatin. Denture stomatitis diagnosed today and systemic fluconazole considered. B, 90-year-old female: frail, on no regular medication. C, 71-year-old female: rheumatoid arthritis on methotrexate, osteoporosis on oral alendronate for six years. D, 79-year-old female: long-standing hypothyroidism, ran out of levothyroxine some weeks ago.
Vital Signs: D: T 94.6°F · HR 48 bpm · RR 8 · BP 96/58 mmHg · drowsy and confused
Findings: A: erythematous denture-bearing palatal mucosa. C: panoramic radiograph taken for pre-operative assessment.
Show answer and explanation
Correct answer: B. Reduced glomerular filtration rate
- A. Gastric acid production DECREASES with age, and gastric emptying slows. These alter the rate of absorption somewhat but rarely the extent, and they are not the governing concern.
- B. CORRECT. Glomerular filtration declines steadily with age — roughly 1% per year after about 40 — so a 90-year-old may have half the renal clearance of a young adult. The trap is that SERUM CREATININE is a poor guide in the elderly: reduced muscle mass keeps it deceptively normal even when clearance is substantially impaired, so an estimated GFR or a Cockcroft-Gault calculation is needed. Renally excreted drugs accumulate, and most of the antibiotics used in dentistry — the penicillins and cephalosporins — are renally cleared. Reduce the dose or lengthen the interval.
- C. Total body water DECREASES with age and body fat proportion increases. That reduces the volume of distribution of water-soluble drugs and INCREASES it for lipid-soluble ones, prolonging their half-life — relevant for benzodiazepines, but not the leading antibiotic consideration.
- D. Hepatic mass and hepatic blood flow both DECREASE with age, so first-pass metabolism FALLS — which raises the bioavailability of drugs with high first-pass extraction rather than lowering it.
Note: The wider geriatric prescribing picture: polypharmacy and interaction risk, reduced serum albumin raising the free fraction of highly protein-bound drugs, and greater CNS sensitivity to sedatives and opioids. Start low and go slow, and review the whole medication list rather than the new prescription alone.