18.2 Special Populations: Older Adults, Extremes of Weight, Pregnancy & Lactation, and Immunocompromised Patients
Key Takeaways
The 2023 AGS Beers Criteria advise avoiding first-generation antihistamines, benzodiazepines, Z-drugs and skeletal muscle relaxants in older adults because they cause delirium and falls.
In obesity, succinylcholine is dosed on total body weight, rocuronium on ideal body weight, and induction agents such as propofol on lean body weight.
4F-PCC (Kcentra) dosing for warfarin reversal uses actual weight capped at 100 kg, so the maximum is 2,500, 3,500 or 5,000 units depending on the INR.
FDA advises avoiding NSAIDs from 20 weeks of pregnancy because of fetal kidney dysfunction and oligohydramnios, and ACE inhibitors and ARBs are fetotoxic in the second and third trimesters.
Ritonavir and cobicistat strongly inhibit CYP3A4, so oral midazolam, simvastatin and inhaled fluticasone are hazardous with boosted HIV regimens; lorazepam avoids the interaction.
18.2 Special Populations: Older Adults, Extremes of Weight, Pregnancy & Lactation, and Immunocompromised Patients
Note
Exam scope: 2025 outline subtopic 2A6 (Considerations for Special Populations: age groups, extremes of weight, pregnancy and lactation, critical illness, immunocompromised patients). Pediatric emergencies are covered in Section 13.1, obstetric emergencies in Section 13.3, and pharmacokinetics in critical illness in Section 1.3.
Older Adults
Older adults make up a growing share of ED visits. They have less physiologic reserve, more medications and more adverse drug events. ACEP's Geriatric Emergency Department Accreditation program encourages medication review as a standard part of ED care.
Key 2023 AGS Beers Criteria for ED Prescribing
| Avoid or use with caution | Reason | Preferred approach |
|---|---|---|
| First-generation antihistamines (diphenhydramine, hydroxyzine, promethazine) | Anticholinergic: delirium, retention, constipation | Second-generation antihistamines; non-drug sleep measures |
| Benzodiazepines and Z-drugs | Delirium, falls, fractures, motor vehicle crashes | Avoid except for alcohol or benzodiazepine withdrawal or seizures |
| Skeletal muscle relaxants (cyclobenzaprine, methocarbamol) | Anticholinergic effects, sedation, weak evidence | Heat, acetaminophen, topical NSAIDs |
| Meperidine | Neurotoxic metabolite; poor oral efficacy | Other opioids at reduced doses |
| Chronic NSAIDs, especially with anticoagulants or CKD | GI bleeding, kidney injury, heart failure | Short courses with gastroprotection, or topical NSAIDs |
| Sliding-scale insulin alone | Hypoglycemia without benefit | Basal or basal-bolus regimens |
| Sulfonylureas | Prolonged hypoglycemia | Other agents; glipizide if one must be used |
| Warfarin as initial therapy; rivaroxaban for long-term AF or VTE | Higher bleeding risk than alternatives | Apixaban is generally preferred |
| Nitrofurantoin when CrCl is below 30 mL/min | Ineffective and toxic | Another agent based on culture |
| Antipsychotics for behavioral symptoms of dementia | Boxed warning for higher mortality and stroke risk | Non-drug measures; use only for danger to self or others |
Kidney Function and Dosing
Serum creatinine falls with muscle mass, so a "normal" creatinine in a frail older adult can hide a CrCl of 30 mL/min. Use the Cockcroft-Gault estimate for renally cleared drugs: CrCl = [(140 − age) × weight] ÷ (72 × serum creatinine), × 0.85 for women. "Start low, go slow" applies to sedatives, opioids and antihypertensives.
Extremes of Body Weight
| Weight term | Definition |
|---|---|
| Total body weight (TBW) | Actual measured weight |
| Ideal body weight (IBW, Devine) | Men 50 kg, women 45.5 kg, + 2.3 kg per inch over 5 feet |
| Adjusted body weight (AdjBW) | IBW + 0.4 × (TBW − IBW) |
| Lean body weight (LBW) | Fat-free mass, calculated from height, weight and sex |
Dosing Weight for Common ED Drugs in Obesity
| Drug | Dosing weight and caps |
|---|---|
| Succinylcholine | TBW (plasma cholinesterase activity rises with body size) |
| Rocuronium | IBW (TBW dosing prolongs paralysis without a meaningful speed benefit) |
| Propofol, etomidate (induction) | LBW; reduce further in shock |
| Vancomycin loading dose | TBW, 20 to 35 mg/kg (maximum 3 g); maintenance by AUC monitoring |
| Aminoglycosides | AdjBW |
| Enoxaparin treatment dose | TBW at 1 mg/kg every 12 hours; check anti-Xa levels above about 150 kg |
| Alteplase for stroke | 0.9 mg/kg, maximum 90 mg |
| Tenecteplase for stroke | 0.25 mg/kg, maximum 25 mg |
| 4F-PCC (Kcentra) for warfarin reversal | Actual weight capped at 100 kg: INR 2 to below 4 → 25 units/kg (max 2,500); INR 4 to 6 → 35 units/kg (max 3,500); INR above 6 → 50 units/kg (max 5,000) |
Underweight patients: when actual weight is below IBW, use actual weight. In patients with low muscle mass, both creatinine-based kidney estimates and fixed doses need care.
After bariatric surgery: avoid NSAIDs (they cause marginal ulcers) and extended-release products (absorption is unpredictable), and expect altered oral absorption.
Pregnancy
Physiology That Changes Dosing
- Plasma volume and volume of distribution increase.
- Glomerular filtration rises by about 50%, lowering levels of renally cleared drugs such as levetiracetam and enoxaparin.
- CYP3A4, CYP2D6 and CYP2C9 activity increases while CYP1A2 decreases. Lamotrigine levels fall sharply because glucuronidation increases.
- Albumin falls, raising the free fraction of highly bound drugs.
Labeling
The FDA Pregnancy and Lactation Labeling Rule (PLLR), effective 2015, removed the A, B, C, D and X letter categories. Labels now give narrative risk summaries in section 8.1 (Pregnancy), 8.2 (Lactation) and 8.3 (Females and Males of Reproductive Potential).
Emergency Drug Choices in Pregnancy
Do not withhold needed treatment. Resuscitation drugs, RSI agents, epinephrine for anaphylaxis, CT pulmonary angiography with contrast and standard ACLS doses are all appropriate. The mother's survival is the fetus's best protection.
| Generally acceptable | Avoid or use only with specialist input |
|---|---|
| Acetaminophen | NSAIDs from 20 weeks (FDA 2020: fetal kidney dysfunction, oligohydramnios; ductal closure later in pregnancy) |
| Penicillins, cephalosporins, azithromycin | ACE inhibitors and ARBs (fetotoxic in the second and third trimesters) |
| LMWH (preferred anticoagulant) | Warfarin (embryopathy; used only for mechanical valves under specialist care); DOACs (too little data) |
| Labetalol, nifedipine, hydralazine (Section 13.3) | Valproate (neural tube defects, lower IQ); carbamazepine and phenytoin (malformations) |
| Insulin | Tetracyclines in the second and third trimesters; fluoroquinolones unless there is no alternative |
| Metoclopramide, ondansetron (after counseling) for nausea | Isotretinoin, methotrexate, misoprostol (outside obstetric use) |
In September 2025 FDA began a labeling change about a possible association between acetaminophen use in pregnancy and neurodevelopmental conditions. ACOG and SMFM responded that acetaminophen remains appropriate when it is needed for pain or fever, since untreated fever also carries risk. Use the lowest effective dose for the shortest time.
Rh(D) immune globulin: for bleeding, trauma or pregnancy loss in Rh-negative patients, follow current ACOG guidance. ACOG's 2024 update says it can be forgone for abortion or pregnancy loss before 12 weeks. Later in pregnancy, the standard dose is 300 mcg within 72 hours.
Lactation
- Most ED medications are compatible with breastfeeding. Check LactMed, the free NIH database.
- Avoid codeine and tramadol (FDA), and use the lowest effective opioid doses for short courses.
- After procedural sedation or anesthesia, the patient can resume breastfeeding once alert; pumping and discarding milk is generally unnecessary.
- Breastfeeding does not need to be interrupted after iodinated or gadolinium contrast (ACR).
Immunocompromised Patients
Solid Organ Transplant Recipients
- Do not stop immunosuppressants without speaking to the transplant team.
- Tacrolimus and cyclosporine interact with azoles, macrolides, diltiazem, verapamil and nirmatrelvir-ritonavir (all raise levels and toxicity) and with rifampin (which lowers levels and risks rejection). Calcineurin inhibitors also cause nephrotoxicity, hyperkalemia and hypomagnesemia.
- Keep PJP prophylaxis (usually trimethoprim-sulfamethoxazole) and expect atypical, opportunistic infections with blunted fever.
People Living With HIV
Ritonavir- or cobicistat-boosted regimens strongly inhibit CYP3A4:
- Oral midazolam and triazolam are contraindicated. Lorazepam, which is glucuronidated, is a safer anxiolytic.
- Simvastatin and lovastatin are contraindicated.
- Inhaled or intranasal fluticasone and budesonide can cause Cushing syndrome and adrenal suppression.
- Fentanyl, oxycodone, DOACs and some calcium channel blockers need dose reduction or another drug.
Integrase inhibitors chelate with antacids and other divalent cations, so separate the doses. Never stop antiretroviral therapy just because the patient has been admitted.
Asplenia and Chronic Corticosteroid Use
- Asplenia: fever is an emergency because of the risk of overwhelming infection from encapsulated organisms. Give ceftriaxone (plus vancomycin where resistant pneumococcus is a concern) within an hour.
- Chronic corticosteroids: prednisone of about 20 mg/day or more for 3 weeks or longer can suppress the adrenal axis. Give stress-dose hydrocortisone 100 mg IV for shock or major stress (Section 11.3).
- Biologics such as TNF inhibitors and JAK inhibitors raise the risk of TB, fungal and opportunistic infections. Live vaccines are contraindicated; tetanus toxoid is not a live vaccine.
- Febrile neutropenia is covered in Section 17.3.
A 168-cm, 150-kg man (IBW about 64 kg) needs rapid sequence intubation. Which dosing-weight approach for the neuromuscular blocker is most appropriate?
Rocuronium 1.2 mg/kg × 64 kg = about 75 mg
Succinylcholine 0.5 mg/kg × 150 kg = 75 mg
Rocuronium 1.2 mg/kg × 150 kg = 180 mg
Succinylcholine 1.5 mg/kg × 64 kg = about 100 mg
A 130-kg woman taking warfarin has an intracranial hemorrhage with an INR of 3.2. Using Kcentra labeling, what 4F-PCC dose should be prepared, along with vitamin K 10 mg IV?
2,500 units (25 units/kg, weight capped at 100 kg)
4,550 units (35 units/kg × 130 kg)
3,250 units (25 units/kg × 130 kg)
5,000 units (50 units/kg, weight capped at 100 kg)
A woman at 28 weeks of pregnancy has an ankle sprain and asks for something stronger than rest and ice. She has no other medical problems. Which analgesic recommendation is most appropriate?
Ketorolac 10 mg orally every 6 hours for 5 days
Naproxen 500 mg twice daily for 5 days
Acetaminophen 650 to 1,000 mg every 6 hours as needed, lowest effective dose
Ibuprofen 600 mg every 6 hours for 7 days
A 45-year-old man taking darunavir boosted with ritonavir needs anxiolysis before a minor procedure. Which agent is most appropriate?
Oral midazolam 7.5 mg
Oral lorazepam 1 mg
Oral triazolam 0.25 mg
Oral alprazolam 1 mg
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