13.2 Renal and Genitourinary Effects

TCO IV.A.5 tests renal and genitourinary treatment effects: what cisplatin, ifosfamide, high-dose methotrexate, nephrotoxic antimicrobials, uric acid, mesna, BK virus, bladder radiation, and a solitary kidney after nephrectomy do to urine, electrolytes, and bladder mucosa. This is not the emergency chapter for tumor lysis syndrome (TLS) staging, syndrome of inappropriate antidiuretic hormone secretion (SIADH), or diabetes insipidus (DI). Those full playbooks live later. Here the CPHON nurse measures intake and output (I&O), daily weight, and the color of the urine, and does not invent a single creatinine cutoff as ONCC fact.

A 3-year-old after Wilms tumor nephrectomy, a 12-year-old receiving cisplatin for osteosarcoma who is wasting magnesium, and a teenager on day +45 after allogeneic HSCT with clots in the urine are the pictures.

Drug nephrotoxicity and what you actually monitor

Cisplatin injures proximal tubules. The child may have a rising creatinine, magnesium wasting (and often potassium and calcium wasting), and reduced concentrating ability. Hydration before, during, and after the infusion is the protocol, not a courtesy. Replace magnesium as ordered even when the serum value looks "borderline"—symptoms (cramps, tetany, QTc risk) lag. Do not hang the next cisplatin because last month's creatinine was normal if urine output has fallen and weight is up from third-spacing.

Ifosfamide causes a Fanconi-like proximal tubular wasting: phosphate, bicarbonate, glucose, and amino acids spill into urine. Watch hypophosphatemia, acidosis, and rickets-like bone injury on repeated courses. It is not "just cisplatin again." Ifosfamide also shares hemorrhagic cystitis risk with cyclophosphamide.

High-dose methotrexate can precipitate in tubules when urine is acidic or the child is volume-depleted. Alkalinization, vigorous hydration, timed levels, and leucovorin rescue are the chemotherapy-chapter skills; the renal chapter's point is that delayed clearance is a kidney problem as well as a mucositis problem. Nonsteroidal anti-inflammatory drugs, proton-pump inhibitors, and some penicillins that delay methotrexate clearance still get flagged here.

Vancomycin and acyclovir add drug nephrotoxicity, especially when stacked with platinum, ifosfamide, or a dehydrated toddler. Troughs, hydration, and a second look at the medication list are the nursing moves. Do not treat one printed creatinine number as the ONCC "hold everything" threshold—centers use age-based ranges, cystatin C, and urine output. A doubling from that child's baseline matters more than a textbook adult cutoff.

TLS uric-acid nephropathy is a signpost with two named drugs. Allopurinol blocks new uric acid formation and is the usual prophylaxis. Rasburicase enzymatically cleaves existing uric acid and is used for high-risk or established hyperuricemia. Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a rasburicase caution: hemolysis can be severe. Do not give rasburicase as a casual extra in a child from a high-prevalence G6PD population without the team's G6PD plan. Send uric acid samples on ice as the laboratory requires after rasburicase or the value will be falsely low. Full TLS electrolyte titration (potassium, phosphate, calcium) lives in the metabolic-emergency chapter.

Hemorrhagic cystitis, SIADH/DI, and the remaining kidney

Hemorrhagic cystitis (HC) splits in time:

• Early, drug: acrolein from cyclophosphamide or ifosfamide. Mesna binds acrolein; hyperhydration and frequent voiding keep the bladder from sitting in toxin. Gross hematuria, clots, and bladder spasm during the alkylator window are HC until proven otherwise. Do not skip mesna because the child "looks well."
• Late, viral: BK virus (and sometimes adenovirus) after allogeneic HSCT, often after engraftment. Hematuria, urgency, and clots need viral testing, hydration, platelet support, pain control, and urology for clot retention—not another dose of mesna as the only plan.

Bladder radiation (selected rhabdomyosarcoma and other pelvic fields) causes acute radiation cystitis and later telangiectasias, fibrosis, and hematuria. Teach families that pink urine months after radiation is reportable, not "just a UTI until antibiotics fail."

SIADH (too little water excreted; falling sodium) and DI (too much water excreted; rising sodium, huge urine output) are signposted. Vincristine-associated SIADH and pituitary or hypothalamic injury (craniopharyngioma, germ-cell CNS tumors, surgery, radiation) belong in their emergency sections. In this chapter, notice a sudden change in urine volume and sodium, weigh the child, and escalate rather than coaching "drink more" or "drink less" from memory.

After nephrectomy for Wilms tumor or other renal tumors, the child has a solitary kidney. Precautions: avoid nephrotoxic stacking when another antibiotic will do, treat dehydration aggressively, protect against sports trauma per surgery and oncology guidance, and teach families that over-the-counter ibuprofen is not a casual fever medicine. Blood pressure surveillance belongs in survivorship. Do not treat the remaining kidney as indestructible because "creatinine is still 0.4."

I&O, weight, hematuria, and what families must call about

Daily tools are simple and pediatric: strict I&O, daily weight on the same scale, urine dip or visual inspection for hematuria, and electrolytes that actually include magnesium and phosphate, not only sodium and potassium. A preschooler in a diaper needs weighed diapers, not a guess. Orthostatic dizziness after cisplatin may be magnesium, volume, or both.

Teach call parameters in family language: no urine for longer than the team specified, weight up overnight with swelling, tea-colored or frankly bloody urine, clots, pain with voiding after cyclophosphamide, or a child who is newly polydipsic with huge wet diapers (DI signpost). Do not send a child home after ifosfamide with "drink a lot" and no mesna teaching.

The CPHON product is a nurse who hydrates cisplatin and methotrexate correctly, replaces magnesium, gives mesna on time, thinks BK when late hematuria follows transplant, holds rasburicase for the G6PD question, and protects the solitary kidney—without quoting a single invented creatinine cutoff as if ONCC printed it.