GC043 Drugs And The Kidney
Drugs and the kidney encompasses the pharmacological principles of how renal function affects drug metabolism, excretion, and dosing, as well as the nephrotoxic potential of various medications and their mechanisms of causing kidney injury.
Drugs and the Kidney
This lecture sits at the intersection of clinical pharmacology and nephrology — two domains that examiners love to combine. The core concept is deceptively simple: the kidney both eliminates drugs and is a target of drug toxicity. This creates a dangerous bidirectional relationship:
- Impaired kidneys → altered drug handling → need dose adjustment → risk of systemic toxicity
- Drugs → kidney injury → functional (haemodynamic) or structural (parenchymal) damage
The lecture teaches you to think like a prescribing physician: before writing any prescription for a patient with kidney disease, ask three questions: (a) Will this drug accumulate? (b) Could this drug hurt the kidney further? (c) What side effects become more dangerous with impaired renal function?
Learning Objectives (from the lecture) [1]
1. Principles of drug prescribing in patients with impaired kidney function 2. Renal complications associated with drugs — examples, prevention & management
The kidneys receive 25% of cardiac output [1]
This is an enormous blood flow relative to organ mass (~3,333 mL/min/kg for kidneys vs. 25 mL/min/kg for adipose tissue) [4]. This means:
- Every drug circulating in the blood is delivered to the kidney in high concentration — the kidney "sees" more drug per gram of tissue than almost any other organ.
- The kidney's job is to filter, secrete, reabsorb, and concentrate substances. Renal tubular cells are metabolically hyperactive, and they actively transport drugs from blood into tubular lumen (and vice versa). This concentrating mechanism means intracellular drug levels in tubular epithelium can be far higher than plasma levels.
- GFR and renal tubular functions determine drug clearance — when these decline, drugs accumulate. [1]
Susceptibility (when there is CKD) to direct or indirect injury → AKI on CKD [1]
A patient with pre-existing CKD has fewer functioning nephrons. Each remaining nephron is already working harder (hyperfiltration). Adding a nephrotoxic drug is like kicking someone who's already down — the margin for error is razor-thin. This is why CKD increases susceptibility to further kidney damage. [1][2]
Core Concept 2: Principles of Drug Prescribing in Renal Impairment
Important Principles in Drug Prescription: [1] 1. Avoid further nephrotoxic insult 2. Attention to correct dose 3. Beware of side-effects in patients with impaired kidney function
| Principle | Rationale | Clinical Example |
|---|---|---|
| Avoid nephrotoxic insult | Damaged kidneys can't tolerate additional toxic hits; may precipitate AKI on CKD or accelerate progression to ESRF | Avoid NSAIDs in CKD patients; use alternatives to aminoglycosides when possible |
| Correct dose | Reduced GFR → reduced drug clearance → accumulation → toxicity. Must adjust dose and/or interval using the metric specified by the drug label | Sitagliptin uses renal-function dose bands; TDF intervals lengthen as renal clearance falls |
| Beware side effects | Some drug side effects are amplified by renal impairment — not because of accumulation, but because renal failure alters physiology | Ethambutol → optic neuritis (accumulates); Acyclovir → CNS toxicity/crystalluria; INAH → peripheral neuropathy; Quinolones → CNS effects/seizures; Imipenem → seizures |
Exam Trap
Students often focus only on dose adjustment. The lecture explicitly highlights that some drugs cause enhanced side effects in renal impairment even at "correct" doses because the underlying physiology has changed (e.g., uraemic patients have altered BBB permeability, electrolyte derangements that lower seizure threshold). Always think beyond just adjusting the milligrams.
Two levers are available: reduce the dose and/or extend the interval. Which lever to use is drug-specific. Concentration-dependent antibiotics such as aminoglycosides often retain an effective peak while the interval is lengthened; time-dependent antibiotics generally need adequate time above the MIC. Do not improvise from these principles alone—use the current product label/local renal-dosing protocol and therapeutic drug monitoring (TDM) where indicated.
Reno-Protection in Patients with Impaired Renal Function (CKD): [1] 1. Prevent additional injury / insult to the kidneys 2. Optimal blood pressure control 3. Proteinuria reduction [RAAS inhibition/blockade] 4. SGLT2 inhibition 5. No smoking 6. Vascular risk factors
This slide is a complete reno-protective strategy checklist. Let's unpack each:
| Strategy | Mechanism / Rationale |
|---|---|
| Prevent additional injury | Avoid or minimize NSAIDs, unnecessary high-risk contrast exposure, aminoglycosides and unregulated nephrotoxic herbal products; recurrent or severe AKI can accelerate CKD progression |
| BP control | Hypertension → intraglomerular hypertension → glomerulosclerosis. KDIGO suggests standardized office SBP < 120 mmHg when tolerated in adults with high BP and non-dialysis CKD; the target must be individualized for frailty, postural symptoms and measurement method [16] |
| RAAS blockade (ACEI/ARB) | Dilates efferent arteriole → ↓ intraglomerular pressure → ↓ proteinuria → slows progression. The single most important pharmacological intervention in proteinuric CKD |
| SGLT2 inhibition | Tubuloglomerular feedback restoration, ↓ intraglomerular pressure, anti-inflammatory/anti-fibrotic effects. Now a pillar of CKD management alongside RAAS blockade [5] |
| No smoking | Smoking accelerates atherosclerosis of renal vasculature, increases oxidative stress, worsens proteinuria |
| Vascular risk factors | DM control, lipid management, weight — CKD is a "vascular disease equivalent" |
Dose Adjustment Examples (Slide-by-Slide High Yield)
DPP-4 inhibitors — endogenous incretin → ↑ insulin & ↓ glucagon in a glucose-dependent manner → blood glucose control [1]
The glucose-dependent mechanism means DPP-4 inhibitors carry low hypoglycaemia risk when used without insulin or a sulfonylurea — important in CKD where hypoglycaemia risk is already elevated (reduced renal gluconeogenesis, reduced insulin clearance).
Lecture Doses vs Current Prescribing
The table below reproduces the 2023 lecture slide and is useful for the principle that most DPP-4 inhibitors require renal adjustment. It is not a prescribing chart: modern labels often use eGFR rather than the older CrCl bands, and thresholds vary by product and jurisdiction. For example, the current US sitagliptin label uses 100 mg daily at eGFR ≥45, 50 mg daily at eGFR 30–44, and 25 mg daily below 30 (including dialysis). Check the current local label before prescribing. [17]
| Drug | Normal Dose | CrCl 30–60 | CrCl < 30 | Dialysis | Key Feature |
|---|---|---|---|---|---|
| Linagliptin (Tradjenta) | 5 mg/day | 5 mg/day | 5 mg/day | 5 mg/day | Hepatobiliary elimination; no renal dose adjustment needed |
| Alogliptin (Nesina) | 25 mg/day | 12.5 mg/day (CrCl ≥30 to < 60) | 6.25 mg/day | 6.25 mg/day | Stepwise reduction |
| Saxagliptin (Onglyza) | 5 mg/day (or 2.5 mg with CYP3A4/5 inhibitor) | — | 2.5 mg/day (CrCl < 50) | Post-HD; no PD data | CYP3A4/5 interaction important |
| Sitagliptin (Januvia) | 100 mg/day (CrCl > 50) | 50 mg/day (CrCl ≥30 to < 50) | 25 mg/day | HD (anytime) or PD | Most commonly used in HK |
Tenofovir — HBV, HIV treatment; renal & bone side-effects; pharmacokinetic interactions with other HIV drugs [1]
| Formulation | CrCl ≥50 | CrCl 30–49 | CrCl 10–29 | CrCl < 10 | HD |
|---|---|---|---|---|---|
| TDF (Tenofovir disoproxil fumarate) | 300 mg daily | 300 mg every other day | 300 mg q72–96h | Not studied | 300 mg q7 days |
| TAF (Tenofovir alafenamide) | 25 mg daily | 25 mg daily | 25 mg daily (CrCl ≥15) | — | — |
Formulation and Indication Matter
These are lecture examples, not interchangeable tenofovir instructions. TAF dosing depends on the indication and the complete product (HBV monotherapy versus an HIV co-formulation). For the current US HBV label for Vemlidy, no adjustment is required at estimated CrCl ≥15 mL/min or in ESRD on chronic haemodialysis (give after dialysis); it is not recommended in ESRD not receiving chronic haemodialysis. Always check the exact formulation and current local label. [17]
Why TAF is better than TDF for the kidney:
- TAF is a prodrug with higher intracellular concentration and lower plasma concentration vs TDF [1]
- Lower plasma levels = less drug exposure to renal tubular cells = better renal (and bone) safety profile [1]
- TDF causes proximal tubular toxicity → can manifest as Fanconi syndrome (hyperphosphaturia, hypophosphataemia, glycosuria, aminoaciduria, type 2 RTA) [7]
- TDF also causes bone mineral density loss via phosphate wasting
- TAF has a better average renal/bone safety profile, but it is not risk-free; monitor kidney markers as required by the exact product label
Tenofovir Toxicity Pearl
TDF-associated Fanconi syndrome is a classic exam question. The mechanism: TDF accumulates in proximal tubular cells, disrupts mitochondrial function → generalized proximal tubular dysfunction → loss of glucose, amino acids, phosphate, bicarbonate, and uric acid in urine. TAF avoids this by achieving high intracellular drug levels with much lower circulating plasma levels.
Drug-induced Renal Impairment: [1]
- Functional — NSAID, ACEI
- Structural → renal parenchymal disease: tubulointerstitial vs glomerular
This is the master classification. Let me explain why this distinction matters:
Functional = the drug alters renal haemodynamics (blood flow/filtration pressure) without directly damaging kidney tissue. If you stop the drug and restore haemodynamics, the kidney recovers. Think of it as a "reversible dial" being turned.
Structural = the drug causes actual tissue damage — inflammation, necrosis, fibrosis. Recovery depends on severity and may be incomplete.
Functional (Haemodynamic) Mechanisms
NSAID → inhibit cyclo-oxygenase → ↓ PG (prostaglandin) → loss of vasodilation [1]
First principles explanation:
- Under normal conditions, the afferent arteriole is kept dilated by prostaglandins (PGE2, PGI2). This maintains renal blood flow and GFR.
- In hypoperfusion states (cardiac failure, hypovolaemia, haemorrhage, nephrotic syndrome, cirrhosis), the kidneys become increasingly dependent on prostaglandin-mediated vasodilation to maintain adequate blood flow. The sympathetic nervous system and RAAS are already causing systemic vasoconstriction — prostaglandins are the kidney's "safety valve."
- NSAIDs block COX → ↓ prostaglandins → afferent arteriole constricts → dramatic fall in renal blood flow and GFR → AKI
Hypoperfusion states — cardiac insufficiency, hypovolaemia, massive haemorrhage, nephrotic, cirrhosis [1]
The two haemodynamic slides are easiest to remember as a pressure-control diagram:
Image-to-clinic translation: NSAIDs restrict inflow; ACEI/ARB reduce the back-pressure that sustains filtration. Add a diuretic-induced fall in circulating volume and all three supports are removed—the “triple whammy.”
Critical Clinical Scenario
The "triple whammy" = ACEI/ARB + diuretic + NSAID in an elderly patient → all three conspire to drop renal perfusion. Diuretic causes volume depletion, ACEI/ARB prevents compensatory efferent constriction, NSAID blocks protective afferent dilation. Result: precipitous AKI. This combination is a common exam question and a real-world prescribing disaster. [1][8]
NSAID can cause: [1]
- Sodium & fluid retention
- Reduce renal blood flow and GFR
- Hyperkalemia
- Tubulointerstitial nephritis
- Minimal change nephrotic syndrome
- Papillary necrosis in diabetic patients
This is a perfect example of the lecture's key teaching point:
One drug can lead to kidney complications through different / multiple mechanisms [1]
| NSAID Renal Effect | Mechanism |
|---|---|
| Na/fluid retention | ↓ PG → ↓ renal blood flow → ↑ Na reabsorption in proximal tubule; ↓ PGE2 in collecting duct → enhanced ADH effect |
| ↓ RBF and GFR | COX inhibition → loss of afferent vasodilation (see above) |
| Hyperkalemia | ↓ renin release (PG stimulates renin) → ↓ aldosterone → ↓ K+ secretion. Also ↓ GFR means less K+ delivery to distal nephron |
| AIN (tubulointerstitial nephritis) | Immunological/hypersensitivity reaction — T-cell mediated |
| Minimal change disease | Unclear; possibly altered T-cell function → podocyte injury → foot process effacement |
| Papillary necrosis | Chronic PG inhibition → medullary ischaemia (medulla has borderline O2 supply); diabetics especially vulnerable |
NSAID-induced nephrotic syndrome + AKI: minimal change glomerulopathy + acute tubulointerstitial nephritis [1] T lymphocytes, eosinophils (40%), ? higher risk in elderly [1]
This is a unique combination: the patient presents with both nephrotic syndrome (massive proteinuria, hypoalbuminaemia, oedema) AND AKI. On biopsy, you see minimal change disease in the glomeruli AND interstitial nephritis simultaneously. The eosinophilic infiltrate (present in ~40% of cases) is a clue to drug-induced AIN. Elderly patients are at higher risk.
Angiotensin II → vasoconstriction of efferent arteriole [1] Conditions: renal artery stenosis, hypovolaemia, cirrhosis [1]
First principles:
- The glomerulus has an afferent arteriole (blood IN) and efferent arteriole (blood OUT).
- GFR depends on the pressure gradient across the glomerular capillary. Angiotensin II preferentially constricts the efferent arteriole → increases pressure within the glomerular capillary → maintains GFR even when systemic BP drops.
- ACEI/ARB blocks angiotensin II → efferent arteriole dilates → intraglomerular pressure drops → GFR falls.
- In normal people, this modest GFR drop (up to ~25%) is tolerable and even beneficial long-term (less hyperfiltration injury).
- But in renal artery stenosis, the kidney is already underperfused. The only thing maintaining GFR is efferent constriction by Ang II. Block it → GFR crashes → AKI.
Cautions with RAAS Blockade (ACEI / ARB / Aldosterone Antagonist / Renin Inhibitor): [1]
- Renal artery stenosis [patients with vascular risk factors]
- Hyperkalaemia
- Metabolic acidosis
The slide lists several RAAS-blocking classes, but they should not be read as a combination regimen: KDIGO recommends avoiding combined ACEI + ARB or either agent with a direct renin inhibitor in CKD. [16]
Why hyperkalaemia? Aldosterone drives K+ secretion in the collecting duct. Block RAAS → ↓ aldosterone → ↓ K+ excretion → hyperK. This risk is compounded in CKD (already ↓ K+ excretion), DM (type 4 RTA), and with concurrent K-sparing drugs.
Why metabolic acidosis? Aldosterone also promotes H+ secretion in the collecting duct (via H+-ATPase). ↓ Aldosterone → ↓ H+ excretion → non-anion gap metabolic acidosis (type 4 RTA).
Clinical Pearl: Acceptable Creatinine Rise on ACEI/ARB
KDIGO advises checking BP, creatinine and potassium within 2–4 weeks after starting or increasing a RAAS inhibitor (earlier in high-risk patients), and continuing ACEI/ARB unless creatinine rises by more than 30% within 4 weeks. A rise beyond that threshold is a trigger to assess volume depletion, NSAID/diuretic exposure, intercurrent AKI and renal artery stenosis—not an automatic diagnosis or automatic permanent stop. Hyperkalaemia can often be managed while preserving RAAS blockade. [16]
Structural Drug-Induced Nephropathy
Mechanisms: [1]
- Haemodynamic (functional)
- Glomerular / Tubulointerstitial (Immunological injury)
- Direct toxicity (tubular cells)
| Pattern | Drugs | Presentation |
|---|---|---|
| Secondary membranous nephropathy | Gold salts, D-penicillamine | Proteinuria, nephrotic syndrome |
| Minimal change disease | NSAIDs | Nephrotic syndrome ± AKI (often combined with AIN) |
Why membranous? Gold and penicillamine cause immune complex deposition along the glomerular basement membrane (subepithelial deposits). This is "secondary" membranous because there is an identifiable cause (vs. primary/idiopathic membranous which involves anti-PLA2R antibodies).
Many drugs implicated: [1]
- Antibiotics (e.g. methicillin, rifampicin)
- NSAIDs, immunotherapy
- May have other 'allergic' features (e.g. allopurinol)
- Not uncommon
Classic triad of drug-induced AIN (an insensitive teaching triad; its absence does not exclude AIN):
- Fever
- Rash
- Eosinophilia [10]
These represent a systemic hypersensitivity reaction. The kidney shows interstitial oedema, inflammatory cell infiltration (lymphocytes, eosinophils, macrophages), and tubular damage.
AKI — may lead to permanent damage [1] Management — STOP the incriminated drug [1] ? Immunosuppression (usually not necessary, except in drug-induced vasculitis, immune CPI-associated AKI?) [1]
Key management principle: The most important step is drug withdrawal. Most cases recover. Steroids are controversial — generally reserved for:
- Cases not improving after drug withdrawal
- Drug-induced vasculitis (requires immunosuppression)
- Immune checkpoint inhibitor (CPI)-associated AIN (emerging indication) [1]
CPIs — monoclonal antibodies targeting molecules on the surface of T cells for treatment of solid organ or haematologic malignancies [1]
This is an increasingly tested topic as immunotherapy becomes more common.
Key data (Cortazar et al., Kidney Int 2016): [1]
- Onset: 21–245 days, one case 2 months after last CPI dose
- Urine WBC present in 8/13
- Peak Cr 3.6–7.3 mg/dL; 4 patients required HD
- Pathology: acute TIN 12/13, granulomatous 3/13, TMA 1/13
- 10 treated with steroid: 2 complete, 7 partial improvement
- 2 with AIN not given steroid did not improve
Historical study, current lesson: The numerical data above come from a 2016, 13-patient case series and should not be treated as a current treatment algorithm. The enduring clinical pearls are:
- CPI nephrotoxicity can present weeks to months after the last dose — late onset!
- The predominant lesion is acute TIN (not glomerular)
- Management is severity- and context-dependent: exclude more common AKI causes, involve oncology/nephrology, hold the checkpoint inhibitor when indicated, and consider corticosteroids for suspected immune-mediated nephritis rather than extrapolating a fixed regimen from this small series
- Extra-renal immune-related adverse events (irAEs) were present in 7/13 — look for colitis, hepatitis, thyroiditis, dermatitis as clues
Direct Tubular Toxicity
Drugs causing direct toxicity to renal tubular cells: [1]
- Aminoglycosides
- Some cephalosporins; quinolones
- Lithium, cisplatin, methotrexate, nitrosoureas
- Adefovir, tenofovir disoproxil fumarate (vs alafenamide)
- Contrast media
- NSAIDs
Concentrated in kidneys → phospholipid brush border of proximal tubular epithelium → endocytosis → inhibit phospholipases → accumulation of lipids → modify enzyme activities → Na-K ATPase inhibition → reduce lysosomal membrane permeability and mitochondrial respiration [1]
Step-by-step mechanism:
- Aminoglycosides (gentamicin, amikacin, tobramycin) are polycationic molecules that bind to megalin receptors on the proximal tubular brush border
- They are internalized via endocytosis into lysosomes
- Inside lysosomes, they inhibit phospholipases → phospholipid accumulation → formation of "myeloid bodies" (lamellar structures seen on EM)
- They also impair mitochondrial respiration and Na-K ATPase activity
- This leads to cellular energy failure and tubular cell necrosis
- Clinically: non-oliguric AKI initially, preceded by polyuria and tubular dysfunction [1]
Pathology: rarefication then disappearance of brush border; enlarged lysosomes with myeloid bodies; mitochondrial swelling; tubular necrosis; regeneration [1]
Why Non-Oliguric AKI?
Aminoglycoside nephrotoxicity classically causes non-oliguric AKI — the patient's creatinine rises but urine output may be maintained or even increased (polyuria). This is because tubular damage impairs the kidney's ability to concentrate urine (damaged medullary concentrating mechanism). Don't be fooled by "good urine output" — the kidneys are still failing! [1][11]
Risk factors for aminoglycoside nephrotoxicity [note narrow therapeutic window]: [1]
- Dose & duration of therapy
- Na depletion, hypovolaemia, K depletion
- Other nephrotoxic agents
- Pre-existing renal impairment
- Clinical state e.g. septicaemia
Clinical approach to safe aminoglycoside use:
- Use extended-interval dosing when appropriate — it achieves a high bactericidal peak with a prolonged low-concentration period, but it is unsuitable for some infections and patient groups; follow the local nomogram
- Use TDM with regimen-specific targets — peak/trough or timed levels and targets vary by aminoglycoside, indication, dosing strategy and local protocol; there is no single universal “toxic trough” for every regimen
- Ensure euvolaemia — dehydration concentrates the drug in tubules
- Limit duration — shortest effective course
- Avoid concurrent nephrotoxins (NSAIDs, contrast, vancomycin)
Lithium nephrotoxicity: [1]
- Nephrogenic diabetes insipidus
- CKD — chronic tubulointerstitial nephropathy (out of proportion to glomerulosclerosis, cysts and tubular dilatation)
- Acute lithium intoxication
- [Lithium could also lead to hypothyroidism and hyperparathyroidism]
Nephrogenic Diabetes Insipidus (NDI):
- Lithium enters collecting duct principal cells via ENaC channels
- It accumulates and interferes with aquaporin-2 (AQP2) trafficking — AQP2 channels cannot be inserted into the apical membrane in response to ADH
- Result: the collecting duct cannot respond to ADH → water cannot be reabsorbed → dilute polyuria (up to 3–12 L/day) with polydipsia
- This is the most common renal effect of lithium (~40% of long-term users)
- Usually reversible if caught early, but may become permanent with prolonged use
Quiz from lecture: "What is nephrogenic diabetes insipidus and how does it manifest?" [1]
- Answer: NDI is the kidney's inability to concentrate urine despite adequate/elevated ADH levels. It manifests as polyuria (large volumes of dilute urine, low urine osmolality) and polydipsia (compensatory water intake). Distinguished from central DI by the water deprivation test — in NDI, urine does NOT concentrate after desmopressin (DDAVP) administration.
Lithium-associated CKD: Chronic tubulointerstitial nephropathy with a characteristic pattern — tubular atrophy, interstitial fibrosis, cysts, and tubular dilatation, with relatively preserved glomeruli (out of proportion to glomerulosclerosis). [1]
Cisplatin: nephrotoxicity, ototoxicity, GI, myelosuppression [1]
- Dose > 100 mg/m² → ↑ risk of nephrotoxicity
- ↑ renal vascular resistance → ↓ renal plasma flow
- Tubular dysfunction may not correlate with ↓ CrCl
Pathology: focal ATN, distal & collecting tubular damage, dilatation of convoluted tubules, casts. Can be irreversible. [1]
Electrolyte consequences: [1]
- Hypo Mg — 70–80%, may persist for months
- Hypo Ca
- Hypo K
The slide's “dose > 100 mg/m²” threshold is an exam-era risk marker, not a safe-versus-toxic boundary. Kidney injury also depends on peak and cumulative exposure, prior cisplatin, concomitant nephrotoxins and patient susceptibility; current guidance describes increased risk at lower doses as well. [20]
Mechanism: Cisplatin is a platinum-based chemotherapy agent that is concentrated in renal tubular cells (especially proximal and distal tubules). It causes:
- Direct DNA damage in tubular cells
- Mitochondrial dysfunction
- Oxidative stress
- Inflammation and apoptosis
Why hypomagnesaemia? Cisplatin damages the thick ascending limb of the Loop of Henle and distal convoluted tubule where Mg²⁺ is reabsorbed via TRPM6 channels. This magnesium wasting can persist for months after cisplatin discontinuation.
Prevention: hydration 200 mL/h during and for 6 hours after cisplatin [1]
This is the lecture's protocol example, not a universal prescription. Current oncology guidance emphasizes pre-treatment assessment (kidney function, volume status, magnesium and other electrolytes), isotonic saline hydration, magnesium replacement and avoidance of concurrent nephrotoxins. The optimal regimen varies by cisplatin dose and patient factors; contemporary short regimens commonly use roughly 2–4 L over 2–6 hours, adapted for fluid-overload risk and the local oncology protocol. [20]
Acute nephrotoxicity — reduced intra-renal blood flow, enhanced by mTOR inhibitors [1] Chronic nephrotoxicity — vasculopathy and fibrosis (TGF-beta) [1] Blood level monitoring [1] Modulatory effect on podocytes [1]
| Type | Mechanism | Clinical Features | Reversibility |
|---|---|---|---|
| Acute | Afferent arteriole vasoconstriction → ↓ RBF → ↓ GFR (haemodynamic) | Dose-related ↑ creatinine | Reversible with dose reduction |
| Chronic | Arteriolar hyalinosis ("striped fibrosis"), TGF-β-mediated interstitial fibrosis | Progressive CKD, proteinuria | Irreversible |
Metabolic effects: [1]
- ↑ K (hyperkalaemia)
- ↑ Cl (hyperchloraemia)
- ↓ Bicarbonate (metabolic acidosis)
Together, ↑K, ↑Cl and ↓bicarbonate describe a hyperkalaemic, hyperchloraemic normal-anion-gap acidosis (a type 4 RTA-like pattern). Calcineurin inhibitors reduce renin–aldosterone signalling and distal potassium/hydrogen secretion; they also activate the thiazide-sensitive NCC pathway, contributing to sodium retention and hypertension.
Why blood level monitoring? These drugs have a narrow therapeutic window — too little = rejection (in transplant), too much = nephrotoxicity. Trough levels are measured routinely. [1][12]
Quiz from lecture: "Which of the following are potential side-effects of calcineurin inhibitors?" [1]
- A. Hypertension — YES (afferent vasoconstriction, Na retention)
- B. Hyperglycaemia — YES (tacrolimus > cyclosporin; ↓ insulin secretion)
- C. Hyperkalaemia — YES
- D. Metabolic acidosis — YES
- E. Nephrotoxicity — YES
- Answer: ALL of the above [1]
Toxicity to renal tubular cells → ↓ renal function / abnormal urine [1]
Susceptibility / Risk Factors: [1]
- Hypovolaemia, renal insufficiency, DM, dose, myeloma, other nephrotoxic agents, elderly
Prevention: [1]
- Patient selection
- Hydration
- ? N-acetyl cysteine
- ? Sodium bicarbonate
- Choose the imaging modality wisely
Use the modern terminology:
- Contrast-associated AKI (CA-AKI) = AKI occurring after contrast, whether or not contrast caused it
- Contrast-induced AKI (CI-AKI) = the causal subset attributable to contrast
- A creatinine rise after imaging is therefore not automatically “contrast nephropathy”; sepsis, hypotension and other nephrotoxins commonly coexist. Diagnose AKI using standard criteria and evaluate competing causes. [18]
Prevention strategy:
- Isotonic IV volume expansion is indicated for patients with AKI or severe CKD when not contraindicated by fluid-overload risk; it is not routinely indicated for the general stable population with eGFR ≥30 mL/min/1.73 m². Individual prophylaxis can be considered at eGFR 30–44 when risk is unusually high. [18]
- N-acetylcysteine is not recommended for IV contrast prophylaxis. Sodium bicarbonate appears similar to normal saline but is not preferred because it requires compounding. [18]
- Use a diagnostically adequate dose while avoiding unnecessary repeat exposure; do not sacrifice image quality with an arbitrarily subdiagnostic dose. Coordinate with radiology when risk is high.
Expansion and fibrosis of dermis → thickened and hardened skin and internal organs [1] MRI with gadolinium in patients with moderate/severe renal failure (esp GFR < 30 mL/min) [1] ? Low risk with group 2 gadolinium [1]
Why does this happen? Gadolinium-based contrast agents (GBCAs) used in MRI are normally cleared by the kidneys. In severe CKD, gadolinium stays in the body longer → free gadolinium dissociates from its chelate → deposits in tissues → triggers a fibrotic response similar to systemic sclerosis.
Risk stratification: Group I agents have the highest NSF risk and are contraindicated in CKD G4–G5. With a standard-dose group II agent, NSF risk is extremely low even with AKI or eGFR < 30; withholding a clinically important MRI may cause more harm. If a patient is already on haemodialysis, schedule an elective study close to the usual session when practical, but do not start or intensify dialysis solely for group II/III gadolinium exposure. [18][19]
Inhibit osteoclast-mediated bone resorption e.g. metastatic bone disease, osteoporosis [1] 40–60% bound to bone, remainder excreted unchanged through kidney (both glomerular filtration and active tubular secretion) [1] Tubular toxicity with ↓ renal function may occur with IV high-dose [1] Collapsing FSGS associated with IV high-dose [1]
Key points:
- Oral bisphosphonates (alendronate, risedronate) — generally safe in mild-moderate CKD
- IV bisphosphonates (zoledronic acid, pamidronate) at high doses for malignancy — risk of ATN or collapsing FSGS
- Many agents have restrictions in advanced CKD, but the threshold and dose/infusion precautions are product-specific; check the individual bisphosphonate rather than applying one universal cutoff.
- Important to check renal function before administering IV bisphosphonates
CKD + uro-epithelial malignancies [1]
This is the classic example of herbal/traditional medicine nephrotoxicity:
- Aristolochic acid is found in certain Chinese herbal medicines (e.g., Aristolochia species, guang fang ji)
- Causes chronic tubulointerstitial nephritis → progressive CKD
- Also a potent carcinogen → increased risk of upper urinary tract transitional cell carcinoma
- First described as "Chinese herb nephropathy" / "Balkan endemic nephropathy"
- Irreversible — no specific treatment once established
- Must screen for uro-epithelial malignancy in affected patients
Oral sodium phosphate bowel purgatives + dehydration → acute/chronic renal failure [1] Intra-tubular calcium phosphate precipitation [1] Avoid in high-risk patients — use alternatives e.g. polyethylene glycol [1]
Clinical scenario: Patient undergoing colonoscopy preparation with oral sodium phosphate (e.g., Fleet Phospho-soda). In patients with CKD, elderly, or dehydrated patients:
- Massive phosphate load → hyperphosphataemia → severe hypocalcaemia (life-threatening)
- Calcium-phosphate product rises → precipitates within renal tubules → acute phosphate nephropathy → may cause permanent CKD
- Prevention: Use polyethylene glycol-based preparations (e.g., GoLYTELY, Klean-Prep) instead — they are osmotic laxatives without phosphate load
| Drug | Renal/Related Complication | Mechanism |
|---|---|---|
| Cyclophosphamide | Urinary dilution (SIADH-like effect); also haemorrhagic cystitis (acrolein metabolite) | ADH-like effect on collecting duct; acrolein damages bladder urothelium |
| Hydralazine | Drug-induced lupus → lupus nephritis possible | Anti-histone antibodies; rarely causes nephritis |
| Propylthiouracil | Drug-induced vasculitis → ANCA-positive (usually anti-MPO/p-ANCA) | Altered neutrophil apoptosis; MPO presented on cell surface |
| Metformin in CKD | Lactic acidosis | Metformin inhibits hepatic gluconeogenesis and mitochondrial complex I; in CKD, metformin accumulates → ↑ lactate production + ↓ lactate clearance |
Metformin and CKD
Metformin is contraindicated when eGFR < 30 mL/min/1.73 m². FDA labelling does not recommend starting it at eGFR 30–45; if eGFR later falls below 45, reassess benefit versus risk and stop if it falls below 30. Acute illness with hypoxia, sepsis, dehydration or AKI is more important to metformin-associated lactic acidosis risk than stable mild CKD alone; use a locally approved sick-day plan rather than a vague blanket instruction. [17]
Drug-Induced Renal Vasculitis [1]
Penicillin, sulphonamides, anti-thyroid drugs → renal + extra-renal manifestations [1] Fibrinoid necrosis of intima and media of small/medium arteries [1] Periarteriolar cellular infiltrate [1] Rx: Immunosuppression [1]
This is distinct from drug-induced AIN. Here, the pathology is vasculitis — inflammation and necrosis of blood vessel walls. The clinical picture may mimic polyarteritis nodosa or ANCA-associated vasculitis. Extra-renal features include skin purpura, arthralgia and pulmonary haemorrhage. First stop the suspected drug and assess severity. Immunosuppression is generally reserved for organ- or life-threatening disease and should be directed by nephrology/rheumatology; the slide's single-line “Rx: immunosuppression” is not a blanket rule for every drug-associated case.
| Classification | Mechanism | Examples | Presentation |
|---|---|---|---|
| Functional / Haemodynamic | Altered renal blood flow/GFR without structural damage | NSAIDs, ACEI/ARB | Reversible AKI; worse in hypoperfusion states |
| Glomerular | Immune-mediated glomerular injury | NSAIDs (MCD), gold/penicillamine (membranous) | Proteinuria, nephrotic syndrome |
| Tubulointerstitial (AIN) | Hypersensitivity/immune-mediated interstitial inflammation | Antibiotics, NSAIDs, allopurinol, PPIs, CPIs | AKI ± fever/rash/eosinophilia |
| Direct tubular toxicity | Drug concentrated in tubular cells → cellular injury | Aminoglycosides, cisplatin, contrast, tenofovir (TDF) | Non-oliguric AKI, electrolyte wasting |
| Vasculitis | Immune-mediated vascular inflammation | Penicillin, sulfonamides, PTU | AKI + systemic vasculitis features |
| Chronic TIN / CKD | Chronic tubular damage, fibrosis | Lithium, aristolochic acid, calcineurin inhibitors (chronic) | Progressive CKD, concentration defects |
| Crystalluria / Obstruction | Intra-tubular crystal precipitation | Acyclovir, methotrexate, phosphate purgatives, sulfonamides | AKI |
Integration with Related Lectures
- Drug-induced kidney disease can be classified temporally: Acute (< 7 days), Subacute (7–90 days), Chronic (> 90 days) [9]
- Manifestations include: vasoconstriction, glomerular disease, tubular toxicity, tubulointerstitial nephritis, nephrolithiasis, crystalluria — "drugs can affect every single step of the pathway" [9]
- Kidneys receive normalized blood flow of 3,333 mL/min/kg — highest of any organ
- Understanding clearance: renal clearance = GFR × free fraction for drugs cleared by filtration; add tubular secretion for drugs like penicillins
- Drug-induced AIN is an important cause of intrinsic renal AKI
- Biopsy findings: interstitial oedema, lymphocytic/eosinophilic infiltrate, tubulitis
- Elderly patients have reduced GFR (age-related decline), making them more susceptible to drug accumulation and nephrotoxicity
- NSAIDs and aminoglycosides appear on Beers Criteria for potentially inappropriate medications in the elderly
- Post-transplant patients require calcineurin inhibitors — understanding acute vs chronic CNI nephrotoxicity is essential for transplant medicine
High Yield Summary
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The kidney receives 25% of cardiac output and concentrates drugs in tubular cells → extremely vulnerable to drug injury.
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Three prescribing principles in CKD: avoid nephrotoxins, adjust dose/frequency, beware amplified side effects (ethambutol→optic neuritis, acyclovir→CNS, quinolones→seizures).
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Drug-induced renal injury = Functional (NSAIDs, ACEI/ARB altering haemodynamics) or Structural (glomerular, tubulointerstitial, direct tubular toxicity, vasculitis).
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NSAIDs cause MULTIPLE kidney complications: ↓GFR, Na retention, hyperK, AIN, MCD nephrotic syndrome, papillary necrosis — ONE drug, MANY mechanisms.
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ACEI/ARB → efferent arteriole dilation → ↓GFR. Dangerous in renal artery stenosis or hypovolaemia and may cause hyperK/type 4 RTA. Check creatinine/K after initiation; investigate a > 30% creatinine rise within 4 weeks rather than reflexively stopping for any small rise.
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Aminoglycosides: proximal tubular toxicity, non-oliguric AKI, narrow therapeutic window. Risk factors: dose, duration, hypovolaemia, concurrent nephrotoxins.
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Cisplatin: tubular toxicity, hypoMg (70–80%), hypoCa, hypoK. Prevention uses protocolized isotonic hydration, electrolyte monitoring/replacement (especially Mg), and nephrotoxin avoidance—not one universal fluid rate.
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Calcineurin inhibitors: acute (haemodynamic) + chronic (fibrosis) nephrotoxicity, hyperK, metabolic acidosis, hypertension, hyperglycaemia. ALL answers are YES.
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Linagliptin = only DPP-4 inhibitor needing no renal adjustment (hepatobiliary excretion). TAF > TDF for renal safety.
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For iodinated contrast, distinguish CA-AKI from causal CI-AKI. Use isotonic prophylaxis for AKI/severe CKD when appropriate; NAC is not recommended. Oral sodium phosphate purgatives → acute phosphate nephropathy in CKD → use PEG instead.
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CPI-associated AKI can be delayed and is often acute TIN; exclude competing AKI causes and coordinate checkpoint-inhibitor interruption and corticosteroid decisions with oncology/nephrology.
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Reno-protection in CKD: prevent injury, BP control, RAAS blockade, SGLT2i, no smoking, vascular risk factor management.
Active Recall - Drugs and the Kidney
[1] Lecture slides: GC 043. Drugs and the Kidney.pdf (all pages) [2] Senior notes: Block A - Drugs and the Kidney.pdf (p1) [3] Past papers: 2023 Fourth Summative MCQ.pdf; 2024 Fourth Summative MCQ.pdf; 2025 Fourth Summative MCQ.pdf [4] Lecture slides: GC 035. Clinical pharmacokinetics.pdf (p7) [5] Lecture slides: GC 034. Chronic Kidney Disease and its Complications [update 2025].pdf (p89) [6] Senior notes: Block A - Deterioration of eyesight in a diabetic patient_ diabetic complications.pdf (p16) [7] Senior notes: Block A - I am a hepatitis B carrier.pdf (p49) [8] Lecture slides: GC 079. Prescribing in older people.pdf [9] Senior notes: Block A - Chronic Kidney Disease and its Complications.pdf (p11-12) [10] Senior notes: Block A - Nephrotology Teaching Clinic RTD.pdf (p1) [11] Senior notes: Block A - Nephrology Interactive Tutorial.pdf (p3) [12] Lecture slides: GC 080. Renal Replacement Therapies.pdf; Senior notes: Block A - Renal Replacement Therapies.pdf (p33-35) [13] Senior notes: Block A - Back pain in an elderly woman_ osteoporosis and related fractures.pdf (p26) [14] Senior notes: Ryan Ho Endocrine.pdf (p88); Endocrine Interactive Tutorial.pdf (p7) [15] Lecture slides: GC 057. Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf [16] KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of CKD: https://kdigo.org/wp-content/uploads/2024/03/KDIGO-2024-CKD-Guideline.pdf [17] US FDA prescribing information: Januvia (sitagliptin), Tradjenta (linagliptin), Vemlidy (tenofovir alafenamide), and Glucophage (metformin): https://www.accessdata.fda.gov/scripts/cder/daf/ [18] American College of Radiology, Manual on Contrast Media (current online manual): https://www.acr.org/Clinical-Resources/Clinical-Tools-and-Reference/Contrast-Manual [19] ACR–NKF Consensus Statement on intravenous gadolinium-based contrast in kidney disease: https://pmc.ncbi.nlm.nih.gov/articles/PMC7873723/ [20] eviQ, Prevention and management of cisplatin-induced nephrotoxicity: https://www.eviq.org.au/clinical-resources/side-effect-and-toxicity-management/prophylaxis-and-treatment/184-prevention-and-management-of-cisplatin-induced
GC042 Deterioration Of Eyesight In A Diabetic Patient Diabetic Complications
Progressive visual impairment in a diabetic patient resulting from complications such as diabetic retinopathy, macular edema, or accelerated cataract formation due to chronic hyperglycemia-induced microvascular and lens damage.
GC044 Electrolyte And Acid-base Disorders
Electrolyte and acid-base disorders are clinical conditions involving abnormal concentrations of key ions (sodium, potassium, calcium, magnesium, phosphate) or disturbances in blood pH homeostasis (acidosis or alkalosis), arising from metabolic or respiratory causes and affecting cellular and organ function.