PKADME — Core Pharmacokinetic Processes
Absorption
Movement of drug from site of administration into bloodstream. Affected by: route of administration, GI motility, pH, formulation, food interactions, first-pass metabolism.
Bioavailability (F)
F = (AUC_oral / AUC_IV) × 100%
- IV = 100% bioavailability (gold standard)
- Oral morphine F ≈ 20–40% (high first-pass)
- Oral midazolam F ≈ 36%
- Sublingual GTN F ≈ 80% (avoids first-pass)
First-Pass Effect: Drugs absorbed orally pass through portal circulation → liver → significant pre-systemic metabolism. High extraction drugs: morphine, propranolol, lidocaine, GTN.
Distribution
Volume of Distribution (Vd)
Vd = Dose / C₀ (L or L/kg)
| Vd Range | Meaning | Example |
|---|
| < 10 L | Plasma only | Heparin, warfarin |
| 10–40 L | Extracellular | Aminoglycosides |
| > 100 L | Tissue distributed | Chloroquine, amiodarone |
Protein Binding
Only free (unbound) drug is pharmacologically active. Albumin binds acidic drugs; alpha-1-acid glycoprotein binds basic drugs.
Hypoalbuminaemia: In liver failure/malnutrition, free fraction increases → toxicity risk with phenytoin, warfarin, valproate, diazepam.
CYPHepatic Metabolism — CYP450 System
Cytochrome P450 enzymes (primarily in liver) are responsible for metabolism of ~75% of drugs. Key isoforms: CYP3A4 (most abundant, ~50% drugs), CYP2C9, CYP2D6, CYP1A2, CYP2C19.
| Isoform | Substrates (examples) | Inhibitors ↑ drug levels | Inducers ↓ drug levels |
|---|
| CYP3A4 |
Midazolam, fentanyl, simvastatin, cyclosporin, amlodipine, tacrolimus |
Fluconazole, erythromycin, grapefruit, ritonavir, clarithromycin |
Rifampicin, carbamazepine, phenytoin, St John's Wort |
| CYP2C9 |
Warfarin (S-form), phenytoin, NSAIDs, glipizide |
Fluconazole, amiodarone, metronidazole |
Rifampicin, carbamazepine |
| CYP2D6 |
Codeine→morphine, tramadol, metoprolol, haloperidol, TCA antidepressants |
Fluoxetine, paroxetine, bupropion |
Rifampicin (weak) |
| CYP1A2 |
Theophylline, clozapine, caffeine |
Ciprofloxacin, fluvoxamine |
Smoking, omeprazole |
Clinical Pearl: Rifampicin (anti-TB drug, common in GCC) is a potent broad-spectrum CYP inducer — dramatically reduces levels of warfarin, antiretrovirals, contraceptive pill, prednisolone. Always review full medication list.
CrClRenal Clearance & Cockcroft-Gault
Cockcroft-Gault Formula
CrCl (mL/min) =
(140 − age) × weight(kg)
──────────────────────
72 × serum creatinine (mg/dL)
× 0.85 if female
Notes: Use ideal body weight (IBW) in obese patients. Use actual weight if patient is malnourished. If creatinine is very low (<0.6 mg/dL) in elderly, use 0.6 as minimum.
CKD Staging (eGFR mL/min/1.73m²)
| Stage | eGFR | Action |
|---|
| G1 | ≥ 90 | Normal, monitor |
| G2 | 60–89 | Mild reduction |
| G3a | 45–59 | Adjust renally cleared drugs |
| G3b | 30–44 | Significant adjustment needed |
| G4 | 15–29 | Major adjustments required |
| G5 | < 15 | Kidney failure — specialist review |
t½Half-Life, Steady State & Therapeutic Drug Monitoring
Half-Life (t½)
t½ = 0.693 × Vd / Clearance
- Time to steady state = 4–5 half-lives
- Time to 50% elimination = 1 half-life
- Time to 97% elimination = 5 half-lives
Examples
| Drug | t½ | Steady State |
|---|
| Digoxin | 36–48 hr | 7–10 days |
| Amiodarone | 40–55 days | Months |
| Aspirin (low dose) | 15–20 min | Hours |
| Vancomycin | 4–8 hr | 24–36 hr |
Therapeutic Drug Monitoring (TDM)
TDM required for drugs with narrow therapeutic index (NTI). Measure trough levels (just before next dose) for most drugs.
| Drug | Therapeutic Range | Sampling Time |
|---|
| Vancomycin | AUC/MIC 400–600 (preferred) | Trough <dose |
| Gentamicin | Peak 5–10, Trough <2 mg/L | 1hr post & trough |
| Digoxin | 0.5–2 ng/mL | 6–12 hr post-dose |
| Phenytoin | 10–20 mg/L (free 1–2) | Trough |
| Lithium | 0.6–1.2 mmol/L | 12 hr post-dose |
| Theophylline | 10–20 mg/L | Trough |
| Carbamazepine | 4–12 mg/L | Trough |
NTI Drugs: Small changes in dose → large changes in effect. Warfarin, digoxin, lithium, phenytoin, theophylline, aminoglycosides, cyclosporin, tacrolimus, methotrexate.
RxCore Drug Calculation Formulas
Basic Formulas
Dose to give =
(Required dose / Stock dose) × Stock volume
Example: Need 250mg, have 500mg/5mL
= (250/500) × 5 = 2.5 mL
IV Infusion Rate (mL/hr) =
Volume (mL) / Time (hr)
Drops/min (gravity) =
(Volume × Drop factor) / Time (min)
IV Rate ↔ Dose Conversion
Dose (mcg/kg/min) =
Rate(mL/hr) × Conc(mcg/mL)
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Weight(kg) × 60
Rate (mL/hr) =
Dose(mcg/kg/min) × Weight(kg) × 60
──────────────────────────────────
Conc (mcg/mL)
Weight-Based Dosing
Total dose = Dose (mg/kg) × Weight (kg)
Body Surface Area — Mosteller
BSA (m²) =
√[ Height(cm) × Weight(kg) / 3600 ]
Average adult: ~1.73 m²
Loading vs Maintenance Dose
Loading Dose =
Target Cp × Vd / F
Maintenance Dose =
Target Cp × CL / F
Loading dose: Rapidly achieves therapeutic level. Not adjusted for renal function (Vd unchanged). Example: Digoxin LD = 0.5–1 mg, then MD 0.0625–0.25 mg/day.
CKDRenal Dose Adjustments
| Drug | eGFR ≥60 | eGFR 30–59 | eGFR 15–29 | eGFR <15 / Dialysis |
|---|
| Metformin | Full dose | Caution, halve dose | STOP | STOP |
| LMWH (enoxaparin) | Full dose | Monitor anti-Xa | Halve or switch UFH | Use UFH (dialysable) |
| Gabapentin | Full dose | 50–75% dose | 25–50% | Supplement post-HD |
| Digoxin | Full dose | Reduce, TDM | Every 48h dosing | Avoid or expert only |
| Amoxicillin | Full dose | Full dose | Halve frequency | Post-dialysis dose |
| Ciprofloxacin | Full dose | Full dose | Halve dose | Halve dose |
| Gentamicin | Full dose (TDM) | Increase interval | Expert guidance + TDM | Specialist only |
| Vancomycin | TDM-guided | TDM-guided, ↑interval | TDM-guided | During/post HD |
| Rivaroxaban | Full dose | Full dose | Avoid if <30 | AVOID |
| Dabigatran | Full dose | Caution | AVOID | AVOID |
CPTHepatic Dose Adjustments — Child-Pugh
| Parameter | 1 Point | 2 Points | 3 Points |
|---|
| Bilirubin (µmol/L) | <34 | 34–50 | >50 |
| Albumin (g/L) | >35 | 28–35 | <28 |
| PT prolongation (sec) | <4 | 4–6 | >6 |
| Ascites | None | Mild (controlled) | Severe (refractory) |
| Encephalopathy | None | Grade 1–2 | Grade 3–4 |
A
5–6 pts — Mild
Normal/slight reduction
B
7–9 pts — Moderate
Reduce to 50%, monitor
C
10–15 pts — Severe
Avoid or specialist only
High extraction drugs: Morphine, fentanyl, lidocaine, propranolol — significantly affected in hepatic impairment. Reduce dose in Child-Pugh B/C.
IBWBody Weight in Dosing
Ideal Body Weight (IBW)
IBW Male = 50 + 2.3 × (height(in) − 60)
IBW Female = 45.5 + 2.3 × (height(in) − 60)
Height inches = cm / 2.54
Adjusted Body Weight (AdjBW)
AdjBW = IBW + 0.4 × (TBW − IBW)
Use AdjBW when TBW > 120% IBW. Used for: aminoglycosides, vancomycin loading dose, heparin.
Paediatric Dosing
- Always use weight (mg/kg) — confirm weight accurately
- Maximum dose = adult dose (cap if needed)
- Neonates: immature hepatic/renal function, unique PK
- Clark's rule: Child dose = (weight/70) × adult dose
- Young's rule: Child dose = (age/(age+12)) × adult dose
Paediatric caution: Always double-check dose AND volume. 10-fold errors common with decimal place. Involve pharmacist for high-risk drugs.
OpioidOpioids — Equianalgesic Conversion & Safety
Equianalgesic Table (Oral Morphine Equivalent)
| Drug | Oral (mg) | Parenteral (mg) | Transdermal | Notes |
|---|
| Morphine | 30 mg | 10 mg IV/SC | — | Reference standard |
| Oxycodone | 20 mg | 10 mg IV | — | 1.5× more potent oral than morphine |
| Codeine | 200 mg | 130 mg IM | — | Prodrug; CYP2D6 converts to morphine |
| Fentanyl | — | 0.1 mg (100 mcg) IV | 25 mcg/hr patch ≈ 60–90 mg/day oral morphine | 100× more potent than morphine IV |
| Tramadol | 150 mg | 100 mg IV | — | Weak opioid + SNRi; CYP2D6 affected |
| Hydromorphone | 7.5 mg | 1.5 mg IV | — | 5× potent oral vs morphine |
| Buprenorphine | 0.4 mg SL | 0.3 mg IV/IM | 5 mcg/hr patch | Partial agonist, ceiling on respiratory depression |
Opioid Conversion Steps
- Calculate total 24h current opioid dose
- Convert to oral morphine equivalents (OME)
- Convert OME to new opioid using equianalgesic table
- Apply cross-tolerance reduction 25–33%
- Establish breakthrough dose: 10–15% of 24h total
Naloxone (Narcan) Dosing
Respiratory depression:
IV 0.04–0.4 mg q2–3min, max 10mg
Opioid overdose:
IV/IM/IN 0.4–2 mg q2–3min
t½ = 30–90 min — may need repeat or infusion
Titrate to RR >12, avoid precipitating withdrawal
GCC Context: Opioids are tightly controlled in UAE/KSA/Qatar. TRAP regulations (UAE) require specific triplicate prescriptions for Schedule I/II. Many patients under-prescribed due to regulatory fear. Cross-border carrying of opioids requires declaration and medical certificate.
ACAnticoagulants — Heparin, DOACs & Reversal
UFH Weight-Based Nomogram (Venous thrombosis)
| aPTT (seconds) | Action |
|---|
| <50 | Bolus 80 units/kg + ↑rate 4 units/kg/hr |
| 50–59 | Bolus 40 units/kg + ↑rate 2 units/kg/hr |
| 60–100 (therapeutic) | No change |
| 101–120 | Hold 30 min + ↓rate 2 units/kg/hr |
| >120 | Hold 60 min + ↓rate 3 units/kg/hr |
Initial bolus: 80 units/kg IV. Initial infusion: 18 units/kg/hr. Check aPTT 6 hr after each change, then every 24 hr when stable.
DOAC Properties & Reversal
| DOAC | Target | Reversal Agent |
|---|
| Rivaroxaban | Factor Xa | Andexanet alfa |
| Apixaban | Factor Xa | Andexanet alfa |
| Dabigatran | Thrombin (IIa) | Idarucizumab 5g IV |
| Edoxaban | Factor Xa | Andexanet alfa |
Warfarin reversal:
INR 4–10, no bleed: Hold warfarin
Any major bleed: Vit K 5–10mg IV + PCC (Beriplex/Octaplex) 25–50 units/kg IV
Heparin reversal: Protamine 1mg per 100 units UFH (max 50mg)
DOAC Bridging with Heparin
Generally NOT required when switching between DOACs or starting DOAC after VTE. Bridging required when interrupting anticoagulation for high-risk procedures in patients with mechanical heart valves (use UFH, not LMWH for mechanical valves).
InsInsulin — Types, Regimens & Safety
Insulin Types & Action Profile
| Type | Onset | Peak | Duration |
|---|
| Aspart/Lispro/Glulisine (RAA) | 5–15 min | 30–90 min | 3–5 hr |
| Regular (soluble) | 30–60 min | 2–4 hr | 5–8 hr |
| NPH (isophane) | 1–2 hr | 4–10 hr | 12–18 hr |
| Detemir | 1–2 hr | Flat | 18–24 hr |
| Glargine (U100/U300) | 1–2 hr | Peakless | 24–36 hr |
| Degludec | 1 hr | Peakless | >42 hr |
Hypoglycaemia Management
BGL <4.0 mmol/L (72 mg/dL):
Conscious: 15–20g fast-acting carbs (3–4 glucose tabs, 150 mL OJ)
Recheck in 15 min (Rule of 15)
Unconscious/NPO: 50 mL 50% glucose IV or Glucagon 1mg IM/SC/IN
Sick Day Rules (T1DM)
- NEVER stop insulin when sick
- Check BGL every 2–4 hours
- Check ketones if BGL >14 mmol/L
- If ketones moderate/large → DKA protocol
- Maintain hydration
Insulin Safety — 10 Rights: Right patient · Right drug (name/type/concentration) · Right dose · Right time · Right route · Right site rotation · Right technique · Right storage (2–8°C unopened; 28 days room temp opened) · Right documentation · Right monitoring. Insulin is a HIGH ALERT medication in all GCC facilities.
DIGDigoxin & Lithium — Narrow Therapeutic Index
Digoxin
Therapeutic range: 0.5–2.0 ng/mL (heart failure: 0.5–0.9 optimal). Sample 6–12h after dose.
Toxicity signs (>2 ng/mL):
GI: Nausea, vomiting, anorexia (FIRST SIGNS)
Cardiac: Bradycardia, heart block, ectopics, VT
CNS: Confusion, visual disturbances (yellow-green halos), xanthopsia
Digoxin Toxicity Precipitants
- Hypokalaemia — potentiates toxicity (competes with K+ at Na/K ATPase)
- Renal impairment — reduced excretion
- Hypothyroidism — reduced clearance
- Amiodarone, quinidine, verapamil — raise digoxin levels
- Dehydration, age, hypomagnesaemia
Management: Hold digoxin, correct electrolytes, Digibind (DigiFab) for severe toxicity — dose = serum digoxin level (ng/mL) × 5.6 × weight(kg) / 1000 vials.
Lithium
Therapeutic range: 0.6–1.2 mmol/L (acute mania may target 0.8–1.2). Sample 12 hours after last dose.
Toxicity levels:
1.2–1.5: Tremor, polyuria, nausea (early)
1.5–2.0: GI distress, ataxia, confusion
2.0–2.5: Gross tremor, drowsiness, dysarthria
>2.5: Seizures, coma, cardiac arrhythmias — EMERGENCY
Monitoring Parameters
- Renal function (eGFR) — lithium is renally cleared
- Thyroid function (causes hypothyroidism)
- Serum lithium levels (weekly initially, then 3-monthly)
- Dehydration risk — diarrhoea, vomiting, febrile illness, fasting (Ramadan) → levels rise sharply
- NSAIDs and ACE inhibitors raise lithium levels
INTPharmacokinetic Interactions
Enzyme Inhibition (↑ substrate drug levels)
| Perpetrator (Inhibitor) | Affected Enzyme | Affected Drugs | Clinical Risk |
|---|
| Fluconazole | CYP3A4, CYP2C9 | Warfarin, midazolam, cyclosporin, phenytoin, statins | Bleeding, sedation, nephrotoxicity |
| Erythromycin/Clarithromycin | CYP3A4 | Simvastatin, QT drugs, digoxin | Rhabdomyolysis, QT prolongation |
| Amiodarone | CYP2C9, CYP2D6 | Warfarin, digoxin, flecainide | Major bleeding, bradycardia |
| Ritonavir | CYP3A4 (potent) | Many drugs including statins, sedatives | Multiple severe interactions |
| Ciprofloxacin | CYP1A2 | Theophylline, clozapine | Seizures, cardiac toxicity |
| Fluoxetine/Paroxetine | CYP2D6 | Codeine, tramadol, TCA, metoprolol | Opioid failure, serotonin syndrome |
Enzyme Induction (↓ substrate drug levels)
| Inducer | Enzyme | Critical Drug Interactions |
|---|
| Rifampicin | CYP3A4, 2C9, P-gp | Warfarin, OCP, DOACs, antiretrovirals, prednisolone, ciclosporin — all levels fall dramatically |
| Carbamazepine | CYP3A4, 2C9 | OCP (contraceptive failure), warfarin, valproate, lamotrigine, many others. Also auto-inducer. |
| Phenytoin | CYP3A4, 2C9 | Similar to carbamazepine. Also complex protein binding interactions. |
| St John's Wort | CYP3A4, P-gp | Ciclosporin (transplant rejection), OCP, antiretrovirals, warfarin |
QTPharmacodynamic Interactions & QT Prolongation
Additive CNS Depression
Risk when combining multiple CNS depressants:
- Opioids + benzodiazepines → respiratory depression (FDA black box)
- Antipsychotics + sedatives → falls, over-sedation
- Alcohol + any sedative → potentiation
- Gabapentinoids + opioids → apnoea risk
Opioid + Benzo: 3.86× increased overdose death risk. Use lowest effective doses; monitor closely; have naloxone accessible.
QT Prolongation Pairs
QTc >500ms or increase >60ms from baseline = high risk of Torsades de Pointes.
| Drug Class | Examples |
|---|
| Antipsychotics | Haloperidol, quetiapine, ziprasidone |
| Antiarrhythmics | Amiodarone, sotalol, flecainide |
| Antibiotics | Azithromycin, moxifloxacin, erythromycin |
| Antiemetics | Ondansetron (>32mg IV), metoclopramide |
| Antifungals | Fluconazole, ketoconazole |
Exacerbating factors: hypokalaemia, hypomagnesaemia, bradycardia, female sex. Check CredibleMeds (ArizonaCERT) database.
SSSerotonin Syndrome vs Neuroleptic Malignant Syndrome
| Feature | Serotonin Syndrome | NMS (Neuroleptic Malignant Syndrome) |
|---|
| Cause | Excess serotonergic activity (SSRI + MAOI, tramadol + SSRI, linezolid + SSRI) | Dopamine D2 blockade (antipsychotics, metoclopramide) |
| Onset | Rapid (hours after drug change) | Gradual (days to weeks) |
| Temperature | Hyperthermia | Hyperthermia (>38°C) |
| Muscle tone | Hyperreflexia, clonus, tremor | Rigidity ("lead pipe") |
| Pupils | Mydriasis | Variable |
| CK | Mildly elevated | Markedly elevated (>1000 IU/L) |
| Treatment | Stop offending drug, cyproheptadine, supportive | Stop antipsychotic, bromocriptine, dantrolene, cooling |
ADRAdverse Drug Reaction Reporting & Severe Reactions
ADR Reporting Systems in GCC
- Saudi Arabia: SFDA National Pharmacovigilance Centre — online portal sfda.gov.sa
- UAE (DHA): Dubai Health Authority ADR reporting — eHMP portal; also MOH UAE system
- UK (for UK-trained nurses): Yellow Card Scheme — yellowcard.mhra.gov.uk
- Qatar: MOPH Qatar drug safety unit
- All GCC countries aligned with WHO Uppsala Monitoring Centre (UMC) VigiBase
Naranjo Algorithm (Causality)
Score ≥9 = definite ADR; 5–8 = probable; 1–4 = possible; ≤0 = doubtful. Considers: prior reports, temporal relationship, dechallenge/rechallenge, alternative explanations.
Stevens-Johnson Syndrome (SJS/TEN)
Warning signs — STOP drug immediately:
Prodrome: fever, malaise, pharyngitis
Skin: Purpuric macules, skin detachment
Mucosal involvement (eyes, mouth, genitals)
Nikolsky sign positive (skin slides on pressure)
Common culprits: Allopurinol, carbamazepine, lamotrigine, sulfonamides, nevirapine, NSAIDs
Management: ICU/burns unit, supportive, ophthalmology, IVIG (TEN).
Anaphylaxis Management
First line — Adrenaline (Epinephrine):
Adult: 500 mcg (0.5 mL 1:1000) IM anterolateral thigh
Child: 150 mcg (<6yr) / 300 mcg (6–12yr) / 500 mcg (>12yr)
Repeat every 5 min if needed
Then: 500 mL IV fluid bolus, chlorphenamine 10mg IV, hydrocortisone 200mg IV, salbutamol nebuliser if wheeze. Position: supine with legs raised (or recovery if unconscious).
Drug Allergy Documentation
Document: drug name (generic), type of reaction (anaphylaxis/rash/GI), severity, date of reaction. Distinguish true allergy from intolerance/side effect. Cross-reactivity: penicillin/cephalosporin ~1–2%; codeine intolerance ≠ opioid allergy.
ElderElderly — START/STOPP & Beers Criteria
STOPP Criteria (drugs to STOP in elderly)
- Long-acting benzodiazepines (diazepam, nitrazepam) — fall risk
- Anticholinergics (oxybutynin, tricyclics) — delirium, urinary retention, constipation
- NSAIDs with CKD or PUD — GI bleed, renal failure
- First-generation antihistamines (chlorphenamine) — sedation, confusion
- Digoxin >125 mcg/day without dose review in eGFR <50
- Duplicate drug class prescribing (two SSRI, two opioids)
- Glibenclamide/glipizide — prolonged hypoglycaemia
Beers List Key Drugs (AGS)
- Amitriptyline, doxepin — anticholinergic
- Diphenhydramine (Benadryl) — delirium
- Sliding scale insulin — hypoglycaemia risk
- Meperidine (pethidine) — neurotoxic metabolite
- Metoclopramide — extrapyramidal effects
START Criteria (drugs to START in elderly)
- Antiplatelet therapy with established CVD
- ACE inhibitor / ARB in heart failure or diabetic nephropathy
- Statin in established CVD (unless life expectancy <1yr)
- Calcium + Vitamin D if osteoporosis/falls risk
- Bisphosphonate with long-term steroids
- Metformin if T2DM with adequate eGFR
Pharmacokinetic Changes in Elderly
| Parameter | Change | Impact |
|---|
| GFR | ↓ 1% per year after 40 | ↑ drug levels (renally cleared) |
| Hepatic blood flow | ↓ 40–45% | ↓ first-pass (↑ oral bioavailability) |
| Albumin | ↓ | ↑ free drug fraction (phenytoin, warfarin) |
| Body fat % | ↑ | ↑ Vd fat-soluble drugs (diazepam) |
| Lean muscle | ↓ | ↓ creatinine — false "normal" CrCl |
PregPregnancy & Breastfeeding
FDA Pregnancy Categories (legacy system)
| Category | Meaning | Examples |
|---|
| A | Adequate studies — no risk | Folic acid, levothyroxine |
| B | Animal studies no risk; no adequate human studies | Metformin, amoxicillin, insulin |
| C | Animal risk; insufficient human data | Fluconazole, codeine, ciprofloxacin |
| D | Evidence of human fetal risk | Valproate, ACE inhibitors (2nd/3rd trimester), lithium |
| X | Contraindicated in pregnancy | Warfarin, isotretinoin, thalidomide, methotrexate, statins |
New FDA PLLR (2015): Replaces A-D/X. Uses narrative subsections: Pregnancy, Lactation, Females & Males of Reproductive Potential. Now standard on new drug labels in GCC-aligned formularies.
Key Teratogens to Remember
- Valproate: Neural tube defects, fetal valproate syndrome (developmental delay)
- Isotretinoin (Accutane): Multiple severe malformations — iPLEDGE programme
- Warfarin: Warfarin embryopathy (1st trimester), CNS/eye defects (any trimester)
- Methotrexate: Spontaneous abortion, skeletal defects
- ACE inhibitors (2nd/3rd): Renal tubular dysplasia, oligohydramnios
- Thalidomide: Phocomelia (limb defects)
Safe Drugs in Pregnancy (commonly used)
- Paracetamol (1st line analgesia, any trimester)
- Penicillins, cephalosporins, erythromycin (not estolate)
- Insulin (all types — preferred for gestational diabetes)
- Low-dose aspirin (GDM prevention, pre-eclampsia prevention)
- LMWH (VTE treatment and prevention)
- Labetalol, methyldopa, nifedipine (hypertension)
- Metoclopramide, ondansetron (nausea — caution in 1st trimester)
Breastfeeding — Hale's Risk Categories
| Level | Category | Examples |
|---|
| L1 | Safest | Paracetamol, ibuprofen (short-term), insulin |
| L2 | Safer | Amoxicillin, sertraline, metformin |
| L3 | Moderately safe | Fluconazole, ciprofloxacin, codeine (short-term) |
| L4 | Possibly hazardous | Chloramphenicol, lithium |
| L5 | Contraindicated | Methotrexate, amiodarone, isotretinoin, radioactive iodine |
LactMed (NIH): Free evidence-based database for drug safety in breastfeeding. Accessible via NLM website. Recommended resource in GCC nursing practice.
ObeseObesity — Body Weight Considerations in Dosing
Weight Definitions
IBW (male) = 50 + 2.3 × [height(in) − 60]
IBW (female) = 45.5 + 2.3 × [height(in) − 60]
AdjBW = IBW + 0.4 × (TBW − IBW)
(Use when TBW > 120% of IBW)
Dosing Weight by Drug Class
| Drug | Use | Rationale |
|---|
| Aminoglycosides | AdjBW | Partial distribution to fat tissue |
| Vancomycin (initial LD) | TBW | Large Vd in obese |
| UFH, LMWH | TBW (with cap) | Weight-based; max 10,000 IU for prophylaxis |
| Succinylcholine | TBW | Pseudocholinesterase activity proportional to TBW |
| Phenytoin (LD) | AdjBW | Partial Vd increase in obesity |
| Digoxin | IBW | Does NOT distribute into fat |
| Propofol (induction) | LBM or IBW | Overdose risk if TBW used |
GCCGCC Regulatory & Formulary Landscape
UAE Drug Regulation
- MOH UAE: Central drug registration authority (federal)
- DHA (Dubai): Dubai Health Authority — separate formulary and ADR system
- DOH Abu Dhabi: Department of Health — manages Abu Dhabi formulary
- HAAD → DOH: Transitioned in 2018; prescribing standards aligned
- UAE National Formulary (UNF) — lists all approved medications
- eHMP system used for prescribing in DHA facilities
Saudi Arabia — SFDA
- Saudi Food and Drug Authority (SFDA) — drug registration, alerts, pharmacovigilance
- MOH Saudi Arabia — hospital formularies in government sector
- Saudi Drug Formulary (SDF) publishes approved drug list
- SFDA drug alerts portal — mandatory reading for clinical pharmacists and advanced nurses
Controlled Substances in GCC
UAE TRAP Regulations: Triplicate prescription system for Schedule I/II controlled drugs (morphine, fentanyl, midazolam). Prescribers must be licensed; specific forms required. Carrying controlled substances internationally requires official permission (health certificate from MOH). Penalties for violations are severe.
- Schedule I/II opioids: Morphine, oxycodone, fentanyl, pethidine — strict controls
- Benzodiazepines: Schedule II or III depending on emirate
- Tramadol: Increasingly regulated across GCC due to misuse (especially UAE, KSA)
- Methadone: Very restricted; limited availability in GCC
- Codeine: Prescription only across most GCC states (previously OTC in some)
Generic Substitution Policies
UAE DHA and MOH encourage generic substitution. KSA SFDA has bioequivalence requirements for generics. Always check INN (International Non-proprietary Name). NTI drugs (cyclosporin, lithium, warfarin, phenytoin) — switching brands requires TDM monitoring.
RamadanRamadan Medication Management
Key Principles
- Fasting = no food/drink/oral medications between Fajr (dawn) and Maghrib (sunset) — ~14–16 hrs
- Injections (therapeutic), IV infusions, eye/ear drops generally considered permissible (Islamic ruling)
- Timing medications: once daily → at Iftar (breaking fast) or Suhoor (pre-dawn meal)
- Twice daily → Suhoor + Iftar; Three times daily → must be reduced to twice daily or formulation changed
Medication Adjustments
| Drug | Ramadan Approach |
|---|
| Metformin | Reduce dose; hypoglycaemia risk lower; once daily at Iftar |
| Sulfonylureas | Highest hypoglycaemia risk — dose reduce or switch; omit if fasting prolonged |
| Insulin | Basal: adjust dose; rapid: give at Iftar and Suhoor. MD to plan pre-Ramadan. Monitor BGL closely. |
| Antihypertensives | Once daily: give at Iftar. Avoid diuretics in heat if possible during day. |
| Anticoagulants | Warfarin INR may change (diet change, dehydration) — more frequent INR monitoring |
| Lithium | High risk — dehydration raises levels. Monitor closely; plan with psychiatrist. |
Diabetic Fasting Risk Categories
HIGH RISK (advise not to fast / intensive monitoring):
T1DM, recent DKA, BGL consistently >16.7 mmol/L, recurrent hypoglycaemia, severe renal/cardiac disease, pregnant with diabetes
MODERATE RISK:
Well-controlled T2DM on insulin, Hb1Ac >10%, reduced kidney function
LOW RISK:
T2DM on diet alone, metformin, or DPP-4 inhibitors; well-controlled, no comorbidities
Cultural Considerations
Many GCC patients will fast regardless of medical advice. Advance "Ramadan medication plan" clinics are held 4–6 weeks before Ramadan in major UAE/KSA hospitals (DHA, SEHA, MOH). Nurses play key role in patient education about hypoglycaemia recognition, timing, and when to break fast.
HerbHerbal & Traditional Medicine Interactions in GCC
Common Herbal Medicines
| Herb | Use | Drug Interactions | Risk |
|---|
| Black Seed (Nigella sativa / Habbatus Sauda) | Immune support, DM, HTN | Anticoagulants (warfarin), antiplatelet, insulin — additive hypoglycaemic effect | Bleeding, hypoglycaemia |
| Sidr Honey | Antimicrobial, wound healing, GI | Generally safe; high-dose — glucose impact in diabetics | Low, monitor BGL |
| Fenugreek (Helba) | Lactation, BGL control | Antidiabetics, anticoagulants | Hypoglycaemia, bleeding |
| Khat (Qat / Catha edulis) | Stimulant (Yemeni, Somali expats) | Sympathomimetics, MAOI, antihypertensives, insulin | HTN crisis, cardiac arrhythmia, hyperglycaemia |
| Senna (Sana Makki) | Constipation, "cleansing" | Digoxin (hypokalaemia worsens toxicity), diuretics | Electrolyte disturbances |
| Zamzam water | General well-being | None significant | Minimal |
Khat — Clinical Alert
Khat (Catha edulis): Illegal in UAE/KSA/UK; legal in Yemen, Ethiopia, Kenya. Active compounds: cathinone (amphetamine-like), cathine. Effects: euphoria, anorexia, hypertension, tachycardia.
Interactions: MAOI → hypertensive crisis; reduces absorption of amoxicillin and ampicillin; prolongs action of ephedrine. May cause dental disease ("khat mouth"), liver toxicity with chronic use.
Asking About Herbal Use
Many GCC patients do not disclose herbal/traditional medicine use unless specifically asked. Use culturally sensitive language. Ask open-ended: "Do you use any traditional medicines, herbal remedies, or supplements from home?" Document in medication reconciliation. Always consider herbal interaction when drug levels are unexpectedly low/high.
Halal Medicine Considerations
- Gelatin capsules: May be porcine-derived — offer tablet alternative when available
- Alcohol-based solutions: Oral liquids, some oral rinses — use only if medically necessary; inform patient
- Heparin: Porcine vs bovine — some patients request bovine-derived (check hospital supply)
- Parenteral nutrition: Contains lipid emulsions (soy/MCT); gelatin-free alternatives preferred
- UAE and GCC hospitals increasingly sourcing halal-certified pharmaceuticals; Halal pharmaceutical certification exists in Malaysia/GCC
PGxPharmacogenomics in GCC Populations
Key Genetic Variants in Arab Populations
| Gene/Variant | Frequency in Arabs | Clinical Impact |
|---|
| CYP2D6 Poor Metaboliser | ~5–10% (higher than European 5–7%) | Codeine → morphine conversion impaired; tramadol analgesia reduced; also affects antidepressants (TCAs, fluoxetine, paroxetine) |
| CYP2D6 Ultra-Rapid Metaboliser | ~16–28% in some Arab sub-groups (highest globally) | Codeine → excess morphine → respiratory depression risk (especially breastfeeding infants) |
| G6PD Deficiency | High prevalence: ~8–25% in GCC males (X-linked) | Haemolytic anaemia with primaquine, dapsone, nitrofurantoin, rasburicase, sulfonamides, some foods (fava beans) |
| CYP2C19 Variants | Poor metaboliser: ~2–5%; Rapid: higher in some | Clopidogrel activation impaired (poor metaboliser = reduced antiplatelet effect); PPI metabolism affected |
| VKORC1 / CYP2C9 | Lower warfarin dose requirements seen in Saudi populations | Standard warfarin doses may cause over-anticoagulation; start low, titrate to INR |
G6PD Deficiency — Drug List
AVOID in G6PD deficiency:
Primaquine, pamaquine
Dapsone
Nitrofurantoin (caution)
Rasburicase
High-dose aspirin (>1g)
Sulfonamides (co-trimoxazole)
Methylene blue
Nalidixic acid
Foods: Fava beans, some herbal supplements
Codeine Safety in GCC
CYP2D6 Ultra-Rapid Metabolisers: Higher prevalence in Arab populations means that codeine can produce dangerously high morphine levels. Contraindicated in:
- Breastfeeding mothers (infant deaths reported)
- Children <12 years (WHO 2013)
- Post-tonsillectomy children
Consider alternative: tramadol, oxycodone (with appropriate monitoring). Check pharmacogenomics testing availability in tertiary GCC hospitals.
Future PGx in GCC
Saudi Human Genome Program (SHGP) established to map genomic variation in Saudi population. UAE, Qatar national biobanks underway. KFSH&RC (King Faisal Specialist) and Cleveland Clinic Abu Dhabi have pharmacogenomics testing services. Growing integration with electronic prescribing in GCC tertiary centres.