Ciprofloxacin

Mechanism

Additive QT prolongation. Amiodarone strongly blocks IKr potassium channels, ciprofloxacin weakly but dose-dependently. Ciprofloxacin also inhibits CYP1A2 (a minor amiodarone clearance route).

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.

Management

Avoid where possible. Alternative antibiotic: a cephalosporin (no QT effect). If ciprofloxacin is needed, ECG before start and at day 3, with potassium and magnesium maintained.

Mechanism

Additive QT prolongation. Ciprofloxacin additionally blocks CYP1A2 – an amitriptyline metabolic route. Amitriptyline plasma levels rise.

Symptoms

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

Management

Avoid the combination. Alternative antibiotics without QT effect: a cephalosporin or nitrofurantoin. Alternative for neuropathic pain instead of TCA: gabapentin or pregabalin.

Mechanism

Ciprofloxacin blocks CYP1A2 and lowers seizure threshold itself. Bupropion is a potent proconvulsant. Ciprofloxacin also weakly blocks CYP2B6 (a minor bupropion route).

Symptoms

Seizures (generalised tonic-clonic or focal), agitation, tremor, insomnia. Patients with prior epilepsy or eating disorders are at particular risk.

Management

Avoid the combination, especially in patients with prior epilepsy. Alternative antibiotics: a cephalosporin, nitrofurantoin, or fosfomycin (no effect on seizure threshold).

Mechanism

Additive QT prolongation (both prolong QT). Ciprofloxacin weakly blocks CYP1A2; citalopram is metabolised by CYP2C19, so the pharmacokinetic effect is minimal. The main risk is additive QT.

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.

Management

Alternative antibiotics: a cephalosporin or nitrofurantoin (no QT effect). If ciprofloxacin is needed: ECG before start, maintain potassium and magnesium, keep citalopram at 20 mg.

Mechanism

Additive tendon injury risk. Fluoroquinolones disrupt collagen synthesis in tendon fibres; glucocorticoids suppress repair and weaken the collagen matrix. FDA carries a boxed warning for tendinitis and Achilles tendon rupture.

Symptoms

Pain and swelling in the Achilles tendon (less often other large tendons: biceps, rotator cuff). Sudden 'snap' and inability to bear weight indicates rupture. Symptoms typically appear within 1–4 weeks and may persist for months after withdrawal.

Management

Avoid the combination, especially in patients over 60, post-kidney-transplant, and with athletic activity. Alternative antibiotics: a cephalosporin or nitrofurantoin (no tendon effect). If ciprofloxacin is needed, limit physical activity for the entire course and 1 month after.

Mechanism

Additive QT prolongation. Dronedarone is on the FDA list of drugs that contraindicate strong QT-prolonging antibiotics. Ciprofloxacin prolongs QT dose-dependently.

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.

Management

Avoid the combination. Alternative antibiotics: a cephalosporin (no QT effect) or nitrofurantoin for urinary tract infection.

Mechanism

Ciprofloxacin is a potent CYP1A2 inhibitor, the main duloxetine metabolic route. Duloxetine plasma levels rise 6-fold. Nausea, sedation, and serotonergic effects emerge.

Symptoms

Serotonin syndrome: agitation, confusion, tremor, myoclonus, hyperreflexia. Autonomic features: sweating, tachycardia, hypertension, fever. First signs appear within hours of co-administration.

Management

Avoid the combination. Alternative antibiotics without CYP1A2 effect: a cephalosporin, nitrofurantoin, or fosfomycin. If ciprofloxacin is needed, halve the duloxetine dose.

Mechanism

Additive QT prolongation. Escitalopram prolongs QT dose-dependently (FDA Lexapro caps at 20 mg/day); ciprofloxacin contributes more weakly but additively.

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.

Management

During ciprofloxacin therapy, cap escitalopram at 10 mg/day. Alternative antibiotics: a cephalosporin or nitrofurantoin (no QT effect).

Mechanism

Ciprofloxacin disrupts insulin secretion from pancreatic β-cells and concurrently inhibits CYP2C9 – the glibenclamide metabolic route. Glibenclamide plasma levels rise, intensifying its hypoglycaemic effect. FDA warning was issued in 2018.

Symptoms

Severe hypoglycaemia: sweating, tremor, hunger, tachycardia, confusion; severe cases progress to seizures and coma. Symptoms appear within 1–7 days, especially in older patients and chronic kidney disease.

Management

Avoid the combination. Alternative antibiotics: a cephalosporin or fosfomycin (no CYP2C9 effect and no β-cell impact). If ciprofloxacin is needed, monitor glucose 4 times daily and warn the patient about hypoglycaemia signs.

Mechanism

Dual mechanism: both prolong QT (additively), and ciprofloxacin blocks CYP1A2 – a partial haloperidol clearance route. Haloperidol levels rise.

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.

Management

Avoid the combination. Alternative antibiotics: a cephalosporin or nitrofurantoin. Alternative antipsychotics with minimal QT effect: olanzapine or aripiprazole.

Mechanism

Additive tendon injury risk. Fluoroquinolones disrupt collagen synthesis in tendon fibres; glucocorticoids suppress repair. FDA carries a boxed warning for tendinitis and Achilles tendon rupture.

Symptoms

Pain and swelling in the Achilles tendon (less often other large tendons). Sudden 'snap' and inability to bear weight indicates rupture. Symptoms typically appear within 1–4 weeks and may persist for months after withdrawal.

Management

Avoid the combination, especially in patients over 60, post-kidney-transplant, and with athletic activity. Alternative antibiotics: a cephalosporin or nitrofurantoin (no tendon effect). If ciprofloxacin is needed, limit physical activity for the entire course and 1 month after.

Mechanism

Additive tendon injury risk. Fluoroquinolones disrupt collagen synthesis in tendon fibres; glucocorticoids suppress repair. FDA carries a boxed warning for tendinitis and Achilles tendon rupture.

Symptoms

Pain and swelling in the Achilles tendon (less often other large tendons). Sudden 'snap' and inability to bear weight indicates rupture. Symptoms typically appear within 1–4 weeks.

Management

Avoid the combination, especially in patients over 60 and athletes. Alternative antibiotics: a cephalosporin or nitrofurantoin (no tendon effect). If ciprofloxacin is needed, limit physical activity for the whole course and 1 month after.

Mechanism

Dual risk: both drugs lower the seizure threshold. Ciprofloxacin also blocks CYP1A2 (a minor tramadol activation route) and weakly affects serotonergic activity.

Symptoms

Seizures, especially in patients with prior epilepsy or head injury. Serotonin syndrome may occur with other serotonergics on board (agitation, tremor, hyperthermia).

Management

Avoid the combination in patients with prior epilepsy. Alternative antibiotics: a cephalosporin or nitrofurantoin (no seizure threshold effect). Alternative analgesics: paracetamol, an NSAID, or morphine.

Mechanism

Ciprofloxacin blocks CYP1A2 and, to a lesser extent, CYP3A4 – warfarin clearance routes. It also suppresses vitamin K-producing gut flora. INR rises 1.5- to 2-fold within 5–7 days of co-administration.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, blood in urine or stool, menorrhagia. Severe cases include gastrointestinal or intracranial haemorrhage. Risk rises in patients over 65 and with prior peptic ulcer disease.

Management

During ciprofloxacin therapy, empirically reduce warfarin by 20%; check INR 3–5 days after starting and 7 days after stopping the antibiotic. Alternatives: cephalosporin or nitrofurantoin (minimal CYP impact).