LPN INTENSIVE CALCULATIONS�� DRUG INTERACTIONS FOR GPHC EXAM ��� INTENSIVE GPHC Exam revision programme

LONDON PHARMACIST NETWORK (LPN)

UK’S MOST INTENSIVE REVISION PROGRAMME

​

DRUG INTERACTIONS FOR GPHC EXAM

​

• LEARN EXAMPLES OF DRUGS WHICH COULD INTERACT.

​

• LEARN MECHANISM OF DRUG INTERACTIONS.

​

• LEARN OUTCOME/EFFCTS OF DRUG INTERACTIONS ON PATIENTS.

​

• LEARN HOW TO MANAGE THE OUTCOME OF DRUG INTERACTIONS.

​

​

​

​

​

SEROTONIN SYDROME

Can occur if patients take one or more drugs which can increase serotonin levels.

• SYMPTOMS - Hypertension • Tachycardia • Hyperthermia • Increased bowel sounds • Dry Eyes • Excessive sweating • Tremor
• CAUSES
• SS may be produced by large doses/ overdose of a single drug or by combinations of drugs. The most common causative combinations include • Antidepressants, St John’s wort, lithium • Analgesics: tramadol, pethidine, fentanyl • Antiemetics: ondansetron, metoclopramide • Recreational: cocaine, MDMA, amphetamines, LSD

Ward Based Management

• Organize immediate medical review • Medications should be reviewed • Fluids should be given for dehydration • Cool patient down • Physical observations: Heart rate, Blood Pressure ,Temperature, Respiratory rate.

• Consider stopping causative drugs if possible.

​

​

​

​

​

QT PROLONGATION

Can occur if patients take one or more drugs which can prolong QT interval.

• SYMPTOMS – Sudden, unexplained fainting, Unexplained seizures, Sudden cardiac arrest or death in the absence of any structural heart disease.
• CAUSES
• may be produced by large doses/ overdose of a single drug or by combinations of drugs. The most common causative combinations include • Domperidone, Antibiotics (some e.g. macrolides, quinolones) , Methadone (opioids), GSL meds (sympathomimetics), Tolterodine, Antidepressants, Haloperidol (anti-psychotics) , Sotalol.
• Ward Based Management

• Consider the risk of QT prolongation when starting a new medicine (if unsure of medicine related risk contact prescriber for advice). Assess patient’s risk factors for QT prolongation. Avoid QT prolonging drugs in patients with congenital long QT syndrome. Correct any modifiable risk factors such as electrolyte disturbance.

Where a patient has risk factors and / or is prescribed an interacting medicine, the first line option is to change to an alternative drug that is not known to prolong the QT interval whenever possible.

​

​

​

​

Increased Bleeding

Can occur if patients take one or more drugs which can increase bleeding.

• SYMPTOMS – Blood shot eye, subconjunctival haemorrhage, confusion, fatigue, loss of consciousness.
• CAUSES
• may be produced by large doses/ overdose of a single drug or by combinations of drugs. The most common causative combinations include • Anti-platelets Aspirin, clopidogrel, prasugrel. WARFARIN, DOACS, Heparins, SSRIs etc.

​

• Ward Based Management

• Check Hemoglobin levels, check platelets levels, Where a patient has risk factors and / or is prescribed an interacting medicine, the first line option is to change to an alternative drug that is not known to increase bleeding, if possible, give an antidote wherever possible, Local hemostatic measures, Mechanical compression, Consider surgical intervention.

​

​

Increased Blood clots

Can occur if patients take one or more drugs which can increase blood clot formation. The clot may break off and travel within the body to cause further damage such as stroke, Pulmonary embolism, DVT etc.

• SYMPTOMS – Pain, swelling and tenderness in one of the legs (usually the calf) • A heavy ache in the affected area • Warm skin in the area of the clot • Red skin, particularly at the back of the leg below the knee. Breathlessness, Chest pain.
• CAUSES
• may be produced by large doses/ overdose of a single drug or by combinations of drugs. The most common causative combinations include • HRT , COC (pill), clopidogrel + omeprazole, cancer drugs + warfarin, VITAMIK K
• Ward Based Management

• Systemic thrombolysis – a clot-busting medicine is given. E.g. heparins. Mechanical thrombectomy- surgery.

• Compression stockings, increased mobility

​

INCREASED MYOPATHY

Can occur if patients take one or more drugs alongside STATINS which can increase the risk of myopathy, muscle breakdown and rhabdomyolysis.

• SYMPTOMS – muscle Pain, muscle tenderness, fatigue, lethargy,
• CAUSES
• Statins can interact with Macrolides, Fusidic acid, grapefruit juice, fibrates (potentially), Ezetimibe (potentially).
• With Ranolazine, Amlodipine, Amiodarone, Verapamil and Diltiazem – give SIMVASTATIN 20MG MAXIMUM
• Ward Based Management

• Check creatinine kinase level

• Check liver function
• Stop interacting drugs

Egfr reduction

Can occur if patients take one or more drugs which can reduce renal function. Renal impairment can lead increased toxicity of certain drugs. E.g. lithium, methotrexate, DOACs, SGLT2 inhibitors.

• SYMPTOMS – fatigue, shortness of breath, ankle swelling, loss of appetite, increased risk of bleeding , increased risk of drug toxicity
• CAUSES
• NSAIDS, ACEi, Diuretics, Aminoglycosides, ARBs, Vancomycin.

​

• Ward Based Management

• Stop drugs affecting renal function.

• Monitor high risk drugs
• Avoid dehydration

ENZYME INDUCTION & INHIBITION

• INDUCERS INDUCE = REDUCE CONCENTRATION OF OTHER DRUGS
• INHIBITORS = INCREASE CONCENTRATION OF OTHER DRUGS

BETA AGONIST & BETA BLOCKERS

An interaction can occur if patients take a beta blocker and a beta agonist together or drugs to treat asthma, COPD etc.

• SYMPTOMS – shortness of breath, spasms, breathlessness, respiratory issues.

​

• CAUSES
• beta-blockers – e.g. propranolol, timolol, metoprolol, nadolol etc.
• Beta agonist – e.g. salbutamol, terbutaline
• Inhalers – fostair , Symbicort, Ventolin.

​

• Ward Based Management

• Stop drugs causing constriction of airways if possible.

• Monitor drugs causing respiratory depression e.g., opioids, benzos, olanzapine.

​

QT PROLONGATION DRUGS

antiarrhythmics, antipsychotics, antidepressants, antibiotics, antihistamines, antiemetics, antifungals, and certain high‑risk agents such as methadone and quinine.

A mnemonic that captures these high‑yield categories is: 🧠 Mnemonic: “A BAD MAPS”

- A — Antiarrhythmics

Includes class IA (quinidine, procainamide, disopyramide) and class III (amiodarone, sotalol).

- B — Broad‑spectrum antibiotics

Especially macrolides (erythromycin, clarithromycin) and fluoroquinolones.

- A — Antidepressants

SSRIs (citalopram, escitalopram), TCAs (amitriptyline, imipramine).

- D — Dopamine‑blocking antipsychotics

Haloperidol, quetiapine, risperidone, thioridazine.

- M — Methadone & other high‑risk medicines

Methadone and quinine appear in UK lists of QT‑prolonging drugs.

- A — Antihistamines

Diphenhydramine, loratadine, terfenadine (historically significant).

- P — Potent antiemetics

Ondansetron and metoclopramide.

- S — Systemic antifungals

Azoles such as fluconazole and voriconazole.

​

​

THE END

​

• THANKS FOR WATCHING
• SUBSCRIBE, SUBCRIBE, SUBSCRIBE
• Instagram - @ Londonpharmacistnetwork
• Website- www.Londonpharmacistnetwork.co.uk
• Tutor Email- Micahaniakor@yahoo.com
• Social media-
• TIKTOK, WhatsApp , Facebook - London pharmacist network members group

​

​

​

​

​