Prescribing. Dr Andrew Smith

Transcription

1 Prescribing Dr Andrew Smith

2 Outline from 2014 Rules of Prescribing Prescribing Controlled Drugs Liver/Renal Disease Pregnancy/Breastfeeding Prescribing in the Elderly Allergies Adverse Drug Reactions Drug Level Monitoring Drug Interactions Practice Questions

3 Outline - Revised

4 Outline - Revised These areas will come up in finals (OSCEs and written) as well as your prescribing exam! I ll leave the detailed slides in for your own use, but will focus more on examples Covered in other lectures

5 Slides on the theory and considerations for prescribing are contained at the end.

6 Prescribing Controlled Drugs Doctors have the ability to prescribe controlled (Class A-C) drugs. Some are limited to those with special licences. In order to meet the legal requirements for prescriptions, you must: Include the name and address of the patient. State the name and strength of the formulation State the dose and frequency State the total amount to be supplied in words and figures. Doctors have a wider responsibility to avoid introducing dependence producing drugs unless clinically needed as well as monitoring for the signs of dependence and overuse.

7 Prescribing Controlled Drugs Which is correct??? Will Dooley?/?/?? Perrin Lecture Theatre?? Will Dooley?/?/?? Perrin Lecture Theatre MORPHINE SULPHATE 10mg oral tablets Take one tablet, three times daily Please supply 28 (TWENTY-EIGHT) tablets. MORPHINE SULPHATE 10mg oral tablets Take one tablet, three times daily. Please supply 28 10mg (TEN MILLIGRAM) tablets.

8 Prescribing Controlled Drugs Which is correct??? Will Dooley?/?/?? Perrin Lecture Theatre?? Will Dooley?/?/?? Perrin Lecture Theatre MORPHINE SULPHATE 10mg oral tablets Take one tablet, three times daily Please supply 28 (TWENTY-EIGHT) tablets. MORPHINE SULPHATE 10mg oral tablets Take one tablet, three times daily. Please supply 28 10mg (TEN MILLIGRAM) tablets. It s the total amount that you need to specify

9 Prescribing Controlled Drugs Which is correct??? Will Dooley?/?/?? Perrin Lecture Theatre?? Will Dooley?/?/?? Perrin Lecture Theatre MORPHINE SULPHATE Liquid (10mg/5ml) Take 10mg when required Please supply 100ml (ONE HUNDRED) MORPHINE SULPHATE Liquid (10mg/5ml) Take 10mg (TEN MILLIGRAM) when required Please supply 100ml

10 Prescribing Controlled Drugs Which is correct??? Will Dooley?/?/?? Perrin Lecture Theatre?? Will Dooley?/?/?? Perrin Lecture Theatre MORPHINE SULPHATE Liquid (10mg/5ml) Take 10mg when required Please supply 100ml (ONE HUNDRED) MORPHINE SULPHATE Liquid (10mg/5ml) Take 10mg (TEN MILLIGRAM) when required Please supply 100ml It s the total amount that you need to specify Including the units. It should read: Please supply 100ml (ONE HUNDRED MILLILITRES)

11 Outline - Revised

12 Adverse Drug Reactions These are unwanted reactions to drugs that occur with normal use of the drug. They can be reported to the Medicines and Healthcare Products Regulations Agency (MHRA) by professionals and patients by the Yellow Card Scheme. Two main types: Type A (Augmented) Common, predictable and often dose dependent. Can be severe and delayed. Type B (Idiosyncratic) No link to expected pharmacological effects. Often serious but rare.

13 Adverse Drug Reactions - Examples Drug Type A (Augmented) Anticoagulants Insulin Antipsychotics Cytotoxics Type B (Idiosyncratic) Penicillin Isoniazid Anaesthetics Sulphonamides Reaction Bleeding Hypoglycaemia Parkinsonism Bone Marrow Suppression Anaphylaxis Hepatotoxity Malignant Hyperthermia Toxic Epidermal Necrolysis

14 Allergies Type 1 allergy (e.g anaphylaxis) to medications is not that common. Many reports of allergy are in fact just intolerances or side-effects of the medication (e.g. nausea). It is important to discern the exact reaction as else important medications may be unnecessarily withheld. True allergic symptoms are urticaria, swelling, laryngeal oedema, anaphylaxis. They can take up to 72 hours to appear and may not appear on the first exposure to the drug. Common culprits: Penicillin, Sulfa drugs, Tetracycline, Codeine, NSAIDs, Phenytoin, Carbamazepine. There is a reported 10% cross-over of penicillin allergy to cephalosporins

15 Penicillin Allergy Which of the following are safe, or useable with caution, in a patient with true penicillin allergy? Augmentin Amikacin Ceftriaxone Gentamicin Tazocin Doxycycline Flucloxacillin Metronidazole Trimethoprim Meropenem

16 Penicillin Allergy Which of the following are safe, or useable with caution, in a patient with true penicillin allergy? CONTRAINDICATED WITH CAUTION SAFE Augmentin Tazocin Flucloxacillin Ceftriaxone Meropenem Amikacin Gentamicin Doxycycline Metronidazole Trimethoprim

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18 Allergic Reaction Management A patient recently given Tazocin despite a Type 1 Penicillin allergy develops shortness of breath, stridor and a widespread urticarial rash. Which are appropriate treatments: A) Chlorphenamine 4mg, PO B) Adrenaline 10ml of 1:10000, IV C) Adrenaline 10ml of 1:10000, IM D) Adrenaline 0.5ml of 1:1000, IV E) Adrenaline 0.5ml of 1:1000, IM F) Hydrocortisone 200mg, IV G) Chlorphenamine 10mg, IV

19 Allergic Reaction Management A patient recently given Tazocin despite a Type 1 Penicillin allergy develops shortness of breath, stridor and a widespread urticarial rash. Which are appropriate treatments: A) Chlorphenamine 4mg, PO only after resuscitation B) Adrenaline 10ml of 1:10000, IV cardiac arrest, 1mg C) Adrenaline 10ml of 1:10000, IM never used D) Adrenaline 0.5ml of 1:1000, IV never used E) Adrenaline 0.5ml of 1:1000, IM e.g. 0.5mg F) Hydrocortisone 200mg, IV G) Chlorphenamine 10mg, IV

20 Allergic Reaction Management Drugs Expressed as Ratios A patient recently given Tazocin despite a Type 1 Penicillin allergy develops weight (g) shortness : volume (ml) of breath, stridor and a widespread urticarial rash. 1:1000 = 1g in 1000ml = 1000mg in 1000ml Used in Which anaphylaxis are appropriate treatments: Therefore, 1mg in 1ml 0.5mg in 0.5ml A) Chlorphenamine 4mg, PO only after resuscitation B) Adrenaline Used 1: ml = of 1g in 1:10000, 10,000ml = 1000mg IV cardiac in 10,000mlarrest, 1mg Cardiac C) Adrenaline Arrest 10ml of Therefore, 1:10000, 1mg in IM 10ml never used D) Adrenaline 0.5ml of 1:1000, IV never used Higher concentrations are given IM so less volume has to be given E) Adrenaline 0.5ml of (IM 1:1000, injections are IM unpleasant) e.g. 0.5mg F) Hydrocortisone 200mg, IV G) Chlorphenamine 10mg, IV

21 Adverse Reactions Management Examples 76 year old on Warfarin for recurrent DVTs. Recent check showed an INR of 7. She is otherwise well 64 year old on Warfarin for Atrial Fibrilliation. Recent check showed an INR of 8.4. He is suffering from epistaxis. 83 year old on Warfarin for a replacement heart valve. Recent check shows INR of 8.7. She is suffering from an upper GI bleed.

22 Warfarin Overtreatment Management Depends on patient factors: High risk patients are age >65, severe hypertension, organ failure, falls risk, trauma, etc. And Bleeding Factors Minor bleeding, e.g. haematuria, epistaxis. Major bleeding, e.g. intracranial, intra-abdominal etc. Any bleed can be major if deemed so by the clinician Mx Options include: Withold Warfarin Vitamin K oral (effect within 24 hours), or IV (4-6 hours) Prothrombin Complex Concentrate (PCC. E.g. Beriplex/Octaplex) immediate action (still need to give Vit K) Fresh Frozen Plasma

23 Adverse Reactions Management Examples 76 year old on warfarin for recurrent DVTs. Recent check showed an INR of 7. She is otherwise well Withhold warfarin. Recheck in 24 hours. If patient is high risk consider oral Vit K. 64 year old on warfarin for atrial fibrilliation. Recent check showed an INR of 8.4. He is suffering from epistaxis. Withhold warfarin. Oral Vitamin K. 83 year old on warfarin for a replacement heart valve. Recent check shows INR of 8.7. She is suffering from an upper GI bleed. Withhold Warfarin. Immediate reversal with Vit K and PCC. Consider why the INR was so high!?drug interaction

24 Outline - Revised

25 Drug Level Monitoring For some drugs, the therapeutic range (or window) is narrow. I.e. They can be easily under-or-overdosed. Other indications include: Potential compliance issue. Benefit (and adverse reactions) which cannot be judged by clinical parameters alone. Drug levels in overdose/self-harm. Drug levels are typically measured as a trough level (pre-dose). However, for drugs with short half-lives peak and trough levels should be taken. They should be taken once a steady-state has been achieved (typically after 3-5 doses)

26 Drug Level Monitoring - Examples Drug Halflife Timing Therapeutic Range* Toxic Level* Extra Care Major Toxic Effects Gentamicin 2h Trough After 2-3 doses <2mcg/ml >2mcg/ml Renal disease, elderly, obesity Nephrotoxity, irreversible ototoxicity Phenytoin 20-40h Trough After 2-3 days Total 10-20mcg/ml Free 1-2mcg/ml Total >20mcg/ml Free >2mcg/ml NB: Zero-order kinetics. Elderly, pregnancy, altered protein states Nystagmus, diplopia, ataxia, confusion, hyperglycaemia Aminophylline 4-16hr N/A 4-6hrs after starting IV infusion Theophylline Trough 5 days 10-20mcg/ml >20mcg/ml Inc. in: Liver disease, elderly Dec. in: Smokers, alcohol Arrhythmias, convulsions, hypotension Digoxin 24-36h Trough 1 week ng/ml >2ng/ml Elderly, hypokalaemia Arrhythmias, visual disturbance, anorexia *can vary between labs/assays

27 Other Drug Monitoring The effects of other drugs need to be monitored also. For example: Warfarin monitor INR Levothyroxine monitor TFTs When starting, monitor TFTs every 4 weeks and titrate dose up in increments of 25-50micrograms. ACE Inhibitors/Diuretics monitor U+Es Clozapine monitor FBC

28 Drug Interactions Drug interactions may be caused by a variety of effects: Drug Absorption Altering gastric ph (Omeprazole/Ranitidine) Chelation (e.g. Aluminium salts) Gastric motility (e.g. Metoclopromide) Drug Distribution (not typically clinically significant) Drug Excretion Urinary ph (e.g. Salicylates, Diuretics, Sodium Bicarbonate) Additive effects of drugs E.g. Multiple anticoagulants Increased side-effects (ACE inhibitors and K-sparing diuretics) Antagonistic effects Competing effects (e.g. Steroids and anti-hypertensives) Confounding effects (e.g Furosemide and Digoxin, Metronidazole and Alcohol) Enzyme Induction/Inhibition

29 Enzyme Inducers/Inhibitors A major cause of drug interactions is the inhibition/induction of the cytochrome P450 family of enzymes (there are 6 main subtypes). Inhibition/induction may occur via direct action on the enzymes or by altering the genes involved in their expression. Inhibitors increase the levels of drug metabolised by the enzymes. Inducers decrease the levels of drugs metabolised by the enzymes. Inducers Carbamazepine Phenytoin Omeprazole Nifedipine Rifampicin Smoking Chronic Alcohol Use Inhibitors Macrolides (e.g. Clarithromycin) Grapefruit juice (flavinoids) Imidazoles (e.g. Fluconazole) Quinolones (e.g. Ciprofloxacin) Amiodarone Isoniazid Acute Alcohol Use

30 Courtesy of

31 Outline - Revised

32 Spot the mistakes

33 Spot the mistakes No unique patient identifier or DOB No details of reaction How many charts? Good practice to fill this in Allergy No signature

34 How should you alter this prescription? 25/2/15 PO FUROSEMIDE 40mg 25/2/15 PO PREDNISOLONE 40mg

35 25/2/15 PO FUROSEMIDE 40mg 25/2/15 PO Should be given in morning will keep patient awake! PREDNISOLONE 40mg Should be given in morning will keep patient awake!

36 What dose should you prescribe?

37 What dose should you prescribe?

38 Spot the mistakes

39 Spot the mistakes Incorrect dose Should be 62.5 MICROgrams What type? Write Units (not just U ) technically should be prescribed on the insulin area of the chart! Write micrograms in full

40 What should you monitor in this patient? Spot the mistake.

41 What should you monitor in this patient? Spot the mistake. POTASSIUM both drugs can cause hyperkalaemia Dose alteration is not signed for

42 What should you monitor in this patient? Spot the mistake. POTASSIUM both drugs can cause hyperkalaemia Dose alteration is not signed for Some drugs causing HYPERKALAEMIA ACE Inhibitors Amiloride Angiotensin Receptor Blockers (ARB) Antifungals (Ketoconazole, Fluconazole) Beta Blockers Cyclosporine Digoxin Heparin NSAIDs Spironolactone Tacrolimus Transfusions of RBC Trimethoprim

43 What is this patient at risk of?

44 What is this patient at risk of? PHENYTOIN TOXICITY Enzyme inhibitor Enzyme inducer (but relatively less so)

45 What is this patient at risk of? 25/2/15 PO OMEPRAZOLE 40mg 25/2/15 PO PAROXETINE 20mg

46 What is this patient at risk of? 25/2/15 PO 40mg 25/2/15 PO OMEPRAZOLE PAROXETINE Drugs commonly causing HYPONATRAEMIA Thiazide diuretics Amiloride Carbamazepine Sulphonylureas (but not gliclazide) Proton pump inhibitors Antidepressants, particularly SSRIs ACE inhibitors and ARBs Opiates 20mg

47 Fluid chart errors 25/2/15 0.9% Saline 1 litre KCl 40mmol STAT A.L.S 25/2/15 Red Blood Cells 2 units hours A.L.S 25/2/15 50% Dextrose 1 litre 12 hours A.L.S

48 Fluid chart errors 25/2/15 0.9% Saline 1 litre KCl 40mmol STAT A.L.S This amount of potassium must be given over at least 4 hours due to risk of arrhythmias 25/2/15 Red Blood Cells 2 units hours A.L.S Each unit needs to be prescribed separately Has to be discarded after 4 hours (from leaving the lab) 25/2/15 50% Dextrose 1 litre 12 hours A.L.S 50% Dextrose is irritant to veins. It should only be given in small volumes (10% or 20% should preferably be used if trying to reverse hypoglycaemia)

49 Some of the theory summarised

50 Rules of Prescribing Prescriptions must be written legibly, in CAPITALS! Ensure the patient s name, DOB and hospital/nhs number is present. The dose and route of administration should be specified. Avoid using decimal places. If mandatory, make them clear e.g. 0.5 rather than.5 Micrograms should be written in full. Not mcg or µg. Write Units in full. Not U.

51 Rules of Prescribing Continued Some drug charts will have specific places for insulin, antimicrobials and anticoagulants use them! If stopping a drug, make it clear and sign and date it. Avoid abbreviations in drug names e.g. Isosorbide Mononitrate rather than ISMN. Accepted abbreviations for routes of administration are often printed on the drug chart.

52 Rules of Prescribing Continued Trade-names should be avoided apart from in special circumstances (e.g. modified release preparations). Ensure special instructions are clear, especially if it is an uncommon drug (e.g. Methotrexate weekly). Use the BNF including the appendices on interactions, and info on hepatic/renal failure, pregnancy and breast-feeding. Don t prescribe a drug you don t know (read about it first).

53 Common Abbreviations Abbreviation Meaning Abbreviation Meaning PO Orally/By mouth OD Once Daily IV Intravenous BD Twice Daily IM Intramuscular TDS X3 Daily SC Subcutaneous QDS X4 Daily TOP Topical PRN When Required SL Sub-lingual MANE Morning INH Inhaled NOCTE At Night NEB Nebulised Others routes (e.g. buccal, intradermal) PV Vaginally should be written in full. It is good practice to try and avoid using the Latin frequency PR Rectally abbreviations on formal prescriptions.

54 Prescribing in Liver Disease Many drugs are metabolised by the liver, but there is a large hepatic reserve. LFTs are a poor indicator of drug metabolism. Some drugs (e.g. Rifampicin) are excreted unchanged in bile and can accumulate in obstructive disorders. Hypoalbuminaemia is associated with decreased drug binding and therefore increased free toxic levels of highly protein bound drugs (e.g. Phenytoin, Prednisolone). Patients with abnormal clotting will be more sensitive to anticoagulants. In severe disease, sedative drugs, opioids, and drugs causing constipation will increase the risk of encephalopathy.

55 Prescribing in Liver Disease Some examples of Hepatotoxic drugs: Amiodarone Isoniazid Coamoxiclav NSAIDs Statins Anti-fungals Anti-retrovirals Consult the BNF for dose alterations

56 Prescribing in Renal Failure Dose adjustments required in renal failure vary depend on the extent of renal excretion and toxicity of the drug. For many drugs, empirical dose reductions will suffice. For drugs with narrow therapeutic ranges, or in patients with extremes of weight, doses based on creatinine clearance should be used. Plasma levels should then be monitored. Some drugs should be avoided altogether. Consult the BNF! Some examples of nephrotoxic drugs: ACE Inhibitors Aminoglycosides NSAIDs Methotrexate.

57 Prescribing in Pregnancy Harm can be caused at any time during pregnancy. Teratogenesis occurs in the first trimester (during organogenesis), but growth and functional disorders can occur throughout pregnancy. Even those prescribed just prior to labour can have an effect on foetus and neonate (e.g. morphine). Drugs should be prescribed only if the expected benefit is thought to be greater than the risk to the foetus.

58 Prescribing in Pregnancy Tried and tested drugs should be used before newer ones, and at lower doses. There is some impact on fertility and risk of paternal teratogenesis for certain medications used by the father near the time of conception (mostly chemotherapeutic agents). Examples of teratogens: Sodium Valproate Warfarin ACE inhibitors Tetracyclines Lithium Alcohol

59 Prescribing in Breast Feeding The amount of drug transferred to the infant via breast-milk is often very small; especially for drugs with poor enteral absorption. Basic drugs transfer more easily due to the more acidic nature of breast milk compared to plasma. Large molecules (e.g. heparin) do not transfer into the milk. Some drugs are known to be present in high levels (e.g. Fluvastatin). Some medications can have effects on lactation (e.g. Bromocriptine) or on the sucking reflex (e.g. Phenobarbital). Insufficient evidence does not equal safety! Examples of drugs to avoid: Aspirin Carbimazole Tetracyclines Fluoroquinolones Lamotrogine Diazepam.

60 Prescribing in the Elderly - Issues Poly-pharmacy increases the risk of drug interactions (but poly-pharmacy does not just occur in the elderly!). Patient compliance decreases as the number of drugs increases. Hepatic and renal excretion decline with age. These are exacerbated by acute illness. There may be exaggerated pharmacodynamic effects on certain systems. E.g.: ß-blockers and bradycardia Nitrates/diuretics and postural hypotension Anticholinergics/hypnotics/opioids and confusion/sedation NSAIDs and gastric erosions. It may be appropriate to change the formulations of medications.

61 Prescribing in the Elderly - Guidelines Always consider whether a drug is indicated at all Limit the range from which you prescribe so your knowledge of each increases Reduce drug doses (consider starting 50% of recommended dose) Review the need for medications regularly. Simplify regimens, minimises doses. Blister packs may help. Explain clearly.

62 Read the PSA Blueprint it gives examples of what to expect! There is a free practice paper at:

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64 Good Luck! Any Questions?