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PRESCRIBING

and prescribing assessment tools

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path: PRESCRIBING

 

Why is prescribing so important?

Prescribing is an integral part of a General Practitioner’s work and several high profile cases have been published when qualified doctors have made catastrophic errors.   Because there are a large number of patient deaths relating to medication errors.   The only way this will improve is if we start regularly reviewing and analysing our prescribing habits.  The best way of looking at an identified need is to pause and reflect on what we are doing rather than bury our heads and just continuing as we are.  Would you agree?

We know GP trainees appear to assessed left-right-and centre.  But this is another important area where we can better ourselves.  Qualified GPs and their practices are often asked to look at their prescribing habits in some way or another and we feel therefore trainees should too.

GP Prescribing Proficiencies

All prescribing GPs are expected to demonstrate the following, across people of all ages which includes extremes of age, for example babies, children and older people with frailty (based on the GMC GPCs 2017):

1.       Assesses the risks and benefits including those posed by other medications and medical conditions, reducing polypharmacy where possible.

2.       Identifies when prescribing unlicensed medicines and informs patients appropriately.

3.       Adheres to national or local guidelines (including recommendations for over the counter  prescribing (OTC) and evidence-based medicine.

4.       Uses antimicrobials appropriately.

5.       Counsels patients appropriately including giving instructions for taking medicines safety in line   with up to date literature.

6.       Reviews and monitors effects including blood testing at appropriate intervals.

The official MRCGP Prescribing Assessment?

Yes.    All trainees in ST3 have to do one.  There is no set standard as it is designed as a learning exercise; however if no errors are highlighted and if no learning is identified this would raise concerns, as to date this has never been the case.

MRCGP Prescribing Assessment - how will it work?

For the official MRCGP prescribing tools  and supporting documents to help you, see the resource items under the QUICKLINKS section at the top of the page.  They are reproduced below for your convenience.

Prescribing Pearls

If  you have  a prescribing pearl to offer, please submit it via the comment box below and I will add it to the list.

  • Try not to give “a pill for every ill” – promote self-help and less reliance on the doctor for small illnesses.
  • Drugs which often interact with other drugs and to be cautious off when adding more medication…
      • Gentamycin
      • Warfarin
      • Lithium
      • Digoxin
      • Theophylline
      • Methotrexate
      • Phenytoin
      • Insulin
      • Cyclosporin
  • Do not prescribe Verapamil with Diltiazem (mnemonic VD).
  • Reduce diuretics in the elderly during Summer time (otherwise can dehydrate).
  • Know the features of Digoxin toxicity (and monitor blood levels).
  • For palliative heart failure
      • Disease-modifying therapies at maximally tolerated doses also help to alleviate symptoms.   This includes ACE inhibitors, beta-blockers and aldosterone antagonists.
      • Opioids can be useful for managing breathlessness in heart failure.
          • Low dose oral morphine is the usual first line opioid (e.g. morphine MR 5mg BD or 2.5-5mg morphine PRN).
          • If there is significant renal impairment (eGFR <50) then consider low dose PRN morphine or oxycodone first line instead – discuss with specialist palliative care if unsure.
          • Evidence suggests that when used for breathlessness, opioid doses in excess of morphine 30mg (or equivalent) are associated with increased mortality, so total daily doses should remain below this
  •  
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  • Thyroxine replacement – be guided by the TSH level generally when deciding whether to increase, decrease or maintain the levothyroxine dose.
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  • Remember to de-prescribe if polypharmacy.  Click here for more on de-prescribing and specific notes on specific drugs.
  • There is good evidence that stopping psychotropic drugs (including opioid analgesics) can reduce falls.  Taking a psychotropic medication approximately doubles the risk of falls.
  • Nitrofurantoin: long-term (greater than six months) use of nitrofurantoin is associated with pulmonary toxicity. CARM have received over 60 reports of serious pulmonary reactions following the use of nitrofurantoin.
  • Overactive bladder or incontinence medications: consider withdrawing if any dizziness, confusion, blurred vision or drowsiness.
  • Nutritional supplements: Discontinue when prescribed for prophylaxis rather than treatment of malnutrition.
  • Remember sick day rules & prescribing – click here
  • Reduce diuretics in the elderly during Summertime (otherwise can dehydrate).
  •  
  • Remember, Lansoprazole cover for those who will be on long term NSAIDs or >= age 45
  • Antidepressants take about 2-4  weeks to work.  So tell patients to persevere for 4 weeks when starting or changing dose regimes.
  • Do not over emphasise that some antidepressants can make you feel worse than better initially.   If you over-egg this, then more patients are likely to experience this because of the nocebo effect (opposite of the placebo effect).
  • If coming off SSRIs – do it slowly.  Otherwise withdrawal effects.
  • No Paroxetine/Fluoxetine for those on Tamoxifen – use Citalopram instead. Paroxetine and fluoxetine should not be prescribed for depression or hot flashes in women who have had breast cancer and are now taking tamoxifen to prevent a recurrence. Citalopram or venlafaxine should be considered instead.  This message comes from a study showing that paroxetine, by interfering with the metabolism of tamoxifen, reduces or abolishes its protective effect against breast cancer recurrence, and that women taking both drugs have an increased risk for death from breast cancer. Paroxetine is a strong inhibitor of the CYP2D6 enzyme that converts tamoxifen to its active metabolite, reducing the amount of active drug that is released
  • Do not prescribe B-Blockers in Asthma
  • Know the features of Lithium toxicity & monitor blood levels.
  • Naproxen vs Ibuprofen vs Diclofenac
  • Don’t use diclofenac (high risk of GI ulcers and bleeds).  Naproxen safer, even more so than Ibuprofen.   May need to prescribe with PPI esp if age =>45 (see CKS guidance).
  • Do not prescribe pentins in general (e.g. gabapentin, pregabalin)
  • Do not generally prescribe diazepam for back pain. 
  • Capsaicin – remember, if using, only use a small amount to rub in.   Too large a blob, and all that will result is chilli-like burning.
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  • If a patient’s pain is not controlled, increase the 24h opioid dose by 1/3rd.  So, if they are on MST 30mg bd, increase to 40mg bd.  
  • If you are increasing the regular pain relief dose, then remember to increase the breakthrough dose too.   
  • The breakthrough dose of opiates is 1/6th of the total daily dose of opiates.
    (MST 15mg bd = breakthrough dose 5mg oramorph.   MST 30mg bd = breakthrough dose = 10mg oramorph).  Please double check with senior if unsure.
    Remember to calculate this and include patches as well as oral medications and syringe drivers. Ask palliative care for advice if needed.
  • When starting a syringe driver don’t remove an existing opiate patch but continue to change it when scheduled.
    If their background opiate analgesia needs to be increased add it into the syringe driver and update the PRN dose calculation.
  • Remember not all pain is opioid responsive.
    It can be helpful to ask the patient whether previous background dose increases made a difference or whether PRN opioid doses help- if the answer is no, consider adding an adjuvant rather than continuing to increase opiates.     For example, bone pain from bone mets – usually responds better to NSAIDs than opioids.
  • Know the features of opioid toxicity (confusions, picking at things in mid air, hallucinating).   Most likely if opioid doses increased too much too suddenly.  
  • Always double check or even triple check your calculations.   Ask a colleague to double check if you want to be even more safe.
  • Levomepromazine is an excellent anti-emetic in palliative care which covers a wide range of receptors and has a long half-life.
    The oral and sub-cutaneous dose for nausea is 2.5-6.25mg..   The 25mg tablets cut into quarters are considerably cheaper than the 6mg tablets but you may need to switch to these if the 6.25mg dose is too sedating.
  • There are loads of good guides on palliative care symptom control drugs (e.g. nausea, vomiting, constipation, pain and so on).  See resources in Palliative Care section.
  • For palliative heart failure:
      • Disease-modifying therapies at maximally tolerated doses also help to alleviate symptoms.   This includes ACE inhibitors, beta-blockers and aldosterone antagonists.
      • Opioids can be useful for managing breathlessness in heart failure.
          • Low dose oral morphine is the usual first line opioid (e.g. morphine MR 5mg BD or 2.5-5mg morphine PRN).
          • If there is significant renal impairment (eGFR <50) then consider low dose PRN morphine or oxycodone first line instead – discuss with specialist palliative care if unsure.
          • Evidence suggests that when used for breathlessness, opioid doses in excess of morphine 30mg (or equivalent) are associated with increased mortality, so total daily doses should remain below this
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  • Do not prescribe B-Blockers in Asthma
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Cytochrome P450 made easy

What is it?

When we mention the cytochrome P450 system, most doctors just want to turn around and run away! So, let’s demystify it once and for all.    The cytochome P450 (CYP45) system is basically the liver’s enzyme system.  The CYP450 is so called because it is found within the membranes of a cell (hence CYTO).  It contains a haem pigment (hence CHROME and P).  And it absorbs light at a wavelength of 450nm.    It has quite a number if functions…

  • It is essential for the production of lots of things in the body including our cholesterol and natural steroids. 
  • It also helps detoxify the body of foreign chemicals
  • It helps with the metabolisation of drugs (so they don’t linger about too long)

Why is it important?

Because so many drugs (including nutrients and herbal therapies) are metabolised via the CYP450 system.  This system can be inhibited or induced by drugs.   And that then leads to drug-drug interactions and all sorts of adverse reactions.   Drugs that cause CYP450 drug interactions are referred to as either inhibitors or inducers.

  • Inducers can increase the rate of another drug’s metabolism by x2/x3 fold over the period of a week!   So, when an inducing agent is prescribed with another drug, the dosage of that other drug may need to be increased.  Otherwise, the HIGHER rate of metabolism means the medication doesn’t last long and its therapeutic effect is reduced leading to therapeutic failure of that medication.
  • Inhibitors can decrease the rate of another drug’s metabolism by x2/x3 fold over the period of a week!   So, when an inhibitor agent is prescribed with another drug, the dosage of that other drug may need to be reduced.  Otherwise, the LOWER rate of metabolism means the medication last longer and its therapeutic effect is enhanced leading to harmful adverse effects.  

And what makes it worse, is that there is genetic variability in about 7% of people.  For example, many clinicians believe that post menopausal women recieving tamoxifen for early breast cancer should be tested for their type of CYP2D6 genotype as it may be valuable in selecting the type of adjuvant homonal therapy to offer.  And of course CYP2D6 inhibitors should be avoided in tamoxifen-treated women.  

And patients come to us with often co-morbidity.  It would be nice if the world was just full of people with just the one thing.  But it isn’t.  It’s a lot more complex.  It’s not uncommon for a patient withy hypertension and bad lipids to present to us at some point with depression, for instance.  Did you know that several antidepressants are CYP450 inhibitors (i.e. reduce metabolism of other drugs).  The effect on drugs like halperidol or metoprolol will then be accentuated.  

In the case of grapefruit juice, there are numerous medications known to interact with grapefruit juice including statins, antiarrhythmic agents, immunosuppressive agents, and calcium channel blockers. Furthermore, the inhibition of the enzyme system seems to be dose dependent; thus, the more a patient drinks, the more the inhibition that occurs. Additionally, the effects can last for several days if grapefruit juice is consumed on a regular basis. Luckily, the effect of this is not seen with other citrus juices.

Examples of INDUCERS 

(i.e. speeds up metabolism of other drug, so it may not be as effective)

Mnemonic: SCRAP GPS

  • Sulphonylureas
  • Carbamezapine
  • Rifampin
  • Alcohol
  • Phenytoin
  • Griseofulvin
  • Phenobarbital
  • St Johns Wort

Examples of INHIBITORS 

(i.e. slows down the metabolism of other drug, so it’s effects may be accentuated)

Mnemonic SICKFACES.COM G

  • Sodium valproate
  • Isoniazid
  • Cimetidine
  • Ketoconazole
  • Fluconazole
  • Alcohol..binge drinking
  • Chloramphenicol
  • Erythromycin
  • Sulfonamides
  • Ciprofloxacin
  • Omeprazole
  • Metronidazole
  • Grapefruit Juice
  • Warfarin
  • COCP
  • Corticosteroids
  • Tricyclics
  • Statins
  • Theophylline
  • Pethidine

Please leave a comment if you have a tip, spot an error, spot something missing or have a suggestion for a web resource. And of course, if you have developed a resource of your own, please email it to me to share with others.

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