Learn and Apply

Introduction

One of the essential qualities that I aim to foster among fresh provisional registered pharmacists is their ability to apply the knowledge acquired in university to their daily work.

In the following sections, I will share a few relevant experiences that highlight the practical application of this knowledge.

Oralizing Augmentin with CKD

This morning, I received a phone call from a doctor in the medical ward. He wanted to switch a patient from IV Augmentin to the oral form. He was seeking guidance on the appropriate oral dosage for a CKD patient with creatinine clearance (CrCl) of 0.41ml/min.

• A first glance, the question seemed straightforward and I could have referred to renal dosing adjustment recommendations from reliable sources like Lexicomp, Micromedex or Medscape.
• However, I find the CrCl value to be unusual, as patients with a CrCl below10 ml/min are typically on renal replacement therapy, such as haemodialysis or intraperitoneal dialysis.
• Consequently, I decided to recalculate the CrCl before providing the final recommendation, and also inquired about the patient's renal replacement therapy status..

Anti-TB Active Phase

On another occasion, I received an outpatient prescription for a smear-positive tuberculosis treatment in a 30 kg child.

• The prescribed regimen included isoniazid 300 mg, rifampicin 450 mg, pyrazinamide 1000 mg, ethambutol 600 mg and pyridoxine 10 mg, with a duration of 4 months.

As part of my routine, I reassessed all the prescribed doses for their appropriately. However, I noticed that the stated duration appeared unusual.

• In tuberculosis management, the standard approach typically involves a 2-month intensive phase, followed by a 4-month of maintenance phase.
• Recognizing this discrepancy, I decided to intervene and discuss the prescription with the doctor.

Colchicine and CKD

Last Thursday, while working at the pharmacy, I encountered a prescription from the nephrology department for colchicine 0.6 mg to be taken as needed.

• The prescription also had "CKD" is written in the bottom right corner.
• At that moment, I faced a dilemma due to the limited information provided.

Regarding renal dosing adjustment for colchicine, according to Lexicomp, the following recommendations are provided:

• Kidney impairment is a significant risk factor for the development of colchicine-induced myotoxicity, even with short-term use.
• CrCl 30 to 80 ml/minute: No dosage adjustment necessary.
• Consider alternative therapy (preferred) for CrCl <30 ml/min. If alternate therapy is not available or tolerated, the following adjustment is recommended.
• CrCl <30 ml/minute: 1.2 mg at the first sign of flare, followed in 1 hour with a single dose of 0.6 mg; repeat treatment should not occur for at least 14 days. Alternatively, some experts recommend a single dose of 0.3 mg at the first sign of flare only; repeat treatment should not occur for at least 3 to 7 days.
• Haemodialysis, intermittent thrice weekly: A single dose of 0.6 mg at the first sign of flare; repeat treatment should not occur for at least 14 days. Alternatively, some experts recommend a single dose of 0.3 mg at the first sign of flare only; repeat treatment should not occur for at least 3 to 7 days.

Similarly, in community pharmacy, you may come across patients seeking acute gout treatment.

• While it is common to prescribe both colchicine and NSAIDs for acute gout attacks, this combination can be unsafe for renal impaired patients.
• Therefore, it is crucial to exercise caution when dispensing these medications.

Penicillin G and Penicillin V

Two weeks ago, during my on-call shift in the inpatient department, I received a phone call from a doctor asking why the ward was not supplied with IV Penicillin V.

• Uncertain about who rejected the request, I patiently explained that Penicillin V only comes in syrup or tablet form.
• I clarified whether the doctor intended to refer to IV Penicillin G or Tablet Penicillin V.

Historically, benzyl penicillin (Penicillin G) and phenoxymethylpenicillin (Penicillin V) were the first naturally occurring penicillin, obtained from the fermentations of Penicillium chrysogenum.

Benzyl penicillin is active against a wide range of organisms, but is inactivated by bacterial β-lactamases.

• Moreover, it is inactivated by gastric acid and its absorption from the gastrointestinal tract is low, necessitating its administration via injection.
• Intravenous administration of Penicillin G is preferred over the intramuscular route due to the irritation and local pain caused by intramuscular injection of large doses.

Phenoxymethylpenicillin (Penicillin V) has a similar antibacterial spectrum to benzyl penicillin sodium, but is less active.

• It is gastric acid-stable, making it suitable for oral administration.
• However, it should not be used for serious infections due to unpredictable absorption and variable plasma concentrations.

NOTE: Procaine Penicillin G and Benzathine Penicillin G are administered IM and serve as depot forms. They are slowly absorbed into the circulation (and hydrolysed to benzyl penicillin) and persist at low levels over a long period.

• Slow-release IM Benzathine Penicillin G is useful for treating syphilis.
• Procaine Penicillin G was once a commonly used treatment for pneumococcal pneumonia and gonorrhoea; however, it is rarely used now because gonococcal strains are penicillin-resistant, and many pneumococci require higher doses of Penicillin G or the use of more potent β-lactams.

Give Me An Example

"As a pharmacist, what do you screen for when you receive a prescription?"

• This question is frequently posed by my senior pharmacist to test provisional registered pharmacist at the end of their outpatient pharmacy rotation.

A standard reply will include screening for indication, dosage/frequency/duration, paediatric considerations, pregnancy, breastfeeding, drug interaction, polypharmacy, renal/liver function, contraindication, among others.

Following that, the subsequent question would be to provide an example for each criterion mentioned above. Here are some examples.

Indication

• If a doctor mistakenly prescribes Lomotil for a patient on opioid pain killers, the actual intention could be to prescribe a laxative for opioid-induced constipation.
• If terazosin is prescribed to a female patient with the indication stated as benign prostatic hyperplasia, it may be necessary to clarify whether the intended use is for the expulsion of renal calculi.
• The prescribing of Betaxolol 1 drop twice daily for a child should be clarified since it is uncommon for a child to have glaucoma.

Dosage

• A prescription of metformin at a dosage of 3 g once daily. While most common drug references, including Lexicomp, suggest a maximum of 2.55 g per day, the Malaysia Clinical Practice Guideline Type 2 Diabetes Mellitus, 2020 recommends a maximum of 1 g three times daily. If doses exceeding 2 g/day are necessary, consider administering in 3 divided doses to minimize GI adverse effects.

Paediatric

• Prescribing bromhexine 3 mg three times daily for a 10kg, 1-year-old infant is not recommended. As of now, the potential adverse effects outweigh the potential benefits, and the use of cough and cold products is not recommended in children under 2 years old.
• Nitrofurantoin is contraindicated in the early weeks of life (neonates) due to the risk of haemolytic anaemia.
• Sulphonamides and ceftriaxone are contraindicated in patients younger than 6 to 8 weeks of age due to their displacement of bilirubin from protein-binding sites and the potential for kernicterus.

Pregnancy

• When cyclophosphamide is prescribed, effective contraception should be planned during and for at least 3 months after treatment for both men and women, as advised by the manufacturer.
• Some known teratogens include ACE inhibitors, angiotensin receptor blockers, isotretinoin, lithium, sodium valproate, thalidomide and warfarin.

Breastfeeding

• Using Clarinase for a blocked nose in a breastfeeding mother may decrease milk production in some women due to the pseudoephedrine content.
• Drugs contraindicated during breastfeeding include antineoplastics, lithium, iodine and amiodarone.

Drug interaction

• Taking both alendronate and antacids simultaneously is not recommended. Antacids, calcium, iron or mineral supplements should not be taken within 30 minutes of alendronate as they may interfere with its absorption.
• Salicylic acid is used to remove scale but as it deactivates calcipotriol, it should not be applied at the same time. If combined use is necessary, apply them at a different time of the day.

Polypharmacy

• Prescribing both etoricoxib and diclofenac together in one prescription.
• A patient being prescribed atorvastatin and simvastatin from two different clinics.
• A prescription consisting of both weekly Fosamax Plus and weekly alendronate.
• A prescription consisting of DuoTrav (Travoprost and Timolol) and Xalatan (Latanoprost).
• A prescription consisting of DuoTrav (Travoprost and Timolol) and TimoComod (Timolol).
• A prescription consisting of Duodart (Dutasteride and Tamulosin) and Harnal OCAS (Tamsulosin).

Renal/liver function

• Prescribing trimetazidine 20 mg three times daily for a ESRF patient is inappropriate. The dosing adjustment for trimetazidine is as follows. CrCl 30-60 ml/min: 20 mg twice daily; Contraindicated when CrCl <30 ml/min.
• Prescribing metformin for a ESRF patient is inappropriate. Metformin should be avoided if CrCl is less than 30 ml/min/1.73 m² due to the risk of lactic acidosis.