Vignettes Peds Pharmacology; # 1

1. Rx of Scabies:

i) Best: Permethrin
ii) Lindane is neuro-toxic and hence best avoided.

iii) Benzyl benzoate: is no longer available in the US; not considered safe.

iv) What about Crotamiton as a local ointment in addition to GBH?

Prep says: Crotamiton cream or lotion is not recommended for treatment of scabies because of lack of efficacy and toxicity data.

Thus:
The most efficacious recommended therapy: Permethrin 5% cream applied from head to toe.
Permethrin 5% cream is a more effective scabicide than lindane, but it also is more expensive. It is poorly absorbed and rapidly metabolized by tissue esterases, which limits its toxicity.

2. Foscarnet:

We know that if a new born baby has CNS involvement of CMV, we give ganciclovir when the criteria are met to treat. That is neonatal story of CMV.
Now Foscarnet: for pediatric age population-

It is approved for:
i) both induction and maintenance treatment of CMV retinitis in immunocompromised patients (eg HIV)
ii) for treatment of severe mucocutaneous disease caused by acyclovir-resistant HSV, and iii) for zoster caused by acyclovir-resistant varicella zoster virus.

So will you treat a newborn with foscarnet if resistant to ganciclovir? It is not indicated.

3. Rx of GER:

i) antacids (eg, magnesium and aluminum hydroxide),

ii) Histamine2 receptor antagonists (eg, cimetidine, ranitidine, famotidine, nizatidine),

iii) prokinetics (eg, metoclopramide, bethanechol)

iv) proton pump antagonists (eg, omeprazole, lansoprazole, pantoprazole, rabeprazole): Of the currently available therapies, it is the most effective class of agents to suppress gastric acid secretion.

4. Relative contra-indication ( C/I) to sucralfate therapy: q 114/07
Answer: End-stage renal disease

Now:
Sucralfate is an aluminum hydroxide complex of sucrose that is effective both for treatment and prevention of peptic ulcers; it is generally less effective as monotherapy compared with either histamine blockers or proton pump inhibitors. It also has been used in a wide variety of other gastrointestinal conditions, including radiation-induced mucositis and proctitis, nonulcer dyspepsia, and bile reflux gastritis.

Mechanism of action: It coats the ulcer region, leaving it less susceptible to acid-induced injury.

Side effects and toxicity:
Generally is well tolerated.
But it may cause: constipation and decrease the bioavailability of certain medications (eg, fluoroquinolones, ketoconazole, warfarin).
In addition, because it contains aluminum and has been reported to increase plasma aluminum concentrations in patients who have renal failure, it is not recommended for use in such patients.
5. Anti- Epileptic Drugs (AEDs) and OCPs:

A 16 y.o girl with seizure disorder is on phenytoin. She needs to be prescribed OCPs now ( q 88/08 ).

= The estrogen dose in OCP should be higher than the usually prescribed in such a scenario.

NB: These antiepileptic drugs (AEDs) induce the cytochrome P450 hepatic enzyme pathway: phenobarbital, primidone, hydantoin, carbamazepine, oxcarbazepine.

Such induction increases the metabolic rate of estrogen and the progestogens, potentially lowering serum concentrations of these hormones by 50% or more.

6. A 16 yrs pt is on theophylline. Which med is likely to increase his theophylline levels?

Rantac/cimetidine/rimfampicin/phenobabr/prednisone

Answer is: Cimetidine
Through cytochrome p 450 system:

** Cimetidine can result in an elevated theophylline level, but ranitidine has no effect on theophylline levels.

**Phenobarbital and rifampin increase drug clearance, resulting in lower theophylline levels.

NB: Prednisone has no effect on theophylline levels.

7. Question 89/08

Presumptive treatmemnt for ac urethritis in a 17 yrs old boy who comes with purulent urethral discharge:

= Azithromycin 1 g POx 1 AND cefixime 400 mg PO x 1

So this is ac Urethritis.

Neisseria gonorrhoeae and Chlamydia trachomatis are common causes and hence both should be treated, as you know!