Anti-Protozoal Agents - Clinical Ocular Pharmacology Spring 2026

free living

Acanthamoeba is a _______ amoeba

swimming pools, hot tubs, lakes, streams, saliva, tap water, & homemade saline

Where is Acanthamoeba commonly found?

2 forms: trophozoite & cyst

How does Acanthamoeba exist?

growing form

Describe the trophozoite form of Acanthamoeba

dormant form

Describe the cyst form of Acanthamoeba

trophozoite form

Medications are only effective against the (trophozoite form/cyst form) of Acanthamoeba

No -- treatment can be long and difficult

When Acanthamoeba becomes cystic, is it easy to treat?

yes -- then recur later

Can cystic form of Acanthamoeba lie dormant?

-persistent red eye

-keratitis

-AC cells & photophobia

What are the common historical presentations of Acanthamoeba?

bacterial or herpetic infection that has failed to respond to treatment

What is Acanthamoeba often misdiagnosed as?

with CL wear that have been worn while swimming, in the shower, hot tub, etc

85% of the time an Acanthamoeba keratitis infection is association with what?

1) EARLY ON: PAIN not consistent with the clinical picture

2) LATER ON (3-8wks): RING INFILTRATE forms

What are the HALLMARK signs of Acanthamoeba keratitis?

Early Acanthamoeba Keratitis (Pic)

Early Acanthamoeba Keratitis (Pic)

Acanthamoeba Keratitis -- Early Ring Infiltrate (Pic)

Acanthamoeba Keratitis -- Early Ring Infiltrate (Pic)

Acanthamoeba Keratitis -- Ring Infiltrate (Pic)

Acanthamoeba Keratitis -- Ring Infiltrate (Pic)

1) PHMB (0.02% polyhexamethylene biguanide)

2) 0.1% propamidine

What are the 2 concurrent topical agents that should be used for an Acanthamoeba Keratitis?

q1h

What is the dosing for PHMB (0.02% polyhexamethylene biguanide) when treating Acanthamoeba keratitis?

Baquacil, pool disinfectant

What is PHMB (0.02% polyhexamethylene biguanide) compounded from?

No :) -- must be specially compounded in the US

Is 0.1% propamidine comercially available in the US?

-ORAL NSAID for pain

-Oral Miltefosine (anti-parasitic) 50mg BID x 4wks

-Oral Voriconazole (anti-fungal) 200mg BID

What are some other methods of treatment for Acanthamoeba keratitis?

6-12 months

Topical treatment for Acantamoeba Keratitis can last how long?

3 months

Medication is continued for ______ after all signs of Acanthamoeba Keratitis have cleared

6-12 months -- to avoid reoccurance of the cystic form of the parasite

How long is PK delayed after all symptoms of Acanthamoeba Keratitis have cleared? Why so long?

a single-celled parasite of cats

What is Toxoplasmosis?

1) Ingested from consuming undercooked meats

2) Ingested from eating with dirty hands

3) Congenitally through the placental blood supply from mother to baby

How is Toxoplasmosis transmitted to humans?

Ocular Toxoplasmosis

What ocular condition does Toxoplasmosis cause?

Ocular Toxoplasmosis (Pic)

Ocular Toxoplasmosis (Pic)

retinal -- common w/in the posterior pole of the retina

Ocular Toxoplasmosis affects the _____ blood supply

Looking through a vitritis

Why is this fundus photo blurry?

Yes

Is this Toxoplasmosis active?

retinochoroiditis

What is the ocular effect of Toxoplasmosis?

Headlight in the fog -- a single, focal, posterior pole retinitis/exudate with an overlaying dense vitritis

What is the hallmark feature of an active Toxoplasmosis infection?

posterior uveitis

Toxoplasmosis is the #1 cause of what?

Toxoplasmosis

What is the most frequent cause of infectious retinitis?

Yes -- since tissue cysts remain in the hosts for the hosts lifetime

Are reoccurances of Toxoplasmosis common? Why?

Recurrent Ocular Toxoplasmosis (Pic)

Recurrent Ocular Toxoplasmosis (Pic)

Focal RPE hyperplasia and white fibrosis

What is the hallmark signs of an OLD Toxoplasmosis lesion in the retina?

No -- OK to monitor if the patient is immunocompetent

Do all cases of active ocular toxoplasmosis require treatment?

-Patient is immunocompetent

-The lesion is OUTSIDE the posterior pole

-The lesion is <1DD in size

When is it OK to monitor an active toxoplasmosis lesion?

1-2

Cases of active toxoplasmosis that do not warrant treatment will resolve on their own in about _____ months

-Any active lesion inside the posterior pole

-Any active lesion >1DD in size

-Significant vitritis causing a 2 line decrease in VA

-No improvement in the condition in 1 month

When does an active toxoplasmosis lesion warrant treatment?

-Oral Pyrimethamine

-Oral Sulfadiazone

-Oral Predisone

What is the classic "Triple Therapy" for Active Ocular Toxoplasmosis Lesion?

4-6wks

How long is treatment with "Triple therapy" for Active Ocular Toxoplasmosis Lesion?

Folic acid synthesis inhibitor -- antibiotic

What is Oral Pyrimethamine?

pregnant/nursing mothers

Who is Oral Pyrimethamine contraindicated in?

folic acid -- to counter bone marrow toxicity

It is recommended to take what when on treatment using Oral Pyrimethamine? Why?

Folic acid synthesis inhibitor -- antibiotic

What is oral Sulfadiazine?

Clindamycin

What is the substitute for Oral Sulfadiazone if the patient has a sulfa drug allergy?

at least 24h after the start of antimicrobials

When can Oral Prednisone treatment be started?

Taper and cease 10 days before stopping anti-microbials

What is the protocol for stopping oral Prednisone during "Triple Therapy" for ocular toxoplasmosis?

Because the inflammatory reaction in active Toxo can be particularly damaging to sensitive retinal tissue

Why is oral prednisone given to patients with ocular toxoplasmosis?